Gross, C., et al. Atomic homodyne detection of continuous-variable entangled twin-atom states. Nature 480, 219-223 (2011). Publisher's VersionAbstract
Historically, the completeness of quantum theory has been questioned using the concept of bipartite continuous-variable entanglement. The non-classical correlations (entanglement) between the two subsystems imply that the observables of one subsystem are determined by the measurement choice on the other, regardless of the distance between the subsystems. Nowadays, continuous-variable entanglement is regarded as an essential resource, allowing for quantum enhanced measurement resolution, the realization of quantum teleportation and quantum memories, or the demonstration of the {Einstein-Podolsky-Rosen} paradox. These applications rely on techniques to manipulate and detect coherences of quantum fields, the quadratures. Whereas in optics coherent homodyne detection of quadratures is a standard technique, for massive particles a corresponding method was missing. Here we report the realization of an atomic analogue to homodyne detection for the measurement of matter-wave quadratures. The application of this technique to a quantum state produced by spin-changing collisions in a {Bose-Einstein} condensate reveals continuous-variable entanglement, as well as the twin-atom character of the state. Our results provide a rare example of continuous-variable entanglement of massive particles. The direct detection of atomic quadratures has applications not only in experimental quantum atom optics, but also for the measurement of fields in many-body systems of massive particles.
Bhaktavatsala Rao, D., Bar-Gill, N. & Kurizki, G. Generation of macroscopic superpositions of quantum states by linear coupling to a bath. Physical review letters 106, (2011).Abstract
We demonstrate through an exactly solvable model that collective coupling to any thermal bath induces effectively nonlinear couplings in a quantum many-body (multispin) system. The resulting evolution can drive an uncorrelated large-spin system with high probability into a macroscopic quantum-superposition state. We discuss possible experimental realizations.
Bar-Gill, N., Kurizki, G., Malomed, B.A. & Sudheesh, C. Dynamical control of nonlinear symmetry breaking under decoherence. Physical Review A 82, (2010).
Sudheesh, C., Bar-Gill, N., Malomed, B.A. & Kurizki, G. Two-dimensional solitons in periodically modulated double-well potentials. Journal of Physics B: Atomic, Molecular and Optical Physics 43, (2010).
Bar-Gill, N., Kurizki, G., Oberthaler, M. & Davidson, N. Dynamic control and probing of many-body decoherence in double-well Bose-Einstein condensates. Physical Review A 80, (2009).
Bar-Gill, N., Rowen, E., Kurizki, G. & Davidson, N. Short-time enhancement of the decay of coherent excitations in Bose-Einstein Condensates. Physical review letters 102, (2009).Abstract
We study, both experimentally and theoretically, short-time modifications of the decay of excitations in a {Bose-Einstein} Condensate {(BEC)} embedded in an optical lattice. Strong enhancement of the decay is observed compared to the Golden Rule results. This enhancement of decay increases with the lattice depth. It indicates that the description of decay modifications of few-body quantum systems also holds for decay of many-body excitations of a {BEC.}
Rowen, E., Bar-Gill, N., Pugatch, R. & Davidson, N. Energy-dependent damping of excitations over an elongated Bose-Einstein condensate. Physical Review A 77, (2008).
Rowen, E., Bar-Gill, N. & Davidson, N. Quantum enhancement of higher-order phononlike excitations of a Bose-Einstein condensate. Physical review letters 101, (2008).Abstract
In a {Bose-Einstein} condensate, the excitation of a Bogoliubov phonon with low momentum (e.g., by a two-photon Bragg process) is strongly suppressed due to destructive interference between two indistinguishable excitation pathways. Here we show that scattering of this sound excitation into a double-momentum mode is strongly enhanced due to constructive interference. This enhancement yields an inherent amplification of second-order sound excitations of the condensate, as we confirm experimentally. We further show that due to parity considerations, this effect is extended to higher-order excitations.
Bar-Gill, N., Rowen, E.E. & Davidson, N. Spectroscopy of strong-pulse superradiance in a Bose-Einstein condensate. Physical Review A 76, 4, 043603 (2007).
Kolář, M., Opatrný, T., Bar-Gill, N., Erez, N. & Kurizki, G. Path–phase duality with intraparticle translational–internal entanglement. New Journal of Physics 9, (2007). Publisher's Version
Kolár, M., tomás Opatrný,, Bar-Gill, N. & Kurizki, G. Betting on interferometric paths and phases using translational-internal entanglement: the greedy king game. International Journal of Modern Physics B 20, (2006). Publisher's Version
Kurizki, G., Bar-Gill, N., Clausen, J., Kolář, M. & Opatrný, T. Cheating on Complementarity and Interference by Translational – Internal Entanglement. Quantum Information Processing 5, (2006). Publisher's Version
Bar-Gill, N. & Kurizki, G. Signatures of strong momentum localization via entanglement of translational and internal states. Physical review letters 97, (2006).Abstract
We show that atoms or molecules subject to fields that couple their internal and translational (momentum) states may undergo a crossover from randomization (diffusion) to strong localization (sharpening) of their momentum distribution. The predicted crossover should be manifest by a drastic change of the interference pattern as a function of the coupling fields.
Bar-Gill, N., Botton, M. & Ron, A. Dynamics of a Lasing Atom in Hot Plasma. Eur. Phys. J. D 30, 3, 317 (2004).