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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Resonant amplification of quantum fluctuations with a spinor gas

Carsten Klempt, O. Topic, M. Scherer, T. Henninger, Grebremedh Gebreyesus, P. Hyllus, Wolfgang A. Ertmer, Luis Santos, J. Arlt

Published Jun 1, 2009• 0 citations
Publisher

Abstract

Bose-Einstein condensates of atoms with non-zero spin makes up an ideal system for the study of macroscopic amplification of quantum and classical fluctuations. This study shows that the efficiency of pair creation is influenced by the interplay between the external trapping potential and the Zeeman effect. This reflects the confinement-induced magnetic-field dependence of elementary spin excitations of the trapped condensate. Pair production at these resonances serves as a strong parametric mater-wave amplifier. Results show that pair creation at resonance is triggered by quantum fluctuations. Therefore, in the vacuum state, this system acts as a matter-wave amplifier.

DOI
10.1109/cleoe-eqec.2009.5192423

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Bose-Einstein condensates of atoms with non-zero spin makes up an ideal system for the study of macroscopic amplification of quantum and classical fluctuations. This study shows that the efficiency of pair creation is influenced by the interplay between the external trapping potential and the Zeeman effect. This reflects the confinement-induced magnetic-field dependence of elementary spin excitations of the trapped condensate. Pair production at these resonances serves as a strong parametric mater-wave amplifier. Results show that pair creation at resonance is triggered by quantum fluctuations. Therefore, in the vacuum state, this system acts as a matter-wave amplifier.
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Parametric amplification of vacuum fluctuations is crucial in modern quantum optics, enabling the creation of squeezing and entanglement. We demonstrate the parametric amplification of vacuum fluctuations for matter waves using a spinor F=2 87Rb condensate. Interatomic interactions lead to correlated pair creation in the mF=±1 states from an initial mF=0 condensate, which acts as a vacuum for mF≠0. Although this pair creation from a pure mF=0 condensate is ideally triggered by vacuum fluctuations, unavoidable spurious initial mF=±1 atoms induce a classical seed which may become the dominant triggering mechanism. We show that pair creation is insensitive to a classical seed for sufficiently large magnetic fields, demonstrating the dominant role of vacuum fluctuations. The presented system thus provides a direct path towards the generation of nonclassical states of matter.
Dynamical instabilities in a 87Rb^{87}\text{R}\text{b}87Rb F=1F=1F=1 spinor Bose-Einstein condensate are used as a parametric amplifier of quantum spin fluctuations. We demonstrate the spectrum of this amplifier to be tunable, in quantitative agreement with theory. We quantify the microscopic spin fluctuations of the initially paramagnetic condensate by applying this amplifier and measuring the resulting macroscopic magnetization. The variance of these fluctuations agrees with predictions of a beyond-mean-field theory. This spin amplifier is thus shown to be nearly quantum limited at a gain as high as 30 dB.
We investigate the parametric amplification of the zero-point fluctuations in the spin modes of a two-component Bose-Einstein condensate, triggered by the dynamical evolution of the condensate density. We first make use of a Thomas-Fermi approximation to develop a tractable theoretical model of the quantum dynamics of the Bogoliubov excitations in a harmonically trapped condensate with a time-dependent trapping frequency. The predictions of this model are then compared to an ab initio numerical study of the correlation functions of density and spin fluctuations for general spatially inhomogeneous configurations. Results are shown for the two cases of expanding and oscillating condensates: while the quantum excitation of spin modes remains weak and relatively featureless in the case of an expanding condensate, clear and experimentally promising signatures of particle creation are anticipated for the oscillating case under suitable resonance conditions between the density and the spin modes.
Spin-changing collisions may lead under proper conditions to the parametric amplification of matter waves in spinor Bose-Einstein condensates. Magnetic dipole-dipole interactions, although typically very weak in alkali-metal atoms, are shown to play a very relevant role in the amplification process. We show that these interactions may lead to a strong dependence of the amplification dynamics on the angle between the trap axis and the magnetic-field orientation. We analyze as well the important role played by magnetic-field gradients, which also modify strongly the amplification process. Magnetic-field gradients, hence, must be carefully controlled in future experiments, in order to observe clearly the effects of the dipolar interactions in the amplification dynamics.
We consider the interaction between a Bose-Einstein condensate and a single-mode quantized light field in the presence of a strong far-off-resonant pump laser. The dynamics is characterized by an exponential instability, hence the system acts as an atom-photon parametric amplifier. Triggered by a small injected probe field, or simply by quantum noise, entangled atom-photon pairs are created which exhibit nonclassical correlations similar to those seen between photons in the optical parametric amplifier. In addition, the quantum statistics of the matter and light field depend strongly on the initial state which triggers the amplifier. Thus, by preparing different initial states of the light field, one can generate matter waves in a variety of quantum states, demonstrating optical control over the quantum statistics of matter waves.