Experimental Studies of Two-Mode Squeezed States in Rubidium Vapor

by

Alberto Marino
(2006)

In this thesis we describe a series of calculations and experiments that use atomic coherence for the generation of two-mode squeezed states of the electromagnetic field. Atomic coherence makes it possible to eliminate the problems of absorption losses and spontaneous emission that have limited the amount of squeezing obtained with atomic systems. Effects such as electromagnetically induced transparency allow for e±cient generation of atomic coherence and are used as the basis for the generation of squeezed states.

We analyze the use of a double-Λ configuration in order to combine a four-wave mixing process and atomic coherence in a single system. The use of this configuration makes it possible to eliminate absorption and enhance the four-wave mixing process responsible for the generation of a two-mode squeezed state.

We implemented a new detection technique, which we devised, based on the use of a bichromatic local oscillator in a balanced heterodyne detection scheme for the characterization of two-mode squeezed states. This new detection technique makes it possible to characterize squeezed states independently of the frequency separation between the modes.

In order to obtain the required phase-coherent lasers, we designed and implemented a laser system that consists of three stabilized external-cavity diode lasers. We obtained a system with a residual phase noise of less than 0.04 rad². We studied electromagnetically induced transparency in the D1 line of ⁸⁷Rb and obtained a reduction in absorption of 92%. Experimentally, we implemented the double-Λ configuration in the D1 line of ⁸⁷Rb in a vapor cell. We were able to verify the presence of correlations between the fields generated from the four-wave mixing process and produced more than 10 decibels of phase-dependent noise modulation.

Finally, we propose a new quantum communication scheme that takes advantage of the properties of a two-mode squeezed state. This new scheme offers the possibility of securely transmitting either a cryptographic key or a deterministic message. We analyze the security of the scheme and find that it can be verified with the use of the quantum correlations present in a two-mode squeezed state.

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