Quantum Communication and Entanglement with Atomic and Optical Systems

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In this project the investigators will carry out a set of experiments to study the physics of quantum communication. They will study two approaches to transmitting data by encoding it onto the quantum states of physical objects - either light fields or collections of atoms in a vapor. The investigators will explore the use of macroscopic light pulses to represent each data bit. Special squeezed states of light will be used to increase the security while at the same time allowing accurate encoding and reading of the bits. Nonlinear-optical amplifiers will be used to create these states. This will be a generalization of current methods that use single photons to store each bit. Relative advantages and disadvantages of the methods for transmitting data securely will be explored. In the other approach the investigators will study a class of systems that uses a macroscopic ensemble of atoms to represent quantum information. The atomic ensemble is excited in a way that lends itself to a description as a collective harmonic-oscillator mode, represented by a Bosonic degree of freedom. As such, the concepts of continuous-variable quantum information will play a role. The goal of this work will be to create quantum states of collective atomic ensemble variables by conditional measurement and to create entanglement between two such distant ensembles. This will set the stage for further development of quantum communication networks over long distances.