Quantum Optics Seminar by Cristian Bonato – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Cristian Bonato

In contrast to classical physics, quantum measurements foster an intriguing interplay between information gain and system disturbance. Although the outcome of the measurement is probabilistic, the back-action imparted on the measured system is accurately described by quantum theory, given the measurement outcome. Therefore, quantum measurements can be used to manipulate a quantum system without the need for control fields.
In this seminar, I will report on the realization of quantum control using sequential partial measurements with real-time feedback on a nuclear spin qubit in diamond. We control the measurement strength via an ancilla qubit (electron spin of a nitrogen-vacancy center). Using post-selection, controlled wavefunction collapse and quantum weak values (spin exceeding 10) are observed. We then exploit a dynamical-stop quantum non-demolition measurement on the ancilla qubit to enable repetitive measurements without post-selection. By incorporating real-time feedback, we demonstrate measurement-only control of a quantum system. Applications to enhanced-sensitivity quantum metrology will be discussed.