Query: Isotopically enhanced triple-quantum-dot qubit

Candidate papers:

abstract: Three coupled quantum dots in isotopically purified silicon enable all electrical qubit control with long coherence time. Like modern microprocessors today, future processors of quantum information may be implemented using all electrical control of silicon based devices. A semiconductor spin qubit may be controlled without the use of magnetic fields by using three electrons in three tunnel coupled quantum dots. Triple dots have previously been implemented in GaAs, but this material suffers from intrinsic nuclear magnetic noise. Reduction of this noise is possible by fabricating devices using isotopically purified silicon. We demonstrate universal coherent control of a triple quantum dot qubit implemented in an isotopically enhanced Si/SiGe heterostructure. Composite pulses are used to implement spin echo type sequences, and differential charge sensing enables single shot state readout. These experiments demonstrate sufficient control with sufficiently low noise to enable the long pulse sequences required for exchange only two qubit logic and randomized benchmarking.
author_names: K Eng

Thaddeus D Ladd

Aaron Smith

Matthew G Borselli

Andrey A Kiselev

Bryan H Fong

Kevin S Holabird

Thomas M Hazard

Biqin Huang

Peter W Deelman

Ivan Milosavljevic

Adele E Schmitz

Richard S Ross

Mark F Gyure

Andrew T Hunter
title: Isotopically enhanced triple quantum dot qubit
venue: Science Advances
year: 2015

abstract: Quantum computation requires qubits that satisfy often conflicting criteria, which include long lasting coherence and scalable control1. One approach to creating a suitable qubit is to operate in an encoded subspace of several physical qubits. Although such encoded qubits may be particularly susceptible to leakage out of their computational subspace, they can be insensitive to certain noise processes2,3 and can also allow logical control with a single type of entangling interaction4 while maintaining favourable features of the underlying physical system. Here we demonstrate high fidelity operation of an exchange only qubit encoded in a subsystem of three coupled electron spins5 confined in gated, isotopically enhanced silicon quantum dots6. This encoding requires neither high frequency electric nor magnetic fields for control, and instead relies exclusively on the exchange interaction4,5, which is highly local and can be modulated with a large on off ratio using only fast voltage pulses. It is also compatible with very low and gradient free magnetic field environments, which simplifies integration with superconducting materials. We developed and employed a modified blind randomized benchmarking protocol that determines both computational and leakage errors7,8, and found that unitary operations have an average total error of 0.35% with half of that, 0.17% coming from leakage driven by interactions with substrate nuclear spins. The combination of this proven performance with complete control via gate voltages makes the exchange only qubit especially attractive for use in many qubit systems.Random sequences of unitary gate operations on an exchange only qubit encoded in three physical electron qubits are performed using only voltage pulses and exhibit an average total error of 0.35% where half of the error originates from leakage out of the computational subspace caused by interactions with substrate nuclear spins.
author_names: Reed W Andrews

Matthew D Reed

Sieu D Ha

Michael P Jura

Joseph Kerckhoff

Mark P Levendorf

Se'an M Meenehan

Seth T Merkel

Aaron Smith

Aaron Weinstein

Matthew T Rakher

Thaddeus D Ladd

Matthew G Borselli
title: Quantifying error and leakage in an encoded Si/SiGe triple dot qubit
venue: Nature Nanotechnology
year: 2019

abstract: Charge qubits realized in the double quantum dot systems have been a subject of many theoretical and experimental studies due to their simplicity and fast operation speed [1] However they exhibit short decoherence times caused by charge noise and phonons. Hentschel et al. [2] followed by Vasiliev and Fedichkin [3] showed enhanced robustness to phonon induced decoherence in the triple quantum dot charge qubit in triangular and linear geometry, respectively. In this paper we develop the concept of triple quantum dot charge qubit. We show that leakage to a higher energy level, limiting the single qubit gate fidelities, can be eliminated by an appropriate modification of tunneling barriers and dot energies. Next we present studies for two capacitively coupled qubits and show a feasibility of implementing of two qubit operation gates for two different coupling topologies.
author_names: Krzysztof Ptaszynski

