InSb Quantum Devices: All-electrically Controlled Electron Spins. (ACES)

Lead Research Organisation: Cardiff University
Department Name: School of Physics and Astronomy


Despite challenges with decoherence, solid state spin qubits remain one of the best practical implementations of quantum device architectures that exploit quantum state entanglement, owing to the possibility of incorporation into existing electronics technology. 'Physics for Quantum Technologies' was acknowledged in a recent EPSRC Physics Grand Challenge survey as the most overwhelmingly recognised challenge in the physical sciences. "New materials for solid-state quantum electronics need to be developed" was a highlighted high level requirement. Physics for Quantum Technology was also acknowledged as having the highest potential UK economic impact should the UK establish an intellectual advantage.

All electrical control of single electron spins in a practical semiconductor device would be a major breakthrough which the UK is in a unique position to achieve owing to the world lead it has in the strong spin-orbit InSb/AlInSb semiconductor material system. There are a number of key stepping stones to achieving the end goal of single electron manipulation in gate confined quantum structures. We propose to address the material growth challenges of highly mismatched InSb/InAlSb epitaxy on GaAs and Si, and achieve world record carrier mobilities and associated ballistic length, and develop device capability for advanced measurement and exploitation by the wider UK scientific community.

Through a series of standard quantum transport devices, this work will ultimately demonstrate the potential for electron spin manipulation (and therefore individual qubit addressing) by the spatial translation of single electrons in complex multiple gate field effect devices, using the Rashba spin-orbit coupling to enable local spin state control.

Planned Impact

The long term societal impact of the quantum information revolution cannot be understated. Even before practical processors are available to engineers and entrepreneurs, the field has identified major applications that would present significant opportunity or major disruption to present day life, some with only the availability of a limited number of quantum bits (qubits). Whilst the threat posed by the breaking of public key encryption has been significant enough to generate large funding in the US, EU and Japan, the opportunities arising from this technology potentially eclipse this. The ability to search mass cctv footage using pattern recognition algorithms that exploit the quantum fourier transform, might one day yield almost real time UK wide search and surveillance, impacting how we think about and coordinate national security, missing persons, crime prevention, facility and infrastructure monitoring etc. Quantum algorithms that solve problems in physics and chemistry will have a major impact on complex system design, such as drug design simulation, leading to greater efficiency in chemical and pharmaceutical manufacturing. However achieving breakthroughs in technology will take sustained effort and must play to UK strengths.

Novel devices that rely on electron spin have been shown to be promising candidates for simple qubit and quantum state study. Only two groups worldwide have reported any form of quantum devices using high mobility 2DEG material based on InSb/AlInSb heterostructures (QinetiQ Malvern (UK), and Oklahoma (US)), and yet there are considerable advantages associated with the large spin-orbit interaction. Now that QinetiQ has withdrawn from this field there are a number of active groups (Imperial (Cohen, Gilbertson), Oxford (Nicholas), Surrey (Murdin, Clowes)) that will not pursue this work without a quality material supply and underpinning device knowledge. The barriers to progress in this material system are significantly lower for the UK owing to this work.

Recent market analysis has put the global market value for quantum enabled technology devices to be ~$410bn by 2015, with a compound annual growth rate of ~39%. The extent to which UK Industry can benefit is difficult to estimate given the potential breadth of applications and differing levels of market presence. Taking the ICT sector alone, the UK electronics industry generated approximately £16BN ($24bn) of output in 2006. This would give the UK an approximate 7% share of the current global market (excluding micro-processors) for electronics and electrical systems. Applying this market share to the future market for quantum technology, the estimated sales to UK producers (from UK and international markets) would be between £9BN and £23BN.

