Quantum and tunneling capacitance in charge and spin qubits

Mizuta, Ryo; Otxoa, R. M.; Betz, Andreas; González-Zalba, M. Fernando

doi:10.1103/physrevb.95.045414

Cited by 72 publications

(82 citation statements)

References 42 publications

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“…At the location of the inter-dot charge transition, we observe a phase shift ∆φ = 2.2 mrad ( Fig. 2a, right), caused by the added quantum capacitance of the electron tunnelling between the dots [9,27,28]…”

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confidence: 98%

Gate-based single-shot readout of spins in silicon

et al. 2019

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Electron spins in silicon quantum dots provide a promising route towards realising the large number of coupled qubits required for a useful quantum processor [1][2][3][4][5][6][7][8]. At present, the requisite single-shot spin qubit measurements are performed using on-chip charge sensors, capacitively coupled to the quantum dots. However, as the number of qubits is increased, this approach becomes impractical due to the footprint and complexity of the charge sensors, combined with the required proximity to the quantum dots [5]. Alternatively, the spin state can be measured directly by detecting the complex impedance of spin-dependent electron tunnelling between quantum dots [9][10][11]. This can be achieved using radio-frequency reflectometry on a single gate electrode defining the quantum dot itself [11][12][13][14][15], significantly reducing gate count and architectural complexity, but thus far it has not been possible to achieve single-shot spin readout using this technique. Here, we detect single electron tunnelling in a double quantum dot and demonstrate that gate-based sensing can be used to read out the electron spin state in a single shot, with an average readout fidelity of 73%. The result demonstrates a key step towards the readout of many spin qubits in parallel, using a compact gate design that will be needed for a large-scale semiconductor quantum processor.

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confidence: 98%

Gate-based single-shot readout of spins in silicon

et al. 2019

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“…The QDs are tunnel coupled to each other via a mutual capacitance C m , and QD1 is further tunnel-coupled to a reservoir via a capacitance C D . The differential capacitance, as seen from the top-gate, can be expressed 40,41 as…”

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confidence: 99%

Quantum interference capacitor based on double-passage Landau-Zener-Stückelberg-Majorana interferometry

et al. 2019

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The implementation of quantum technologies in electronics leads naturally to the concept of coherent singleelectron circuits, in which a single charge is used coherently to provide enhanced performance. In this work, we propose a coherent single-electron device that operates as an electrically-tunable capacitor. This system exhibits a sinusoidal dependence of the capacitance with voltage, in which the amplitude of the capacitance changes and the voltage period can be tuned by electric means. The device concept is based on double-passage Landau-Zener-Stückelberg-Majorana interferometry of a coupled two-level system that is further tunnel-coupled to an electron reservoir. We test this model experimentally by performing Landau-Zener-Stückelberg-Majorana interferometry in a single-electron double quantum dot coupled to an electron reservoir and show that the voltage period of the capacitance oscillations is directly proportional to the excitation frequency and that the amplitude of the oscillations depends on the dynamical parameters of the system: intrinsic relaxation and coherence time, as well as the tunneling rate to the reservoir. Our work opens up an opportunity to use the non-linear capacitance of double quantum dots to obtain enhanced device functionalities.

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“…We choose this transition because it is purely capacitive and hence produces a purely dispersive shift of the resonant frequency. To demonstrate this, we fit a linear combination of an inverse square cosh function, due to the tunneling capacitance 21 , and a Lorentzian, due to tunnel-rate broadening 22,23 . We find that the peak is predominantly Lorentzian with a tunnel rate of γ = 40 ± 3 GHz.…”

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confidence: 99%

Low-temperature tunable radio-frequency resonator for sensitive dispersive readout of nanoelectronic devices

Ibberson

Smithson

et al. 2019

Applied Physics Letters

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We present a sensitive, tunable radio-frequency resonator designed to detect reactive changes in nanoelectronic devices down to dilution refrigerator temperatures. The resonator incorporates GaAs varicap diodes to allow electrical tuning of the resonant frequency and the coupling to the input line. We find a resonant frequency tuning range of 8.4 MHz at 55 mK that increases to 29 MHz at 1.5 K. To assess the impact on performance of different tuning conditions, we connect a quantum dot in a silicon nanowire field-effect transistor to the resonator, and measure changes in the device capacitance caused by cyclic electron tunneling. At 250 mK, we obtain an equivalent charge sensitivity of 43 µe/ √ Hz when the resonator and the line are impedancematched and show that this sensitivity can be further improved to 31 µe/ √ Hz by re-tuning the resonator. We understand this improvement by using an equivalent circuit model and demonstrate that for maximum sensitivity to capacitance changes, in addition to impedance matching, a high-quality resonator with low parasitic capacitance is desired.High-frequency reflectometry is a technique widely used to study the dynamical properties of nanoelectronic devices due to its enhanced sensitivity and large bandwidth when compared to direct current measurements 1,2 . By embedding a device in an electrical resonator, resistive or reactive changes in the device can be inferred from the resonator's response.Previous work has shown that, for sensitive detection of resistive changes, good impedance matching between the high frequency line and the resonator, as well as large fractional changes in resistance, are paramount 3,4 . Tunable resonators have recently been explored for sensitive capacitance readout 5,6 , concluding that optimal sensitivity occurs when the resonator is impedance matched to the line. In this Letter, we extend the work of Ares et al. and demonstrate that for maximal sensitivity to capacitance changes, in addition to an optimally matched resonator, large fractional changes in capacitance and a high internal-Q resonator are essential. We focus on dispersive changes because, for quantum computing technologies, measurement via detection of reactive changes is preferred since it allows for quantum-limited measurements of the qubits 7-9 .To achieve this, we present a tunable high-frequency resonator that remains operational at the base temperature of a dilution refrigerator and allows matching to be achieved at 200 mK. In previous reports, impedance matching was limited to temperatures of 1 K and above 5,10 . We couple our resonator to a quana) david.ibberson@bristol.ac.uk b) mg507@cam.ac.uk tum dot (QD) in a silicon nanowire field-effect transistor (NWFET) and measure changes in the device capacitance due to adiabatic single-electron tunneling events. We observe that sensitive detection of capacitance changes relies on an optimal balance of maximum power transfer to the resonator, maximal internal quality factor and minimized resonator capacitance, and that all three paramet...

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Quantum and tunneling capacitance in charge and spin qubits

Cited by 72 publications

References 42 publications

Gate-based single-shot readout of spins in silicon

Gate-based single-shot readout of spins in silicon

Quantum interference capacitor based on double-passage Landau-Zener-Stückelberg-Majorana interferometry

Low-temperature tunable radio-frequency resonator for sensitive dispersive readout of nanoelectronic devices

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