Logical Qubit in a Linear Array of Semiconductor Quantum Dots

Jones, Cody; Fogarty, Michael A.; Morello, Andrea; Gyure, Mark F.; Dzurak, A. S.; Ladd, Thaddeus D.

doi:10.1103/physrevx.8.021058

Cited by 76 publications

(74 citation statements)

References 194 publications

(652 reference statements)

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“…T * 2 ∼120 µs [24]). Decoupling schemes can then be used to yield longer qubit operation times (T 2 ∼ 28 ms [39]), and these can be integrated into algorithms [30,40] or single qubit gates designed via gradient ascent pulsed engineering [41] to be inherently robust against environmental noise [26].…”

Section: Data Qubits and Single-qubit Gatesmentioning

confidence: 99%

“…Our proposed ancilla qubit is represented by the spin state of a pair of electrons distributed across two quantum dots (each similar in size to the data dots). By initialising in a singlet state, a failed stabiliser check of its neighbouring data qubits transforms the ancilla spins into a triplet state [30], such that we can use Pauli spin blockade (PSB) and its effect on interdot tunnelling [43,44], to determine the outcome of the stabiliser cycle. PSB can be detected in singleshot through charge sensing [45], or via gatebased dispersive readout [46][47][48] as suggested by the measurement devices in Figure 1 [45,49].…”

Section: Ancilla Qubits and Read-outmentioning

confidence: 99%

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A Silicon Surface Code Architecture Resilient Against Leakage Errors

Cai

Fogarty

Schaal

et al. 2019

Quantum

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Spin qubits in silicon quantum dots are one of the most promising building blocks for large scale quantum computers thanks to their high qubit density and compatibility with the existing semiconductor technologies. High fidelity single-qubit gates exceeding the threshold of error correction codes like the surface code have been demonstrated, while two-qubit gates have reached 98% fidelity and are improving rapidly. However, there are other types of error -such as charge leakage and propagation -that may occur in quantum dot arrays and which cannot be corrected by quantum error correction codes, making them potentially damaging even when their probability is small. We propose a surface code architecture for silicon quantum dot spin qubits that is robust against leakage errors by incorporating multi-electron mediator dots. Charge leakage in the qubit dots is transferred to the mediator dots via charge relaxation processes and then removed using charge reservoirs attached to the mediators. A stabiliser-check cycle, optimised for our hardware, then removes the correlations between the residual physical errors. Through simulations we obtain the surface code threshold for the charge leakage errors and show that in our architecture the damage due to charge leakage errors is reduced to a similar level to that of the usual depolarising gate noise. Spin leakage errors in our architecture are Zhenyu Cai: zhenyu.cai@materials.ox.ac.uk John J. L. Morton: jjl.morton@ucl.ac.uk constrained to only ancilla qubits and can be removed during quantum error correction via reinitialisations of ancillae, which ensure the robustness of our architecture against spin leakage as well. Our use of an elongated mediator dots creates spaces throughout the quantum dot array for charge reservoirs, measuring devices and control gates, providing the scalability in the design.

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Section: Data Qubits and Single-qubit Gatesmentioning

confidence: 99%

Section: Ancilla Qubits and Read-outmentioning

confidence: 99%

A Silicon Surface Code Architecture Resilient Against Leakage Errors

Cai

Fogarty

Schaal

et al. 2019

Quantum

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“…It has, therefore, become topical to understand its operational boundaries or limitations. In the specific case of accumulation-mode devices, it has been proposed that the same gate(s) used to define the qubit(s) may be used for dispersive readout 26,27 . This would require operating the gate(s) above threshold voltage.…”

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confidence: 99%

“…In addition to providing much higher bandwidth than standard electrometry, gate-based reflectometry has an enormous potential for realizing scalable quantum architectures. In fact, a number of proposals has been already put forward to exploit high frequency techniques to different extents [26][27][28][29][30][31] .…”

mentioning

confidence: 99%

Dispersive readout of a silicon quantum dot with an accumulation-mode gate sensor

