Browsing by Subject "Bose-Einstein condensates"

Now showing 1 - 10 of 10

Open Access
Different scattering regimes in two-dimensional Bose-Einstein condensates
(Springer, 2003) Tanatar, Bilal; Shumovsky, Alexander S.; Rupasov, V. I.
Motivated by the recent efforts to produce low-dimensional condensates, we study the ground-state density profiles of two-dimensional Bose-Einstein condensed atoms at zero temperature within a mean-field theory. The interplay between the tight harmonic confinement in the axial direction and collisional properties of the condensate atoms help identify three distinct regimes of experimental interest. Each regime is described by a different atom-atom coupling which depends on the density of the condensate as the system starts to be influenced by two-dimensional collisions. We trace the regions of experimentally accessible system parameters for which the crossover between different dimensionality behaviors in the scattering properties may become observable.
Open Access
Photonic band gap via quantum coherence in vortex lattices of Bose-Einstein condensates
(The American Physical Society, 2005) Müstecaplioǧlu, O. E.; Oktel, M. Ö.
We investigate the optical response of an atomic Bose-Einstein condensate with a vortex lattice. We find that it is possible for the vortex lattice to act as a photonic crystal and create photonic band gaps, by enhancing the refractive index of the condensate via a quantum coherent scheme. If high enough index contrast between the vortex core and the atomic sample is achieved, a photonic band gap arises depending on the healing length and the lattice spacing. A wide range of experimentally accessible parameters are examined and band gaps in the visible region of the electromagnetic spectrum are found. We also show how directional band gaps can be used to directly measure the rotation frequency of the condensate.
Open Access
Quantum correlations among superradiant bose-einstein condensate atoms
(M A I K Nauka - Interperiodica, 2010) Taşgin, M. E.; Öztop, B.; Oktel, M. Ö.; Müstecapliog̃lu, Ö. E.
Quantum correlations among atoms in superradiant Bose-Einstein condensates are discussed. It is shown that atoms in the superradiant atomic condensate can exhibit continuous variable quantum entanglement analogous to Einstein-Podolsky-Rosen (EPR)-type quantum correlations. Comparison to quantum entanglement in the Dicke model in thermal equilibrium is provided.
Open Access
Quantum Dynamics of Long-Range Interacting Systems Using the Positive-P and Gauge-P Representations
(American Physical Society, 2017) Wüster, S.; Corney, J. F.; Rost, J. M.; Deuar, P.
We provide the necessary framework for carrying out stochastic positive-P and gauge-P simulations of bosonic systems with long-range interactions. In these approaches, the quantum evolution is sampled by trajectories in phase space, allowing calculation of correlations without truncation of the Hilbert space or other approximations to the quantum state. The main drawback is that the simulation time is limited by noise arising from interactions. We show that the long-range character of these interactions does not further increase the limitations of these methods, in contrast to the situation for alternatives such as the density matrix renormalization group. Furthermore, stochastic gauge techniques can also successfully extend simulation times in the long-range-interaction case, by making using of parameters that affect the noise properties of trajectories, without affecting physical observables. We derive essential results that significantly aid the use of these methods: estimates of the available simulation time, optimized stochastic gauges, a general form of the characteristic stochastic variance, and adaptations for very large systems. Testing the performance of particular drift and diffusion gauges for nonlocal interactions, we find that, for small to medium systems, drift gauges are beneficial, whereas for sufficiently large systems, it is optimal to use only a diffusion gauge. The methods are illustrated with direct numerical simulations of interaction quenches in extended Bose-Hubbard lattice systems and the excitation of Rydberg states in a Bose-Einstein condensate, also without the need for the typical frozen gas approximation. We demonstrate that gauges can indeed lengthen the useful simulation time.
Open Access
Quantum entanglement via superradiance of a Bose-Einstein condensate
(Institute of Physics Publishing, 2010) Taşgın, M. E.; Oktel, M. Ö.; You, L.; Müstecaploǧlu, Ö. E.
