arXiv subjects

D. J. Papoular

Publications and source records attributed to D. J. Papoular.

14 recordsLinked to original sources

arXiv2026

Measured dynamics of an XXZ quantum simulator in a highly symmetrical double-ringed geometry

We theoretically identify observable consequences of spatial and spin symmetries on the dynamics of a small XXZ quantum simulator. Our proposed protocol relies on the choice of suitable initial states, and involves the measurement scheme whose experimental implementation is the simplest. We analyze a system of $N=2n=6$ to $12$ particles, trapped in a planar geometry comprised of two rings which exhibits point group symmetry $D_{nh}$. The particles represent effective spins whose interaction is described by the XXZ or Heisenberg Hamiltonian. The system is prepared in an initial state which is sitewise-factorized and invariant under all spatial symmetries, it evolves for a given time, after which the $z$-components of all $N$ spins are measured. We show that symmetries dictate (i) the qualitative behaviour of the measurement probabilities as a function of the evolution time, and (ii) the number of measurement results with different probabilities. We highlight the role of a twofold rotation of all spins. We also demonstrate that, in larger systems, the collapse of the initial state may be observed.

quant-ph↗

arXiv2024

Quantum signatures of the mixed classical phase space for three interacting particles in a circular trap

We study theoretically two consequences of the mixed classical phase space for three repulsively-interacting bosonic particles in a circular trap. First, we show that the energy levels of the corresponding quantum system are well described by a Berry-Robnik distribution. Second, we identify stationary quantum states whose density is enhanced along the stable classical periodic trajectories, and calculate their energies and wavefunctions using the semiclassical Einstein-Brillouin-Keller (EBK) theory. Our EBK results are in excellent agreement with our full-fledged finite-element numerics. We discuss the impact of discrete symmetries, including bosonic exchange symmetry, on these classically localized states. They are within experimental reach, and occur in the same range of energies as the quantum scar reported in our previous work [Phys. Rev. A 107, 022217 (2023)].

quant-ph↗

arXiv2023

Quantum scar affecting the motion of three interacting particles in a circular trap

We theoretically propose a quantum scar affecting the motion of three interacting particles in a circular trap. We numerically calculate the quantum eigenstates of the system and show that some of them are scarred by a classically unstable periodic trajectory, in the vicinity of which the classical analog exhibits chaos. The few-body scar we consider is stabilized by quantum mechanics, and we analyze it along the lines of the original quantum scarring mechanism [Heller, Phys. Rev. Lett. 53, 1515 (1984)]. In particular, we identify towers of scarred quantum states which we fully explain in terms of the unstable classical trajectory underlying the scar. Our proposal is within experimental reach owing to very recent advances in Rydberg atom trapping.

quant-ph↗

arXiv2017

"Haldane" phases with ultracold fermionic atoms in double-well optical lattices

We propose to realize one-dimensional topological phases protected by SU($N$) symmetry using alkali or alkaline-earth atoms loaded into a bichromatic optical lattice. We derive a realistic model for this system and investigate it theoretically. Depending on the parity of $N$, two different classes of symmetry-protected topological (SPT) phases are stabilized at half-filling for physical parameters of the model. For even $N$, the celebrated spin-1 Haldane phase and its generalization to SU($N$) are obtained with no local symmetry breaking. In stark contrast, at least for $N=3$, a new class of SPT phases, dubbed chiral Haldane phases, that spontaneously break inversion symmetry, emerge with a two-fold ground-state degeneracy. The latter ground states with open-boundary conditions are characterized by different left and right boundary spins which are related by conjugation. Our results show that topological phases are within close reach of the latest experiments on cold fermions in optical lattices.