Rossi

Zhao

Dzurak

et al. 2017

Applied Physics Letters

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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.Reliable measurements of the charge state of nanoscale electronic devices may represent a key ingredient for the realization of future quantum technologies. Typically, non-invasive and sensitive charge readout is achieved by means of on-chip electrometers 1,2 . The scope of applicability of these sensing techniques is quite broad, ranging from charge noise characterization 3-5 to cryogenic thermometry 6-8 , as well as Maxwell's demon implementations 9,10 and quantum metrology 11-13 . Arguably, one of the research fields that has more largely benefitted from advancements in charge sensing is solid-state quantum information processing [14][15][16][17][18] .Recently, an alternative approach to implement charge readout has emerged based on radio-frequency (rf) resonant circuit techniques [19][20][21] . Using in-situ gate electrodes embedded into LC resonators, fast and sensitive charge detection has been attained 22-25 by measuring the dispersive shift of the resonator frequency when electron tunneling occurs. In addition to providing much higher bandwidth than standard electrometry, gate-based reflectometry has an enormous potential for realizing scalable quantum architectures. In fact, a number of proposals has been already put forward to exploit high frequency techniques to different extents [26][27][28][29][30][31] .Lately, spin-based qubits have been realised in planar silicon-based accumulation-mode quantum dots 18,32,33 . Gate-based dispersive readout may be an appealing technique to scale these systems up.In fact, CMOS-compatible architectures have been recently proposed 27,28 which identify routes toward large scalability of silicon-based spin qubit systems. The suggested readout protocol crucially relies on the gate-based dispersive technique discussed here. It has, therefore, become topical to understand its operational boundaries or limitations. In the specific case of accumulation-mode devices, it has been proposed that the same gate(s) used to define the qubit(s) may be used for dispersive readout 26,27 . This would require operating the gate(s) above threshold voltage. However, one has to be aware that the gate capacitance may significantly vary upon bias voltage and, in some circumstances, its contribution may dominate over the tunnelin...

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“…Indeed, by expedients like frequency multiplexing 10,34 and use of specific RF cryo-electronics, 35 multi-gate reflectometry may represent a viable technique for scalable singleshot readout of quantum dot arrays. 36 Supporting Information Available: RF modulation amplitudes analysis and discussion on possible regimes to realize coherent oscillations. This material is available free of charge via the Internet at http://pubs.acs.org/.…”

mentioning

confidence: 99%

Level Spectrum and Charge Relaxation in a Silicon Double Quantum Dot Probed by Dual-Gate Reflectometry

et al. 2017

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We report on dual-gate reflectometry in a metaloxide-semiconductor double-gate silicon transistor operating at low temperature as a double quantum dot device. The reflectometry setup consists of two radio-frequency resonators respectively connected to the two gate electrodes. By simultaneously measuring their dispersive responses, we obtain the complete charge stability diagram of the device. Electron transitions between the two quantum dots and between each quantum dot and either the source or the drain contact are detected through phase shifts in the reflected radio-frequency signals. At finite bias, reflectometry allows probing charge transitions to excited quantum-dot states, * To whom correspondence should be addressed † Université thereby enabling direct access to the energy level spectra of the quantum dots. Interestingly, we find that in the presence of electron transport across the two dots the reflectometry signatures of interdot transitions display a dip-peak structure containing quantitative information on the charge relaxation rates in the double quantum dot.Keywords: dispersive readout, reflectometry, double quantum dot, charge relaxation, highfrequency resonator, silicon.Integration of charge sensors for the readout of quantum bits (qubits) is one of the necessary ingredients for the realization of scalable semiconductor quantum computers. 1 In most qubits developed so far in silicon, like electron or nuclear spins in quantum dots and single atoms, 2-4 charge 5 or hybrid spin-charge states, 6 qubit readout has been performed with the aid of quantum point contacts (QPCs) or single-electron transistors (SETs). These charge-sensitive devices, however, involve a significant overhead in terms of gates and contact leads, posing an issue for scalability towards many-qubit architectures. Gate-coupled radio-frequency (RF) reflectome-1 arXiv:1610.03657v2 [cond-mat.mes-hall]

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Logical Qubit in a Linear Array of Semiconductor Quantum Dots

Cited by 76 publications

References 194 publications

A Silicon Surface Code Architecture Resilient Against Leakage Errors

A Silicon Surface Code Architecture Resilient Against Leakage Errors

Dispersive readout of a silicon quantum dot with an accumulation-mode gate sensor

Level Spectrum and Charge Relaxation in a Silicon Double Quantum Dot Probed by Dual-Gate Reflectometry

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