All-optical logic processing unit using Kerr nonlinearity of MXene

Domain: biology
Published: 2026-03-17
Editorial outcome: minor_revision

Abstract
Optical logic computing harnesses the speed of light and the high bandwidth of optical signals to achieve ultrafast, highly parallel and energy-efficient operations. In particular, all-optical logic gates can perform Boolean functions using only photons, acting as core elements of future optical computing and communication systems. However, the multifunctional integration and flexible reconfiguration of optical devices remain challenging. Here, we present an electrically reconfigurable all-optical logic processing unit that leverages the Kerr nonlinear effect in conjunction with modulation of high-entropy MXene surface terminations. This architecture enables dynamic switching among seven fundamental Boolean operations — including AND, OR, NOT, NOR, NAND, XOR and XNOR — within a single optical configuration. With our platform we demonstrate handwritten digit recognition on the MNIST dataset, achieving a classification accuracy of 97.7%. By combining reconfigurable nonlinear optics with multifunctional two-dimensional materials, our approach establishes an alternative logic architecture pathway with the potential to enhance throughput and energy efficiency in response to AI workloads.

Introduction
Digital computation fundamentally relies on Boolean logic1, 2. Logic gates serve as the building blocks of all electronic circuits, underpinning processors, memory units, and digital systems that perform logical operations (AND, OR, NOT, etc.) on binary data to realize complex arithmetic and decision-making1. However, conventional electronic logic is approaching its limits: resistive heating and finite carrier mobility impose speed and power constraints on chip-based circuits2-5. Optical computing offers a promising alternative, by encoding information in photons, optical logic can circumvent many electronic bottlenecks6, 7. Owing to the inherent parallelism, low latency, and broad bandwidth of light, integrated optical logic gates can, in principle, enable ultrafast and energy-efficient computation3, 7.

All-optical logic gates (AOLGs) perform the same logic functions as their electronic counterparts using only optical signals8. One of the critical bottlenecks in realizing all-optical computation is the efficient execution of logic operations. Current optical logic gates are largely designed with fixed functionalities, lacking programmability and dynamic adaptability, which are essential for optimizing deep learning tasks. The advent of reconfigurable AOLGs offers a key solution to this problem7, 9, 10. AOLGs manipulate light-matter interactions to control interference8, 11, 12, diffraction13, or self-focusing14, 15 of light waves, enabling high-speed information processing7. Compared to traditional fixed-function logic gates, AOLGs show inherent capability of hardware programmability, allowing for dynamic tuning of their logical functions and improving the versatility and flexibility of optical computing systems across various AI tasks.

However, the dynamic reconfigurability of AOLGs is still hindered by challenges such as limited speed, bandwidth constraints, and difficulties in switching between multiple functions. Recent advancements indicate that high-entropy MXenes (HE-MXenes) hold unique potentials as optical device16-18. Regarding HE-MXene, the multi-principal element composition not only introduces localized lattice strain18,19 but also influences the basal plane electrical conductivity20, structural defects21, and termination chemistry22. The complex interplay of these factors may facilitate the separation of photo-generated charge carriers and regulate electron transport. A comprehensive understanding of the underlying mechanisms, however, warrants further systematic investigation. Consequently, HE-MXenes might exhibit superior photo responsivity and saturable absorption compared to pristine MXene, which benefits from their broadband nonlinear optical response, multi-element composition, and rich surface functional groups19-24. In the meanwhile, electrochemical tuning of surface terminations in MXenes can modulate their nonlinear optical absorption, enabling MXene to be applicable to more complex application scenarios, such as optical modulator, optical computing and energy storage22, 25-27. These characteristics make HE-MXenes promising candidates for multifunctional optical logic gates. However, the modulation of their nonlinear optical properties at surface terminations—an unexplored avenue—could unlock the dynamic reconfigurability required for advanced optical logic operations.

Beyond hardware, logic-based neural architectures are gaining attention28-33. Conventional deep networks rely on weighted sums and nonlinearities, making them opaque and resource-intensive34-36. As an alternative, differentiable logic gate networks (DLGNs) are emerging architectures in which each neuron is a logic gate (AND, OR, XOR, etc.) chosen via gradient-based training37, 38. During training, logic selections are relaxed to real values, but at inference the network collapses to a fixed Boolean circuit. The result is a sparse, binary-valued network with no arithmetic beyond logic operations. Critically, inference in DLGNs is efficient. By using only native Boolean gates, DLGNs achieve inference speeds far exceeding conventional neural models. DLGNs has been shown to classify over one million MNIST images per second on a single CPU core, roughly 100× faster than a comparable full-precision network37. The logic-only structure also greatly reduces parameter count and energy per inference, while its inherent binary structure enhances interpretability. On visual benchmarks, DLGNs can match standard accuracy with far fewer resources. Integrating all-optical logic gates with reconfigurable MXene materials and logic-based network architectures may enable ultrafast, parallel, binary-logic AI hardware operating at the speed of light.

Here, we introduce an all-optical logic processing unit (LPU), which utilizes the Kerr nonlinearity effects of HE-MXene TiVCrMoC3Tx in combination with surface termination modulation to enable versatile all-optical computing capabilities. As illustrated in Fig. 1, this LPU dynamically switches among seven fundamental Boolean operations (AND, OR, NOT, NOR, NAND, XOR, XNOR) within a single optical configuration, enabling efficient and flexible logic functionality. By integrating these reconfigurable gates into an electrically tunable optical computing framework, we establish the first platform capable of end-to-end, in-optics training of logic networks. The system achieves 97.7% classification accuracy on the MNIST dataset, demonstrating its promise for ultrafast, energy-efficient, and interpretable optical AI systems. This contribution effectively bridges symbolic logic with electro-reconfigurable neural computing, paving the way for high-speed and interpretable optical AI systems.

Results
Characterization and Modulation of HE-MXene TiVCrMoC3Tx Surface Terminations

Spatial phase modulation (SPM) is one of the all-optical modulation technologies, which can realize the phase modulation of incident light by using the Kerr nonlinearity in low-dimensional materials. The strength of SPM is highly dependent on the intrinsic properties of the materials, such as thickness, number of layers, and lateral dimensions. A transmission electron microscopy (TEM) image of few-layer TiVCrMoC3Tx at a scale of 200 nm has been presented in Figure 2a, indicating that the lateral dimensions of the TiVCrMoC3Tx exhibit a layered structure on the order of hundreds of nanometers. The height distribution curve of HE-MXene also be measured, which exhibits smooth surface flatness (see Supplementary Figure 1 for details). The accordion-like multilayer structure formed after HF etching and exfoliation is evident from SEM characterization (Fig. 2b). It is clearly observed that the original aluminum layers corresponding to the TiVCrMoAlC3 MAX phase have been successfully etched away. To confirm the distribution of elements in the transition metal layer, Figure 2c presents the EDS mapping image of HE-MXene. The results signify the content of transition metals in HE-MXene is nearly equal. The corresponding XRD spectra can be found in Supplementary Figure 1, confirming the synthesis of HE-MXene39, 40.

The modulation of surface terminations can alter the nonlinear optical properties of 2D MXenes, as it affects the electronic structure and band arrangement of the material27, 41. In this work, the surface functional groups of TiVCrMoC3Tx were modulated by applying an external voltage in a transparent electrochemical cell. To further confirm the variation in the surface terminations when samples are subjected to a positive voltage (VA), The X-ray photoelectron spectroscopy (XPS) experiments were carried out. The XPS spectra indicate distinct surface chemical-state evolution between the pristine sample and the sample subjected to a VA of 0.2 V (Fig. 2d). The survey-scan XPS spectrum of the TiVCrMoC3Tx (pristine), confirms the coexistence of constituent transition metals and surface functional groups. The spectrum provides a fingerprint of the as-synthesized material, demonstrating the successful synthesis of a multi-metallic HE-MXene with a complex surface chemistry prior to the electrochemical treatment. The XPS survey spectrum of the TiVCrMoC3Tx (0.2 V) is shown as the red curve. For a clearer quantitative comparison between the pristine and treated states, we performed peak deconvolution on the high-resolution XPS spectra (including C 1s, O 1s, Ti 2p, V 2p, Cr 2p, Mo 3d regions) and extracted compositional changes of each chemical component through quantitative analysis, as shown in Supplementary Fig. 2 and Table 1. These XPS results demonstrate the synergistic regulation of mixed terminal groups in the HE-MXene following electrochemical treatment42, 43. To further comparison of the materials under different applied VA, Raman spectroscopy is carried out (Figure 2e). The pristine sample exhibits a peak at 645 cm-1, corresponding to complex vibrations of the mixed heterogeneous terminal groups (-O, -OH, -F)44, 45. When the sample is subjected to a VA of 0.2 V, the Raman peak at 645 cm-1 shifts to 606 cm-1. Based on the XPS results, this shift can be attributed to the spectroscopic signature of surface termination reorganization and chemical state redistribution in the HE-MXene induced by electrochemical treatment. However, its precise assignment in this system still requires further investigation. The linear optical absorption spectrum under different VA is shown in the Figure 2f. While a slight blue shift and reduced absorbance occur at TiVCrMoC3Tx (0.2 V) in the visible range, the near-infrared region shows strongly overlapping spectra with no wavelength shift and minimal amplitude variations.

In single-/few-layer HE-MXene flakes, nonlinear optical responses originate from intrinsic electronic transitions and carrier dynamics, with surface termination modulation acting uniformly on the electronic structure. In contrast, multilayer stacked films are dominated by thickness effects and electrochemical screening. Thus, the electrically programmable nonlinearity arises from intrinsic single-/few-layer TiVCrMoC3Tx properties. Further discussion can be found in Supplementary Note 1.

Tunable Nonlinear Optics in HE-MXene Controlled by Surface Terminations modulation

While pristine MXenes exhibit inherent metallic conductivity, deliberate functionalization of surface groups enables engineered transitions into semiconducting states or topological insulators42. This transformation occurs due to the interaction between the outer transition metal layers of MXenes and the negatively charged surface functional groups, which can adsorb individual metal cations from the outer layer through charge interactions, thereby altering the original MXene's band structure and leading to the formation of new energy bands. Such modifications in the band structure can influence the optical properties of the materials. Gogotsi et al. investigated the MXene with different functional groups, revealing that the band gap functionalized with -F and -OH groups varied from 0 to 0.1 eV and 0.05 eV, respectively47. Additionally, Berdiyorov et al. conducted first-principles calculations, demonstrating that the absorption coefficient of MXene with -F and -OH functional groups is lower in the visible light region compared to that of pristine MXene with =O groups48. These findings further corroborate the influence of different functional groups on the optical characteristics of MXenes. Therefore, it is feasible to modify the electronic structure or band arrangement of HE-MXenes by regulating the surface terminations, thereby controlling their nonlinear optical response.