cond-mat.str-el↗

arXiv2017

Entangling two atoms of different isotopes via Rydberg blockade

Quantum entanglement is crucial for simulating and understanding exotic physics of strongly correlated many-body systems, such as high--temperature superconductors, or fractional quantum Hall states. The entanglement of non-identical particles exhibits richer physics of strong many-body correlations and offers more opportunities for quantum computation, especially with neutral atoms where in contrast to ions the interparticle interaction is widely tunable by Feshbach resonances. Moreover, the inter-species entanglement forms a basis for the properties of various compound systems, ranging from Bose-Bose mixtures to photosynthetic light-harvesting complexes. So far, the inter-species entanglement has only been obtained for trapped ions. Here we report on the experimental realization of entanglement of two neutral atoms of different isotopes. A ${}^{87}\mathrm{Rb}$ atom and a ${}^{85}\mathrm{Rb}$ atom are confined in two single--atom optical traps separated by 3.8 $μ$m. Creating a strong Rydberg blockade, we demonstrate a heteronuclear controlled--NOT (C--NOT) quantum gate and generate a heteronuclear entangled state, with raw fidelities $0.73 \pm 0.01$ and $0.59 \pm 0.03$, respectively. Our work, together with the technologies of single--qubit gate and C--NOT gate developed for identical atoms, can be used for simulating any many--body system with multi-species interactions. It also has applications in quantum computing and quantum metrology, since heteronuclear systems exhibit advantages in low crosstalk and in memory protection.

quant-ph↗

arXiv2016

Quantized conductance through the quantum evaporation of bosonic atoms

We analyze theoretically the quantization of conductance occurring with cold bosonic atoms trapped in two reservoirs connected by a constriction with an attractive gate potential. We focus on temperatures slightly above the condensation threshold in the reservoirs. We show that a conductance step occurs, coinciding with the appearance of a condensate in the constriction. Conductance relies on a collective process involving the quantum condensation of an atom into an elementary excitation and the subsequent quantum evaporation of an atom, in contrast with ballistic fermion transport. The value of the bosonic conductance plateau is strongly enhanced compared to fermions and explicitly depends on temperature. We highlight the role of weak repulsive interactions between the bosons in preventing them from collapsing into the constriction.

cond-mat.quant-gas↗

arXiv2015

Interaction induced decay of a heteronuclear two-atom system

Two-atom systems in small traps are of fundamental interest, first of all for understanding the role of interactions in degenerate cold gases and for the creation of quantum gates in quantum information processing with single-atom traps. One of the key quantities is the inelastic relaxation (decay) time when one of the atoms or both are in a higher hyperfine state. Here we measure this quantity in a heteronuclear system of $^{87}$Rb and $^{85}$Rb in a micro optical trap and demonstrate experimentally and theoretically the presence of both fast and slow relaxation processes, depending on the choice of the initial hyperfine states. The developed experimental method allows us to single out a particular relaxation process and, in this sense, our experiment is a "superclean platform" for collisional physics studies. Our results have also implications for engineering of quantum states via controlled collisions and creation of two-qubit quantum gates.

physics.atom-ph↗

arXiv2014

Fast thermalization and Helmholtz oscillations of an ultracold Bose gas

We analyze theoretically the transport properties of a weakly-interacting ultracold Bose gas enclosed in two reservoirs connected by a constriction. We assume that the transport of the superfluid part is hydrodynamic, and we describe the ballistic transport of the normal part using the Landauer-Buttiker formalism. Modeling the coupled evolution of the phase, atom number, and temperature mismatches between the reservoirs, we predict that Helmholtz (plasma) oscillations, induced by an initial imbalance in atom numbers, can be observed at non-zero temperatures below Tc. We show that, because of its strong compressibility, the ultracold Bose gas is characterized by a fast thermalization compared to the damping time for plasma oscillations, accompanied by a fast transfer of the normal component through the constriction. This fast thermalization also affects the gas above Tc, where we present an explicit comparison to the ideal fermionic case.