We adopt the coherence and built-in swap mechanism in sequential superradiance as a tool for obtaining continuous-variable (electric/magnetic fields) quantum entanglement of two counter-propagating pulses emitted from the two end-fire modes. In the first-sequence, end-fire modes are entangled with the side modes. In the second sequence, this entanglement is swapped to in between the two opposite end-fire modes. Additionally, we also examine the photon number correlations. No quantum correlations is observed in this variable.
Open Access
Refractive index-enhanced vortex lattices
(SPIE, 2005) Müstecaplıoǧlu, Ö. E.; Öktel, M. Özgür
Light propagation through vortex matter in atomic Bose-Einstein condensates is examined. It is shown that vortex matter can be used as a photonic crystal by a refractive index enhancement scheme. Band structure of the vortex lattice is numerically calculated. Index enhanced vortex matter is shown to exhibit large refractive index contrast with the dilute thermal gas background in the vortex core. Depending on the depth of the index contrast full or directional photonic band gaps are found in the band structure. Experimental parameters required to generate band gaps in the visible region of the electromagnetic spectrum are calculated.
Open Access
Rotons and Bose condensation in Rydberg-dressed Bose gases
(American Physical Society, 2020) Seydi, I.; Abedinpour, S. H.; Zillich, R. E.; Asgari, R.; Tanatar, Bilal
We investigate the ground-state properties and excitations of Rydberg-dressed bosons in both three and two dimensions, using the hypernetted-chain Euler-Lagrange approximation, which accounts for correlations and thus goes beyond the mean-field approximation. The short-range behavior of the pair distribution function signals the instability of the homogeneous system with respect to the formation of droplet crystals at strong couplings and large soft-core radius. This tendency to spatial density modulation coexists with off-diagonal long-range order. The contribution of the correlation energy to the ground-state energy is significant at large coupling strengths and intermediate values of the soft-core radius while for a larger soft-core radius the ground-state energy is dominated by the mean-field (Hartree) energy. We have also performed path integral Monte Carlo simulations at selected system parameters to verify the performance of our hypernetted-chain Euler-Lagrange results in three dimensions. In the homogeneous phase, the two approaches are in very good agreement. Moreover, Monte Carlo simulations predict a first-order quantum phase transition from a homogeneous superfluid phase to the quantum droplet phase with face-centered cubic symmetry for Rydberg-dressed bosons in three dimensions.
Open Access
Strongly interacting one-dimensional Bose-Einstein condensates in harmonic traps
(American Physical Society, 2000) Tanatar, Bilal; Erkan, K.
The properties of strongly interacting one dimensional boson condensates in harmonic trap potentials were studied. An equation describing the condensate wave function in the limit of very strong interactions between the bosons was obtained using a density functional type formalism. It was found that the two component system exhibits coexisting and segregated phases similar to the weakly interacting system.
Open Access
Temperature-dependent density profiles of dipolar droplets
(American Physical Society, 2019) Aybar, Enes; Öktel, M. Özgür
Recently, trapped dipolar gases were observed to form high-density droplets in a regime where mean-field theory predicts collapse. These droplets present a form of equilibrium where quantum fluctuations are critical for stability. So far, the effect of quantum fluctuations has only been considered at zero temperature through the local chemical potential arising from the Lee-Huang-Yang correction. Here, we extend the theory of dipolar droplets to nonzero temperatures using Hartree-Fock-Bogoliubov theory (HFBT) and show that the equilibrium is strongly affected by temperature fluctuations. HFBT, together with local density approximation for excitations, reproduces the zero-temperature results and predicts that the condensate density can change dramatically even at low temperatures where the total depletion is small. In particular, we find that typical experimental temperatures (T∼100 nK) can significantly modify the transition between low-density and droplet phases.
Open Access
Vortex lattices in dipolar two-compenent Bose-Einstein condensates
(American Physical Society, 2014-02-21) Ghazanfari, N.; Keles, A.; Oktel, M. O.
We consider a rapidly rotating two-component Bose-Einstein condensate with short-range s-wave interactions as well as dipolar coupling. We calculate the phase diagram of vortex lattice structures as a function of the intercomponent s-wave interaction and the strength of the dipolar interaction. We find that the long-range interactions cause new vortex lattice structures to be stable and lead to a richer phase diagram. Our results reduce to the previously found lattice structures for short-range interactions and single-component dipolar gases in the corresponding limits.