In order to verify this conjecture in experiments, the surface terminations of HE-MXene TiVCrMoC3Tx were modulated by applying an external voltage in a transparent electrochemical cell. As shown in Figure 3a, two pieces of indium tin oxide (ITO) coated on silica (SiO2) functions as working electrodes in order to assemble a transparent electrochemical cell. TiVCrMoC3Tx powder is uniformly dispersed in the electrolyte, which consists of EMIBF4 through ultrasonic agitation.

Applying a forward external voltage for 10 minutes within a transparent electrochemical cell drives the cooperative regulation of mixed terminations on the surface of TiVCrMoC3Tx nanosheets (denoted TiVCrMoC3Tx 0.2V). This operation dictates the nonlinear optical (NLO) response of the hierarchically etched HE-MXene, with group concentration directly modulating the photon absorption cross-section and carrier relaxation dynamics. To identify optimal voltage amplitudes for surface functional group modulation in HE-MXene, we systematically investigate voltage-dependent NLO responses through spatial self-phase modulation (SSPM). Originating from optical Kerr effects in TiVCrMoC3Tx nanosheets, SSPM generates tunable diffraction ring, enabling all-optical logic operations via intensity-dependent beam steering. The experimental configuration employs a 532 nm continuous-wave laser (50 mW), collimated through an f = 25 cm lens and directed onto a transparent electrochemical cell containing HE-MXene TiVCrMoC3Tx (Fig. 3b). The SSPM manifests as concentric diffraction rings observed on a white screen positioned behind the sample. This phenomenon arises from laser-induced optical coherence in HE-MXene flakes, where photoexcited charge carriers alter the material's refractive index via ultrafast carrier dynamics (see Supplementary Figure 3 for details). In Figure 3c, the number of rings is shown as a function of laser intensity under different charging voltages. At a charging voltage of +0.4 V, HE-MXene requires the highest laser intensity to initiate SSPM formation. The number of rings increases linearly with light intensity. Furthermore, the SSPM threshold of the samples depends on the charging voltage, resulting in distinct intensity characteristics for a given number of rings (Fig. 3d). It is evident that under positive charging voltages ranging from 0 to 0.4 V, an increase in co-regulation of mixed terminations correlates with a rise in voltage, culminating in its peak at +0.4 V. At this voltage, the light intensity required for ring formation reaches its maximum. We therefore conclude that charging at +0.4 V exerts the most pronounced effect on the SSPM response of the samples. This enhancement can be attributed to the enhanced synergies of mixed terminal groups following charging, which elevates the material's refractive index at the incident laser wavelength, thereby strengthening the SSPM effect.

We further examined the nonlinear absorption properties of HE-MXene dispersed electrolyte under various applied voltages (Fig. 3e). The results demonstrate that electrochemically modulating the functional groups effectively enhance optical nonlinearity. With increasing voltage, the saturable absorption (SA) of the material shows a marked enhancement compared to the uncharged state (0 V). Notably, at a charging voltage of +0.4 V, the SA reaches its maximum, exhibiting an enhancement of approximately 12%. Under conditions of SA, the nonlinear absorption coefficient (β) assumes a negative value; a larger absolute value of β indicates stronger nonlinear performance. The values of β under different applied voltages were derived by fitting to the SA model, as summarized in Fig. 3f. The value of β decreases across the charging range from 0 to +0.4 V, reaching a minimum at +0.4 V. Concurrently, the saturable absorption reaches its maximum, resulting in the highest optical transmittance of the material under both constant and high-intensity illumination, indicative of suppressed light absorption. Since the formation of SSPM in 2D materials requires surpassing a specific intensity threshold, a reduction in absorption necessitates higher incident energy to initiate the SSPM process. Consequently, after charging at +0.4 V, the samples demand increased light intensity to generate SSPM patterns with equivalent numbers of rings.

Here we demonstrate that the surface terminations modulation directly affects the magnitude of the NOL response in the HE-MXene TiVCrMoC3Tx. It is evident that when the applied voltage reaches +0.4 V, the co-regulation of mixed surface terminations in TiVCrMoC3Tx is maximized. The responses of optical nonlinearity arise from variation in the density of states (DOS) above the Fermi level so that different excited-state absorption occurs for TiVCrMoC3Tx (pristine) and TiVCrMoC3Tx (0.4 V). Based on the experimental results, it can be inferred that the diminished DOS above Fermi level in the TiVCrMoC3Tx (0.4 V) reduces the number of unoccupied states available for excited electrons27, thereby suppressing excited-state absorption (as shown in Fig. 3g). As the incident laser intensity increases, the accumulation of electrons in the excited states inhibits further interband transitions, which is signature of Pauli blocking. This mechanism is manifested in the differential transmission between the 0 V and 0.4 V of HE-MXene (Fig. 3e), with the underlying light absorption process elucidated in Figure 3g.

Electrically reconfigurable All-optical Logic Gates

When two optical beams at different wavelengths are co-incident at a small angle on the same spot of a material exhibiting spatial self-phase modulation properties, and the intensity of one beam is held constant below the SSPM threshold, spatial cross-phase modulation (SXPM) can be observed by increasing the intensity of the second beam. In this regime, the weaker beam is modulated by the stronger one, thereby enabling SSPM generation for the weak light wave. To investigate the SXPM effect in HE-MXene, an experimental setup utilizing a multi-wavelength configuration was employed, as illustrated in Fig. 4a. and Fig. 4b demonstrates the SXPM effects observed under simultaneous irradiation with 532 nm and 671 nm laser beams. The rechargeable TiVCrMoC3Tx sample was positioned within the SXPM optical path, where the 532 nm laser served as the signal light (input laser A) and the 671 nm laser operated as the control light (input laser B). Given that both SSPM and SXPM in the material exhibit a minimum excitation threshold, an input light intensity above the threshold (20 W/cm²) is defined as the “1” state, while an intensity below the threshold (10 W cm-2) corresponds to the “0” state. The two beams intersect at a small angle at the same spot on the sample, and the output signal is collected from the 532 nm beam. An observation screen placed at the output end captures the pattern of the 532 nm light. The presence of an SSPM ring pattern is interpreted as an output signal “1”, and its absence as output “0”.

By applying the proposed modulation scheme, we experimentally demonstrate all seven fundamental Boolean logic operations (AND, NOT, NAND, OR, NOR, PXOR, and XNOR) within a single programmable circuit. Representative performance metrics for the AND and XOR operations are shown in Fig. 4c and 4d, respectively. For the AND gate operation, a bias voltage of + 0.4 V is applied to the sample. When both the 532 nm and 671 nm inputs are in the logical '1' state, SXPM induces a discernible SSPM pattern for the 532 nm light, resulting in a logical '1' output (1+1 =1). Conversely, when one input is '1' and the other is '0', no SSPM pattern is observed for the 532 nm beam, yielding a logical output of '0', meaning 1+0=0. Furthermore, when both inputs are set to '0', and the sample is translated axially, the resulting SSPM pattern at 532 nm similarly produces a logical '0' output (0+0=0). By manipulating whether the sample is charged and adjusting its position relative to the focal point, various logical gate functions can be achieved, as illustrated in Supplementary Fig. 6. In addition, transient absorption spectroscopy (see Supplementary Figure 4 for details) reveals that the material reaches its maximum carrier concentration within 550 fs after pumping. Therefore, the theoretical switching speed of the Kerr-based AOLG can reach the sub-picosecond regime, while the experimentally observed operation is typically slower due to optical field buildup and detection latency.

Architecture of the Optical Logic Processing Unit

The Logic Processing Unit (LPU) is the fundamental building block of our optical computing framework. As shown in Fig. 5a, its design is motivated by the need for a modular, reconfigurable, and scalable architecture that can serve as a bridge between material-level nonlinear optics and system-level logic computing. The LPUs performs Boolean computation entirely in the optical domain while maintaining programmability.

The LPUs integrates three essential stages: input encoding, programmable logic operation, and optical readout. Input data are first quantized into discrete values and encoded into light intensities using a spatial light modulator (SLM), which allows pixel-level precision in mapping digital information onto optical carriers. The encoded beams are then directed into the computing core, where they interact with reconfigurable AOLGs. These gates rely on the Kerr nonlinearity of HE-MXenes, combined with electrochemical surface termination modulation, to enable the dynamic programming of logic functions such as AND, OR, XOR, and their complements. By electrically tuning the termination states, we adjust the nonlinear absorption and phase modulation properties of the material, effectively reconfiguring the Boolean operation performed by the gate. Finally, the output is collected by a charge-coupled device (CCD), which records the diffraction patterns and intensity distributions, as illustrated in Fig. 5b, logical outputs are extracted through statistical analysis of the recorded patterns, ensuring robustness against experimental fluctuations and noise49.

The modularity of the LPUs enables flexible scaling, to enable large-scale reconfigurable processing, multiple AOLGs can be integrated into an array configuration. As depicted in Fig. 5c, each AOLG is connected to an independent electrical control source, allowing its logic function to be dynamically selected without affecting neighboring units. In this way, each gate in the array can perform a distinct Boolean operation in parallel, providing a high degree of flexibility and scalability. Unlike fixed-function optical devices such as Mach–Zehnder interferometer–based logic gates, which are limited to one or two predefined operations, the LPUs can flexibly switch among multiple logic functions without redesigning the optical hardware. This property makes it particularly suited for adaptive computing tasks, where the required logic operations may vary dynamically.

When extended beyond a single layer, LPUs can be interconnected to form more complex networks. As shown in Fig. 5d, stacking multiple LPUs enables the construction of a multilayer optical logic gate network.

From a systems perspective, LPUs can be interconnected to construct larger photonic networks. Diffraction naturally provides free-space fan-in and fan-out, while electrical control allows independent programming of each unit. This modularity enables the construction of multilayer architectures capable of performing complex computational tasks, such as image recognition and decision-making. By uniting material-level tunability, device-level programmability, and system-level scalability, the LPUs forms the foundation for the optical differentiable logic gate networks presented in the following section, this hierarchical architecture allows the system to process increasingly complex data by combining multiple reconfigurable logic units.