Specialist skills developed in this project are essential in any future high technology exploitation chain, and are sought after by industries that use such controlled environment (cleanroom) laboratories (ranging from semiconductor devices to advanced drug research). This project will drive forward complex semiconductor device concepts and in the process train PhD students and postdoctoral level workers in advanced, novel, and creative nano-device fabrication and measurement. There will be excellent opportunity for high profile publication and presentation for early career workers.
The UK must contribute to this field with a unique angle and not simply duplicate multi-billion pound investments made elsewhere in the world, notably in America, Japan and continental Europe. The UK has the infrastructure and in depth expertise in III-V technologies, together with specialist knowledge gained from years of MoD and commercial investment to lead the world in InSb technology. This brings to the table a significant 'slant' on the realisation of solid state spin qubits with advantages for practical realisation and long term commercialisation.


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Description Material growths for novel Indium Antimonide electronic quantum devices has been performed by Sheffield Universty NC for III-V technologies. It has become apparent that development of key technology has required extensive resource (eg TEM and transport characterisation). This is coupled with process development which has hampered progress.
Progress toward greater mobility proved difficult, and reliable enough gate technology was not established enough for device demonstration. Considerable work has been done (and continues to be done) on material understanding and characterisation, and in particularthe timely role this material may play in the exploitation of Majorana Fermions, and promising, if challenging, route to quantum processing on a conventional like semiconductor chip
Exploitation Route At present this is only of direct benefit to other academic groups, with clear exploitation some time off yet. However growth of this material, at a world leading level has been established at the National Centre for III-V technologies, and the UK still has a leading position on this. Device development will be highly dependent on initiatives such as the Compound Semiconductor Cluster which will aid robust fabrication. There is emerging excitement in this material system for the realisation of Majorana Fermion states. These are robust topologically protected quantum states that are predicted to be excellent candidates for quantum information. Realisation in a planar semiconductor material would be an immense leap forward in the possible implementation of quantum processing in a solid state device .
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Healthcare

