ORCID Profile
0000-0001-7935-7560
Current Organisation
University Of Strathclyde
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Nanometrology | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Nanotechnology | Nanoelectronics
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering |
Publisher: American Chemical Society (ACS)
Date: 19-05-2014
DOI: 10.1021/NL500927Q
Abstract: Nanoscale single-electron pumps can be used to generate accurate currents, and can potentially serve to realize a new standard of electrical current based on elementary charge. Here, we use a silicon-based quantum dot with tunable tunnel barriers as an accurate source of quantized current. The charge transfer accuracy of our pump can be dramatically enhanced by controlling the electrostatic confinement of the dot using purposely engineered gate electrodes. Improvements in the operational robustness, as well as suppression of nonadiabatic transitions that reduce pumping accuracy, are achieved via small adjustments of the gate voltages. We can produce an output current in excess of 80 pA with experimentally determined relative uncertainty below 50 parts per million.
Publisher: AIP Publishing
Date: 28-03-2011
DOI: 10.1063/1.3573991
Abstract: Reliable detection of single electron tunneling in quantum dots (QDs) is paramount to use this category of device for quantum information processing. Here, we report charge sensing in a degenerately phosphorus-doped silicon QD by means of a capacitively coupled single-electron tunneling device made of the same material. Besides accurate counting of tunneling events in the QD, we demonstrate that this architecture can be operated to reveal asymmetries in the transport characteristic of the QD. Indeed, the observation of gate voltage shifts in the detector’s response as the QD bias is changed is an indication of variable tunneling rates.
Publisher: American Physical Society (APS)
Date: 13-04-2023
Publisher: American Physical Society (APS)
Date: 30-10-2017
Publisher: IEEE
Date: 08-2014
Publisher: IOP Publishing
Date: 06-08-2021
Abstract: Single-charge pumps are the main candidates for quantum-based standards of the unit ere because they can generate accurate and quantized electric currents. In order to approach the metrological requirements in terms of both accuracy and speed of operation, in the past decade there has been a focus on semiconductor-based devices. The use of a variety of semiconductor materials enables the universality of charge pump devices to be tested, a highly desirable demonstration for metrology, with GaAs and Si pumps at the forefront of these tests. Here, we show that pumping can be achieved in a yet unexplored semiconductor, i.e. germanium. We realise a single-hole pump with a tunable-barrier quantum dot electrostatically defined at a Ge/SiGe heterostructure interface. We observe quantized current plateaux by driving the system with a single sinusoidal drive up to a frequency of 100 MHz. The operation of the prototype was affected by accidental formation of multiple dots, probably due to disorder potential, and random charge fluctuations. We suggest straightforward refinements of the fabrication process to improve pump characteristics in future experiments.
Publisher: American Physical Society (APS)
Date: 12-08-2013
Publisher: American Physical Society (APS)
Date: 17-04-2020
Publisher: AIP Publishing
Date: 22-05-2017
DOI: 10.1063/1.4984224
Abstract: Sensitive charge detection has enabled qubit readout in solid-state systems. Recently, an alternative to the well-established charge detection via on-chip electrometers has emerged, based on in situ gate detectors and radio-frequency dispersive readout techniques. This approach promises to facilitate scalability by removing the need for additional device components devoted to sensing. Here, we perform gate-based dispersive readout of an accumulation-mode silicon quantum dot. We observe that the response of an accumulation-mode gate detector is significantly affected by its bias voltage, particularly if this exceeds the threshold for electron accumulation. We discuss and explain these results in light of the competing capacitive contributions to the dispersive response.
Publisher: MyJove Corporation
Date: 03-06-2015
DOI: 10.3791/52852
Publisher: AIP Publishing
Date: 10-08-2015
DOI: 10.1063/1.4928589
Abstract: Schottky Barrier-MOSFET technology offers intriguing possibilities for cryogenic nano-scale devices, such as Si quantum devices and superconducting devices. We present experimental results on a device architecture where the gate electrode is self-aligned with the device channel and overlaps the source and drain electrodes. This facilitates a sub-5 nm gap between the source/drain and channel, and no spacers are required. At cryogenic temperatures, such devices function as p-MOS Tunnel FETs, as determined by the Schottky barrier at the Al-Si interface, and as a further advantage, fabrication processes are compatible with both CMOS and superconducting logic technology.
