Fast and High-Fidelity State Preparation and Measurement in Triple-Quantum-Dot Spin Qubits

• Main Authors: Andrews, R.W (Author), Barnes, D.W (Author), Blumoff, J.Z (Author), Borselli, M.G (Author), Brecht, T.L (Author), Croke, E.T (Author), Eng, K. (Author), Euliss, L.E (Author), Fast, J.A (Author), Hunter, A.T (Author), Jackson, C.A.C (Author), Jones, A.M (Author), Keating, T.E (Author), Kerckhoff, J. (Author), Ladd, T.D (Author), Lanza, R.K (Author), Pan, A.S (Author), Raach, K. (Author), Rakher, M.T (Author), Thomas, B.J (Author), Velunta, R. (Author), Weinstein, A.J (Author)
• Format: Article
• Language: English
• Published: American Physical Society 2022
• Subjects: Fast measurement; High-fidelity; Measurement integration; Nanocrystals; Quantum dot qubits; Quantum dot spins; Quantum optics; Qubits; Semiconductor quantum dots; Si/SiGe; Spin qubit; State measurements; State preparation; Triple quantum
• Online Access: View Fulltext in Publisher
• ISBN: 26913399 (ISSN)
• DOI: 10.1103/PRXQuantum.3.010352

We demonstrate rapid high-fidelity state preparation and measurement in exchange-only Si/SiGe triple-quantum-dot qubits. Fast measurement integration (980-ns) and initialization (approximately 300-ns) operations are performed with all-electrical baseband control. We emphasize a leakage-sensitive joint initialization and measurement metric, developed in the context of exchange-only qubits but applicable more broadly, and report an infidelity of 2.5±0.5×10-3. This result is enabled by a high-valley-splitting heterostructure, initialization at the two- to three-electron charge boundary, and careful assessment and mitigation of T1 during spin-to-charge conversion. The ultimate fidelity is limited by a number of comparably important factors and we identify clear paths toward further improved fidelity and speed. Along with an observed single-qubit randomized benchmarking error rate of 1.7×10-3, this work demonstrates initialization, control, and measurement of Si/SiGe triple-dot qubits at fidelities and durations that are promising for scalable quantum information processing. © 2022 authors. Published by the American Physical Society.