Abstract
Strong spin-orbit interactions make hole quantum dots central to the quest for electrical spin qubit manipulation enabling fast, low-power, scalable quantum computation. Yet it is important to establish to what extent spin-orbit coupling exposes qubits to electrical noise, facilitating decoherence. Here, taking Ge as an example, we show that group IV gate-defined hole spin qubits generically exhibit optimal operation points, defined by the top gate electric field, at which they are both fast and long-lived: the dephasing rate vanishes to first order in the electric field noise along with all directions in space, the electron dipole spin resonance strength is maximized, while relaxation is drastically reduced at small magnetic fields. The existence of optimal operation points is traced to group IV crystal symmetry and properties of the Rashba spin-orbit interaction unique to spin-3/2 systems. Our results overturn the conventional wisdom that fast operation implies reduced lifetimes and suggest group IV hole spin qubits as ideal platforms for ultra-fast, highly coherent scalable quantum computing.
Highlights
Quantum computing architectures require reliable qubit initialization, robust single-qubit operations, long coherence times, and a clear pathway towards scaling up
Electric fields are much easier to apply and localize than magnetic fields used in electron spin resonance
The existential question that will determine the future of hole quantum dot (QD) spin qubits is: Does the strong spin-orbit interaction that allows fast qubit operation enhance undesired couplings to stray fields such as phonons and charge noise leading to intractable relaxation and dephasing? In this paper, we demonstrate theoretically that this is emphatically not the case for hole spin qubits in group IV materials taking Ge as the most prominent example
Summary
Quantum computing architectures require reliable qubit initialization, robust single-qubit operations, long coherence times, and a clear pathway towards scaling up. The key realization is that holes in group IV materials are qualitatively different from group III–V materials They have tremendous potential for qubit coherence, with Ge and Si possessing isotopes with no hyperfine interaction, as well as a near-inversion symmetry that eliminates piezo-electric phonons. The qualitative difference between the Rashba and Dresselhaus interactions for holes is vital for qubit coherence Thanks to this nonlinearity, dephasing due to electric field fluctuations in all spatial directions can be essentially eliminated at specific optimal operation points defined by the gate electric field[15,16,38,49,50,51,52,53,54].
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