Three-Layer Optical Differentiable Logic Gate Network

Building on the modular LPUs, we implemented a three-layer optical DLGNs to demonstrate scalability and practical functionality50-53. As illustrated in Fig. 6a, the network architecture consists of three cascaded LPUs layers, interconnected via optical diffraction. Each LPUs performs programmable Boolean operations, and the outputs of one layer are propagated forward as inputs to the next. This hierarchical design allows feature representations to be extracted and refined across multiple stages, mimicking the layered structure of conventional neural networks but with reconfigurable Boolean logic as the core computational primitive.

The feature extraction capability of this network is demonstrated in Fig. 6b, which shows the classification process for the MNIST digits “0” and “9”. Input images are sequentially transformed into optical feature maps across the three layers, with each stage capturing progressively more abstract representations. By the third layer, the system achieves clear separation between classes, illustrating the effectiveness of hierarchical Boolean logic processing in the optical domain.

The classification performance of the optical DLGNs was quantitatively evaluated on the MNIST and CIFAR-10 benchmark datasets. As shown in Fig. 6c, the confusion matrices54 reveal a high overall accuracy of 97.7% on MNIST, with digits such as “0” and “1” recognized at nearly 99% accuracy. This demonstrates the strong feature extraction ability of the network for simple images. On CIFAR-10, the system achieved 50.7% accuracy, reflecting the greater challenge of classifying natural images with complex textures and multiple objects. Category-dependent variations were evident: simple classes such as “airplane” and “automobile” were identified with relatively higher accuracy, while visually complex categories such as “cat” and “dog” remained difficult to distinguish.

The learning dynamics of the network are shown in Fig. 6d, where the convergence curves highlight the contrast between the two datasets. For MNIST, the network converges rapidly within just a few epochs, reaching stable performance. In contrast, on the more challenging CIFAR-10 dataset, which contains natural images with complex textures and multiple objects, the optical DLGNs achieved 50.7% accuracy. While lower than MNIST, this result is notable given that no task-specific optimization was applied and that performance was limited by the CCD dynamic range and SLM refresh rate. The accuracy distribution varied across classes: simpler categories such as “airplane” and “automobile” were identified with relatively higher accuracy, while visually complex categories such as “cat” and “dog” were more difficult to distinguish. This situation may be related to the fact that more complex tasks typically require a larger number of neurons to extract and represent high-level features, whereas our current three-layer implementation offers limited representational capacity. Nevertheless, the system demonstrates robust adaptability without task-specific optimization, underscoring the potential of optical DLGNs as a scalable architecture for diverse AI tasks and suggesting that deeper or larger-scale implementations may further enhance performance.

Together, these results demonstrate the three-layer optical DLGNs as a scalable, interpretable, and energy-efficient computing framework, capable of achieving close-to-state-of-the-art performance on simple datasets while showing promising adaptability to more complex scenarios. This contribution provides an effective bridge between symbolic logic and electrically reconfigurable neural computing, paving the way for high-speed and interpretable optical AI systems.

Methods
Materials Preparation and Characterization

To synthesize the high-entropy MXene TiVCrMoC3Tx, 1 g of TiVCrMoAlC3 MAX phase powder was slowly added to 10 mL of 40 wt% hydrofluoric acid (HF) solution and stirred continuously at 50 °C for 80 h to selectively etch the Al layers. The resulting precipitate was repeatedly washed with deionized (DI) water until the pH of the supernatant exceeded 6, ensuring the complete removal of acid residues. The etched product was then dried in a vacuum oven at 80 °C for 6 h to obtain the multilayer TiVCrMoC3Tx powder. Subsequently, the dried TiVCrMoC3Tx powder was redispersed in DI water, followed by centrifugation at 5720 g for 20 min to remove unexfoliated aggregates. The supernatant was finally diluted with DI water to obtain a stable aqueous dispersion of few-layer TiVCrMoC3Tx nanosheets with a concentration of approximately 5 mg mL⁻¹. For electrochemical termination tuning, the electrolyte was EMIBF₄ (1-ethyl-3-methylimidazolium tetrafluoroborate, 98% purity), and a bias of 0 to +0.4 V was applied across the conductive glass electrodes.

Material Characterization

The morphology, thickness, and structural characteristics of the exfoliated HE-MXenes were examined by atomic force microscopy (AFM, Bruker Dimension Icon), cyclic voltammetry (CV) X-ray diffraction (XRD, Bruker D8 Advance), and high-resolution X-ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250Xi). AFM confirmed that the nanosheets possessed a smooth surface with a typical thickness of about 2 nm, indicating a few-layer structure. XPS was employed to analyze the chemical states of the transition-metal elements and carbon, while XRD verified the successful conversion from the TiVCrMoAlC3 MAX phase to TiVCrMoC3Tx MXene. The electrochemical properties of TiVCrMoC3Tx were investigated by CV in the EMIBF₄ ionic liquid electrolyte. Detailed spectra and analyses are provided in Supplementary Figure 1 and Figure 2.

Spatial Self-Phase Modulation (SSPM) Measurements

The SSPM effect of TiVCrMoC3Tx dispersions was studied using continuous-wave lasers at 405 nm, 532 nm, and 671 nm, each focused by a convex lens with a focal length of 25 cm into a 1 mm quartz cuvette containing the MXene dispersion. The incident beam followed a Gaussian intensity distribution, and the nonlinear phase shift Δψ(r) was determined by the Kerr effect-induced refractive index change. The resulting interference between annular regions satisfying Δψ(r1) − Δψ(r2) = mπ (m = integer) produced a diffraction-ring pattern on the observation screen. The number of rings (N) was linearly related to the laser intensity (I), and the slope dN/dI was used to estimate the third-order nonlinear susceptibility χ(3) and nonlinear refractive index n₂. Ring patterns were captured by a CCD camera, and the effective optical length Leff of the 2D medium was calculated considering the light path through the cuvette. The optical bandgap (1.69 eV) of TiVCrMoC3Tx was determined by a Tauc plot (Supplementary Fig. 3).

Transient-Absorption Spectroscopy

The ultrafast carrier dynamics of TiVCrMoC3Tx were measured using a femtosecond transient-absorption (TA) spectrometer. A 420 nm pump pulse excited the sample, and a supercontinuum probe (480–730 nm) monitored the time-resolved absorption changes. The delay range was 0–300 ps, with data recorded at 652 nm to extract the relaxation dynamics of photogenerated carriers. A broad photobleaching band and sub-picosecond decay confirmed the ultrafast response of the HE-MXene, supporting its application in femtosecond all-optical modulation (Supplementary Fig. 4).

Z-Scan Measurements

The nonlinear refractive index n2 of TiVCrMoC3Tx was measured using a closed-aperture Z-scan technique at 800 nm. A femtosecond laser (repetition rate = 1000 Hz) was split into reference and signal paths by a 50:50 beam splitter. The signal beam was focused onto the sample through a 25 mm lens, and transmitted light was recorded by two detectors to calculate normalized transmittance. The Rayleigh length was z0 = 2π ω02/λ, and the normalized position x = z/z0 was scanned across the focal region. The nonlinear refractive index was obtained by fitting the transmission curve using the standard Sheik-Bahae model, yielding n2 = -9.44 × 10-20 m2 W-1, indicating a self-defocusing Kerr nonlinearity (Supplementary Fig. 4). Supplementary Table 2 listed the progress of nonlinear optical parameters (β, n2) of other 2D materials.

All-Optical Logic Gate Experiments

The SSPM-based all-optical logic gates were realized using TiVCrMoC3Tx dispersions under 532 nm excitation. Light intensities were encoded as binary states: “1” = above SSPM threshold (≈ 30 W cm-2) and “0” = below threshold (≈ 10 W cm-2). The output was defined as “1” when diffraction rings appeared and “0” otherwise. Electrochemical modulation of surface terminations (by applying +0.4 V in a transparent ITO–ITO cell filled with EMIBF₄ electrolyte) dynamically tuned the SSPM threshold, enabling real-time switching among seven Boolean functions (AND, OR, NOT, NAND, NOR, XOR, XNOR) through combinations of sample charging and axial translation. Representative results of NOT and OR gates are shown in Supplementary Figs. 4-5.

Definition of Logic Operations

The binary logic functions implemented in this work are summarized in Supplementary Table 3. Inputs A and B correspond to two optical beams, and their binary states (“0” or “1”) are defined by light intensities below or above the SSPM threshold, respectively. The output is determined by the presence (“1”) or absence (“0”) of a diffraction-ring pattern on the CCD screen.

