Quantum Optics Seminar by Morgan Mitchell – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Morgan Mitchell

Non-gaussian states of continuous-variable systems are closely related to quantum information processing; e.g. algorithmic speed-up and entanglement distillation require non-gaussian states.  

Here we study experimentally and theoretically the efficient quantification of non-gaussianity, important for relatively slow experiments such as those with spin ensembles.  I describe an experiment which generates (classical) non-gaussian states in a cold rubidium-87 spin ensemble, and then uses quantum non-demolition (QND) measurement and classical statistics (Fisher 1928) to estimate third and fourth cumulants.  The method is both very efficient relative to histogram-based estimation, and gives uncertainties for the cumulants, as needed for hypothesis testing and proofs of non-classicality. 

In a separate experiment, we are studying quantum control of spin systems using QND measurements and incoherent feedback by optical pumping.  We show "spin cooling," i.e. movement of a noisy initial spin state toward the origin of the spin phase space, achieving a noise reduction of 9 dB using an optimized feedback scheme.  Potential for generation of novel squeezed/entangled states by this method will be discussed if time permits.