Full-Permutation Dynamical Decoupling in Triple-Quantum-Dot Spin Qubits

Abstract

Dynamical decoupling of spin qubits in silicon can increase fidelity and can be used to extract the frequency spectra of noise processes. We demonstrate a full-permutation dynamical decoupling technique that cyclically exchanges the spins in a triple-quantum-dot qubit. This sequence not only suppresses both low-frequency charge-noise-induced and magnetic-noise-induced errors; it also refocuses leakage errors to first order, which is particularly interesting for encoded exchange-only qubits. For a specific construction, which we call "NZ1y,"the qubit is isolated from error sources to such a degree that we measure a remarkable exchange pulse error of 2.8×10-5. This sequence maintains a quantum state for roughly 18,000 exchange pulses, extending the qubit coherence from T2 - =2μs to T2=720μs. We experimentally validate an error model that includes 1/f charge noise and 1/f magnetic noise in two ways: by direct exchange-qubit simulation and by integration of the assumed noise spectra with derived filter functions, both of which reproduce the measured error and leakage with respect to a change of the repetition rate.