Statistics

The data are displayed as mean ± standard deviation, all measurements were performed in three parallel experiments (n =3). Correlations were performed with linear regression to determine the goodness of fit (Pearson’s correlation coefficient, R2). For inter-sample comparisons, multiple pairs of samples were analyzed using a two-tailed t-test. The resulting P values were adjusted for multiple hypothesis testing using Bonferroni correction. *P< 0.05, **P<0.01, and ***P <0.001 indicate obvious statistical differences. All statistical analyses were performed using OriginPro.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The study presents an electrically controlled and reconfigurable optical LPU device which works on the Kerr non-linearity principle. This is achieved by modulating the surface terminations of a multi-principal element MXene: TiVCrMoC3Tx. They later demonstrate the efficiency of the unit by testing digit classification accuracy.\nThe study is interesting in its premise and utilization of an electrolyte stage to alter surface terminations on the MXene to derive switching capability and perform Boolean operations. I recommend acceptance of the study with after revision.\nMy comments are as follows:\nMAJOR\n1) The transport of electrons in multi-principal element MXenes is not limited to separation of photo-generated charge carriers due to lattice strains. It is also largely dependent on the electrical conductivities of the basal plane, defects, and termination chemistry. This is an emerging area of research and requires more systematic investigation. I recommend that the authors rephrase this statement and the need for further study in this area.\n2) In figure 2f the authors discuss a blue shift in the MXene. This is interesting because MXenes with 4 layers are expected to show near IR activity. Can the authors comment on near IR behavior and if it can be relevant from a neuromorphic computing standpoint (800-2500 nm range)?\n3) XPS and Raman data: In the XPS data, seemingly, there is no significant difference in the spectrum at 458 eV attributed to increase in Ti-O concentrations. However, the Ti 2p region contains overlapping which requires deconvolution. The 459-459.1 region for example shows TiO2/oxyfluoride species. I recommend the authors quantify this map further for clarity.\n4) It is interesting that the other transition metals do not alter their oxidation states due to the input bias which is a significant drawback of this study. For example, in a V2CTx MXene, the 645 cm-1 peak is attributed to mixed terminal species, not just O. The authors cite Kennedy and Benchakar, however, these studies are on a Ti3C2 (312) system which is different in chemistry to the multi-principal element MXene (413) system.\n5) In the SI, the XRD patterns need indexing. There are peaks seen at 12 degree which shows that the MXene likely has a 211 MAX impurity and is not a pure 413 MXene, as well as not completely etched. I recommend that the authors refer: Nemani, S. K., et al. ACS nano, 15(8), 12815-12825; Zhiguo, et al. Advanced Materials 33.39 (2021): 2101473.\n6) Can the authors comment of the response of the parent MAX phase TiVCrMoAlC3. Seemingly, the outcome is not effected by the presence of MAX phase based on XRD. It will be interesting to note the author's observations on this aspect.", "reviewer_3": "This manuscript presents the design, fabrication, and demonstration of an electrically reconfigurable all-optical logic processing unit (LPU) that exploits the Kerr nonlinearity of a high-entropy MXene. Through surface-termination engineering achieved via electrochemical modulation, the authors dynamically tune the nonlinear optical response of the material, enabling a single optical configuration to perform seven distinct Boolean logic functions without reconfiguring the optical setup.\nThe experimental design is comprehensive, encompassing detailed structural characterizations (TEM, SEM, EDS, XRD, XPS, Raman) that confirm the composition and uniformity of the HE-MXene, as well as systematic optical studies (SPM, Z-scan, transient absorption) that establish the material’s nonlinear coefficients and carrier dynamics. Functional demonstrations of logic operations based on self- and cross-phase modulation further validate the concept. The experimental data are supported by a plausible physical mechanism involving Pauli blocking and termination-dependent modulation of the density of states.\nBy implementing differentiable logic-gate networks in optics, the authors provide a framework that merges symbolic Boolean logic with neural-style training and parallel optical propagation. The integration of these reconfigurable logic units into a three-layer differentiable optical logic-gate network achieves a 97.7% recognition accuracy on the MNIST dataset, underscoring the potential for AI-oriented photonic computing.\nOverall, the manuscript bridges nonlinear photonics, materials engineering, and logic-based computation, addressing a timely challenge in reconfigurable photonic hardware. The combination of HE-MXene tunability and reconfigurable optical logic computing is both novel and compelling. The work is of high quality and should be suitable for publication after minor revisions addressing the points listed below.\n1. Authors may consider providing quantitative data (e.g., modulation speed, cycling stability, or hysteresis behavior) to substantiate the “electrically reconfigurable” nature of the HE-MXene device.\n2. It would be beneficial to include a brief comparison of the nonlinear optical parameters (β, n₂) of TiVCrMoC₃Tₓ with those of other 2D materials (e.g., Ti₃C₂Tₓ, MoS₂, BP) to highlight the advantages of high-entropy MXene.\n3. Please clarify whether the MNIST recognition accuracy (97.7%) was obtained from experimental optical readouts or numerical simulations based on recorded diffraction data. A short methodological note would improve reproducibility.\n4. Because the modulation relies on electrochemical biasing, the authors are encouraged to clarify whether heating, ion migration, or redox reactions could influence the optical response or long-term device stability.\n5. In the Methods section, please clarify the electrolyte composition (EMIBF₄ concentration) and voltage range used during surface termination modulation, as this is essential for reproducibility.\n6. Please ensure consistent use of the term “HE-MXene” throughout the manuscript. The current text alternates between “HE-MXene” and “HE-MXenes,” which may confuse readers."}, "author_response": "Response to the reviewers\nReviewer 1\nThe study presents an electrically controlled and reconfigurable optical LPU device\nwhich works on the Kerr non-linearity principle. This is achieved by modulating the\nsurface terminations of a multi-principal element MXene: TiVCrMoC T . They later\n3 x\ndemonstrate the efficiency of the unit by testing digit classification accuracy.\nThe study is interesting in its premise and utilization of an electrolyte stage to alter\nsurface terminations on the MXene to derive switching capability and perform Boolean\noperations. I recommend acceptance of the study with after revision.\nReply: We would like to thank the reviewer for the careful reading, constructive\nevaluations, and helpful suggestions on our manuscript. In the following, we respond\nto the comments point by point and have revised the manuscript accordingly, our\nresponses in BLUE; revisions in the manuscript in RED.\nMy comments are as follows:\nMAJOR\n1) The transport of electrons in multi-principal element MXenes is not limited to\nseparation of photo-generated charge carriers due to lattice strains. It is also largely\ndependent on the electrical conductivities of the basal plane, defects, and termination\nchemistry. This is an emerging area of research and requires more systematic\ninvestigation. I recommend that the authors rephrase this statement and the need for\nfurther study in this area.\nReply: We appreciate the valuable suggestion of the reviewer.\nThe electron transport behavior in multi-principal element MXenes arises from the\ninterplay of multiple factors—not only lattice strain–induced carrier separation but also\nthe electrical conductivity of the basal planes, structural defects, and surface\ntermination chemistry. To more accurately reflect this multifactorial nature and to\nemphasize the need for further systematic investigation, we have revised the related\nstatement in the revised manuscript “Regarding HE-MXene, the multi-principal\nelement composition not only introduces localized lattice strain18,19 but also influences\nthe basal plane electrical conductivity20, structural defects21, and termination\nchemistry22. The complex interplay of these factors may facilitate the separation of\nphoto-generated charge carriers and regulate electron transport. A comprehensive\nunderstanding of the underlying mechanisms, however, warrants further systematic\ninvestigation.” to replace “Regarding HE-MXenes, due to the incorporation of\nabundant metal elements, the occupancy of multiple sites can result in localized strains\nin the lattice structure18,19. These changes may facilitate the separation of photo-\ngenerated charge carriers and regulate the transportation of the electrons.” in Page 2\n(3rd paragraph of Introduction) with RED color.\nAdded References\nexfoliated MXene flakes employing spatially resolved impedance analysis. Inorganic\nChemistry Communications 179, 114859 (2025).\nthin films: insights from weak localization in the role of thickness, interflake coupling\nand defects. Small 21, 2406334 (2025).\n2) In figure 2f the authors discuss a blue shift in the MXene. This is interesting because\nMXenes with 4 layers are expected to show near IR activity. Can the authors comment\non near IR behavior and if it can be relevant from a neuromorphic computing standpoint\n(800-2500 nm range)?\nReply: We thank the reviewer for this insightful comment.\nWe agree with the reviewer's remark regarding the expected near-IR activity of few-\nlayered HE-MXene. To illustrate the broadband absorption feature. Linear optical\nabsorption spectrum (with a wider range of wavelengths from 350 nm to 1700 nm) of\nthe electrochemical cell containing TiVCrMoC T MXene in electrolyte under different\n3 x\nV\nA\nhas been updated in the Figure 2(f). In the visible range, the TiVCrMoC\nx\n(0.2 V)\nshows a slight blue shift together with a modest reduction of the overall absorbance. As\nfor the near-IR region (~ 800 nm -1800 nm), both spectra exhibit strong and similar\nabsorption, with the curves nearly overlapping. We observe no pronounced wavelength\nshift in this range, only minor variations in absorption amplitude. Beyond\napproximately 1800 nm, the data both two devices are compromised by significant\nbaseline fluctuations and non-physical oscillations. These parts correlate directly with\nthe declining sensitivity of our UV-Vis-NIR instrumentation and the onset of strong\nvibrational absorption from the ionic liquid electrolyte and polymeric spacer. As these\nfeatures are present in both samples and coincide with the instrument's low signal-to-\nnoise regime, we attribute them to experimental artifacts rather than intrinsic material\nproperties. Consequently, we have confined our spectral analysis to the reliable 400–\n1800 nm range. We have added the discussions in the revised manuscript “While a\nslight blue shift and reduced absorbance occur at TiVCrMoC T (0.2 V) in the visible\n3 x\nrange, the near-infrared region shows strongly overlapping spectra with no significant\nwavelength shift and minimal amplitude variations.” to replace “The spectrum indicates\nthat the absorption curve within the range of 400-800 nm shows a blue shift, and the\nsurface termination affects the linear optical absorption property of TiVCrMoC T .” in\n3 x\nPage 4 (last sentence in 2nd paragraph of Results)with RED color.