Full-permutation dynamical decoupling in triple-quantum-dot spin qubits

TL;DR

This paper introduces a full-permutation dynamical decoupling method for triple-quantum-dot spin qubits that significantly enhances coherence times and suppresses various noise-induced errors, advancing quantum information processing.

Contribution

The authors develop and experimentally validate a novel full-permutation decoupling sequence, NZ1y, that reduces errors and extends qubit coherence in silicon-based spin qubits.

Findings

Extended qubit coherence from 2 μs to 720 μs.

Achieved an exchange pulse error of 5×10⁻⁵.

Validated noise models with experimental data.

Abstract

Dynamical decoupling of spin qubits in silicon can enhance fidelity and 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-dot qubit. This sequence not only suppresses both low frequency charge-noise- 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 $5\times10^{-5}$. This sequence maintains a quantum state for roughly 18,000 exchange pulses, extending the qubit coherence from $T_2^*=2~\mu$s to $T_2 = 720~\mu$s. 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 changing the repetition rate.