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Ph.D. Candidate:  Emily Davis
Research Advisor:  Monika Schleier-Smith

Date: Wednesday, April 29, 2020
Time: 9:00 am

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Title: Engineering and Imaging Nonlocal Spin Dynamics in an Optical Cavity


Photon-mediated interactions between atoms coupled to an optical cavity are a powerful tool for engineering entangled states and many-body Hamiltonians. These applications motivate the construction of an optical cavity enabling coherent nonlocal spin interactions, with transverse optical access for high-resolution imaging and addressing of atomic sub-ensembles. Using this apparatus, we implement a nonlocal Heisenberg Hamiltonian, where the relative strength and sign of spin-exchange and Ising couplings are controllable parameters. This tunability enables the demonstration of protected spin coherence against single-atom dephasing terms, showing that spin-exchange interactions may enhance the robustness of spin squeezing protocols. The optical access afforded by a near-concentric cavity enables local addressing and imaging with micron-scale resolution, which enables Hamiltonian tomography and direct imaging of the spin coherence. Imaging also enables spatially-resolved measurements of cavity-mediated spin-mixing in a spin-1 system, a new mechanism for generating correlated atom pairs. Whereas the single-mode cavity most naturally mediates all-to-all couplings, I will also discuss progress in generalizing to control the distance-dependence of the interactions, with prospects in engineering the spatial structure of entanglement. I furthermore propose and analyze two specific protocols in quantum state engineering enabled by strong and tunable atom-light interactions. I first introduce a protocol which enables Heisenberg-limited phase sensitivity while reducing technical requirements on detection. This is accomplished via an interaction-enhanced readout of the phase that relies on reversing the sign of a one-axis twisting Hamiltonian. Dispersive atom-light interactions also enable heralded schemes, in which a high-fidelity pure state is produced upon probabilistic detection of a single photon. In this context, I show how a time-shaped single photon pulse can "paint’’ an arbitrary atomic superposition in the fully permutation-symmetric subspace while avoiding infidelities due to finite cavity linewidth.



April 29, 2020 - 9:00am