ORCID Profile
0000-0001-7892-7963
Current Organisation
UNSW Sydney
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Quantum Information, Computation and Communication | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Quantum Physics | Quantum Optics | Optical Physics | Photonics, Optoelectronics and Optical Communications
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering |
Publisher: American Physical Society (APS)
Date: 26-10-2021
Publisher: Springer Science and Business Media LLC
Date: 12-01-2023
Publisher: Springer Science and Business Media LLC
Date: 03-12-2019
DOI: 10.1038/S41467-019-13416-7
Abstract: Single-electron spin qubits employ magnetic fields on the order of 1 Tesla or above to enable quantum state readout via spin-dependent-tunnelling. This requires demanding microwave engineering for coherent spin resonance control, which limits the prospects for large scale multi-qubit systems. Alternatively, singlet-triplet readout enables high-fidelity spin-state measurements in much lower magnetic fields, without the need for reservoirs. Here, we demonstrate low-field operation of metal-oxide-silicon quantum dot qubits by combining coherent single-spin control with high-fidelity, single-shot, Pauli-spin-blockade-based ST readout. We discover that the qubits decohere faster at low magnetic fields with $${T}_{2}^{\\,\\text{Rabi}\\,}=18.6$$ T 2 Rabi = 18.6 μs and $${T}_{2}^{* }=1.4$$ T 2 * = 1.4 μs at 150 mT. Their coherence is limited by spin flips of residual 29 Si nuclei in the isotopically enriched 28 Si host material, which occur more frequently at lower fields. Our finding indicates that new trade-offs will be required to ensure the frequency stabilization of spin qubits, and highlights the importance of isotopic enrichment of device substrates for the realization of a scalable silicon-based quantum processor.
Publisher: Wiley
Date: 16-12-2022
Abstract: Quantum computers have the potential to efficiently solve problems in logistics, drug and material design, finance, and cybersecurity. However, millions of qubits will be necessary for correcting inevitable errors in quantum operations. In this scenario, electron spins in gate‐defined silicon quantum dots are strong contenders for encoding qubits, leveraging the microelectronics industry know‐how for fabricating densely populated chips with nanoscale electrodes. The sophisticated material combinations used in commercially manufactured transistors, however, will have a very different impact on the fragile qubits. Here some key properties of the materials that have a direct impact on qubit performance and variability are reviewed.
Publisher: American Physical Society (APS)
Date: 09-08-2023
Publisher: Springer Science and Business Media LLC
Date: 11-03-2020
Publisher: American Physical Society (APS)
Date: 27-02-2023
Publisher: American Chemical Society (ACS)
Date: 22-01-2021
Publisher: American Chemical Society (ACS)
Date: 27-10-2020
Publisher: American Association of Physics Teachers (AAPT)
Date: 12-2020
DOI: 10.1119/10.0001905
Abstract: The room temperature compatibility of the negatively charged nitrogen-vacancy (NV−) center in diamond makes it the ideal quantum system for a university teaching lab. Here, we describe a low-cost experimental setup for coherent control experiments on the electronic spin state of the NV− center. We implement spin-relaxation measurements, optically detected magnetic resonance, Rabi oscillations, and dynamical decoupling sequences on an ensemble of NV− centers. The relatively short times required to perform each of these experiments (& min) demonstrate the feasibility of the setup in a teaching lab. Learning outcomes include basic understanding of quantum spin systems, magnetic resonance, the rotating frame, Bloch spheres, and pulse sequence development.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 13-08-2021
Abstract: Large-scale qubit control in spin-based quantum computers can be realized using a global microwave field, generated off chip.
Publisher: American Physical Society (APS)
Date: 31-05-2022
Publisher: Springer Science and Business Media LLC
Date: 05-07-2021
DOI: 10.1038/S41467-021-24371-7
Abstract: A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits.
Publisher: Research Square Platform LLC
Date: 14-07-2023
DOI: 10.21203/RS.3.RS-3057916/V1
Abstract: Spins of electrons in CMOS quantum dots combine exquisite quantum properties and scalable fabrication. In the age of quantum technology, however, the metrics that crowned Si/SiO$_2$ as the microelectronics standard need to be reassessed with respect to their impact upon qubit performance. We chart spin qubit variability due to the unavoidable atomic-scale roughness of the Si/SiO$_2$ interface, compiling experiments across 12 devices, and develop theoretical tools to analyse these results. Atomistic tight binding and path integral Monte Carlo methods are adapted to describe fluctuations in devices with millions of atoms by directly analysing their wavefunctions and electron paths instead of their energy spectra. We correlate the effect of roughness with the variability in qubit position, deformation, valley splitting, valley phase, spin-orbit coupling and exchange coupling. These variabilities are found to be bounded, and they lie within the tolerances for scalable architectures for quantum computing as long as robust control methods are incorporated.
