Bragg spectroscopic interferometer and quantum measurement-induced correlations in atomic Bose-Einstein condensates

New Journal of Physics (Impact Factor: 3.56). 04/2012; 14(7). DOI: 10.1088/1367-2630/14/7/073057
Source: arXiv


We theoretically analyze the Bragg spectroscopic interferometer of two
spatially separated atomic Bose-Einstein condensates that was experimentally
realized by Saba et al. [Science 2005 v307 p1945] by continuously monitoring
the relative phase evolution. Even though the atoms in the light-stimulated
Bragg scattering interact with intense coherent laser beams, we show that the
phase is created by quantum measurement-induced back-action on the homodyne
photo-current of the lasers, opening possibilities for quantum-enhanced
interferometric schemes. We identify two regimes of phase evolution: a running
phase regime which was observed in the experiment of Saba et al., that is
sensitive to an energy offset and suitable for an interferometer, and a trapped
phase regime, that can be insensitive to applied forces and detrimental to
interferometric applications.

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    ABSTRACT: Off-resonant optical imaging is a popular method for continuous monitoring of a Bose–Einstein condensate. However, the disturbance caused by scattered photons places a serious limitation on the lifetime of such continuously monitored condensates. In this paper, we demonstrate that a new choice of feedback control can overcome the heating effects of the measurement backaction. In particular, we show that the measurement backaction caused by off-resonant optical imaging is a multi-mode quantum-field effect, as the entire heating process is not seen in single-particle or mean-field models of the system. Simulating such continuously monitored systems is possible with the number- phase Wigner particle filter, which currently gives both the highest precision and largest timescale simulations amongst competing methods. It is a hybrid between the leading techniques for simulating non-equilibrium dynamics in condensates and particle filters for simulating high-dimensional non-Gaussian filters in the field of engineering. The new control scheme will enable long- term continuous measurement and feedback on one of the leading platforms for precision measurement and the simulation of quantum fields, allowing for the possibility of single-shot experiments, adaptive measurements and robust state- preparation and manipulation.
    New Journal of Physics 11/2013; 15(11):113060. DOI:10.1088/1367-2630/15/11/113060 · 3.56 Impact Factor
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    Physical Review A 07/2014; 90(2). DOI:10.1103/PhysRevA.90.023628 · 2.81 Impact Factor
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    ABSTRACT: We study cavity quantum electrodynamics of Bose-condensed atoms that are subjected to continuous monitoring of the light leaking out of the cavity. Due to a given detection record of each stochastic realization, individual runs spontaneously break the symmetry of the spatial profile of the atom cloud and this symmetry can be restored by considering ensemble averages over many realizations. We show that the cavity optomechanical excitations of the condensate can be engineered to target specific collective modes. This is achieved by exploiting the spatial structure and symmetries of the collective modes and light fields. The cavity fields can be utilized both for strong driving of the collective modes and for their measurement. In the weak excitation limit the condensate-cavity system may be employed as a sensitive phonon detector which operates by counting photons outside the cavity that have been selectively scattered by desired phonons.
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