Approaching ideal visibility in singlet-triplet qubit operations using energy-selective tunneling-based Hamiltonian estimation

TL;DR

This paper presents an energy-selective tunneling method for precise Hamiltonian estimation in a two-electron spin qubit, significantly improving measurement fidelity, coherence time, and enabling advanced quantum control protocols.

Contribution

It introduces an optimized, real-time Bayesian inference-based Hamiltonian estimation technique that enhances qubit readout fidelity and coherence without nuclear polarization.

Findings

Single-shot measurement time of 16 units achieved

40-fold increase in qubit coherence time observed

Fidelity of state initialization and measurement exceeds 97.7% and 99%

Abstract

We report energy selective tunneling readout-based Hamiltonian parameter estimation of a two-electron spin qubit in a GaAs quantum dot array. Optimization of readout fidelity enables a single-shot measurement time of 16 on average, with adaptive initialization and efficient qubit frequency estimation based on real-time Bayesian inference. For qubit operation in a frequency heralded mode, we observe a 40-fold increase in coherence time without resorting to dynamic nuclear polarization. We also demonstrate active frequency feedback with quantum oscillation visibility, single-shot measurement fidelity, and state initialization fidelity up to 97.7%, 99%, and over 99.7%, respectively. By pushing the sensitivity of the energy selective tunneling-based spin to charge conversion to the limit, the technique is useful for advanced quantum control protocols such as error mitigation schemes, where fast qubit parameter calibration with a large signal-to-noise ratio is crucial.