arXiv subjects

Mourad Telmini

Publications and source records attributed to Mourad Telmini.

8 recordsLinked to original sources

arXiv2025

Fast momentum-selective transport of Bose-Einstein condensates via controlled non-adiabatic dynamics in optical lattices

We present a detailed numerical study of a protocol for momentum-selective transport of a Bose-Einstein condensate (BEC) in a one-dimensional optical lattice, achieving narrow momentum distributions through controlled non-adiabatic dynamics. The protocol consists of non-adiabatic loading into the lattice, coherent acceleration using a symmetric trapezoidal acceleration profile, and non-adiabatic release into free space. Using the time-dependent Gross-Pitaevskii equation, we simulate the full sequence and analyze the role of non-adiabatic excitations on the final momentum distribution. We identify the intra-site breathing dynamics as the dominant mechanism governing spectral purity under fast loading conditions. By tracking the condensate's spatial width during the evolution, we demonstrate a direct correlation with the final momentum spread. A variational model based on a Gaussian ansatz quantitatively reproduces the observed dynamics and provides physical insight into the breathing mechanism. Our results reveal the existence of "magic" times, i.e., specific loading or acceleration durations synchronized with the breathing oscillation period, where quasi-monochromatic momentum distributions can be achieved even with loading times as short as 100 microseconds. In the tight-binding regime, this approach offers speedup factors of 3 to 6 compared to adiabatic protocols while maintaining high transfer fidelities, providing a practical route to coherent transport for quantum sensors operating under stringent timing constraints.

cond-mat.quant-gas↗

arXiv2025

Hermitian vs non-Hermitian quantum thermometry

We investigate the dephasing dynamics of a qubit as an effective mechanism for estimating the temperature of its surrounding environment for different symmetrizes. Our approach is fundamentally quantum, leveraging the qubit's susceptibility to decoherence without necessitating thermal equilibrium with the system under study. We also examine how symmetry properties affect the accuracy of information retrieval and the robustness of quantum information storage in such systems, highlighting their potential advantages in mitigating decoherence effects. The optimization of quantum Fisher information is performed with respect to both the interaction duration and the environmental temperature, focusing on Ohmic-like spectral density environments. Furthermore, we explicitly identify the optimal qubit measurement that attains the quantum Cramer-Rao bound for precision. Our findings reveal that optimal estimation arises from a complex interplay between the qubit's dephasing dynamics and the Ohmic characteristics of the environment with a particular focus on non-Hermitian systems that exhibit enhanced resilience to decoherence. Notably, optimal estimation does not occur when the qubit reaches a stationary state nor under conditions of complete dephasing.

quant-ph↗

arXiv2025

Electron impact ro-vibrational transitions and dissociative recombination of H2+ and HD+: Rate coefficients and astrophysical implications

Context. Molecular hydrogen and its cation H+2 are among the first species formed in the early Universe, and play a key role in the thermal and chemical evolution of the primordial gas. In molecular clouds, H+2 ions formed through ionization of H2 by particles react rapidly with H2 to form H+3 , triggering the formation of almost all detected interstellar molecules. Aims. We present a new set of cross sections and rate coefficients for state-to-state ro-vibrational transitions of the H+2 and HD+ ions, induced by low-energy electron collisions. Study includes the major electron-impact processes relevant for low-metallicity astrochemistry: inelastic and superelastic scattering, and dissociative recombination. Methods. The electron-induced processes involving H+2 and HD+ are treated using the multichannel quantum defect theory. Results. The newly calculated thermal rate coefficients show significant differences compared to those used in previous studies. When introduced into astrochemical models, particularly for shock-induced chemistry in metal-free gas, the updated dissociative recombination rates produce substantial changes in the predicted molecular abundances. Conclusions. These data provide updated and improved input for the modeling of hydrogen-rich plasmas in environments

