Abstract
Semiconductor spin qubits have recently seen major advances in coherence time and control fidelities, leading to a single-qubit performance that is on par with other leading qubit platforms. Most of this progress is based on microwave control of single spins in devices made of isotopically purified silicon. For controlling spins, the exchange interaction is an additional key ingredient which poses new challenges for high-fidelity control. Here, we demonstrate exchange-based single-qubit gates of two-electron spin qubits in GaAs double quantum dots. Using careful pulse optimization and closed-loop tuning, we achieve a randomized benchmarking fidelity of (99.50±0.04)% and a leakage rate of 0.13% out of the computational subspace. These results open new perspectives for microwave-free control of singlet-triplet qubits in GaAs and other materials.
Highlights
Semiconductor spin qubits have recently seen major advances in coherence time and control fidelities, leading to a single-qubit performance that is on par with other leading qubit platforms
While semiconductor spin qubits have been pioneered with GaAs-based quantum dot devices[1,2,3,4,5,6,7], the adoption of isotopically purified silicon to avoid decoherence from nuclear spins has led to coherence times approaching one second[8,9] and control fidelities above 99.9%10–12, meeting the requirements for scalable quantum computing regarding single-qubit performance
We numerically optimized control pulses for exchange-based single-qubit gates with fidelities approaching 99.9% in previous work[18]. Remaining inaccuracies in these optimized pulses can be removed by a closed-loop gate set calibration protocol (GSC), which allows the iterative tune-up of gates using experimental feedback[18,19]
Summary
Semiconductor spin qubits have recently seen major advances in coherence time and control fidelities, leading to a single-qubit performance that is on par with other leading qubit platforms. Qubit control via the exchange interaction is associated with certain challenges like the need for strong driving well beyond the rotating wave approximation, nonlinear coupling to control fields, a susceptibility to charge noise that scales with the interaction strength[17], and a high sensitivity to the detailed shape of baseband control pulses To address these difficulties, we numerically optimized control pulses for exchange-based single-qubit gates with fidelities approaching 99.9% in previous work[18]. It allows us to optimize roughly an order of magnitude more parameters than before[12,20,21] to fully leverage the degrees of freedom provided by our hardware With this approach we achieve accurate control of GaAs-based singlet-triplet qubits encoded in two-electron spins with a fidelity of 99.50 ± 0.04% (in contrast to a preliminary preprint[22] of the present study we used a device with a more representative charge noise level compared to other groups[17]).
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