Coherent excitation of an ensemble of quantum objects offers the opportunity to realise robust entanglement generation and information storage in a quantum memory. In quantum dots, a single electron spin qubit is a coherent interface to an isolated nuclear spin ensemble. Recently, we have developed an all-optical electron spin resonance technique that, together with our ability to optically cool the nuclear ensemble , has allowed us to perform complex qubit manipulations on the electron spin, such as to run a spin-locking sequence , to coherently excite spin-wave modes in the nuclear spin ensemble , and to sense the effective magnetic field from a single nuclear-spin excitation . Combined, these results open a promising avenue for quantum state engineering of a mesoscopic ensemble, and we have recently proposed a realistic path to a nuclear quantum memory based on electron-activated spin waves in GaAs quantum dots . In my talk, I will briefly summarise these recent experimental results and proposals for the future.
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