\nBased on previous studies [Laser & Photonics Reviews, 2024, 18], HE-MXene is\nexpected to maintain appreciable optical activity into the longer-wavelength NIR region\n(800–2500 nm). Such broadband responsiveness is advantageous for neuromorphic\ncomputing, where low-power operation and compatibility with telecommunication\nwavelengths are essential. The near IR activity of HE-MXene may enable it to serve as\na key material for broadband neuromorphic computing. We appreciate the reviewer’s\nquestions and fully agree that examining the extended NIR response is an important\ndirection. In the future work, we plan to further evaluate the device-level neuromorphic\nperformance of HE-MXene across this broader wavelength window. We have added the\nfollowing comment to the revised manuscript “Notably, few-layer HE-MXene is\nexpected to exhibit more pronounced optical activity in the near-infrared region,\nsuggesting a potential breakthrough direction for low-power broadband neuromorphic\ncomputing devices.” in Page 12 (2nd paragraph of Discussion) with RED color.\nFigure 2. (f) Linear optical absorption spectrum at different V values.\nA\n3) XPS and Raman data: In the XPS data, seemingly, there is no significant difference\nin the spectrum at 458 eV attributed to increase in Ti-O concentrations. However, the\nTi 2p region contains overlapping which requires deconvolution. The 459-459.1 region\nfor example shows TiO /oxyfluoride species. I recommend the authors quantify this\n2\nmap further for clarity.\nReply: We thank the reviewer for pointing out the need for a more detailed\ninterpretation of the Ti 2p region. We agree that the apparent similarity of the spectra in\nthe Ti 2p region can obscure subtle but meaningful changes in Ti-O related components,\nand a full deconvolution is indeed required for reliable quantification. Following this\nsuggestion, we performed detailed spectral deconvolution of the Ti 2p spectra before\nand after electrochemical treatment, as show in the Supplementary Fig. 2 and Table 1.\nThe quantitative results show that the relative content of the Ti(IV) component\n(~458.7 eV, attributed to TiO₂/titanium oxyfluoride) decreased from 21.74% to 19.70%\nafter treatment. This result confirms that the concentration of the highest oxidation state\ntitanium Ti(IV) on the surface slightly decreases. To comprehensively understand the\nsurface terminals evolution, we integrated the quantitative data of all elements. In the\nO 1s spectra, the lattice oxygen (Metal-O, ~529.9 eV) content increased significantly\nby 8.57%, while the hydroxyl oxygen (C=O, ~531.3 eV) content decreased\nsynchronously by 8.68%. This reveals a pronounced trend of “lattice oxidation” of\nsurface oxygen species. As for other metal valence states, the content of V(II) valence\nstates increased markedly by 10.71%, indicating that some V species were reduced\nduring the process. Concurrently, the content of V(V) and Cr(OH)₃ increased, while\nthat of the higher-valence Mo(VI) decreased. These data collectively illustrate the\nphenomenon of chemical-state-selective reconstruction of surface oxygen species. The\nelectrochemical treatment induces a divergent chemical response among metal centers:\nV is reduced toward lower valence states, Cr undergoes further hydroxylation, while Ti\nand Mo show a tendency toward lower oxidation states. Concurrently, oxygen species\nundergo a marked shift from hydroxyl to lattice coordination. This dynamic process,\ncharacterized by surface oxygen transfer and chemical state reconstruction, is attributed\nto the synergistic effects of surface terminal groups.\nIn the Supporting Information, we have added the description: \"The deconvoluted\nXPS spectra for different elements are shown in Figure 2, and the corresponding\nquantitative data are summarized in Table 1.\" in Page 3 (4th paragraph of “S1.\nCharacterization of high-entropy MXene”) with BLACK color.\nIn the revised manuscript, we have added the description “To further confirm the\nvariation in the surface terminations when samples are subjected to a positive voltage\n(V ), The X-ray photoelectron spectroscopy (XPS) experiments were carried out.\nA\nFigure 2d shows the XPS spectra of the pristine sample and the sample subjected to a\nV of 0.2 V. The survey-scan XPS spectrum of the TiVCrMoC T (pristine), confirms\nA 3 x\nthe coexistence of constituent transition metals and surface functional groups. The\nspectrum provides a fingerprint of the as-synthesized material, demonstrating the\nsuccessful synthesis of a multi-metallic HE-MXene with a complex surface chemistry\nprior to the electrochemical treatment. The XPS survey spectrum of the TiVCrMoC T\n3 x\n(0.2 V) is shown as the red curve. For a clearer quantitative comparison between the\npristine and treated states, we performed peak deconvolution on the high-resolution\nXPS spectra (including C 1s, O 1s, Ti 2p, V 2p, Cr 2p, Mo 3d regions) and extracted\ncompositional changes of each chemical component through quantitative analysis, as\nshown in Supplementary Fig. 2 and Table 1. These XPS results demonstrate the\nsynergistic regulation of mixed terminal groups in the HE-MXene following\nelectrochemical treatment42, 43.” to replace “To further confirm this point, we also\nconducted XPS characterization. The Figure 2e shows the Ti 2p window of the pristine\nsample and the sample subjected to a V of 0.2 V. For ease of comparison, the two\nA\ncurves have been normalized with the maximum intensity set to 1. Obviously, there is\ndifference in XPS spectral intensities between TiVCrMoC T (=O rich) and\n3 x\nTiVCrMoC T (pristine). The peak at 455 eV corresponds to Ti 2p3/2, and the peak at\n3 x\n461 eV to Ti 2p1/2. The peak near 458.53 eV can be attributed to Ti-C, and the changes\nwithin the 458-461 eV range are related to the increase in Ti=O40, 41” in Page 4 (2nd\nparagraph of Results) with RED color.\nWe sincerely appreciate your expert advice, which has greatly helped us improve the\nclarity of our data analysis and the rigor of our conclusions.\nRevised Reference:\n42. Tang J, Mathis T S, Kurra N, et al. Tuning the electrochemical performance of\ntitanium carbide MXene by controllable in situ anodic oxidation. Angewandte Chemie\n131, 18013–18019 (2019).\nFigure 2. (d) XPS spectra\nSupplementary Figure 2. HR-XPS spectra recorded for HE-MXene at different V values\nA\nSupplementary Table 1: Quantitative HR-XPS deconvolution results of the HE-MXene before\nand after electrochemical treatment.\nElement Chemical State BE(eV) Area_before Area_after Δ\nTi 2p Ti-C 2p3/2 455.04 53.56% 53.14% -0.42%\nTi-C 2p1/2 460.86\nTi(II) 2p3/2 456.21 13.45% 17.57% 4.12%\nTi(II) 2p1/2 462.30\nTi(III) 2p3/2 457.64 11.25% 9.59% -1.66%\nTi(III) 2p1/2 463.66\nTi(IV) 2p3/2 458.72 21.74% 19.70% -2.04%\nTi(IV) 2p1/2 464.89\nV 2p V(II) 2p3/2 513.61 29.99% 40.70% 10.71%\nV(II) 2p1/2 521.11\nV(III) 2p3/2 514.80 26.56% 20.88% -5.68%\nV(III) 2p1/2 522.47\nV(IV) 2p3/2 516.02 17.35% 11.67% -5.68%\nV(IV) 2p1/2 523.52\nV(V) 2p3/2 517.09 26.10% 26.75% 0.65%\nV(V) 2p1/2 524.79\nCr 2p Cr(III) 2p3/2 575.01 42.26% 40.63% -1.63%\nCr(III) 2p1/2 584.28\nCr(OH) 2p3/2 577.11 37.65% 42.64% 4.99%\nMo(IV) 3d3/2 232.18\nMo(V) 3d5/2 230.45 21.06% 22.34% 1.28%\nMo(V) 3d3/2 233.71\nMo(VI) 3d5/2 232.58 22.50% 20.69% -1.81%\nMo(VI) 3d3/2 235.60\nC 1s Metal-C 282.35 5.64% 11.34% 5.70%\nC-C 284.80 66.75% 63.24% -3.51%\nC-O 286.23 15.77% 16.14% 0.37%\nC=O 288.52 11.84% 9.28% -2.56%\nO 1s Metal-O 529.90 15.31% 23.88% 8.57%\nC=O 531.34 37.03% 28.35% -8.68%\nC-O 532.67 47.66% 47.77% 0.11%\n4) It is interesting that the other transition metals do not alter their oxidation states due\nto the input bias which is a significant drawback of this study. For example, in a V CT\n2 x\nMXene, the 645 cm-1 peak is attributed to mixed terminal species, not just O. The\nauthors cite Kennedy and Benchakar, however, these studies are on a Ti C (312) system\n3 2\nwhich is different in chemistry to the multi-principal element MXene (413) system.\nReply: Thanks for your comments.\nWe fully agree with your perspective on the chemical complexity of the HE-MXene\nsystem and acknowledge that directly citing literature on the Ti C T system to interpret\n3 2 x\nthe Raman peak at ~645 cm⁻¹ in the initial draft was insufficiently rigorous. In the\nrevised manuscript, we have amended the relevant description to more cautiously state\n“To further comparison of the materials under different applied V , Raman\nA\nspectroscopy is carried out (Figure 2e). The pristine sample exhibits a peak at 645 cm-\n1, corresponding to complex vibrations of the mixed heterogeneous terminal groups (-\nO, -OH, -F)44, 45. When the sample is subjected to a V of 0.2 V, the Raman peak at 645\nA\ncm-1 shifts to 606 cm-1. Based on the XPS results, this shift can be attributed to the\nspectroscopic signature of surface termination reorganization and chemical state\nredistribution in the HE-MXene induced by electrochemical treatment. However, its\nprecise assignment in this system still requires further investigation.” to replace\n“Kennedy38 and Benchakar39 et al. separately synthesized Ti C T under different\n3 2 x\nchemical etching conditions and found that the Raman peak showed a similar red shift\nnear 620 cm-1. By means of quantitative XPS characterization, they revealed that this\nshift corresponded to samples with more =O terminations. Therefore, the shift of the\nRaman spectrum in the Figure 2d indicates that at a potential of 0.2 V, more =O\nterminals are formed than TiVCrMoC T (pristine).” in Page 4 (2nd paragraph of\n3 x\nResults) with RED color.\nAdded Reference:\nElectrochemical Behavior of Layered Vanadium Nitride MXene. ACS nano 19, 34438-\n34448 (2025).\nof 2D carbide and carbonitride MXenes. Chemistry of Materials 35, 8239-8247 (2023).\nFollowing your suggestion, we have obtained more detailed surface chemical\nevidence through systematic XPS quantitative analysis. The data reveal that upon\napplying bias, the oxidation states of the transition metals undergo significant and\nselective changes. V and Cr parts are oxidized/hydroxylated, while Mo and Ti show a\ntrend toward reduction. Oxygen species undergo a marked shift from hydroxyl to lattice\ncoordination. In the revised manuscript, we have made comprehensive corrections\nrelated to the new conclusion of selective surface reconstruction, replacing the previous\ndescription of \"=O rich.