Towards spin-valley qubits based on in-gap quantum dots in the transition metal dichalcogenides*

Spins confined to point defects and colour centres have become active components in emerging quantum technologies, with applications in quantum sensing, computation, simulation, and communication. Different from conventional semiconductors, electron spins in atomically-thin (2D) semiconductors with hexagonal lattices – in the presence of inversion asymmetry and strong spin-orbit coupling – are strongly coupled to an additional valley degree of freedom. Such “spin-valley locking” can be inherited by in-gap states due to atomic point defects [1] making them promising candidates for spin-valley quantum bits (qubits), that may be coherently controlled electrically and optically.

Towards this end, we have developed a robust device architecture allowing for transparent electrical contact to atomically-thin layers of MoS₂, down to temperatures as low as T=150mK. The high spectral resolution (50 μeV) enables us to probe the spin-valley eigenspectrum in the ground state transitions of in-gap quantum dots [1]. For the first time, we demonstrate spin-valley locking at the single-electron level, reflected in a pronounced Zeeman anisotropy with an effective out-of-place g-factor as large as g ≈ 8. From a small but finite in-plane g-factor (g ≅ 0.7) we quantify the spin-orbit coupling strength, and hence the degree of spin-valley locking. 

Our results provide new insights into the spin texture of spin-valley locked in-gap states in MoS₂, relevant towards their application as electrically-driven spin-valley qubits.

[1] Krishnan et al. Nano Letters 23, 6171 (2023)