Observation of anomalous T₁relaxation during exchange in Si/SiGe spin qubits

Encoded triple-quantum-dot qubits are promising for quantum information processing as they rely solely on the exchange interaction for qubit control. Here, we report on spin population relaxation observed during electron-electron exchange but not detected in coherent exchange oscillation measurements. This relaxation, which is distinct from well-known dephasing from charge and magnetic hyperfine noise, has been observed impacting randomized benchmarking fidelity. We characterize this relaxation time, denoted T_1J, using a variety of experiments, including the full-permutation dynamical decoupling technique [1] where this decoherence process may manifest as leakage from the qubit subspace. We also demonstrate experiments which highlight exchange biases that extend this timescale, and discuss possible sources for this relaxation. We expect T_1J processes may be relevant to the performance of other spin qubit technologies that utilize the exchange interaction.

 

[1] Bo Sun, https://meetings.aps.org/Meeting/MAR20/Session/L17.8