Magnetic Gradient Fluctuations from Quadrupolar 
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Kerckhoff, Joseph; Sun, Bo; Fong, Bryan H.; Jones, Cody; Kiselev, A. A.; Barnes, David W.; Noah, Ramsey; Acuna, Edwin; Akmal, M.; Ha, Sieu D.; Wright, Jeffrey A.; Thomas, Bryan J.; Jackson, Clayton A.; Edge, L. F.; Eng, Kevin; Ross, Richard S.; Ladd, Thaddeus D.

doi:10.1103/prxquantum.2.010347

Cited by 14 publications

(18 citation statements)

References 53 publications

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“…At fields > 3 mT, error increases again due to a combination of spin-orbit effects and Meissner screening effects from superconducting parts of the gate-stack (see Appendix C). This effect is stronger in earlier devices employing aluminum metal [20], but is much weaker in the present device due to the non-or weakly-superconducting TiN gates used in the SLEDGE process [18]. From this plot we may infer that the IRB shown in Fig.…”

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confidence: 55%

“…4(e) we plot average two-qubit Clifford fidelity measured using RB as a function of both applied field and t idle , and find that error initially decreases by nearly a factor of two with increasing field strength. We understand this improvement as the suppression of nuclear magnetic fluctuations transverse to the field direction [20]. At fields > 3 mT, error increases again due to a combination of spin-orbit effects and Meissner screening effects from superconducting parts of the gate-stack (see Appendix C).…”

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confidence: 96%

“…Three recent advances enabled the result we report on here: the Single Layer Etch-Defined Gate Electrode (SLEDGE) process [18] for making high-yielding devices, the use of narrow Si/Si 0.3 Ge 0.7 quantum wells to increase the probability that dots have sufficiently large valley energy for measurement and initialization [9], and improved control software to manage the complexity of these larger quantum manipulations [1]. Using these, we demonstrate an average 2-qubit Clifford fidelity of 97.1 ± 0.2% and the FW controlled-NOT gate [17,19] (FW-CNOT) with 96.3 ± 0.7% fidelity, both limited by well-understood sources of magnetic noise [20], and an encoded SWAP operation with 99.3 ± 0.5% fidelity. We also demonstrate a "leakage controlled" controlled-Z (LCCZ) gate, requiring 45 exchange pulses, with 93.8 ± 0.7% fidelity.…”

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confidence: 99%

“…2 , where T * 2 ≈ 3.5µs is the 1/e decay time of an idle singlet state (see Appendix C) [20]. Unlike charge noise, magnetic noise acts during both pulsing and idling [32], and so dephasing occurs continuously during evolution, leading to a total error scaling as (t gate /T * 2 ) 2 .…”

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confidence: 99%

“…Unlike charge noise, magnetic noise acts during both pulsing and idling [32], and so dephasing occurs continuously during evolution, leading to a total error scaling as (t gate /T * 2 ) 2 . The prefactor of that scaling (generally ≤ 1), however, depends on how much the sequence permutes spins and decouples magnetic noise [20]. For this reason, most sequences in Fig.…”

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confidence: 99%

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Universal logic with encoded spin qubits in silicon

Weinstein¹,

Reed²,

Jones³

et al. 2022

Preprint

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Qubits encoded in a decoherence-free subsystem and realized in exchange-coupled silicon quantum dots are promising candidates for fault-tolerant quantum computing. Benefits of this approach include excellent coherence, low control crosstalk, and configurable insensitivity to certain error sources. Key difficulties are that encoded entangling gates require a large number of control pulses and high-yielding quantum dot arrays. Here we show a device made using the single-layer etchdefined gate electrode architecture that achieves both the required functional yield needed for full control and the coherence necessary for thousands of calibrated exchange pulses to be applied. We measure an average two-qubit Clifford fidelity of 97.1 ± 0.2% with randomized benchmarking. We also use interleaved randomized benchmarking to demonstrate the controlled-NOT gate with 96.3 ± 0.7% fidelity, SWAP with 99.3 ± 0.5% fidelity, and a specialized entangling gate that limits spreading of leakage with 93.8 ± 0.7% fidelity.

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confidence: 55%

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confidence: 96%

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confidence: 99%

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confidence: 99%

mentioning

confidence: 99%

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Universal logic with encoded spin qubits in silicon

Weinstein¹,

Reed²,

Jones³

et al. 2022

Preprint

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Charge-noise spectroscopy of Si/SiGe quantum dots via dynamically-decoupled exchange oscillations

et al. 2022

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Electron spins in silicon quantum dots are promising qubits due to their long coherence times, scalable fabrication, and potential for all-electrical control. However, charge noise in the host semiconductor presents a major obstacle to achieving high-fidelity single- and two-qubit gates in these devices. In this work, we measure the charge-noise spectrum of a Si/SiGe singlet-triplet qubit over nearly 12 decades in frequency using a combination of methods, including dynamically-decoupled exchange oscillations with up to 512 π pulses during the qubit evolution. The charge noise is colored across the entire frequency range of our measurements, although the spectral exponent changes with frequency. Moreover, the charge-noise spectrum inferred from conductance measurements of a proximal sensor quantum dot agrees with that inferred from coherent oscillations of the singlet-triplet qubit, suggesting that simple transport measurements can accurately characterize the charge noise over a wide frequency range in Si/SiGe quantum dots.

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