Query: Quantum communication using single photons from a semiconductor quantum dot emitting at a telecommunication wavelength

Candidate papers:

abstract: Quantum key distribution with single photons from a telecommunication wavelength quantum dot source is performed over a standard optical fibre link. The source was operated at a temperature of 70 K and gave g(2)(0)~0.166 with an efficiency of 5% after coupling into the single mode fibre. Correlation results are quoted without subtraction of detector dark counts and g(2)(0) as low as 0.1 was measured, at reduced efficiency. This source enabled a proof of principle demonstration of quantum key distribution over 35 km of fibre using the BB84 protocol and phase encoding.
author_names: P M Intallura

Martin Ward

O Z Karimov

Zhiliang Yuan

Patrick See

Paola Atkinson

David A Ritchie

Andrew J Shields
title: Quantum communication using single photons from a semiconductor quantum dot emitting at a telecommunication wavelength
year: 2009

abstract: We present the first demonstration of telecom fiber based quantum key distribution using single photons from a quantum dot in a pillar microcavity. The source offers both telecommunication wavelength operation at 1.3 microns and Purcell enhancement of the spontaneous emission rate. Several emission lines from the InAs/GaAs quantum dot are identified, including the exciton biexciton cascade and charged excitonic emission. We show an order of magnitude increase in the collected intensity of the emission from a charged excitonic state when temperature tuned onto resonance with the HE11 mode of the pillar microcavity, as compared to the off resonance intensity. Above and below GaAs bandgap optical excitation was used and the effect of the excitation energy on the photoluminescence investigated. Exciting below the GaAs bandgap offers significant improvement in the quality of the single photon emission and a reduction of the multi photon probability to 0.1 times the value for Poissonian light was measured, before subtraction of detector dark counts, the lowest value recorded to date for a quantum dot source at a fibre wavelength. We observe also the first evidence of Purcell enhancement of the spontaneous emission rate for a single telecommunication wavelength quantum dot in a pillar microcavity. We have incorporated the source into a phase encoded interferometric scheme implementing the BB84 quantum cryptography protocol and distributed a key, secure from the pulse splitting attack, over standard telecommunication optical fibre. We show a transmission distance advantage over that possible with (length optimized) uniform intensity weak coherent pulses at 1310 nm in the same system.
author_names: P M Intallura

Martin Ward

O Z Karimov

Zhiliang Yuan

Patrick See

Andrew J Shields

Paola Atkinson

David A Ritchie
title: Quantum key distribution using a semiconductor quantum dot source emitting at a telecommunication wavelength
venue: SPIE OPTO
year: 2008

abstract: On demand indistinguishable single photon sources are essential for quantum networking and communication. Semiconductor quantum dots are among the most promising candidates, but their typical emission wavelength renders them unsuitable for use in fiber networks. Here, we present quantum frequency conversion of near infrared photons from a bright quantum dot to the telecommunication C band, allowing integration with existing fiber architectures. We use a custom built, tunable 2400 nm seed laser to convert single photons from 942 nm to 1550 nm in a difference frequency generation process. We achieve an end to end conversion efficiency of 35% demonstrate count rates approaching 1 MHz at 1550 nm with g 2 0 0.043 1 and achieve Hong Ou Mandel (HOM) visibilities of 60% We expect this scheme to be preferable to quantum dot sources directly emitting at telecom wavelengths for fiber based quantum networking.
author_names: Christopher L Morrison

