Closed-loop control of a GaAs-based singlet-triplet spin qubit with 99.5% gate fidelity and low leakage

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.

Towards a realistic GaAs-spin qubit device for a classical error-corrected quantum memory

“…In the case of GaAs, the nuclear background field can be locally polarized by so-called dynamic nuclear polarization (DNP) [23], creating the desired gradient field. Fast control of the exchange interaction allows for gate operations with fidelities above 99% by numerical optimization of the pulse sequence [24,25]. We go into more detail on gate operations in Sec.…”

“…II A). For the chosen qubit type, material system, and architecture, leakage induction will be dominantly due to execution of gates (with, e.g., the single-qubit gate leakage rate measured to be 0.13% [25]). Therefore, most of the leakage will be accumulated during the echoing sequence executed on the data qubits while the ancilla qubits are being measured.…”

Deep reinforcement learning for efficient measurement of quantum devices

“…Semiconductor quantum dot devices are a promising candidate technology for the development of scalable quantum computing architectures. Singlet-triplet qubits encoded in double quantum dots 22 have demonstrably long coherence times 23,24 , as well as high one- 25 and two-qubit [26][27][28] gate fidelities. Promising qubit performance was also demonstrated in single-spin qubits [29][30][31] , and exchange only qubits 32,33 .…”

Universal Singlet‐Triplet Qubits Implemented Near the Transverse Sweet Spot

“…Quantum computing using the spin states of the electrons confined in the semiconductor quantum dots [ 1–16 ] is promising due to the long coherence time and the possibility for scalability. [ 3 ] Singlet‐triplet (ST) qubits in double quantum dot (DQD) [ 2,17–23 ] is particularly standing out of various proposals that are encoded using the spin states because of its all‐electrical operation and strong exchange interaction. However, in the operation for the ST qubits, both single‐ and two‐qubit gates are susceptible to the charge fluctuation (charge noise).…”

“…However, in the operation for the ST qubits, both single‐ and two‐qubit gates are susceptible to the charge fluctuation (charge noise). Although recent experiments have shown that the single‐qubit gate fidelity for the ST qubits can be higher than 99%, [ 20,22,23 ] the fidelity for the two‐qubit gate reported until now has been lower than the requirement for the fault‐tolerant quantum computing. [ 20,24 ] This motivates us to further search for useful methods to suppress the charge noise.…”