A dressed singlet-triplet qubit in germanium

TL;DR

This paper demonstrates a highly coherent dressed singlet-triplet hole spin qubit in germanium, achieving long coherence times and high-fidelity control at low magnetic fields and exchange interactions, advancing semiconductor quantum computing.

Contribution

It introduces a method to operate a germanium-based ST qubit at low magnetic field and exchange interaction, significantly enhancing coherence time while maintaining high gate fidelity.

Findings

Achieved a gate fidelity of 99.68%

Extended coherence time to 20.3 microseconds with dressing

Demonstrated universal control via frequency modulation

Abstract

In semiconductor hole spin qubits, low magnetic field ($B$) operation extends the coherence time ($T_\mathrm{2}^*$) but proportionally reduces the gate speed. In contrast, singlet-triplet (ST) qubits are primarily controlled by the exchange interaction ($J$) and can thus maintain high gate speeds even at low $B$. However, a large $J$ introduces a significant charge component to the qubit, rendering ST qubits more vulnerable to charge noise when driven. Here, we demonstrate a highly coherent ST hole spin qubit in germanium, operating at both low $B$ and low $J$. By modulating $J$, we achieve resonant driving of the ST qubit, obtaining an average gate fidelity of $99.68\%$ and a coherence time of $T_\mathrm{2}^*=1.9\,\mu$s. Moreover, by applying the resonant drive continuously, we realize a dressed ST qubit with a tenfold increase in coherence time ($T_\mathrm{2\rho}^*=20.3\,\mu$s). Frequency modulation of the driving signal enables universal control, with an average gate fidelity of $99.63\%$. Our results demonstrate the potential for extending coherence times while preserving high-fidelity control of germanium-based ST qubits, paving the way for more efficient operations in semiconductor-based quantum processors.