arXiv subjects

Iacopo Carusotto

Publications and source records attributed to Iacopo Carusotto.

206 records · Page 12Linked to original sources

arXiv2004

Imaging of spinor gases

We explore the dielectric properties of spinor condensates. Gases with vector (nematic) order, such as spin-1 condensates with ferromagnetic (antiferromagnetic) interactions, display optical activity (birefringence). This optical activity/birefringence is respectively seen for light detuned from resonance by a frequency which is not too large compared with the fine/hyperfine structure. Careful tuning of the light frequency can isolate either of these two effects. These features can be used to image spin textures in clouds of spin 1 bosons, and to discern states showing different types of spin order.

cond-mat↗

arXiv2003

Transverse Fresnel-Fizeau drag effects in strongly dispersive media

A light beam normally incident upon an uniformly moving dielectric medium is in general subject to bendings due to a transverse Fresnel-Fizeau light drag effect. In conventional dielectrics, the magnitude of this bending effect is very small and hard to detect. Yet, it can be dramatically enhanced in strongly dispersive media where slow group velocities in the m/s range have been recently observed taking advantage of the electromagnetically induced transparency (EIT) effect. In addition to the usual downstream drag that takes place for positive group velocities, we predict a significant anomalous upstream drag to occur for small and negative group velocities. Furthermore, for sufficiently fast speeds of the medium, higher order dispersion terms are found to play an important role and to be responsible for peculiar effects such as light propagation along curved paths and the restoration of the spatial coherence of an incident noisy beam. The physics underlying this new class of slow-light effects is thoroughly discussed.

cond-mat↗

arXiv2002

In-situ velocity imaging of ultracold atoms using slow--light

The optical response of a moving medium suitably driven into a slow-light propagation regime strongly depends on its velocity. This effect can be used to devise a novel scheme for imaging ultraslow velocity fields. The scheme turns out to be particularly amenable to study in-situ the dynamics of collective and topological excitations of a trapped Bose-Einstein condensate. We illustrate the advantages of using slow-light imaging specifically for sloshing oscillations and bent vortices in a stirred condensate.

cond-mat.soft↗

arXiv2002

Condensate statistics in interacting Bose gases: exact results

Recently, a Quantum Monte Carlo method alternative to the Path Integral Monte Carlo method was developed for the numerical solution of the N-boson problem; it is based on the stochastic evolution of classical fields. Here we apply it to obtain exact results for the occupation statistics of the condensate mode in a weakly interacting trapped one-dimensional Bose gas. The temperature is varied across the critical region down to temperatures lower than the trap level spacing. We verify that the number-conserving Bogoliubov theory gives accurate predictions provided that the non-condensed fraction is small.

cond-mat.stat-mech↗

arXiv2002

Exact reformulation of the bosonic many-body problem in terms of stochastic wave functions: convergence issues

There exist methods to reformulate in an exact way the many-body problem of interacting bosons in terms of the stochastic evolution of single particle wave functions. For one such reformulation, the so-called simple Fock scheme, we present an elementary derivation, much simpler than the original one. Furthermore, we show that two other schemes, based on coherent states of the matter field rather than on Fock states, lead to an infinite statistical uncertainty in the continuous time limit. The simple Fock scheme is therefore, up to now, the only one that was proved to lead to a convergent Monte Carlo simulation scheme at all times.

cond-mat.soft↗

arXiv2001

Nonlinear atom optics and bright gap soliton generation in finite optical lattices

We theoretically investigate the transmission dynamics of coherent matter wave pulses across finite optical lattices in both the linear and the nonlinear regimes. The shape and the intensity of the transmitted pulse are found to strongly depend on the parameters of the incident pulse, in particular its velocity and density: a clear physical picture for the main features observed in the numerical simulations is given in terms of the atomic band dispersion in the periodic potential of the optical lattice. Signatures of nonlinear effects due the atom-atom interaction are discussed in detail, such as atom optical limiting and atom optical bistability. For positive scattering lengths, matter waves propagating close to the top of the valence band are shown to be subject to modulational instability. A new scheme for the experimental generation of narrow bright gap solitons from a wide Bose-Einstein condensate is proposed: the modulational instability is seeded in a controlled way starting from the strongly modulated density profile of a standing matter wave and the solitonic nature of the generated pulses is checked from their shape and their collisional properties.

cond-mat.soft↗

arXiv2001

An exact stochastic field method for the interacting Bose gas at thermal equilibrium

We present a new exact method to numerically compute the thermodynamical properties of an interacting Bose gas in the canonical ensemble. As in our previous paper (Phys. Rev. A, 63 023606 (2001)), we write the density operator $ρ$ as an average of Hartree dyadics $\ketbra{N:ϕ_1}{N:ϕ_2}$ and we find stochastic evolution equations for the wave functions $ϕ_{1,2}$ such that the exact imaginary-time evolution of $ρ$ is recovered after average over noise. In this way, the thermal equilibrium density operator can be obtained for any temperature $T$. The method is then applied to study the thermodynamical properties of a homogeneous one-dimensional $N$-boson system: although Bose-Einstein condensation can not occur in the thermodynamical limit, a macroscopic occupation of the lowest mode of a finite system is observed at sufficiently low temperatures. If $k_B T \gg μ$, the main effect of interactions is to suppress density fluctuations and to reduce their correlation length. Different effects such as a spatial antibunching of the atoms are predicted for the opposite $k_B T\leq μ$ regime. Our exact stochastic calculations have been compared to existing approximate theories.

cond-mat.soft↗

arXiv2000

Coherence properties of a continuous atom laser

We investigate the coherence properties of an atomic beam evaporatively cooled in a magnetic guide, assuming thermal equilibrium in the quantum degenerate regime. The gas experiences two-dimensional, transverse Bose-Einstein condensation rather than a full three-dimensional condensation because of the very elongated geometry of the magnetic guide. First order and second order correlation functions of the atomic field are used to characterize the coherence properties of the gas along the axis of the guide. The coherence length of the gas is found to be much larger than the thermal de Broglie wavelength in the strongly quantum degenerate regime. Large intensity fluctuations present in the ideal Bose gas model are found to be strongly reduced by repulsive atomic interactions; this conclusion is obtained with a one-dimensional classical field approximation valid when the temperature of the gas is much higher than its chemical potential, k_B T >> |mu|.

cond-mat.stat-mech↗