Download 5 Bose-Einstein condensate (BEC)

5 Bose-Einstein condensate (BEC)
We have focused on two topics related to BEC:
a) entanglement of continuous variables via collisions;
b) dynamical control of decoherence relevant to many-body systems, control of decoherence &
entanglement.
Selected Publications
Atomic homodyne detection of CV-entangled twin-atom states NATURE 480, 219-223 (2011)
Continuous-variable (CV) entanglement is regarded as an essential resource, allowing for quantum
enhanced measurement resolution, the realization of quantum teleportation and quantum memories,
or the demon- stration of the Einstein-Podolsky-Rosen (EPR) 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 (in collaboration with M. Oberthaler’s group) 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 CV entanglement, as well as the twin-atom character of the state.
Our results provide a rare example of CV entanglement of massive particles.
Nonclassical States of Bose-Einstein Condensates by Dephasing Collisions PRL 107, 010404
(2011)
We show, using an exactly solvable model, that nonlinear dynamics is induced in a double-well BoseEinstein condensate (BEC) by collisions with a thermal reservoir. This dynamics can facilitate the
creation of phase or number squeezing and, at longer times, the creation of macroscopic nonclassical
superposition states. Enhancement of these effects is possible by loading the reservoir atoms into an
optical lattice.
Einstein-Podolsky-Rosen Correlations of Ultracold Atomic Gases PRL 106, 120404 (2011)
We demonstrate (in collaboration with M. Oberthaler’s group) that collective continuous variables of
two species of trapped ultracold bosonic gases can be EPR- correlated (entangled) via inherent
interactions between the species. We propose two different schemes for creating these correlations: a
dynamical scheme and a static scheme analogous to two-mode squeezing in quantum optics. We
quantify the correlations by using known measures of entanglement and study the effect of finite
temperature on these quantum correlations.
Creation of macroscopic quantum superposition states by a measurement EPL 83 60004 (2008)
We propose a novel protocol for the creation of macroscopic quantum superposition (MQS) states
based on a measurement of a non-monotonous function of a quantum collective variable. The main
advantage of this protocol is that it does not require switching on and off nonlinear interactions in the
system. We predict this protocol to allow the creation of multiatom MQS by measuring the number of
atoms coherently outcoupled from a two-component (spinor) Bose-Einstein condensate.
Bosonic amplification of noise-induced suppression of phase diffusion PRL 100, 220403 (2008)
We study the effect of noise-induced dephasing on collisional phase diffusion in the two- site BoseHubbard model. Dephasing of the quasimomentum modes may slow down phase diffusion in the
quantum Zeno limit. Remarkably, the degree of suppression is enhanced by a bosonic factor of order
N/logN as the particle number N increases.
Decoherence and entanglement in a bosonic Josephson junction PRA 80, 023609 (2009)
We study the effect of decoherence on dynamical phase diffusion in the two-site Bose-Hubbard model.
The inclusion of local-site noise, measuring the relative number difference between the modes, is shown
to enhance phase diffusion. In comparison, site-indiscriminate noise measuring the population
imbalance between the two quasimomentum modes slows down the loss of single-particle coherence.
Decoherence thus either enhances or suppresses phase diffusion, depending on the overlap of
decoherence pointer states with collisional-entanglement pointer states.
Short-time Enhancement of Coherent Excitations Decay in BEC PRL 102, 110401 (2009)
We study, both experimentally and theoretically (in collaboration with N. Davidson’s group), shorttime mod- ifications of the decay of excitations in a 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 our description of decay modifications of few-body
quantum systems also holds for decay of many-body excitations of a BEC.
Dynamic control and probing of many-body decoherence in double-well BEC PRA 80, 053613
(2009)
We present an approach to dynamic decoherence control of finite-temperature BEC in a double-well
potential. Due to the many-body interactions the standard “echo” control method becomes less
effective. The approach described here takes advantage of the interaction-induced change of the
spectrum, to obtain the optimal rate of pi flips of the relative phase between maximally distinguishable
collective states. This method is particularly useful for probing and diagnosing the decoherence
dynamics.
Dynamical control of nonlinear symmetry breaking under decoherence PRA 82, 013610 (2010)
We propose a control mechanism for the stabilization of symmetry-broken modes in BEC trapped in
double-well potentials in the presence of symmetric or asymmetric noise. The control, based on
periodic pi shifts of the phase in one well, is demonstrated for solitons and in the two-mode
approximation. The latter setting is considered in both the mean-field and quantum (Bose-Hubbard)
regimes.
Geometry-dependent interactions in ultracold fermionic gases NJP 10 045013 (2008)
We study two mechanisms of the interplay of long- and short-range interactions in different geometries
of ultra- cold fermionic atomic or molecular gases. We show that in the range of validity of the onedimensional (1D) approximation, both mechanisms yield similar superconductivity. We show that
electromagnetically induced isotropic dipole-dipole interactions in a spin-polarized non-degenerate
fermionic gas can cause an extremely exothermic phase transition, analogous to the isothermal collapse
in gravitationally interacting star clusters. This collapse may result in fragmentation of the gas into a
hot “halo” and a highly degenerate “core”.