Coherent spin-wave excitations in an optically cooled nuclear ensemble

Collective excitations of isolated many-body systems offer the opportunity to control complex quantum dynamics. A simple quantum system, such as a central spin, can act as a probe and a control over a larger and more complex quantum system in ways otherwise intractable, and can help us perform spectroscopy and engineering over its quantum dynamics. Driving the central spin can stimulate exchange of energy with its surrounding spins, and thus modify the mean-field state of its own environment. In this work, we engineer this very interaction between an InGaAs quantum dot electron spin and its isolated ensemble of nuclear spins in a driven-dissipative regime to remove entropic heat from the ensemble, and so vastly reduce the mean-field state uncertainty tied to its thermal fluctuations. Having cooled the system, we reveal an absorption spectrum of transitions between many-body states that are collectively-enhanced by the creation of single spin-wave excitations – nuclear magnons. Resonantly driving such a transition, we stimulate coherent exchange of single magnons between the electron and the nuclear spin ensemble, which is consistent with the controlled creation of entanglement among all constituent particles.