\"\nIn the Supporting Information, we have added the description: \"Systematic XPS\nanalysis reveals that Ti and Mo tend to be reduced (e.g. Ti(IV) and Mo(VI)), whereas\nV and Cr tend to be oxidized or hydroxylated (e.g. V(V) and Cr(OH)₃), suggesting\nselective migration and re-coordination of oxygen species among different metal sites\nafter electrochemical treatment. Furthermore, O 1s spectra indicate that the oxygen\nspecies themselves undergo chemical state reconstruction (an increase in lattice oxygen\nand a decrease in hydroxyl oxygen). In summary, these results demonstrate that the\ninherent oxygen/hydroxyl groups on the surface undergo desorption, transformation,\nand redistribution upon electrochemical stimulation, leading to selective modification\nof the surface terminals. This also implies synergistic regulation by mixed terminal\ngroups (-O, -OH, and -F)1,2.\" in Page 3 (4th paragraph of “S1. Characterization of high-\nentropy MXene”) with BLACK color.\nWe believe these revisions have substantially strengthened the clarity and rigor of\nour interpretation. Thank you again for your valuable suggestions.\nAdded Supplementary Reference\n1. Tang J, Mathis T S, Kurra N, et al. Tuning the electrochemical performance of titanium carbide\nMXene by controllable in situ anodic oxidation. Angewandte Chemie 131, 18013–18019 (2019).\n2. Schultz T, Frey N C, Hantanasirisakul K, et al. Surface Termination Dependent Work Function\nand Electronic Properties of Ti₃C₂Tₓ MXene. Chem. Mater 31, 6590–6597 (2019).\n5) In the SI, the XRD patterns need indexing. There are peaks seen at 12 degree which\nshows that the MXene likely has a 211 MAX impurity and is not a pure 413 MXene,\nas well as not completely etched. I recommend that the authors refer: Nemani, S. K., et al.\nACS nano, 15(8), 12815-12825; Zhiguo, et al. Advanced Materials 33.39 (2021):\n2101473.\nReply: We sincerely thank the reviewer for the insightful comment regarding the XRD\npattern.\nA detailed indexing of the XRD pattern has been shown in the Supplementary Figure\n1d. The features in the XRD pattern can be distinguished based on the angular regions.\nThe peaks at 5.2°, 10°, and 15.4° form a consistent 001 series, confirming the presence\nof a layered TiVCrMoC T MXene phase with partial restacking.\n3 x\nWe fully agree with the reviewer that the peak observed between 30-45° corresponds\nwell to those of the TiVCrMoAlC₃ MAX phase, indicating an incomplete etching of the\nprecursor. We appreciate the reviewer's guidance in directing us to the highly relevant\nwork by Nemani and Zhiguo. Nemani et al. showed that ideal and fully etched MXenes\nexhibit minimal intensity in this angle range. The fact that these peaks are still\nobservable in our sample suggests that a small amount of MAX phase, which is\nreasonable considering the etching conditions and the multilayer nature of our material.\nWe note that the key evidence for the successful formation of the TiVCrMoC T HE-\n3 x\nMXene phase remains the dominant (002) peak at ~5.0°. The significant shift to a lower\nangle confirms a large expansion of the interlayer spacing, which is a definitive\nsignature of HE-MXene. The relative peak intensities indicate that the MAX phase is a\nminor component, with the HE-MXene phase constituting the overwhelming majority\nof the material. The nonlinear optical response reported herein is dominated by the HE-\nMXene phase. We therefore conclude that the presence of this trace impurity does not\ncompromise the key conclusions of this study. Future efforts will be directed toward\nfurther refining the synthesis to minimize these secondary phases.\nWe have added a discussion in the revised Supplementary Information “XRD\nanalysis confirms successful synthesis of HE-MXene, indicated by a dominant peak at\n~5.0° signifying expanded interlayer spacing post-exfoliation. A minor peak from the\nunetched MAX phase precursor is attributed to the complex multi-metal precursor\nchemistry but constitutes only a trace impurity. The phase-pure HE-MXene is the\ndominant component, and the presence of this minor impurity does not affect the\nexperiment conclusions regarding the material's intrinsic nonlinear optical properties.”\nto replace “We also used XRD spectra to verify the formation of HE-MXene. According\nto the TiVCrMoC T patterns, which is first reported by Srinivasa et al., it indicates that\n3 x\nour sample exhibits a multilayer structure.” in Page 2 (3rd paragraph of “S1.\nCharacterization of high-entropy MXene”) with BLACK color.\nWe also revised the description in the revised manuscript “The corresponding XRD\nspectra can be found in Supplementary Figure 1, confirming the synthesis of HE-\nMXene39,40.” to replace “The corresponding XRD spectra can be found in\nSupplementary Figure S1.” in Page 4 (from Line 14 to Line 15) with RED color.\nAdded References\nTiVNbMoC and TiVCrMoC . ACS Nano 15, 12815-12825 (2021).\n3 3\n(MXenes). Advanced Materials 33, 2101473 (2021).\nSupplementary Figure 1. (d) XRD pattern\n6) Can the authors comment of the response of the parent MAX phase TiVCrMoAlC .\nIt will be interesting to note the author's observations on this aspect.\nReply: We thank the reviewer for this insightful comment.\nWe agree with the reviewer that the modulation performance of TiVCrMoC Tₓ HE-\nTiVCrMoAlC₃ MAX phase. MAX phases may exhibit weak or detectable nonlinear\nresponses under high-intensity irradiation, but their contribution is negligible under our\nexperimental conditions. As a MAX-phase ceramic that crystallizes in a hexagonal\nstructure, its electronic structure is anticipated to host second- and third-order optical\nnonlinearities. However, in this work, due to the HE-MXene’s two-dimensional nature,\nsurface plasmon effect, lower threshold and abundant functional groups, the nonlinear\nresponse is still attributed to the action of HE-MXene nanosheets. Furthermore, the\nelectrochemical activity of MAX phase is significantly lower than that of MXene,\nwhich makes it insensitive for the electrochemical control of its nonlinear optical\nproperties. This is not conducive to the realization of the functionality of reconfigurable\nlogic gates.\nIt is worth noting that the reviewer's suggestions are very attractive. In the future,\nconducting high-power optical experiments based on pure MAX materials might lead\nto more interesting optical discoveries. We thank the reviewer again for prompting this\nimportant discussion, which has strengthened the scientific rigor of our manuscript. We\nhave added a prospect in the revised Supplementary Information “In the future, if\nmaterial engineering can effectively reduce their optical losses, MAX materials are\nexpected to be applied in the field of LPU.” in Page 3 (3rd paragraph of “S1.\nCharacterization of high-entropy MXene”) with BLACK color.\nReviewer 3\nThis manuscript presents the design, fabrication, and demonstration of an\nelectrically reconfigurable all-optical logic processing unit (LPU) that exploits the Kerr\nnonlinearity of a high-entropy MXene. Through surface-termination engineering\nachieved via electrochemical modulation, the authors dynamically tune the nonlinear\noptical response of the material, enabling a single optical configuration to perform\nseven distinct Boolean logic functions without reconfiguring the optical setup.\nThe experimental design is comprehensive, encompassing detailed structural\ncharacterizations (TEM, SEM, EDS, XRD, XPS, Raman) that confirm the composition\nand uniformity of the HE-MXene, as well as systematic optical studies (SPM, Z-scan,\ntransient absorption) that establish the material’s nonlinear coefficients and carrier\ndynamics. Functional demonstrations of logic operations based on self- and cross-phase\nmodulation further validate the concept. The experimental data are supported by a\nplausible physical mechanism involving Pauli blocking and termination-dependent\nmodulation of the density of states.\nBy implementing differentiable logic-gate networks in optics, the authors provide\na framework that merges symbolic Boolean logic with neural-style training and parallel\noptical propagation. The integration of these reconfigurable logic units into a three-\nlayer differentiable optical logic-gate network achieves a 97.7% recognition accuracy\non the MNIST dataset, underscoring the potential for AI-oriented photonic computing.\nOverall, the manuscript bridges nonlinear photonics, materials engineering, and\nlogic-based computation, addressing a timely challenge in reconfigurable photonic\nhardware. The combination of HE-MXene tunability and reconfigurable optical logic\ncomputing is both novel and compelling. The work is of high quality and should be\nsuitable for publication after minor revisions addressing the points listed below.\nReply: We thank the reviewer for the careful review of our manuscript. We greatly\nappreciate the comprehensive summary, insightful comments and high regard for our\nresearch. In the following, we will response to these comments point to point.\n1. Authors may consider providing quantitative data (e.g., modulation speed, cycling\nstability, or hysteresis behavior) to substantiate the “electrically reconfigurable” nature\nof the HE-MXene device.\nReply: Thanks for your suggestion.\nWe agree with your point that quantitative metrics are essential to demonstrate the\nelectrically reconfigurable nature of our HE-MXene-based device. We have added\nexplanation in the Supplementary Information “To gain a more quantitative insight into\nthe electrical reconfigurability and cycling stability of the HE-MXene device, we\nfurther carried out cyclic voltammetry (CV) measurements on TiVCrMoC₃T in the\nx\nsame EMIBF₄ ionic liquid electrolyte, as shown in the Figure c. In this configuration, a\nthin TiVCrMoC₃T film was drop-cast onto the positive electrode and the device was\nx\ncycled between -0.5 and 0.5 V (high-potential limit set to 0.6 V in the instrument) at a\nscan rate of 50 mV s⁻¹ for 30 consecutive segments.” in Page 2 (2nd paragraph of “S1.\nCharacterization of high-entropy MXene”) with BLACK color.\nCorresponding guidance have also been added to the Material Characterization in\nrevised manuscript “The electrochemical properties of TiVCrMoC T were\n3 x\ninvestigated by CV in the EMIBF₄ ionic liquid electrolyte. Detailed spectra and\nanalyses are provided in Supplementary Figure 1 and Figure 2.” in Page 14 (1st\nparagraph of “Material Characterization”) with RED color.\nSupplementary Figure 1. (c) CV curve,\n2. It would be beneficial to include a brief comparison of the nonlinear optical\nparameters (β, n₂) of TiVCrMoC₃Tₓ with those of other 2D materials (e.g., Ti₃C₂Tₓ,\nMoS₂, BP) to highlight the advantages of high-entropy MXene.\nReply: Thanks for your suggestion.