Bogdan R Bulka
title: Logic operations of charge qubit in a triple quantum dot
year: 2016

abstract: The isolation of qubits from noise sources, such as surrounding nuclear spins and spin electric susceptibility1 4, has enabled extensions of quantum coherence times in recent pivotal advances towards the concrete implementation of spin based quantum computation. In fact, the possibility of achieving enhanced quantum coherence has been substantially doubted for nanostructures due to the characteristic high degree of background charge fluctuations5 7. Still, a sizeable spin electric coupling will be needed in realistic multiple qubit systems to address single spin and spin spin manipulations8 10. Here, we realize a single electron spin qubit with an isotopically enriched phase coherence time (20 ms)11,12 and fast electrical control speed (up to 30 MHz) mediated by extrinsic spin electric coupling. Using rapid spin rotations, we reveal that the free evolution dephasing is caused by charge noise rather than conventional magnetic noise as highlighted by a 1/f spectrum extended over seven decades of frequency. The qubit exhibits superior performance with single qubit gate fidelities exceeding 99.9% on average, offering a promising route to large scale spin qubit systems with fault tolerant controllability.Quantum control on an isotopically enriched Si spin qubit is demonstrated with ultrahigh gate fidelities and long coherence times even in the presence of sizeable charge noise.
author_names: Jun Yoneda

Kenta Takeda

Tomohiro Otsuka

Takashi Nakajima

Matthieu R Delbecq

Giles Allison

Takumu Honda

Tetsuo Kodera

Shunri Oda

Yusuke Hoshi

Noritaka Usami

Kohei M Itoh

Seigo Tarucha
title: A quantum dot spin qubit with coherence limited by charge noise and fidelity higher than 99.9%
venue: Nature Nanotechnology
year: 2017

author_names: Thaddeus D Ladd
title: Nuclear Dynamics in Isotopically Enhanced Silicon Spin Qubits
year: 2019

abstract: The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low frequency noise. During the last decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit. However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood. We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by high frequency charge noise rather than the quasi static noise inherent to any semiconductor device. We employed a feedback control technique to actively suppress the latter, demonstrating a \pi$ flip gate fidelity as high as $99.04\pm 0.23\ in a gallium arsenide quantum dot. We show that the driven evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the $1/f$ noise observed in isotopically purified silicon qubits.
author_names: Takashi Nakajima

Akito Noiri

Kento Kawasaki

Jun Yoneda

Peter Stano

Shinichi Amaha

Tomohiro Otsuka

Kenta Takeda

Matthieu R Delbecq

Giles Allison

Arne Ludwig

Andreas Dirk Wieck

Daniel Loss

Seigo Tarucha
title: Coherence of a Driven Electron Spin Qubit Actively Decoupled from Quasistatic Noise
year: 2020

abstract: This thesis presents research on the initialization, control, and readout of electron spin states in gate defined GaAs quantum dots. The first three experiments were performed with Singlet Triplet spin qubits in double quantum dots, while the remaining two experiments were performed with an Exchange Only spin qubit in a triple quantum dot. The first experiment examines the relationship between a dynamic nuclear polarization (DNP) process and the increase in measured singlet return probability in a SingletTriplet qubit. We find that the DNP process creates an Overhauser field difference, Bz, between dots, which enhances the relaxation of triplet states during the measurement. We propose a model which explains this relaxation mechanism, and find it in good agreement with the data. The second and third experiments investigate the effects of dynamical decoupling sequences on the Singlet Triplet qubit. We demonstrate the preservation of singlet triplet superpositions by interlacing qubit rotations with Carr Purcell (CP) sequences. We test the preservation of a singlet state with different dynamical decoupling schemes, finding a maximum coherence time of T2 80ms for the CP sequence. The coherence time is studied for a number of p pulses in the CP sequence, yielding an exponential dependence on even numbers of p pulses. This allowed us to estimate the functional form of the noise spectrum influencing the qubit. The fourth experiment studied the initialization, complete electrical control, and readout of an Exchange only spin qubit in a triple quantum dot. We demonstrate over 75 qubit rotations at 47 GHz and create a method of measurement and state tomography,
author_names: James Medford
title: Spin qubits in double and triple quantum dots
year: 2013