Markus Rambach

Zhe Xian Koong

Francesco Graffitti

Fiona E Thorburn

Ajoy Kar

Yonghong Ma

Sukin Park

Jin Dong Song

Nick G Stoltz

Dirk Bouwmeester

Alessandro Fedrizzi

Brian D Gerardot
title: A bright source of telecom single photons based on quantum frequency conversion
year: 2021

abstract: (c) 2017 American Physical Society. The development of quantum relays for long haul and attack proof quantum communication networks operating with weak coherent laser pulses requires entangled photon sources at telecommunication wavelengths with intrinsic single photon emission for most practical implementations. Using a semiconductor quantum dot emitting entangled photon pairs in the telecommunication O band, we demonstrate a quantum relay fulfilling both of these conditions. The system achieves a maximum fidelity of 94.5% for implementation of a standard four state protocol with input states generated by a laser. We further investigate robustness against frequency detuning of the narrow band input and perform process tomography of the teleporter, revealing operation for arbitrary pure input states, with an average gate fidelity of 83.6% The results highlight the potential of semiconductor light sources for compact and robust quantum relay technology that is compatible with existing communication infrastructures.
author_names: Jan Huwer

Martin Felle

R Mark Stevenson

Joanna Skiba-Szymanska

Martin Ward

Ian Farrer

Richard Vincent Penty

David A Ritchie

Andrew J Shields
title: Quantum Dot Based Telecommunication Wavelength Quantum Relay
year: 2017

abstract: Entangled light sources are considered as core technology for multiple quantum network architectures. Of particular interest are sources that are based on a single quantum system as these offer intrinsic security due to the sub Poissonian nature of the photon emission process. This is important for applications in quantum communication where multi pair emission generally compromises performance. A large variety of sources has been developed, but the generated photons remained far from being utilized in established standard fiber networks, mainly due to lack of compatibility with telecommunication wavelengths. In this regard, single semiconductor quantum dots are highly promising photon pair sources as they can be engineered for direct emission at telecom wavelengths. In this work we demonstrate the feasibility of this approach. We report a week long transmission of polarization entangled photons from a single InAs/GaAs quantum dot over a metropolitan network fiber. The photons are in the telecommunication O band, favored for fiber optical communication. We employ a polarization stabilization system overcoming changes of birefringence introduced by 18.23 km of installed fiber. Stable transmission of polarization encoded entanglement with a high fidelity of 91% is achieved, facilitating the operation of sub Poissonian quantum light sources over existing fiber networks.
author_names: Z-H Xiang

Jan Huwer

R Mark Stevenson

Joanna Skiba-Szymanska

Martin Ward

Ian Farrer

David A Ritchie

Andrew J Shields
title: Long term transmission of entangled photons from a single quantum dot over deployed fiber
venue: Scientific Reports
year: 2019

abstract: One promising technology expected to enable long haul quantum communication networks with untrusted nodes are quantum relays. Their most practical implementation requires an entanglement source with operation at telecom wavelength and intrinsic single photon character. Here, we use a semiconductor quantum dot emitting in the O band to demonstrate for the first time a system fulfilling both of these criteria. For implementation of a standard 4 state QKD protocol with weak coherent input states, the system achieves mean fidelities above 88% Further characterization of the relay with process tomography reveals teleportation for arbitrary input states. The results represent a significant advance in demonstrating feasibility of semiconductor light sources for the development of infrastructure compatible quantum communication technology for multi node networks.
author_names: Jan Huwer

Martin Felle

R Mark Stevenson

Joanna Skiba-Szymanska

Martin Ward

Ian Farrer

Richard Vincent Penty

David A Ritchie

Andrew J Shields
title: Telecom wavelength quantum relay using a semiconductor quantum dot
venue: 2017 Conference on Lasers and Electro Optics (CLEO)
year: 2017

abstract: Single photons and entangled photon pairs are a key resource of many quantum secure communication and quantum computation protocols, and non Poissonian sources emitting in the low loss wavelength region around 1,550 nm are essential for the development of fibre based quantum network infrastructure. However, reaching this wavelength window has been challenging for semiconductor based quantum light sources. Here we show that quantum dot devices based on indium phosphide are capable of electrically injected single photon emission in this wavelength region. Using the biexciton cascade mechanism, they also produce entangled photons with a fidelity of 87 4% sufficient for the application of one way error correction protocols. The material system further allows for entangled photon generation up to an operating temperature of 93 K. Our quantum photon source can be directly integrated with existing long distance quantum communication and cryptography systems, and provides a promising material platform for developing future quantum network hardware.Quantum light sources operating at telecom wavelength are a long sought goal for quantum technologies. Here, the authors show electrically injected emission of single photons and entangled photon pairs from indium phosphide based quantum dots, operating up to a temperature of 93 K.
author_names: Tina Muller

