# A dressed singlet-triplet qubit in germanium

## TL;DR

Researchers created a highly coherent qubit in germanium that operates efficiently at low magnetic fields and maintains high control fidelity.

## Contribution

A dressed singlet-triplet qubit in germanium with a tenfold increase in coherence time and high gate fidelity is demonstrated.

## Key findings

- A dressed singlet-triplet qubit in germanium achieved a coherence time of 20.3 μs.
- High gate fidelity of 99.63% was achieved using frequency-modulated control.
- Resonant driving enabled universal control while preserving high fidelity.

## Abstract

In semiconductor hole spin qubits, low magnetic field (B) operation extends the coherence time (\documentclass[12pt]{minimal}
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\begin{document}$${T}_{2}^{*}$$\end{document}T2*) 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 \documentclass[12pt]{minimal}
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\begin{document}$${T}_{2}^{*}=1.9\,\mu {{{\rm{s}}}}$$\end{document}T2*=1.9μs. Moreover, by applying the resonant drive continuously, we realize a dressed ST qubit with a tenfold increase in coherence time (\documentclass[12pt]{minimal}
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\begin{document}$${T}_{2\rho }^{*}=20.3\,\mu {{{\rm{s}}}}$$\end{document}T2ρ*=20.3μs). 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.

Hole spin qubits in germanium have seen significant advancements, though improving control and noise resilience remains a key challenge. Here, the authors realize a dressed singlet-triplet qubit in germanium, achieving frequency-modulated high-fidelity control and a tenfold increase in coherence time.