abstract: BODY: Extremely long electron and nuclear spin coherence times have recently been demonstrated in isotopically pure Si 28 [1,2] making silicon one of the most promising semiconductor materials for spin based quantum information. The two level spin state of single electrons bound to shallow phosphorus donors in silicon in particular provide well defined, reproducible qubits [3] and represent a promising system for a scalable quantum computer in silicon. An important challenge in these systems is the realisation of an architecture, where we can position donors within a crystalline environment with approx. 20 50nm separation, individually address each donor, manipulate the electron spins using ESR techniques and read out their spin states. We have developed a unique fabrication strategy for a scalable quantum computer in silicon using scanning tunnelling microscope lithography to precisely position individual P donors in Si [4] aligned with nanoscale precision to local control gates [5] necessary to initialize, manipulate, and read out the spin states [6] During this talk I will focus on demonstrating single shot spin read out [8] and ESR control of preciselypositioned P donors in Si. I will also describe our approaches to scale up using rf reflectometry [9] and the investigation of 3D architectures for implementation of the surface code [10] and highlight that the device produced have the lowest noise characteristics of any silicon device to date [11] References [1] K. Saeedi et al. Science 342, 130 (2013) [2] J. T. Muhonen et al. Nature Nanotechnology 9, 986 (2014) [3] B.E. Kane, Nature 393, 133 (1998) [4] M. Fuechsle et al. Nature Nanotechnology 7, 242 (2012) [5] B. Weber et al. Science 335, 6064 (2012) [6] H. Buch et al. Nature Communications 4, 2017 (2013) [7] B. Weber et al. Nature Nanotechnology 9, 430 (2014) [8] T. F. Watson et al. Science Advances 3, e1602811 (2017) [9] M.G. House et al. Nature Communications 6, 8848 (2015) [10] C. Hill et al. Science Advances 1, e1500707 (2015) [11] S. Shamim et al. Nano Letters 16, 5779 (2016) Interlayer Excitons and Magneto Exciton Condensation in van der Waals Heterostructures A pair of electron and hole across the interface of semiconductor heterostructure can form a bound quantum state of the interlayer exciton. In a coupled interface between atomically thin van der Waals layers, the Coulomb interaction of the interlayer exciton increases further. Coulomb drag effect is a mesoscopic effect which manifests many body interactions between two low dimensional systems, which has served an extremely useful probe the strong correlation in quantum systems. In this presentation, we will first discuss observing interlayer exciton formation in semiconducting transition metal dichalcogenide (TMDC) layers. Unlike conventional semiconductor heterostructures, charge transport in of the devices is found to critically depend on the interlayer charge transport, electron hole recombination process mediated by tunneling across the interface. We demonstrate the enhanced electronic, optoelectronic performances in the vdW heterostructures, tuned by applying gate voltages, suggesting that these a few atom thick interfaces may provide a fundamental platform to realize novel physical phenomena. In addition, spatially confined quantum structures in TMDC can offer unique valley spin features, holding the promises for novel mesoscopic systems, such as valleyspin qubits. In the second part of the presentation, we will discuss magneto exciton condensation. In this electronic double layer subject to strong magnetic fields, filled Landau states in one layer bind with empty states of the other layer to form an exciton condensate. Driving current in one graphene layer generates a near quantized Hall voltage in the other layer, resulting in coherent exciton transport. In our experiment, capitalizing strong Coulomb interaction across the atomically thin hBN separation layer, we realize a superfluid condensation of magnetic field induced excitons. For small magnetic fields (the BEC limit) the counter flow resistance shows an activation behavior. On the contrary, for large magnetic fields limit where the inter exciton separation decreases (the BCS limit) the counter flow resistance exhibits sharp transitions in temperature showing characters of Berezinskii Kosterlitz Thouless (BKT) transition. Furthermore, complete experimental control of density, displacement and magnetic fields in our graphene double layer system enables us to explore the rich phase diagram of several superfluid exciton phases with the different internal quantum degrees of freedom. Franckeite: a naturally occurring superlattice Andres Castellanos Gomez 1 1 Materials Science Factory, Instituto de Ciencia de Materiales de Madrid (ICMM CSIC) Campus Universitario de Cantoblanco, 28049 Madrid, Spain In his Nobel lecture in 2010, Kostya Novoselov already anticipated that van der Waals heterostructures would have a strong impact on the scientific community. Nowadays, it is clearly one of the hottest areas of research in 2D materials. The assembly of these heterostructures is typically done by artificial stacking of individual 2D layers (manually) and thus with all the corresponding challenges and issues; mainly controlling the relative orientation of the stacked layers and avoiding interlayer adsorbates and contaminants. Thererfore, the manual stacking seems a cumbersome method that is hampering the fabrication of superlattices based on 2D materials. Here we discuss a radically approach to fabricate heterostructures based on 2D layers: one can isolate thin layers of a heterostructure based on alternating SnS2 based and PbS based 2D layers (with remarkably high crystalline and stacking order) by mechanical and liquid phase exfoliation of franckeite, a naturally occurring sulfosalt mineral.[1 4] As the bulk material is already composed of these alternating SnS2 and PbS layers, the exfoliation process minimizes stacking missorientation and avoids interlayer adsorbates in the isolated nanosheets of franckeite. Franckeite is then a naturally occurring atomic superlattice with high crystal and orientation stacking quality. These ultrathin van der Waals heterostructures have been thoroughly characterized by microscopy (SEM, TEM, AFM, STM) spectroscopy (Raman, UV VIS IR, synchrotron XPS) and electrical transport measurements. We found that the franckeite layers are highly stable in air and they show a p type semiconducting behaviour with a narrow gap of 0.5 0.7 eV.[1] Thus this material can be an interesting replacement for black phosphorus (the most studied narrow gap p type 2D semiconductor so far) which tends to degrade rapidly in air. [1] Molina Mendoza, Aday J. et al. "Franckeite as a naturally occurring van der Waals heterostructure." Nature Communications 8 (2017) [2] Velicky, Matej, et al. "Exfoliation of natural van der Waals heterostructures to a single unit cell thickness." Nature Communications 8 (2017) [3] Prando, Giacomo. "Van der Waals heterostructures: The natural way." Nature Nanotechnology 12.3 (2017) 191 191. [4] Gant, Patricia, et al. "Optical contrast and refractive index of natural van der Waals heterostructure nanosheets of franckeite." Beilstein journal of nanotechnology 8 (2017)
author_names: Tony F Heinz
title: Versatile Spin Control with Triple Quantum Dots Hybrid Spin Qubit QND and Coherent Entanglement Transfer

