Quantum Control of Mesoscopic Spin Ensembles
Control of complex quantum systems has applications in many-body physics, quantum information processing, and high-precision metrology. Mesoscopic ensembles of cold atomic spins are an ideal testbed for such explorations, given the growing quantum-control toolbox. In a cigar-shaped trap, when the ensemble is optically thick on resonance, the spins coherently couple to the polarization state of a paraxial laser probe. The photons serve as a “quantum bus” that transfers quantum correlations between atoms and entangles them. Spin-squeezed states based on this mechanism have recently been produced, representing an important step toward more complex control. In this seminar I will discuss new approaches to achieving more sophisticated and general control, including unitary evolution through coherent optical feedback and quantum erasure, exponential squeezing via phase matching, and the production of Schroedinger kittens via heralded scattering of single photons.