Description Welsh European Funding Office
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Participation in a national consultation
Impact Work in this field has enabled a strong drive to developing the Compound Semiconductor Cluster in South Wales, spearheaded by the Universoity Institute of Compound Semiconductors, the innovative joint venture company CSC (compound semiconductor centre), and has stimulated the environment for the Compound Semiconductor Applications Catapult. This is coupled with the recent award of the EPSRC CS Manufacturing Hub, striving to take University research and placing it in a framework that enables efficient exploitation.
Description RPIF
Amount £17,300,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2015 
End 03/2017
Title Optical Microscopy as a probe of the rate limiting transport lifetime in InSb/Al1-xInxSb quantum wells 
Description Differential interference contrast DIC (Nomarski) imaging has been performed on various InSb QW 2DEG materials at an optical magnification of ×50. Image analysis techniques were employed to extract the average number of features and corresponding feature size for each sample. Data for this is presented in a tab separated .txt file, with data columns corresponding to the experimentally measured sample mobility (in [cm^2/Vs]) and corresponding Drude mean free path (in [um]), measured using standard Hall techniques at 3K, and over a range of magnetic field from -0.6T to 0.6T, average feature diameter (in [um]) and associated error (in [um]). Files containing the measured mobility and 2D carrier density from the standard Hall measurements described above are presented in two files. One file contains data for a single growth batch, broadly defining 3 regimes in the mobility vs carrier density, firstly increasing, then plateauing and finally decreasing. The other file contains Hall data for other growth batches. Files are tab separated .txt files with columns corresponding to carrier concentration (n2D) (in [m^-3]) and mobility (in [m^2/Vs]). A transport lifetime model has been employed to match predicted mobility given measured carrier density to the measured mobility. Standard scattering terms have been implemented, including a non-parabolic effective mass, and a modified remote ionised impurity scattering term to account for a spread of dopant as opposed to a single dopant plain. Also included is a scattering term related to the surface features observed through Nomarski imaging. Files are tab separated .txt files with columns corresponding to: Temperature[K], Remote Ionised Impurity Mobility[cm^2/Vs], Background Impurity[cm^2/Vs], Interface Roughness[cm^2/Vs], Acoustic Phonon[cm^2/Vs], Optical Phonon[cm^2/Vs], Surface Feature[cm^2/Vs] and Total Mobility[cm^2/Vs]. Also included is a tab separated .txt file containing experimentally measured mobility [cm^2/Vs] as a function of temperature [K]. A Monte-Carlo simulation has been used combining Landauer-Buttiker theory and a Drude model to simulate mobilities and currents due to potential barriers at surface feature boundaries. The resultant mobility for barriers of 1 to 50 monolayers (MLs) is presented in a tab separated file, where the first column corresponds to temperature [K] and the remaining columns are the mobility (in [cm^2/Vs]) for barrier thicknesses (in [ML]), with the header giving the specific barrier width. Also included is a tab separated file .txt containing data for barrier transmission as a function of energy, T(E), for barriers from 1 to 50 ML, and fermi distributions, f(E), as a function of energy for 3K and 300K. The first column corresponds to temperature [K], the next columns give T(E) for the barrier thickness given in the header and the final columns give f(E) for the thicknesses given in the header. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Description Lancaster Material Growth 
Organisation Lancaster University
Department Department of Physics
Country United Kingdom 
Sector Academic/University 
PI Contribution Material designs and ongoing discussion about MBE growth of InSb and GaSb based 2DEGs
Collaborator Contribution Lancaster are going to growth InSb based 2DEG's and GaSb 2DEG's for ongoign collaboration, looking at spin transport.
Impact None yet
Start Year 2015
Description Palmstrom Research Group 
Organisation University of California, Santa Barbara
Country United States 
Sector Academic/University 
PI Contribution We are receiving material to characterise, and potentially fabricate quantum devices from.
Collaborator Contribution Partners have supplied material after initial engagement at EP2DS confer4ence 2017. Common research interests, and the fact that we have key process knowledge, enabled interaction and discussion. We have agreed to characterise material that is grown in Santa Barabara and then shipped across to us for low temperature assessment (Hall and quantum Hall at >20mK).
Impact None as yet.
Start Year 2017
Description UCLA MBE growth 
Organisation University of California, Los Angeles (UCLA)
Country United States 
Sector Academic/University 
PI Contribution We have described work and requirement for material growth at a recent visit by Professor Huffaker, and have supplied detailed growth parameters after a number of email exchanges.
Collaborator Contribution Diana Huffaker's group at UCLA are supplying wafers along with our official collaborators (University of Sheffield NC for III-V technologies). They will attempt to use there extensive knowledge of mismatched buffer systems to reduce the total layer thickness whilst decreasing defect density within the active layer. This will bring benefit to device processing and ultimately to device operation. Update Material is now (Feb 16) being grown by Dr Baolai Liang at UCLA with a target to try to reduce buffer thickness for improved processing, and also important for long term exploitation of this material. This is a world leading group working on Interfacial misfit arrays (which they pioneered), which enables efficient strain relaxation to enable rapid material recovery after mismatched epitaxy. Layers are expected early March 16 for assessment.
Impact There were no significant outputs from this work. Material proved to be poor quality with significant resource required to progress this work, which neither institute could commit.
Start Year 2014
Description University of Surrey - Clowes 
Organisation University of Surrey
Department Department of Microbial Sciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Three meetings and samples exchanged for measurement at each institute, including discussion of the results andf physics involved
Collaborator Contribution Measurement of samples at high magnetic field with optical access for magneto-optical photconductivity measurements
Impact Draft paper in preparation
Start Year 2016
Description University of Warwick (Engineering) 
Organisation University of Warwick
Country United Kingdom 
Sector Academic/University 
PI Contribution Regular collaboration meeting (~every 3 months) to disseminate technology progress for devices, and investigate future extension of work
Collaborator Contribution Regular dissemination (presentations and discussion) of work, and technical progress. Joint work undertaken to do with technology transfer and technology progression. Face to face meetings are supplimented with monthly Skype meetings
Impact Full agenda, and minutes of meetings are produced
Start Year 2015