abstract: The nuclear spins in nanostructured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resource while suppressing the noise. NMR techniques are challenging: the group III and V isotopes have large spins with widely different gyromagnetic ratios; in strained material there are large atom dependent quadrupole shifts; and nanoscale NMR is hard to detect. We report NMR on 100,000 nuclear spins of a quantum dot using chirped radiofrequency pulses. Following polarization, we demonstrate a reversal of the nuclear spin. We can flip the nuclear spin back and forth a hundred times. We demonstrate that chirped NMR is a powerful way of determining the chemical composition, the initial nuclear spin temperatures and quadrupole frequency distributions for all the main isotopes. The key observation is a plateau in the NMR signal as a function of sweep rate: we achieve inversion at the first quantum transition for all isotopes simultaneously. These experiments represent a generic technique for manipulating nanoscale inhomogeneous nuclear spin ensembles and open the way to probe the coherence of such mesoscopic systems.
author_names: Mathieu Munsch

Gunter Wust

A V Kuhlmann

Fei Xue

Arne Ludwig

Dirk Reuter

Andreas Dirk Wieck

Martino Poggio

Richard John Warburton
title: Manipulation of the nuclear spin ensemble in a quantum dot with chirped magnetic resonance pulses.
venue: Nature nanotechnology
year: 2014

abstract: A major challenge for realizing quantum computation is finding suitable systems to embody quantum bits (qubits) and quantum gates (qugates) in a robust and scalable architecture. An emerging bottom up approach uses the electronic spins of lanthanides. Universal qugates may then be engineered by arranging in a molecule two interacting and different lanthanide ions. Preparing heterometallic lanthanide species is, however, extremely challenging. We have discovered a method to obtain [LnLn' complexes with the appropriate requirements. Compound [CeEr] is deemed to represent an ideal situation. Both ions have a doubly degenerate magnetic ground state and can be addressed individually. Their isotopes have mainly zero nuclear spin, which enhances the electronic spin coherence. The analogues [Ce2] [Er2] [CeY] and [LaEr] have also been prepared to assist in showing that [CeEr] meets the qugate requirements, as revealed through magnetic susceptibility, specific heat, and EPR. Molecules could now be used for quantum information processing.
author_names: David Aguila

Leoni A Barrios

Veronica Velasco

Olivier Roubeau

Ana Repolles

Pablo J Alonso

Javier Sese

Simon J Teat

Fernando Luis

Guillem Aromi
title: Heterodimetallic [LnLn' Lanthanide Complexes: Toward a Chemical Design of Two Qubit Molecular Spin Quantum Gates
venue: Journal of the American Chemical Society
year: 2014