Publisher: American Physical Society (APS)
Date: 25-09-2020
Publisher: Springer Science and Business Media LLC
Date: 09-12-2020
DOI: 10.1038/S41565-019-0587-7
Abstract: Single nuclear spins in the solid state are a potential future platform for quantum computing
Publisher: Springer Science and Business Media LLC
Date: 05-2019
DOI: 10.1038/S41586-019-1197-0
Abstract: Universal quantum computation will require qubit technology based on a scalable platform
Publisher: American Physical Society (APS)
Date: 09-12-2021
Publisher: Springer Science and Business Media LLC
Date: 19-01-2022
DOI: 10.1038/S41586-021-04292-7
Abstract: Nuclear spins were among the first physical platforms to be considered for quantum information processing
Publisher: Springer Science and Business Media LLC
Date: 04-11-2022
DOI: 10.1038/S41534-022-00645-W
Abstract: Silicon spin qubits promise to leverage the extraordinary progress in silicon nanoelectronic device fabrication over the past half century to deliver large-scale quantum processors. Despite the scalability advantage of using silicon technology, realising a quantum computer with the millions of qubits required to run some of the most demanding quantum algorithms poses several outstanding challenges, including how to control many qubits simultaneously. Recently, compact 3D microwave dielectric resonators were proposed as a way to deliver the magnetic fields for spin qubit control across an entire quantum chip using only a single microwave source. Although spin resonance of in idual electrons in the globally applied microwave field was demonstrated, the spins were controlled incoherently. Here we report coherent Rabi oscillations of single electron spin qubits in a planar SiMOS quantum dot device using a global magnetic field generated off-chip. The observation of coherent qubit control driven by a dielectric resonator establishes a credible pathway to achieving large-scale control in a spin-based quantum computer.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2022
Publisher: Springer Science and Business Media LLC
Date: 28-05-2021
DOI: 10.1038/S41467-021-23437-W
Abstract: An error-corrected quantum processor will require millions of qubits, accentuating the advantage of nanoscale devices with small footprints, such as silicon quantum dots. However, as for every device with nanoscale dimensions, disorder at the atomic level is detrimental to quantum dot uniformity. Here we investigate two spin qubits confined in a silicon double quantum dot artificial molecule. Each quantum dot has a robust shell structure and, when operated at an occupancy of 5 or 13 electrons, has single spin- $$\\frac{1}{2}$$ 1 2 valence electron in its p - or d -orbital, respectively. These higher electron occupancies screen static electric fields arising from atomic-level disorder. The larger multielectron wavefunctions also enable significant overlap between neighbouring qubit electrons, while making space for an interstitial exchange-gate electrode. We implement a universal gate set using the magnetic field gradient of a micromagnet for electrically driven single qubit gates, and a gate-voltage-controlled inter-dot barrier to perform two-qubit gates by pulsed exchange coupling. We use this gate set to demonstrate a Bell state preparation between multielectron qubits with fidelity 90.3%, confirmed by two-qubit state tomography using spin parity measurements.
Publisher: Springer Science and Business Media LLC
Date: 15-04-2019
Publisher: Springer Science and Business Media LLC
Date: 15-04-2020
Publisher: American Chemical Society (ACS)
Date: 17-05-2021
Publisher: American Association for the Advancement of Science (AAAS)
Date: 03-07-2020
Abstract: The presence or absence of an electron controls the freezing of the nuclear spin bath coupled to a single-atom qubit in silicon.
Publisher: Springer Science and Business Media LLC
Date: 08-01-2021
DOI: 10.1038/S41467-020-20424-5
Abstract: Silicon nanoelectronic devices can host single-qubit quantum logic operations with fidelity better than 99.9%. For the spins of an electron bound to a single-donor atom, introduced in the silicon by ion implantation, the quantum information can be stored for nearly 1 second. However, manufacturing a scalable quantum processor with this method is considered challenging, because of the exponential sensitivity of the exchange interaction that mediates the coupling between the qubits. Here we demonstrate the conditional, coherent control of an electron spin qubit in an exchange-coupled pair of 31 P donors implanted in silicon. The coupling strength, J = 32.06 ± 0.06 MHz, is measured spectroscopically with high precision. Since the coupling is weaker than the electron-nuclear hyperfine coupling A ≈ 90 MHz which detunes the two electrons, a native two-qubit controlled-rotation gate can be obtained via a simple electron spin resonance pulse. This scheme is insensitive to the precise value of J , which makes it suitable for the scale-up of donor-based quantum computers in silicon that exploit the metal-oxide-semiconductor fabrication protocols commonly used in the classical electronics industry.
Publisher: Springer Science and Business Media LLC
Date: 29-11-2021
DOI: 10.1038/S41565-021-00994-1
Abstract: For the past three decades nanoscience has widely affected many areas in physics, chemistry and engineering, and has led to numerous fundamental discoveries, as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing, has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this Review according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system, such as charge, spin, mechanical motion and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations.