Publisher: AIP Publishing
Date: 26-03-2012
DOI: 10.1063/1.3697832
Abstract: Charge-based quantum computation can be attained through reliable control of single electrons in lead-less quantum systems. Single-charge transitions in electrically isolated double quantum dots (DQDs) realised in phosphorus-doped silicon can be detected via capacitively coupled single-electron tunnelling devices. By means of time-resolved measurements of the detector’s conductance, we investigate the dots’ occupancy statistics in temperature. We observe a significant reduction of the effective electron temperature in the DQD as compared to the temperature in the detector’s leads. This sets promises to make isolated DQDs suitable platforms for long-coherence quantum computation.
Publisher: IOP Publishing
Date: 02-07-2019
Publisher: American Physical Society (APS)
Date: 12-09-2012
Publisher: Wiley
Date: 07-06-2021
DOI: 10.1002/QUA.26306
Publisher: American Chemical Society (ACS)
Date: 19-06-2202
DOI: 10.1021/ACS.NANOLETT.8B00874
Abstract: In quantum metrology, semiconductor single-electron pumps are used to generate accurate electric currents with the ultimate goal of implementing the emerging quantum standard of the ere. Pumps based on electrostatically defined tunable quantum dots (QDs) have thus far shown the most promising performance in combining fast and accurate charge transfer. However, at frequencies exceeding approximately 1 GHz the accuracy typically decreases. Recently, hybrid pumps based on QDs coupled to trap states have led to increased transfer rates due to tighter electrostatic confinement. Here, we operate a hybrid electron pump in silicon obtained by coupling a QD to multiple parasitic states and achieve robust current quantization up to a few gigahertz. We show that the fidelity of the electron capture depends on the sequence in which the parasitic states become available for loading, resulting in distinctive frequency-dependent features in the pumped current.
Publisher: Springer Science and Business Media LLC
Date: 17-06-2019
Publisher: AIP Publishing
Date: 18-04-2012
DOI: 10.1063/1.4707165
Abstract: We have observed a negative differential conductance with singular gate and source-drain bias dependences in a phosphorus-doped silicon quantum dot. Its origin is discussed within the framework of weak localization. By measuring the current-voltage characteristics at different temperatures as well as simulating the tunneling rates dependences on energy, we demonstrate that the presence of shallow energy defects together with an enhancement of localization satisfactory explain our observations. Effects observed in magnetic fields are also discussed.
Publisher: IEEE
Date: 2003
Publisher: AIP Publishing
Date: 08-2010
DOI: 10.1063/1.3467963
Abstract: Resonant microwave-assisted and dc transport are investigated in degenerately doped silicon single electron transistors. A model based on hopping via localized impurity states is developed and first used to explain both the dc temperature dependence and the ac response. In particular, the non-monotonic power dependence of the resonant current under irradiation is proved to be consistent with spatial Rabi oscillations between these localized states.
Publisher: American Physical Society (APS)
Date: 19-07-2018
Publisher: IOP Publishing
Date: 11-10-2011
Publisher: Wiley
Date: 06-05-2021
DOI: 10.1002/QUA.26688
Abstract: Within the last decade much progress has been made in the experimental realization of quantum computing hardware based on a variety of physical systems. Rapid progress has been fuelled by the conviction that sufficiently powerful quantum machines will herald enormous computational advantages in many fields, including chemical research. A quantum computer capable of simulating the electronic structures of complex molecules would be a game changer for the design of new drugs and materials. Given the potential implications of this technology, there is a need within the chemistry community to keep abreast with the latest developments as well as becoming involved in experimentation with quantum prototypes. To facilitate this, here we review the types of quantum computing hardware that have been made available to the public through cloud services. We focus on three architectures, namely superconductors, trapped ions and semiconductors. For each one we summarize the basic physical operations, requirements and performance. We discuss to what extent each system has been used for molecular chemistry problems and highlight the most pressing hardware issues to be solved for a chemistry‐relevant quantum advantage to eventually emerge.