\nWe have added the table to the revised Supplementary Information “Table 2 listed the\nprogress of nonlinear optical parameters (β, n₂) of other 2D materials. Compared with\nother MXene materials, TiVCrMoC₃Tₓ nanosheets exhibit a slightly larger nonlinear\nabsorption coefficient and nonlinear refractive index.” in Page 9 (4th paragraph of “S3.\nNonlinear optical properties of TiVCrMoC T ”) with BLACK color.\n3 x\nSupplementary Table 2 Nonlinear optical parameters of TiVCrMoC₃Tₓ with other materials\nMaterials λ (nm) β (cm/GW) n (m2/W) Ref.\n3 x\nTi C T 515 -0.0176 -1.81×10-20 3\n3 2 x\nTa C T 515 -0.076 -5.1×10-20 3\n4 3 x\nTi CN 800 -0.054 - 4\nBlack phosphorus 800 -0.0138 - 6\nMoS 488 - 9.32×10-11 7\n3. Stavrou, M., Chacon, B., Farsari, M., et al. Emerging Ta₄C₃ and Mo₂Ti₂C₃ MXene nanosheets for\nultrafast photonics. Adv. Opt. Mater. 13, 2403277 (2025).\n4. Gao L, Chen H, Kuklin A V, et al. Optical properties of few-layer Ti₃CN MXene: from\nexperimental observations to theoretical calculations. ACS Nano 16, 3059-3069 (2022).\n5. Zhang, J., Yu, X., Han, W., et al. Broadband spatial self-phase modulation of black phosphorus.\nOpt. Lett. 41, 1704–1707 (2016).\n6. Wang K, Beata M. Szydłowska, Wang G ,et al. Ultrafast nonlinear excitation dynamics of black\nphosphorus nanosheets from visible to mid-infrared. ACS Nano 10, 6923–6932 (2016).\n7. Wang G , Zhang S , Zhang X ,et al. Tunable nonlinear refractive index of two-dimensional MoS₂,\nWS₂, and MoSe₂ nanosheet dispersions. Photonics Res. 3, 51–55 (2015).\n8. Zhang H, Lu SB, Zheng J, et al. Molybdenum disulfide (MoS₂) as a broadband saturable absorber\nfor ultrafast photonics. Opt. Express 22, 7249–7260 (2014).\n3. Please clarify whether the MNIST recognition accuracy (97.7%) was obtained from\nexperimental optical readouts or numerical simulations based on recorded diffraction\ndata. A short methodological note would improve reproducibility.\nReply: We appreciate the reviewer’s valuable comment.\nThe reported 97.7% MNIST recognition accuracy is obtained through a hybrid optical–\nnumerical workflow. The optical computation is performed entirely in the experimental\ndomain, while only the final label assignment is carried out digitally. Specifically: The\ninput MNIST images are encoded onto an SLM and sequentially processed through the\nthree-layer optical logic processing unit. The nonlinear SSPM/SXPM-based logic\noperations occur physically in the AOLG. The resulting diffraction patterns are\nrecorded experimentally using a CCD, without any numerical simulation of optical\npropagation or nonlinear response. The CCD-measured diffraction intensities are then\nconverted into binary logic outputs through a simple numerical mapping (threshold-\nbased classifier), which assigns the final recognition label. This step does not emulate\noptical behavior; it only interprets the experimentally generated patterns to ensure\nreproducibility and consistent benchmarking. Thus, the logic computation is entirely\noptical, while the final classification step is numerical.\n4. Because the modulation relies on electrochemical biasing, the authors are encouraged\nto clarify whether heating, ion migration, or redox reactions could influence the optical\nresponse or long-term device stability.\nReply: We sincerely thank the reviewer for raising this important point regarding\npossible parasitic effects during electrochemical biasing. In our device, the applied\npotentials (-0.4 to +0.4 V) are intentionally kept far below the electrochemical stability\nwindow of the EMIBF₄ ionic liquid (~4 V)1, ensuring that neither noticeable Joule\nheating nor electrolyte decomposition occurs during modulation. The ionic\nconductivity of EMIBF₄ is relatively low, and the electric field applied in our\nconfiguration is weak; therefore, long-range ion migration is strongly suppressed. This\nis further supported by the absence of measurable hysteresis in repeated modulation\ncycles and the nearly unchanged linear optical absorption after multiple voltage sweeps.\nTo examine whether irreversible redox reactions or structural changes take place, we\nperformed in-situ Raman and XPS measurements before and after biasing. Both\ncharacterizations show only minor and reversible adjustments in surface coordination\nenvironments—consistent with the cooperative behavior of mixed O/OH/F\nterminations—without the emergence of new oxidation states or signatures of lattice\ndegradation. These observations indicate that the optical modulation originates from a\nmild reconfiguration of surface terminations mediated by mixed-termination synergy,\nrather than redox-driven bulk chemical transformations.\nWe also conducted cycling-stability tests (CV measurements and repeated optical-\nnonlinearity measurements), which show stable response over multiple cycles,\nindicating that no cumulative structural or chemical deterioration is introduced under\nthe applied bias. Together, these findings indicate that heating, long-range ion migration,\nand irreversible redox reactions are unlikely to make a substantial contribution within\nour operating voltage range, and that the observed optical response is predominantly\nassociated with a reversible surface-termination modulation.\n[1] Wu F, Zhu N, Bai Y, et al. Highly Safe Ionic Liquid Electrolytes for Sodium-Ion Battery: Wide\nElectrochemical Window and Good Thermal Stability. ACS Appl. Mater. Interfaces 8, 21381–21386\n(2016).\n5. In the Methods section, please clarify the electrolyte composition (EMIBF₄\nconcentration) and voltage range used during surface termination modulation, as this is\nessential for reproducibility.\nReply: We thank the reviewer for highlighting the need for precise experimental details\nto ensure reproducibility. In response, we have added the explanation to Methods\nsection of revised manuscript “For electrochemical termination tuning, the electrolyte\nwas EMIBF₄ (1-ethyl-3-methylimidazolium tetrafluoroborate, 98% purity), and a bias\nof 0 to +0.4 V was applied across the conductive glass electrodes.” in Page 13 (1st\nparagraph of “Materials Preparation and Characterization”) with RED color.\n6. Please ensure consistent use of the term “HE-MXene” throughout the manuscript.\nThe current text alternates between “HE-MXene” and “HE-MXenes,” which may\nconfuse readers.\nReply: Thanks for your careful observation. We have carefully reviewed the entire\nmanuscript and standardized the terminology. The term “HE-MXene” is now used\nconsistently when referring to the specific material studied in this work, whereas “HE-\nMXenes” is reserved only for general discussions involving multiple compositions or\nthe material family. All occurrences have been revised accordingly throughout the main\ntext and Supplementary Information to ensure clarity and consistency."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have revised the manuscript and have addressed my comments satisfactorily. I recommend acceptance of the study with minor revisions. My comments are as follows:\n1. Quantified percentages and metrics need std. deviations. For example in the revised XPS quantification discussions, the standard deviations are missing.\n2. The authors have now mapped the oxidation states for the transition metals which was essential. I recommend that the authors provide a comprehensive table of data as it will be helpful to the reader.\n3. I recommend that the discussion on single flake vs multi-flake MXene be moved to the main section in an abridged manner while keeping the discussion in detail in the SI as it is critical for distinguishing the study from a single flake MXene vs multi-flake stacked MXene study.\n4. on point 6, I strongly recommend the authors to elaborate the MAX vs MXene discussion and provide inputs on why the presence of the precursor MAX may not impact LPU at large.", "reviewer_3": "This manuscript is well revised."}, "author_response": "Response to the reviewers\nReviewer 1\nThe authors have revised the manuscript and have addressed my comments\nsatisfactorily. I recommend acceptance of the study with minor revisions. My\ncomments are as follows:\n1. Quantified percentages and metrics need std. deviations. For example in the revised\nXPS quantification discussions, the standard deviations are missing.\nReply: Thank you for your review and valuable suggestion.\nWe have added the standard deviations, \"Deviation_before\" and \"Deviation_after\"\nfrom the Quantitative HR-XPS, to the Table 1 in Supporting Information section. The\nresults show that the variations before and after electrochemical treatment are\nminimal, indicating the reliability of the data.\nTable 1: Quantitative HR-XPS deconvolution results of the HE-MXene before and\nafter electrochemical treatment.\nElement Chemical BE FWHM_ FWHM_ Area_ Deviations Area_ Deviations\nΔ Area\nState (eV) before after before _before after _after\n(eV) (eV)\nTi 2p Ti-C 2p3/2 455.04 1.05 1.08 53.56% 0.4201 53.14% 0.2571 -0.42%\nTi-C 2p1/2 460.86 1.55 1.81\nTi(II) 2p3/2 456.21 1.15 1.45 13.45% 17.57% 4.12%\nTi(II) 2p1/2 462.30 1.70 1.86\nTi(III) 2p3/2 457.64 1.47 1.29 11.25% 9.59% -1.66%\nTi(III) 2p1/2 463.66 2.45 1.65\nTi(IV) 2p3/2 458.72 1.44 1.44 21.74% 19.70% -2.04%\nTi(IV) 2p1/2 464.89 2.41 1.84\nV 2p V(II) 2p3/2 513.61 1.16 1.30 29.99% 0.1717 40.70% 0.1821 10.71%\nV(II) 2p1/2 521.11 1.16 1.30\nV(III) 2p3/2 514.80 1.47 1.45 26.56% 20.88% -5.68%\nV(III) 2p1/2 522.47 1.47 1.45\nV(IV) 2p3/2 516.02 1.47 1.16 17.35% 11.67% -5.68%\nV(IV) 2p1/2 523.52 1.47 1.16\nV(V) 2p3/2 517.09 1.45 1.44 26.10% 26.75% 0.65%\nV(V) 2p1/2 524.79 1.45 1.44\nCr 2p Cr(III) 2p3/2 575.01 2.23 2.08 42.26% 0.4615 40.63% 0.3938 -1.63%\nCr(III) 2p1/2 584.28 2.23 2.08\nCr(OH)3 2p3/2 577.11 2.42 2.58 37.65% 42.64% 4.99%\nCr(OH)3 2p1/2 586.72 2.42 2.58\nCrF3 2p3/2 579.57 2.87 3.35 20.09% 16.73% -3.36%\nCrF3 2p1/2 589.34 2.87 3.35\nMo 3d Mo(IV) 3d5/2 229.04 1.12 1.22 56.44% 0.3346 56.97% 0.1113 0.53%\nMo(IV) 3d3/2 232.18 1.12 1.22\nMo(V) 3d5/2 230.45 1.48 1.73 21.06% 22.34% 1.28%\nMo(V) 3d3/2 233.71 1.48 1.73\nMo(VI) 3d5/2 232.58 1.44 1.51 22.50% 20.69% -1.81%\nMo(VI) 3d3/2 235.60 1.44 1.51\nC 1s Metal-C 282.35 1.14 1.11 5.64% 0.7455 11.34% 0.3968 5.70%\nC-C 284.80 1.47 1.61 66.75% 63.24% -3.51%\nC-O 286.23 1.58 1.73 15.77% 16.14% 0.37%\nC=O 288.52 1.30 1.55 11.84% 9.28% -2.56%\nO 1s Metal-O 529.90 1.53 1.48 15.31% 0.4074 23.88% 0.493 8.57%\nC=O 531.34 1.64 1.85 37.03% 28.35% -8.68%\nC-O 532.67 1.92 2.01 47.66% 47.77% 0.11%\n2. The authors have now mapped the oxidation states for the transition metals which\nwas essential. I recommend that the authors provide a comprehensive table of data as\nit will be helpful to the reader.\nReply: We thank the reviewer for this valuable suggestion and agree that a\ncomprehensive data table is essential for clarity. As suggested, Table 1 in the\nSupporting Information has been expanded to include the Full Width Half Maximum\n(FWHM) data before and after electrochemical treatment, with separate columns for\n\"FWHM_before (eV)\" and \"FWHM_after (eV)\".\n3. I recommend that the discussion on single flake vs multi-flake MXene be moved to\nthe main section in an abridged manner while keeping the discussion in detail in the\nSI as it is critical for distinguishing the study from a single flake MXene vs\nmulti-flake stacked MXene study.