Joanna Skiba-Szymanska

Andrey B Krysa

Jan Huwer

Martin Felle

M Anderson

R Mark Stevenson

J Heffernan

David A Ritchie

Andrew J Shields
title: A quantum light emitting diode for the standard telecom window around 1,550 nm
venue: Nature Communications
year: 2018

abstract: We demonstrate experimental results based on time resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the internal quantum efficiency (IQE) of InGaAs quantum dots (QDs) Using a strain reducing layer (SRL) these QDs can be employed for the manufacturing of single photon sources (SPS) emitting in the telecom O Band. The OS and IQE are evaluated by determining the radiative and non radiative decay rate under variation of the optical density of states at the position of the QD as proposed and applied in J. Johansen et al. Phys. Rev. B 77, 073303 (2008) for InGaAs QDs emitting at wavelengths below 1 mm. For this purpose, we perform measurements on a QD sample for different thicknesses of the capping layer realized by a controlled wet chemical etching process. From numeric modelling the radiative and nonradiative decay rates dependence on the capping layer thickness, we determine an OS of 24.6 3.2 and a high IQE of about (85 10) for the long wavelength InGaAs QDs. Introduction Semiconductor quantum dots (QDs) are well established solid state nanocrystalline structures that can be used as close to ideal two level quantum emitters applicable for instance in quantum communication [1, 2, 3] or quantum computing [4, 5] In recent years, performance of singlephoton emission based on InGaAs QDs could be pushed towards the physical limits for instance in terms of photon indistinguishability up to 99.7% [6] for QD emitting in the 930 950 nm range. Moreover, by material engineering the range of applications could be extended to the telecom O band at 1.3 mm [7, 8, 9, 10] which enables long distance fiber based quantum communication [11] A very promising way to achieve the required redshift of QD emission is the introduction of a strain reducing layer of lower Indium content on top of the QD layer [12] maintaining the high quality of emission in terms of multi photon suppression [9] An additional advantage of this technology route is the usage of a mature and well established GaAs based technology platform which facilitates the fabrication of advanced quantum light sources with enhanced photon extraction efficiency [13, 14, 15] and the possibility of spectral fine tuning by external strain fields [16] The QDs used in this work have been carefully optimized for the manufacturing of single photon sources emitting in a wavelength range around 1.3 mm at temperatures up to 40 K as detailed in previously published works [15, 16, 17] An important intrinsic property of any QD emitter is the internal quantum efficiency (IQE) which describes the ratio of quantum conversion from exciton formation into single photon emission. The IQE plays a major role in the total quantum efficiency of a fully processed device and directly impacts the photon extraction efficiency being a key parameter of quantum light sources. Thus, knowing and increasing the IQE is crucial for device optimization. Another important QD parameter is the oscillator strength (OS) of the optical transition. The OS is directly related to the radiative decay time of the emitter and determines the light matter coupling strength of QD devices using effects of cavity quantum electrodynamics [18] The exciton decay dynamics and IQE of In(Ga)As QDs emitting in the 920 to 1030 nm range have been experimentally examined by several groups [19, 20, 21, 22] with a method introduced by Johansen et al. [19] which allows for a direct measurement of the QD properties without being influenced by QD density or relying on assumptions based on theoretical considerations of the exciton radius and the dimensions of the QDs [23, 24] This method was also used to investigate an InGaAs quantum dot quantum well system [25] So far however, to our best knowledge, no such measurements have been performed on InGaAs QDs emitting in the telecom O band, so that reliable information on their IQE has not been available. In order to determine the IQE and OS of telecom wavelength InGaAs QDs their total decay rate G(o, z) at a frequency o and at z position below the sample surface is determined experimentally. The associated decay rate is given by the following relation: G(o, z) Gnrad(o) Grad (o) r(o,z) rhom(o) (1) where Gnrad(o) represents the nonradiative decay rate and Grad (o) is the radiative decay in a homogeneous medium, r(o, z) is the projected local density of states (LDOS) divided by the LDOS in a homogenous medium rhom(o) (the GaAs surrounding the QD) The total decay rate G(o, z) in dependance from z can be measured experimentally by means of time resolved micro photoluminescence (mPL) under variation of the capping layer thickness of the QD sample. Subsequently, the experimental components Grad(o) and Gnrad hom (o) are obtained by fitting parameters of a curve that has been derived from simulated values of the LDOS in dependance from z to the experimental data. The IQE can then be calculated as: IQE Grad hom Gnrad+Grad hom (2) and the OS can easily be derived from fosc(o) 6mee0pc0 3 q2no2 Grad (o) (3) where the electron mass me, the vacuum permittivity e0, the vacuum speed of light c0, the elementary charge q and the refractive index n of the surrounding GaAs is given [9] Sample Preparation The purpose of this work is to obtain a quantitative understanding of 1.3 mm InGaAs QDs, which were optimized for the development of quantum light sources emitting in the telecom Oband, in terms of their IQE and the OS. Using metal organic chemical vapor deposition (MOCVD) the corresponding sample was prepared in the following way. First, a 300 nm GaAs buffer is grown on n doped GaAs (100) substrate and followed by 1 mm thick Al0.90Ga0.10As layer. Then a 2 mm thick GaAs layer and another 100 nm thick Al0.90Ga0.10As layer is deposited. These three layers are originally designed as sacrificial layers to be removed during a postgrowth flip chip processing, as described in more detailed way in Refs. [15, 16] The final 879 nm thick layer of GaAs formerly designed to function as active device membrane includes a single InGaAs QD layer together with the SRL. The QD layer with a density of 5x10 cm is located 637 nm above the second etch stop layer and is formed by 1.5 monolayers of In0.7Ga0.3As followed by GaAs flush corresponding to a nominal thickness of half a monolayer. The subsequent 5.5 nm thick InGaAs SRL has a gradual decrease of the In content from 30% to 10% over the first 3.5 nm. This layer is followed by a GaAs capping layer with a thickness of 236 nm. An overview of the whole sample structure is given in Fig. 1(a) Further information on the QD growth and optimization can be found in the supplementary information. In order to vary the thickness of the caping layer as required for extracting the radiative and non radiative emission rate of the QDs the grown sample was prepared as described in the following. First, the surface of the sample was cleaned thoroughly and the photo resist AZ 701 MIR was applied using spin coating. UV lithography was used to pattern the surface with several slim rectangular structures to form a height reference to determine the capping layer thickness after the upcoming etching process. The sample was cut into 25 pieces to undergo wet chemical etching after thorough cleaning with isopropanol. The etching solution [26] was prepared with the following ingredients: Hydrobromic acid (HBr) hydrogen peroxide (H2O2) and water (H2O) in a volumetric ratio of 2:1:60. The solution was continuously agitated with a magnetic stirrer and left to rest for 600 seconds after adding the H2O2. The etching rate had been previously determined to be 0.5 nm/s by etching and measuring a set of test sample pieces of GaAs. The 25 pieces were put together into the solution and subsequently removed piece after piece after a set time interval to etch away the desired amount of GaAs capping and put into clean water to stop the etching process. The remaining thickness of the GaAs separating the QD layer from the sample surface was determined with comparative measurement in a stylus profiler and an atomic force microscope (AFM) setup. Both measurements agree within a margin of less than 10 nanometers. Because of local deviations in the etching rate the exact position of the photoluminescence lifetime measurement is later marked on an optical microscopic image and the local top GaAs layer thickness remeasured via AFM. These values, as given in Fig. 1(b) are used in later analysis of the mPL data. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 0 50 100 150 200 250 (b) D is ta n c e Q D s u rf a c e n m
author_names: Jan Grosse

