Two-mode squeezing in a cold atomic ensemble
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2019-11
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Abstract
We investigate experimentally and theoretically the generation of a continuous variable entanglement using laser cooled atomic gas in free space and cavity mode. This is of a fundamental interest due to the nonclassical correlation of quadrature observables of the two-mode squeezed (TMS) state. The TMS state is the basis for complete quantum teleportation and continuous variable quantum repeaters. It is also used in quantum metrology and quantum key distribution. We employ a novel scheme for generating a TMS vacuum based on a non-degenerate four-wave mixing process in a cold atomic cloud coupled to a cavity. We send two pumps collinear to the cavity mode and ensure that the two generated quantum fields are simultaneously resonant with the cavity. The cavity enhancement enables us to demonstrate results close to a free space in hot atomic gases (-5.2 dB) where optical densities are much higher. Our system is versatile because, together with continuous variables, it is suitable for the discrete variable domain using the Duan-Lukin-Cirac-Zoller protocol. The design is oriented to make the delay between two modes possible and could be used for hybrid continuous repeaters. The system is devised and built fully as a part of my PhD, wherein we characterize our system and demonstrate the squeezing of -3.7 dB. Since the quantum dynamics of the system is not intuitive, we provide simple models and consolidate segmental information on generation of TMS states. To make sure that the dynamics is not oversimplified, we construct a novel theory where we treat both fields and atoms as quantum objects. The theory supports and enriches our understanding and confirms our experimental data. Based on the experimental and theoretical results we spotlight the detrimental effects and propose improvements to our system. We theoretically investigate that the certain class of TMSV states are optically dark. These states propagate through a polarized to one hyperfine level Λ atoms without degradation or evolution. Based on this we propose a new way of generation of TMSV through the dissipation or dynamically controlled broadening.
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Tashchilina, A. Y. (2019). Two-mode squeezing in a cold atomic ensemble (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.