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Quantum Electronics and Laser Science Conference

Squeezing of vacuum fluctuations via Zeeman coherence

Irina V. Novikova, Andrey B. Matsko, George R. Welch

Published Jun 25, 2003• 0 citations
Publisher

Abstract

Summary form only given. We suggest a promising way to obtain the squeezing of vacuum fluctuations. We study the interaction of linearly polarized light with atoms in a double-/spl Lambda/ configuration, where the two lower levels are Zeeman sublevels of the atomic ground state and the upper levels are the hyperfine components of the atomic excited state. In such systems, Kerr nonlinearity associated with the ac-Stark effect causes self-rotation of the elliptical polarization. At the same time when the linearly polarized light traverses such a medium, a squeezed vacuum is produced in the orthogonal polarization.

DOI
10.1109/qels.2002.1031276

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Summary form only given. We suggest a promising way to obtain the squeezing of vacuum fluctuations. We study the interaction of linearly polarized light with atoms in a double-/spl Lambda/ configuration, where the two lower levels are Zeeman sublevels of the atomic ground state and the upper levels are the hyperfine components of the atomic excited state. In such systems, Kerr nonlinearity associated with the ac-Stark effect causes self-rotation of the elliptical polarization. At the same time when the linearly polarized light traverses such a medium, a squeezed vacuum is produced in the orthogonal polarization.
When linearly polarized light propagates through a medium in which elliptically polarized light would undergo self-rotation, squeezed vacuum can appear in the orthogonal polarization. A simple relationship between self-rotation and the degree of vacuum squeezing is developed. Taking into account absorption, we find the optimum conditions for squeezing in any medium that can produce self-rotation. We then find analytic expressions for the amount of vacuum squeezing produced by an atomic vapor when light is near-resonant with a transition between various low-angular-momentum states. Finally, we consider a gas of multilevel Rb atoms, and analyze squeezing for light tuned near the D lines under realistic conditions.
We have numerically solved the Heisenberg-Langevin equations describing the propagation of quantized fields through an optically thick sample of atoms. Two orthogonal polarization components are considered for the field, and the complete Zeeman sublevel structure of the atomic transition is taken into account. Quantum fluctuations of atomic operators are included through appropriate Langevin forces. We have considered an incident field in a linearly polarized coherent state (driving field) and vacuum in the perpendicular polarization and calculated the noise spectra of the amplitude and phase quadratures of the output field for two orthogonal polarizations. We analyze different configurations depending on the total angular momentum of the ground and excited atomic states. We examine the generation of squeezing for the driving-field polarization component and vacuum squeezing of the orthogonal polarization. Entanglement of orthogonally polarized modes is predicted. Noise spectral features specific to (Zeeman) multilevel configurations are identified.
We present a theoretical study of an ensemble of X-like four-level atoms placed in an optical cavity driven by a linearly polarized field. We show that the self-rotation (SR) process leads to polarization switching (PS). Below the PS threshold, both the mean field mode and the orthogonal vacuum mode are squeezed. We provide a simple analysis of the phenomena responsible for the squeezing and trace the origin of vacuum squeezing not to SR, but to a crossed Kerr effect induced by the mean field. Last, we show that this vacuum squeezing can be interpreted as polarization squeezing .
The interaction of classical and quantized electromagnetic fields with an ensemble of atoms in an optical cavity is considered. Four fields drive a double-lambda level scheme in the atoms, consisting of a pair of lambda systems sharing the same set of lower levels. Two of the fields produce maximum coherence, rho12 = -1/2, between the ground state sublevels 1 and 2. This pumping scheme involves equal intensity fields that are resonant with both the one and two-photon transitions of the lambda system. There is no steady-state absorption of these fields, implying that the fields induce a type electromagnetically-induced transparency (EIT) in the medium. An additional pair of fields interacting with the second lambda system, combined with the EIT fields, leads to squeezing of the atom spin associated with the ground state sublevels. Our method involves a new mechanism for creating steady-state spin squeezing using an optical cavity. As the cooperativity parameter C is increased, the optimal squeezing varies as C^{-1/3}. For experimentally accessible values of C, squeezing as large as 90% can be achieved.
We present experimental and theoretical analysis of quantum fluctuation in a vacuum field in the presence of an orthogonal linearly polarized pump field propagating through a Rb vapor cell. Previously reported theoretical and experimental studies provided somewhat contradictory conclusions regarding the possibility of observing the ‘squeezed vacuum’–the reduction of vacuum fluctuations below the standard quantum limit–in this system. Here, using the D1 transitions of Rb in a cell without a buffer as an example, we demonstrate that vacuum squeezing is corrupted by incoherent processes (such as spontaneous emission, elastic scattering, etc), and its observation is only possible in a specific small region of the experimental parameter space. Numerical simulations, in good agreement with the experiment, demonstrate that the two excited state hyperfine levels play a crucial role in the squeezing and excess noise production. The significant influence of far-detuned atoms on the field fluctuations at low noise frequencies imposes the explicit consideration of the full velocity distribution of the atomic vapor.
We present experimental and theoretical analysis of quantum fluctuation in a vacuum field in the presence of orthogonal linearly polarized pump field propagating through a Rb vapor cell. Previously reported theoretical and experimental studies provided somewhat contradictory conclusions regarding the possibility to observe the "squeezed vacuum" -- the reduction of vacuum fluctuations below standard quantum limit -- in this system. Here, using the D1 transitions of Rb in a cell without buffer as as an example, we demonstrate that vacuum squeezing is corrupted by incoherent processes (such as spontaneous emission, elastic scattering, etc.), and its observation is only possible in a specific small region of the experimental parameter space. Numerical simulations, in good agreement with the experiment, demonstrate that the two excited state hyperfine levels play a crucial role in the squeezing and excess noise production. The significant influence of far-detuned atoms on the field fluctuations at low noise frequencies imposes the explicit consideration of the full velocity distribution of the atomic vapor.