Pawel Mrowinski

Nicole Srocka

Stephan Reitzenstein
title: Quantum efficiency and oscillator strength of InGaAs quantum dots for single photon sources emitting in the telecommunication O band
venue: Applied Physics Letters
year: 2021

abstract: Quantum communication networks are formed of secure links, where information can be transmitted with security guaranteed by the quantum nature of light. An essential building block of such a network is a source of single photons and entangled photon pairs, compatible with the low loss fibre telecom window around 1550 nm. Previous work based on semiconductor quantum dots (QDs) colour centres in diamond and single atoms has been limited by emission wavelengths unsuitable for long distance applications. Efforts have been made to use standard gallium arsenide based QDs by extending their operating wavelength range, however, electrically driven quantum light emission from quantum dots in this telecommunication window has not yet been demonstrated. In this work, indium phosphide based QD devices have been developed to address this problem. The industry favoured growth method, metalorganic vapour phase epitaxy (MOVPE) has been used to create droplet QDs with low fine structure splitting (FSS) This growth scheme allows us to produce the first optoelectronic devices for single and entangled photon emission in the 1550 nm telecom window. We show single photon emission with multi photon events suppressed to 0.11+ 0.02. Furthermore, we obtain entangled light from the biexciton cascade with a maximum fidelity of 0.87+ 0.04 which is sufficient for error correction protocols. We also show extended device operating temperature up to 93 K, allowing operation with liquid nitrogen or simple closed cycle coolers. Our device can be directly integrated with existing long distance quantum communication, cryptography and quantum relay systems providing a new platform for developing quantum networks.
author_names: Tina Muller

Joanna Skiba-Szymanska

Andrey B Krysa

Jan Huwer

Martin Felle

Matthew Anderson

Mark Stevenson

J Heffernan

David A Ritchie

Andrew J Shields
title: A quantum light emitting diode for the standard telecom window around 1550 nm (Conference Presentation)
venue: Advances in Photonics of Quantum Computing, Memory, and Communication XII
year: 2019

abstract: The coherent manipulation of the frequency of single photons is an important requirement for future quantum network technologies. It allows, for instance, quantum systems emitting in the visible range to be connected to the telecommunication wavelengths, thus extending the communication distances. Here we report on quantum frequency conversion of memory compatible narrow bandwidth photons at 606 nm to the telecom C band at 1552 nm. The 200 ns long photons, compatible with praseodymium based solid state quantum memories, are frequency converted using a single step difference frequency generation process in a periodically poled lithium niobate waveguide. We characterize the noise processes involved in the conversion and, by applying strong spectral filtering of the noise, we demonstrate high signal to noise ratio conversion at the single photon level (SNR>100, for a mean input photon number per pulse of 1) We finally observe that a memory compatible heralded single photon with a bandwidth of 1.8 MHz, obtained from a spontaneous parametric down conversion pair source, still shows a strong non classical behavior after conversion. We first demonstrate that correlations between heralding and converted heralded photons stay in the non classical regime. Moreover, we measure the heralded autocorrelation function of the heralded photon using the converter device as a frequency domain beam splitter, yielding a value of 0.19+ 0.07. The presented work represents a step towards the connection of several quantum memory systems emitting narrowband visible photons to the telecommunication wavelengths.
author_names: N Maring

Dario Lago-Rivera

Andreas Lenhard

Georg Heinze

Hugues de Riedmatten
title: Quantum frequency conversion of memory compatible single photons from 606 nm to the telecom C band
year: 2018