Amichay Vardi

Anisotropic Solitons in Dipolar Bose-Einstein Condensates

Starting with a Gaussian variational ansatz, we predict anisotropic bright solitons in quasi-2D Bose-Einstein condensates consisting of atoms with dipole moments polarized perpendicular to the confinement direction. Unlike isotropic solitons predicted for the moments aligned with the confinement axis [Phys. Rev. Lett. 95, 200404 (2005)10.1103/PhysRevLett.95.200404], no sign reversal of the dipole-dipole interaction is necessary to support the solitons. Direct 3D simulations confirm their stability.

Bose-Einstein Condensates beyond Mean Field Theory: Quantum Backreaction as Decoherence

We propose an experiment to measure the slow log(N) convergence to mean field theory (MFT) around a dynamical instability. Using a density matrix formalism instead of the standard macroscopic wave function approach, we derive equations of motion which go beyond MFT and provide accurate predictions for the quantum break time. The leading quantum corrections appear as decoherence of the reduced single-particle quantum state.

Dynamics of a two-mode Bose-Einstein condensate beyond mean-field theory

We study the dynamics of a two-mode Bose-Einstein condensate in the vicinity of a mean-field dynamical instability. Convergence to mean-field theory (MFT), with increasing total number of particles N, is shown to be logarithmically slow. Using a density-matrix formalism rather than the conventional wave-function methods, we derive an improved set of equations of motion for the mean-field plus the fluctuations, which goes beyond MFT and provides accurate predictions for the leading quantum corrections and the quantum break time. We show that the leading quantum corrections appear as decoherence of the reduced single-particle quantum state; we also compare this phenomenon to the effects of thermal noise. Using the rapid dephasing near an instability, we propose a method for the direct measurement of scattering lengths.

Bosonic Amplification of Noise-Induced Suppression of Phase Diffusion

We study the effect of noise-induced dephasing on collisional phase diffusion in the two-site Bose-Hubbard 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.

On the role of intermolecular interactions in establishing chiral stability

I study the effect of intermolecular interactions on coherent tunneling racemization within the framework of the Hund double well model. Two self-consistent equations for the well population amplitudes, coupled by a tunneling matrix element, are used to describe the system dynamics. It is shown that the equations of motion are nonlinear due to the difference between homochiral interactions and heterochiral interactions. The consequence of this nonlinearity is that chiral molecular configurations are far more stable than expected by the Hund model for isolated molecules. Moreover, when the homochiral interactions are energetically favorable to heterochiral interactions (weaker homochiral repulsive interactions or stronger homochiral attractive interactions), spontaneous symmetry breaking may amplify the optical activity of a nearly racemic mixture.

Incoherent matter-wave solitons and pairing instability in an attractively interacting Bose-Einstein condensate.

The dynamics of matter-wave solitons in Bose-Einstein condensates (BEC) is considerably affected by the presence of a thermal cloud and the dynamical depletion of the condensate. Our numerical results, based on the time-dependent Hartree-Fock-Bogoliubov theory, demonstrate the collapse of the attractively interacting BEC via collisional emission of atom pairs into the thermal cloud, which splits the (quasi-one-dimensional) BEC soliton into two partially coherent solitonic structures of opposite momenta. These incoherent matter waves are analogous to optical random-phase solitons.

Phase-Diffusion Dynamics in Weakly Coupled Bose-Einstein Condensates

We study the phase sensitivity of collisional phase diffusion between weakly coupled Bose-Einstein condensates, using a semiclassical picture of the two-mode Bose-Hubbard model. When weak coupling is allowed, zero relative phase locking is attained in the Josephson-Fock transition regime, whereas a pi relative phase is only locked in Rabi-Josephson point. Our analytic semiclassical estimates agree well with the numerical results.

Vortex solitons in dipolar Bose-Einstein condensates

We predict solitary vortices in quasiplanar condensates of dipolar atoms, polarized parallel to the confinement direction, with the effective sign of the dipole-dipole interaction inverted by means of a rapidly rotating field. Energy minima corresponding to vortex solitons with topological charges

Many-body effects on adiabatic passage through Feshbach resonances

\ensuremath{\ell}=1

Decoherence and entanglement in a bosonic Josephson junction: Bose-enhanced quantum Zeno control of phase diffusion

and 2 are predicted for moderately strong dipole-dipole interaction, using an axisymmetric Gaussian Ansatz. The stability of the solitons with