\nReply: We sincerely thank the reviewer for this insightful suggestion. We fully agree\nthat clearly distinguishing single-/few-layer MXene flakes from multi-flake stacked\nMXene assemblies is critical for accurately positioning the present work.\nIn response, we have added a concise discussion on the distinction between\nsingle-/few-layer and multi-flake MXene systems to the revised manuscript (Results\nand Discussion section). Specifically, we now explicitly clarify in the main text that\nthe TiVCrMoC₃T used in this study consists predominantly of single- and few-layer\nx\nMXene flakes, as evidenced by XRD/AFM analysis. We further emphasize that the\nobserved electrically programmable nonlinear optical response arises from intrinsic\nsingle-/few-layer MXene properties and voltage-induced surface termination\nmodulation, rather than interflake multiple scattering, thermal accumulation, or\nthickness-dependent optical path effects that are typically present in multi-flake\nstacked MXene films.\nThe detailed discussion comparing single-/few-layer flakes versus multi-flake\nstacked MXene behavior, including extended morphological statistics and control\nexperiments, has been preserved in the Supporting Information.\nWe have added the discussion to the revised manuscript \"In single-/few-layer\nHE-MXene flakes, nonlinear optical responses originate from intrinsic electronic\ntransitions and carrier dynamics, with surface termination modulation acting\nuniformly on the electronic structure. In contrast, multilayer stacked films are\ndominated by thickness effects and electrochemical screening. Thus, the electrically\nprogrammable nonlinearity arises from intrinsic single-/few-layer TiVCrMoC₃Tₓ\nproperties. Further discussion can be found in Supplementary Section 1.\" in Page 5\n(3rd paragraph of “Characterization and Modulation of HE-MXene TiVCrMoC₃Tₓ\nSurface Terminations”) with RED color.\nWe have added the detailed discussion to the Supporting Information \"To\ndistinguish the performance of single-/few-layer HE-MXene nanosheets from that of\nmulti-flake stacked assemblies, the following discussion highlights why\nsingle-/few-layer TiVCrMoC T serves as a superior platform for electrically\n3 x\nprogrammable nonlinear optics. This distinction is essential for designing reliable,\nhigh-performance nonlinear optical modulators, where precise and fast electrical\ncontrol over the optical response is paramount.\nStructurally, the electronic and optical properties of HE-MXenes are strongly\ndimension-dependent. In this study, we focus on single- and few-layer TiVCrMoC T\n3 x\nnanosheets, which exhibit a structural configuration distinct from that of multilayer\nassemblies. AFM thickness profiling and XRD analyses confirm that the synthesized\nmaterials consist predominantly of isolated flakes with minimal layer stacking. This\nconfiguration ensures maximal exposure of active metal sites and minimal interlayer\nelectronic coupling. In contrast, conventional multilayer HE-MXene films are\ncomposed of randomly restacked flakes, leading to significant interlayer shielding,\nreduced interfacial accessibility, and heterogeneous thickness distributions—features\nthat introduce extrinsic complexities into both optical and electrochemical\nresponses12.\nIn terms of nonlinear optical response, the behavior of single-/few-layer\nTiVCrMoC T originates from the intrinsic electronic structure of individual flakes.\n3 x\nMechanisms such as saturable absorption, excited-state absorption, and Kerr-type\nnonlinear refraction are governed directly by band-structure-mediated carrier\ndynamics. The well-defined, homogeneous interaction volume offered by these flakes\nto ultrafast laser pulses enables precise quantification of nonlinear coefficients and\nmodulation depth13. Conversely, in multilayer stacks, the apparent nonlinear response\nis often dominated by extrinsic effects, including interflake scattering, extended\noptical-path absorption, and thermal accumulation across layers. These\nthickness-dependent phenomena produce nonlinear signatures that obscure the\nintrinsic material properties and are challenging to deconvolute due to spatial\ninhomogeneity in flake orientation and interlayer spacing14.\nRegarding the efficacy of surface-termination electrochemical modulation, tuning\nsurface terminations (-O, -OH, -F) electrochemically requires efficient interaction\nbetween terminal groups and electrolyte ions. In single-/few-layer TiVCrMoC T ,\n3 x\nnearly all surface metal sites are accessible, allowing uniform and rapid modulation of\ntermination chemistry under an applied bias15. This direct accessibility promotes\nstrong coupling between surface chemical states and the local electronic structure,\nthereby directly influencing optical nonlinearity. In multilayer films, however, limited\nelectrolyte penetration into interlayer galleries, combined with electrochemical\nscreening and non-uniform potential distribution, largely confines termination\nmodulation to the outermost layers. This results in incomplete and spatially\nheterogeneous chemical tuning15. Moreover, interlayer charge screening decouples\nsurface chemistry changes from the collective optical response, leading to attenuated\nand delayed nonlinear modulation.\" in Page 5 (6th paragraph of “S1. Characterization of high-entropy MXene”) with BLACK color.\n12. Lukatskaya M. R., Mashtalir O., Ren C. E., et al. Cation intercalation and high\nvolumetric capacitance of two-dimensional titanium carbide. Science 341, 1502–1505\n(2013).\n13. Dong Y., Chertopalov S., Maleski K., et al. Saturable absorption in 2D Ti₃C₂\nMXene thin films for passive photonic diodes. Adv. Mater. 30, 1705714 (2018).\n14. Jin D., Liu W., Jia L., et al. Thickness- and wavelength-dependent nonlinear\noptical absorption in 2D layered MXene films. Small Sci. 4, 2400179 (2024).\n15. Gao X., Du X., Mathis T. S., et al. Maximizing ion accessibility in\nMXene-knotted carbon nanotube composite electrodes for high-rate electrochemical\nenergy storage. Nat. Commun. 11, 6160 (2020).\n4. on point 6, I strongly recommend the authors to elaborate the MAX vs MXene\ndiscussion and provide inputs on why the presence of the precursor MAX may not\nimpact LPU at large.\nReply: Thank you for your review and valuable suggestion.\nIn the revised SI, we have sharpened the conceptual distinction by systematically\ncomparing the parent MAX phase with the derived MXene, and by elucidating why\nthe observed electrically tunable nonlinear response is inherently specific to MXenes\nfeaturing accessible and reconfigurable surface terminations.\nFirst, regarding the MAX versus MXene contrast, the parent MAX phase exhibits\nnegligible or substantially weaker nonlinear optical modulation compared to the\ncorresponding MXene. Prior comparative studies under similar nonlinear optical\nframeworks consistently report stronger nonlinear responses in MXenes. For instance,\nChen et al. directly contrasted Ti AlC (MAX) and Ti C (MXene) quantum sheets,\n3 2 3 2\nobserving significantly greater absolute modulation depth and nonlinear response in\nthe MXene, confirming that the etching/exfoliation process markedly enhances the\nthird-order nonlinear susceptibility relative to the MAX precursor. This supports our\nconclusion that the strong, electrically programmable nonlinear activation in our\ndevice originates from the MXene itself, not from the MAX phase.\nSecond, concerning surface terminations, MAX phases lack the characteristic\nsurface termination chemistry of MXenes, which fundamentally limits their\nelectrochemical tunability. Unlike MXenes, MAX phases do not possess abundant,\nexposed surface groups (e.g., -O, -OH, -F) that critically govern electronic and optical\nproperties and provide a chemical degree of freedom for voltage-driven modulation.\nExtensive evidence in the MXene field has established that surface terminations\ndominantly influence material properties, and that mixed termination environments\nenable tunable functionalities. Moreover, in situ studies have directly correlated\ntermination evolution with property changes and demonstrated that electrical bias can\ndrive termination modifications in MXenes, providing a mechanistic basis for\nelectrically programmable responses.\nThus, the electrically tunable nonlinear activation demonstrated here is\nfundamentally enabled by the termination-rich, electrochemically addressable surface\nof MXenes, rather than by the parent MAX phase or structural artifacts related to\nstacking. Thank you for your valuable suggestion. This revision not only reinforces\nthe conceptual advance of our work but also underscores a key differentiator between\nelectrically responsive single-/few-layer MXenes and conventional multilayer MXene\nassemblies.\nWe have added the discussion to the Supporting Information \"The parent MAX\nphases and their derived MXenes exhibit fundamentally different nonlinear optical\nand electrochemical characteristics. Comparative studies have shown that, although\ncertain MAX phases may display measurable nonlinear optical responses under\nintense excitation, their effective nonlinear modulation is generally absent or\nsignificantly weaker than that of the corresponding MXenes. For example, a direct\ncomparison between Ti₃AlC₂ (MAX) and Ti₃C₂ (MXene) quantum sheets\ndemonstrated that the MXene exhibits a substantially higher absolute modulation\ndepth and enhanced nonlinear optical response, indicating that the etching and\nexfoliation process plays a critical role in activating strong third-order nonlinearity9.\nFurthermore, unlike MXenes, MAX phases do not possess the abundant, accessible\nsurface terminations (e.g., -O/-OH/-F or other tunable terminations) that critically\ngovern electronic/optical properties and provide a direct chemical degree of freedom\nfor voltage-driven modulation. Large-scale evidence from the MXene community has\nestablished that MXene properties are strongly controlled by surface terminations and\nthat mixed terminations enable tunable functionality10. Moreover, in situ studies have\ndirectly correlated surface termination evolution with property changes and\ndemonstrated that electrical biasing can drive termination-related modifications in\nMXenes, highlighting the mechanistic basis for electrically programmable\nresponses11.\" in Page 3 (3rd paragraph of “S1. Characterization of high-entropy\nMXene”) with BLACK color.\n9. Chen Z., Sui X., Li Y., et al. Ti₃AlC₂ MAX and Ti₃C₂ MXene quantum sheets for\nrecord-high optical nonlinearity. J. Phys. Chem. Lett. 13, 3929–3936 (2022).\n10. VahidMohammadi A., Rosen J., Gogotsi Y. The world of two-dimensional\ncarbides and nitrides (MXenes). Science 372, eabf1581 (2021).\n11. Hart J. L., Hantanasirisakul K., Lang A. C., et al. Control of MXenes' electronic\nproperties through termination and intercalation. Nat. Commun. 10, 522 (2019)."}]

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