astro-ph.IM↗

arXiv2011

Bose-Einstein condensation with a finite number of particles in a power-law trap

Bose-Einstein condensation (BEC) of an ideal gas is investigated, beyond the thermodynamic limit, for a finite number $N$ of particles trapped in a generic three-dimensional power-law potential. We derive an analytical expression for the condensation temperature $T_c$ in terms of a power series in $x_0=ε_0/k_BT_c$, where $ε_0$ denotes the zero-point energy of the trapping potential. This expression, which applies in cartesian, cylindrical and spherical power-law traps, is given analytically at infinite order. It is also given numerically for specific potential shapes as an expansion in powers of $x_0$ up to the second order. We show that, for a harmonic trap, the well known first order shift of the critical temperature $ΔT_c/T_c \propto N^{-1/3}$ is inaccurate when $N \leqslant 10^{5}$, the next order (proportional to $N^{-1/2}$) being significant. We also show that finite size effects on the condensation temperature cancel out in a cubic trapping potential, e.g. $V(\mathbi{r}) \propto r^3$. Finally, we show that in a generic power-law potential of higher order, e.g. $V(\mathbi{r}) \propto r^α$ with $α> 3$, the shift of the critical temperature becomes positive. This effect provides a large increase of $T_c$ for relatively small atom numbers. For instance, an increase of about +40% is expected with $10^4$ atoms in a $V(\mathbi{r}) \propto r^{12}$ trapping potential.

cond-mat.quant-gas↗

arXiv2010

Bose-Einstein condensation in dark power-law laser traps

We investigate theoretically an original route to achieve Bose-Einstein condensation using dark power-law laser traps. We propose to create such traps with two crossing blue-detuned Laguerre-Gaussian optical beams. Controlling their azimuthal order $\ell$ allows for the exploration of a multitude of power-law trapping situations in one, two and three dimensions, ranging from the usual harmonic trap to an almost square-well potential, in which a quasi-homogeneous Bose gas can be formed. The usual cigar-shaped and disk-shaped Bose-Einstein condensates obtained in a 1D or 2D harmonic trap take the generic form of a "finger" or of a "hockey puck" in such Laguerre-Gaussian traps. In addition, for a fixed atom number, higher transition temperatures are obtained in such configurations when compared with a harmonic trap of same volume. This effect, which results in a substantial acceleration of the condensation dynamics, requires a better but still reasonable focusing of the Laguerre-Gaussian beams.

quant-ph↗

arXiv2009

Controlled deflection of cold atomic clouds and of Bose-Einstein condensates

We present a detailed, realistic proposal and analysis of the implementation of a cold atom deflector using time-dependent far off-resonance optical guides. An analytical model and numerical simulations are used to illustrate its characteristics when applied to both non-degenerate atomic ensembles and to Bose-Einstein condensates. Using for all relevant parameters values that are achieved with present technology, we show that it is possible to deflect almost entirely an ensemble of $^{87}$Rb atoms falling in the gravity field. We discuss the limits of this proposal, and illustrate its robustness against non-adiabatic transitions.

quant-ph↗

arXiv2007

Optical Devices for Cold Atoms and Bose-Einstein Condensates

The manipulation of cold atoms with optical fields is a very promising technique for a variety of applications ranging from laser cooling and trapping to coherent atom transport and matter wave interferometry. Optical fields have also been proposed as interesting tools for quantum information processing with cold atoms. In this paper, we present a theoretical study of the dynamics of a cold 87Rb atomic cloud falling in the gravity field in the presence of two crossing dipole guides. The cloud is either deflected or split between the two branches of this guide. We explore the possibilities of optimization of this device and present preliminary results obtained in the case of zero-temperature dilute Bose-Einstein condensates.

quant-ph↗

arXiv2006

Theoretical study of a cold atom beam splitter

A theoretical model is presented for the study of the dynamics of a cold atomic cloud falling in the gravity ﬁeld in the presence of two crossing dipole guides. The cloud is split between the two branches of this laser guide, and we compare experimental measurements of the splitting efﬁciency with semiclassical simulations. We then explore the possibilities of optimization of this beam splitter. Our numerical study also gives access to detailed information, such as the atom temperature after the splitting.

quant-ph↗