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.
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.
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
Alexander-Webber JA
(2017)
Engineering the Photoresponse of InAs Nanowires.
in ACS applied materials & interfaces
Delfanazari K
(2019)
Andreev reflections and magnetotransport in 2D Josephson junctions
in Journal of Physics: Conference Series
Delfanazari K
(2017)
On-Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb-In0.75 Ga0.25 As-Quantum-Well-Nb Josephson Junctions.
in Advanced materials (Deerfield Beach, Fla.)
Delfanazari K
(2018)
On-chip Hybrid Superconducting-Semiconducting Quantum Circuit
in IEEE Transactions on Applied Superconductivity
Delfanazari K
(2018)
Proximity induced superconductivity in indium gallium arsenide quantum wells
in Journal of Magnetism and Magnetic Materials
Kalhor S
(2017)
Thermal Tuning of High-$T_{c}$ Superconducting Bi$_{2}$Sr $_{2}$CaCu$_{2}$ O$_{8+\delta }$ Terahertz Metamaterial
in IEEE Photonics Journal
Smith LW
(2022)
Giant Magnetoresistance in a Chemical Vapor Deposition Graphene Constriction.
in ACS nano
Smith LW
(2020)
High-Throughput Electrical Characterization of Nanomaterials from Room to Cryogenic Temperatures.
in ACS nano
| 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. (3) We have achieved the integration of new materials, including graphene, with the multiplexer. This capability is allowing us to measure quantum physical properties of these new nanomaterials, and allowing us to develop new nanomaterial-based quantum electronic circuitry. |
| Exploitation Route | This work is a precondition for high-volume manufacture. Advanced device manufacturers (E2V, Thales, etc) will be able to use our work to expedite device development. NPL is using our work to set the SI (International System of Units) standard for the Ampere. A programme grant in Oxford led by Prof. Briggs is building on our multiplexer ideas for his quantum computing applications. Dr Mark Blumenthal from the University of Cape Town in South Africa is using multiplexers for standards applications. We have received new grant, Multiplexed Quantum Integrated Circuits, led by PI Prof. Charles Smith, to develop the multiplexer and its applications. |
| Sectors | Digital/Communication/Information Technologies (including Software),Electronics |
| Description | The project has brought advances to quantum metrology and quantum information processing, including quantum computing. The National Physical Laboratory (NPL) is using our work to set the SI (International System of Units) standard for the Ampere. We have established new collaborations with academic and industrial partners, including with the University of Strathclyde, the Australian National University and National Cheng Kung University. The two postdoctoral research associates who worked on the project have emerged as well-rounded specialists at the physics/engineering interface. They have both secured permanent academic (associate professor/assistant professor-level) roles at world-leading universities and now lead their own research teams. Finally, we have established a mini-facility around our capability, which is accelerating the spread of the use of the multiplexing and addressing technology in quantum coherence circuits. |
| Sector | Digital/Communication/Information Technologies (including Software),Education,Electronics |
| Impact Types | Societal,Economic |
| Description | EPSRC |
| Amount | £940,489 (GBP) |
| Funding ID | EP/S019324/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| 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. |
| Title | Research data supporting "Engineering the Photoresponse of InAs Nanowires" |
| Description | Raw data from the figures in "Engineering the Photoresponse of InAs Nanowires". InAs nanowires were grown by metal-organic chemical vapor deposition (MOCVD). The growth conditions were chosen to grow wurtzite crystal structures with minimal stacking faults, minimal tapering, and hexagonal cross sections with {11¯00} side facets, as confirmed by transmission electron microscopy (TEM). The nanowire diameter was tightly controlled by selecting the diameter of the Au catalyst. Nanowire diameters, inclusive of surface oxide, of 30 ± 5 nm, 40 ± 5 nm, 65 ± 5 nm, and 110 ± 5 nm, respectively, were obtained, as confirmed by SEM. For TEM measurements, nanowires were mechanically transferred to a holey carbon grid. TEM was performed using a JEOL 2100F instrument operated at 200 keV. The nanowires were transferred to a doped Si wafer with 300 nm of thermally grown SiO2 which served as a global back gate. Contacts with a separation of 1 µm were patterned using e-beam lithography and sputter deposition of 70 nm Ni, followed by lift-off. To obtain low contact resistivity, prior to Ni deposition, the contact region of the nanowire was etched in 2% aqueous (NH4)2S solution at 40 °C for 10 min. Electrical measurements were carried out using a probe station connected to a Keithley 4200-SCS semiconductor characterization system. Illumination of the samples to measure the photoresponse was applied using a 3200 K halogen lamp with a power density of 30 mW cm-2. All measurements were carried out at room temperature under ambient conditions unless otherwise specified. For ALD passivation, after device fabrication, a 90 nm capping layer of Al2O3 was deposited using a Cambridge NanoTech ALD system at 120 °C using trimethylaluminum and H2O precursors. The probe pads were then exposed by etching through the Al2O3 with phosphoric acid. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2018 |
| Provided To Others? | Yes |
| Title | Research data supporting "Proximity induced superconductivity in indium gallium arsenide quantum wells" |
| Description | The hybrid Josephson junctions fabricated, and measured by the authors at the Cavendish Laboratory, University of Cambridge UK, in the period Jan 2016 to April 2017. The measurements were done at low temperature (50 to 800 mK). The experimental methods are described in the associated publication. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2022 |
| Provided To Others? | Yes |
| URL | https://www.repository.cam.ac.uk/handle/1810/332625 |
| 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. Our 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. Our 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 |