Publisher: Springer Science and Business Media LLC
Date: 16-08-2021
Publisher: IOP Publishing
Date: 13-01-2014
Publisher: Springer Science and Business Media LLC
Date: 11-03-2019
DOI: 10.1038/S41565-019-0400-7
Abstract: Electron spins in silicon quantum dots provide a promising route towards realizing the large number of coupled qubits required for a useful quantum processor
Publisher: IOP Publishing
Date: 16-10-2015
Publisher: AIP Publishing
Date: 29-11-2010
DOI: 10.1063/1.3524490
Abstract: The ability to control and detect single electrons is paramount for the implementation of a scalable charge-based quantum computer and single-electron memory devices. Here, we report charge detection in degenerately phosphorus-doped silicon double quantum dots (DQD) that are electrically connected to an electron reservoir. The sensing device is a single-electron transistor patterned in close proximity to the DQD. We observe steplike behavior and shifts of the Coulomb blockade oscillations in the detector’s current as the reservoir’s potential is swept. By means of a classical capacitance model, we demonstrate that these features can be used to detect changes in the DQD charge occupancy.
Publisher: Springer Science and Business Media LLC
Date: 27-06-2013
DOI: 10.1038/NCOMMS3069
Abstract: Although silicon is a promising material for quantum computation, the degeneracy of the conduction band minima (valleys) must be lifted with a splitting sufficient to ensure the formation of well-defined and long-lived spin qubits. Here we demonstrate that valley separation can be accurately tuned via electrostatic gate control in a metal-oxide-semiconductor quantum dot, providing splittings spanning 0.3-0.8 meV. The splitting varies linearly with applied electric field, with a ratio in agreement with atomistic tight-binding predictions. We demonstrate single-shot spin read-out and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 s. Spin relaxation occurs via phonon emission due to spin-orbit coupling between the valley states, a process not previously anticipated for silicon quantum dots. An analytical theory describes the magnetic field dependence of the relaxation rate, including the presence of a dramatic rate enhancement (or hot-spot) when Zeeman and valley splittings coincide.
Publisher: IEEE
Date: 06-2014
Publisher: IEEE
Date: 06-2012
Publisher: IEEE
Date: 06-2014
Publisher: AIP Publishing
Date: 03-11-2014
DOI: 10.1063/1.4901218
Abstract: Semiconductor quantum dots provide a two-dimensional analogy for real atoms and show promise for the implementation of scalable quantum computers. Here, we investigate the charge configurations in a silicon metal-oxide-semiconductor double quantum dot tunnel coupled to a single reservoir of electrons. By operating the system in the few-electron regime, the stability diagram shows hysteretic tunnelling events that depend on the history of the dots charge occupancy. We present a model which accounts for the observed hysteretic behaviour by extending the established description for transport in double dots coupled to two reservoirs. We demonstrate that this type of device operates like a single-electron memory latch.
Publisher: American Physical Society (APS)
Date: 10-12-2019
Publisher: AIP Publishing
Date: 19-12-2016
DOI: 10.1063/1.4972514
Abstract: Silicon-based metal-oxide-semiconductor quantum dots are prominent candidates for high-fidelity, manufacturable qubits. Due to silicon's band structure, additional low-energy states persist in these devices, presenting both challenges and opportunities. Although the physics governing these valley states has been the subject of intense study, quantitative agreement between experiment and theory remains elusive. Here, we present data from an experiment probing the valley states of quantum dot devices and develop a theory that is in quantitative agreement with both this and a recently reported experiment. Through s ling millions of realistic cases of interface roughness, our method provides evidence that the valley physics between the two s les is essentially the same.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2020
End Date: 2023
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2020
End Date: 2022
Funder: Australian Research Council
View Funded ActivityStart Date: 2016
End Date: 2018
Funder: European Commission
View Funded ActivityStart Date: 2021
End Date: 2025
Funder: UK Research and Innovation
View Funded ActivityStart Date: 2016
End Date: 06-2019
Amount: $470,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 12-2020
End Date: 12-2023
Amount: $550,000.00
Funder: Australian Research Council
View Funded Activity