Optical locking of a quantum dot electron spin qubit

InGaAs quantum dots (QDs) can function as solid state quantum network nodes, offering a field-leading interface between a single spin and an optical mode [1]. Exploiting this interface requires complete control of a QD spin, to tailor spin-photon entanglement in such a network. Whilst the rotations offered by the current state of the art are highly coherent [2], full SU(2) control relies on varying delays between sequential pulses, limiting the scheme to simple few-gate sequences.
Spectral splitting of a laser into two sidebands through modulation allows us to resonantly address a Raman transition between the two ground states of a spin in our QD. This all-optical scheme gives direct access to the phase and frequency of the field linking our states, releasing us from the need for well-defined sequence delays. We use Rabi oscillations and Ramsey interferometry to demonstrate complete control of our Rabi vector.
This enables us to perform spin-locking, protecting our qubit state for longer than the homogeneous dephasing time and allowing high-fidelity gates on this timescale. Our work represents versatile spin control and provides a way towards on-chip all-optical spin manipulation.
[1] Somaschi, N. et al, Nat. Photonics 10 340-345 (2016)
[2] Press, D. et al, Nature 456 218-221 (2008)