Publisher: Wiley
Date: 22-06-2023
Abstract: Quantum key distribution (QKD) is considered the most immediate application to be widely implemented among a variety of potential quantum technologies. QKD enables sharing secret keys between distant users by using photons as information carriers. An ongoing endeavor is to implement these protocols in practice in a robust, and compact manner so as to be efficiently deployable in a range of real‐world scenarios. Single photon sources (SPS) in solid‐state materials are prime candidates in this respect. This article demonstrates a room temperature, discrete‐variable quantum key distribution system using a bright single photon source in hexagonal‐boron nitride, operating in free‐space. Employing an easily interchangeable photon source system, keys with one million bits length, and a secret key of approximately 70000 bits, at a quantum bit error rate of 6%, with ε‐security of 10 −10 are generated. This study demonstrates the first proof of concept finite‐key BB84 QKD system realized with hBN defects.
Publisher: American Physical Society (APS)
Date: 10-05-2019
Publisher: American Physical Society (APS)
Date: 07-01-2021
Publisher: Springer Science and Business Media LLC
Date: 11-02-2020
DOI: 10.1038/S41467-019-14053-W
Abstract: Once the periodic properties of elements were unveiled, chemical behaviour could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots, and quantum computation could be performed by merely controlling the outer-shell electrons of dot-based qubits. Imperfections in semiconductor materials disrupt this analogy, so real devices seldom display a systematic many-electron arrangement. We demonstrate here an electrostatically confined quantum dot that reveals a well defined shell structure. We observe four shells (31 electrons) with multiplicities given by spin and valley degrees of freedom. Various fillings containing a single valence electron—namely 1, 5, 13 and 25 electrons—are found to be potential qubits. An integrated micromagnet allows us to perform electrically-driven spin resonance (EDSR), leading to faster Rabi rotations and higher fidelity single qubit gates at higher shell states. We investigate the impact of orbital excitations on single qubits as a function of the dot deformation and exploit it for faster qubit control.
Publisher: IOP Publishing
Date: 05-02-2021
Abstract: Quantum phenomena are typically observable at length and time scales smaller than those of our everyday experience, often involving in idual particles or excitations. The past few decades have seen a revolution in the ability to structure matter at the nanoscale, and experiments at the single particle level have become commonplace. This has opened wide new avenues for exploring and harnessing quantum mechanical effects in condensed matter. These quantum phenomena, in turn, have the potential to revolutionize the way we communicate, compute and probe the nanoscale world. Here, we review developments in key areas of quantum research in light of the nanotechnologies that enable them, with a view to what the future holds. Materials and devices with nanoscale features are used for quantum metrology and sensing, as building blocks for quantum computing, and as sources and detectors for quantum communication. They enable explorations of quantum behaviour and unconventional states in nano- and opto-mechanical systems, low-dimensional systems, molecular devices, nano-plasmonics, quantum electrodynamics, scanning tunnelling microscopy, and more. This rapidly expanding intersection of nanotechnology and quantum science/technology is mutually beneficial to both fields, laying claim to some of the most exciting scientific leaps of the last decade, with more on the horizon.
Publisher: AIP Publishing
Date: 08-2021
DOI: 10.1063/5.0055318
Abstract: Magnetic fields are a standard tool in the toolbox of every physicist and are required for the characterization of materials, as well as the polarization of spins in nuclear magnetic resonance or electron paramagnetic resonance experiments. Quite often, a static magnetic field of sufficiently large, but fixed, magnitude is suitable for these tasks. Here, we present a permanent magnet assembly that can achieve magnetic field strengths of up to 1.5 T over an air gap length of 7 mm. The assembly is based on a Halbach array of neodymium magnets, with the inclusion of the soft magnetic material Supermendur to boost the magnetic field strength inside the air gap. We present the design, simulation, and characterization of the permanent magnet assembly, measuring an outstanding magnetic field stability with a drift rate of |D| & 2.8 ppb/h. Our measurements demonstrate that this assembly can be used for spin qubit experiments inside a dilution refrigerator, successfully replacing the more expensive and bulky superconducting solenoids.
Publisher: AIP Publishing
Date: 09-2022
DOI: 10.1063/5.0096467
Abstract: Quantum computing based on solid state spins allows for densely packed arrays of quantum bits. However, the operation of large-scale quantum processors requires a shift in paradigm toward global control solutions. Here, we report a proof-of-principle demonstration of the SMART (sinusoidally modulated, always rotating, and tailored) qubit protocol. We resonantly drive a two-level system and add a tailored modulation to the dressing field to increase robustness to frequency detuning noise and microwave litude fluctuations. We measure a coherence time of 2 ms, corresponding to two orders of magnitude improvement compared to a bare spin, and an average Clifford gate fidelity exceeding 99%, despite the relatively long qubit gate times. We stress that the potential of this work lies in the scalability of the protocol and the relaxation of the engineering constraints for a large-scale quantum processor. This work shows that future scalable spin qubit arrays could be operated using global microwave control and local gate addressability, while increasing robustness to relevant experimental inhomogeneities.
Publisher: American Physical Society (APS)
Date: 14-05-2019
Start Date: 2016
End Date: 12-2017
Amount: $370,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 06-2018
End Date: 05-2025
Amount: $33,700,000.00
Funder: Australian Research Council
View Funded Activity