Versatile Quantum Multiplexing

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

Although we have known about one-dimensional electron transport at semiconductor interfaces for 25 years, little work has been done to investigate complex integrated circuits of such devices, or to evaluation the statistics of yield and reproducibility of the quantum effects seen in different devices, and so discern if manufacturable circuits might be possible.
We have developed a way of making a fully addressable 16x16 array of split-gate transistors (also known as quantum point contacts), and we have used this to study the fabrication and functional yield of these devices, and to make the first full statistical analysis of the so-called '0.7 spin phenomenon' in the ballistic 1D conductance of electrons. We are in the process of making parallel gates used for pumping charge, one electron at a time to produce measureable currents. We are also developing a means of biasing each split gate so that all 256 are at threshold before an experiment starts. This capability opens up a whole new area of physics and real-world technological applications which we now want to exploit to the full. In particular we will be able to study integrated circuits made of many quantum gates where the electrons retain quantum phase coherence from the input to the output of the circuit.
In this proposal we want to take our ideas forward to realise quantum metrology applications, examples of real integrated circuits exhibiting quantum coherence throughout, and a whole range of qualitatively new physics of quantum coherent electrons. We want to accelerate the decisions about exploitability by examining yield and reproducibility of devices as an integral part of the initial investigations.
Because of the breath of potential, we are developing the capability as a mini-facility and we will invite other research groups to come and use the multiplexer concept to pursue their own experiments with devices we can make and the dedicated evaluation equipment we are bidding for.

Planned Impact

A detailed Impact Statement is attached, which is summarised as follows:
We intend to impact on several topics by providing qualitatively and quantitatively new results.
In all of quantum metrology, quantum information processing, including quantum computing, and quantum computing, we anticipate major advances that will be robust and applicable.
We will be generating new intellectual property which we will protect.
We think that the two PDRA working on this topic will emerge as well-rounded specialists at the physics/engineering interface.
By establishing a mini-facility around our capability, we will accelerate the spread of the use of the multiplexing and addressing technology in quantum coherence circuits.

Publications

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Alexander-Webber JA (2017) Engineering the Photoresponse of InAs Nanowires. in ACS applied materials & interfaces

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Delfanazari K (2018) Proximity induced superconductivity in indium gallium arsenide quantum wells in Journal of Magnetism and Magnetic Materials

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Delfanazari K (2018) On-chip Hybrid Superconducting-Semiconducting Quantum Circuit in IEEE Transactions on Applied Superconductivity

 
Description The programme has taken several steps forward.
(1) A new dilution fridge and a high-speed electronics data logging system have been designed and implemented.
(2) We have introduced superconducting gates and have seen some novel effects in superconducting-semiconducting-superconducting systems that offer a physical basis for quantum computing in the longer term if some of the technologies can be refined and controlled adequately.
Exploitation Route A programme grant in Oxford led by Prof. Briggs is building on our multiplexer ideas for his quantum computing applications.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

 
Description EPSRC
Amount £940,489 (GBP)
Funding ID EP/S019324/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 02/2019 
End 01/2022
 
Title Cryostat, magnet and multiplexer 
Description We have established a dedicated self-contained cryostat and magnet, and measurement equipment for the rapid collection of large amounts of data, both at DC and high frequencies, from our quantum multiplexer chip. This equipment enables high-throughput data collection and analysis, at low temperature, a capability not available elsewhere in the UK. This facility, with web-accessible controls, is accessible to external UK research groups and industry. 
Type Of Material Improvements to research infrastructure 
Year Produced 2017 
Provided To Others? Yes  
Impact By establishing a mini-facility around our capability, we have accelerated the spread of the use of the multiplexing and addressing technology in quantum coherence circuits. 
 
Description National Physical Laboratory 
Organisation National Physical Laboratory
Department Quantum Metrology Institute
Country United Kingdom 
Sector Public 
PI Contribution We have successfully fabricated multiplexers with electron pumps. Yi Teng recently graduated and wrote his thesis on multiplexing electron pumps. Dr Luke Smith is continuing this work with Dr Joanna Waldie, a postdoc. Preliminary results show that we can put electron pumps on different channels of the multiplexer.
Collaborator Contribution NPL has shared with us their substantial expertise in device fabrication and characterisation, and in obtaining accurate measurements of sensitive quantum phenomena.
Impact We have successfully fabricated multiplexers with electron pumps. Yi Teng recently graduated and wrote his thesis on multiplexing electron pumps. Dr Luke Smith is continuing this work with Dr Joanna Waldie, a postdoc. Preliminary results show that we can put electron pumps on different channels of the multiplexer.
Start Year 2016
 
Description The Australian National University 
Organisation Australian National University (ANU)
Department Department of Electronic Materials Engineering (EME)
Country Australia 
Sector Academic/University 
PI Contribution Our team has fabricated the multiplexer and have measured the properties of nanowires integrated onto the multiplexer.
Collaborator Contribution Prof. Jagadish's group at the Australian National University has fabricated very high quality InAs nanowires for integration with the multiplexer.
Impact Successful integration of III-V nanowires into quantum multiplexer. Observation of quantised conductance in III-V nanowires integrated on quantum multiplexer.
Start Year 2017
 
Description University of Oxford - Materials Science 
Organisation University of Oxford
Country United Kingdom 
Sector Academic/University 
PI Contribution We have hosted Dr Xinya Bian from the group of Prof. Andrew Briggs, and together we have been integrating their graphene devices with our multiplexer. We have supplied Dr Xinya Bian with multiplexer samples and provided research infrastructure and expertise. We have supported our partners' EPSRC programme grant "Quantum Effects in Electronic Nanodevices (QuEEN)."
Collaborator Contribution Our partners' work has demonstrated the versatility of the multiplexer by applying it to another very different materials system: that of low-dimensional carbon/graphene.
Impact This work has demonstrated the versatility of the multiplexer by applying it to another very different materials system: that of low-dimensional carbon/graphene.
Start Year 2015
 
Description University of Strathclyde 
Organisation University of Strathclyde
Department Institute of Photonics
Country United Kingdom 
Sector Academic/University 
PI Contribution Our team has fabricated the multiplexer and have measured the properties of nanowires integrated onto the multiplexer.
Collaborator Contribution Dr Antonio Hurtado's team at the University of Strathclyde has developed nanoscale transfer printing techniques enabling the selective pick up and release of individual nanowires with an unparalleled level of control over the position and orientation of the nanowires, achieving a positional accuracy and alignment well below 1 µm (see for example Jevtics et al, Nano Lett., 17: 5990-5994, 2017). This transfer printing technique has been used successfully for integrating horizontal III-V nanowires at predefined locations on Cambridge's multiplexer circuit.
Impact Successful transfer printing and integration of III-V nanowires into quantum multiplexer. Observation of quantised conductance in III-V nanowires integrated on quantum multiplexer. Demonstration of the versatility and scalability of the transfer printing technique. Demonstration of the versatility of the quantum multiplexer.
Start Year 2017