Controlling a mesoscopic spin system with coherent optics
Atomic, Mesoscopic and Optical Physics, Cavendish Laboratory
University of Cambridge
Quantum correlations are at the heart of quantum science and technologies. In recent years, there has been tremendous progress in harnessing quantum correlations in various physical systems, paving the way to applications such as quantum networks, quantum computers and quantum simulators. Self-assembled semiconductor quantum dots are an outstanding system to explore quantum correlations from both technological and fundamental perspectives: on the one hand, they offer the brightest spin-photon interface, which has been used to entangle distant spins with a record-high rate. On the other hand, the strong interaction of the electron with the surrounding ~105 nuclei forming the quantum dot offers opportunities to probe many-body quantum phenomena.
In this talk, I will show that the nuclear spin environment of a quantum dot can be optically controlled and prepared in non-trivial states by exploiting the hyperfine interaction between a single electron and the mesoscopic nuclear ensemble. By driving Raman transitions between the spin states of the electron, a feedback mechanism locking the nuclei to a reduced-entropy state is engineered. This process is analogous to Raman sideband cooling developed in atomic physics. The immediate implication of the nuclear cooling for quantum information processing is a thirtyfold extension of the electron T2*, which will increase the fidelity of spin-photon entanglement in quantum dots.
Our control over the nuclear ensemble can be used to optically generate quantum correlations within the nuclear spin ensemble. I will describe possible avenues to achieve this goal, including optically-driven nuclear excitations and ensemble spin squeezing. Our results set the stage for investigations of quantum many-body physics in quantum dots and are a stepping-stone towards the realization of quantum memories.