cond-mat.quant-gas↗

arXiv2013

Dipolar-Induced Resonance for Ultracold Bosons in a Quasi-1D Optical Lattice

We study the role of the Dipolar-Induced Resonance (DIR) in a quasi-one-dimensional system of ultracold bosons. We first describe the effect of the DIR on two particles in a harmonic trap. Then, we consider a deep optical lattice loaded with ultracold dipolar bosons. In order to describe this system, we introduce a novel atom-dimer extended Bose-Hubbard model, which is the minimal model correctly accounting for the DIR. We analyze the impact of the DIR on the phase diagram at T=0 by exact diagonalization of a small-sized system. We show that the DIR strongly affects this phase diagram. In particular, we predict the mass density wave to occur in a narrow domain corresponding to weak nearest-neighbor interactions, and the occurrence of a collapse phase for stronger dipolar interactions.

cond-mat.quant-gas↗

arXiv2012

Increasing Quantum Degeneracy by Heating a Superfluid

We consider a uniform superfluid confined in two compartments connected by a superleak and initially held at equal temperatures. If one of the two compartments is heated, a fraction of the superfluid will flow through the superleak. We show that, under certain thermodynamic conditions, the atoms flow from the hotter to the colder compartment, contrary to what happens in the fountain effect observed in superfluid Helium. This flow causes quantum degeneracy to increase in the colder compartment. In superfluid Helium, this novel thermomechanical effect takes place in the phonon regime of very low temperatures. In dilute quantum gases, it occurs at all temperatures below Tc . The increase in quantum degeneracy reachable through the adiabatic displacement of the wall separating the two compartments is also discussed.

cond-mat.quant-gas↗

arXiv2012

Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields

We have observed Feshbach resonances for 133Cs atoms in two different hyperfine states at ultra-low static magnetic fields by using an atomic fountain clock. The extreme sensitivity of our setup allows for high signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have reproduced these resonances using coupled-channels calculations which are in excellent agreement with our measurements. We justify that these are s-wave resonances involving weakly-bound states of the triplet molecular Hamiltonian, identify the resonant closed channels, and explain the observed multi-peak structure. We also describe a model which precisely accounts for the collisional processes in the fountain and which explains the asymmetric shape of the observed Feshbach resonances in the regime where the kinetic energy dominates over the coupling strength.

cond-mat.quant-gas↗

arXiv2010

Microwave-induced Fano-Feshbach resonances

We investigate the possibility to control the s-wave scattering length for the interaction between cold bosonic atoms by using a microwave field. Our scheme applies to any atomic species with a ground state that is split by hyperfine interaction. We discuss more specifically the case of alkali-metal atoms and calculate the change in the scattering length for 7Li, 23Na, 41K, 87Rb, and 133Cs. Our results yield optimistic prospects for experiments with the four latter species.

cond-mat.quant-gas↗

arXiv2008

Harmonic Stability Analysis of the 2D Square and Hexagonal Bravais Lattices for a Finite--Ranged Repulsive Pair Potential. Consequence for a 2D System of Ultracold Composite Bosons

We consider a classical, two-dimensional system of identical particles which interact via a finite-ranged, repulsive pair potential. We assume that the system is in a crystalline phase. We calculate the normal vibrational modes of a two-dimensional square Bravais lattice, first analytically within the nearest-neighbour approximation, and then numerically, relaxing the preceding hypothesis. We show that, in the harmonic approximation, the excitation of a transverse vibrational mode leads to the breakdown of the square lattice. We next study the case of the hexagonal Bravais lattice and we show that it can be stable with respect to lattice vibrations. We give a criterion determining whether or not it is stable in the nearest-neighbour approximation. Finally, we apply our results to a two-dimensional system of composite bosons and infer that the crystalline phase of such a system, if it exists, corresponds to a hexagonal lattice.

cond-mat.other↗

arXiv2007

Crystalline phase of strongly interacting Fermi mixtures

We show that the system of weakly bound molecules of heavy and light fermionic atoms is characterized by a long-range intermolecular repulsion and can undergo a gas-crystal quantum transition if the mass ratio exceeds a critical value. For the critical mass ratio above 100 obtained in our calculations, this crystalline order can be observed as a superlattice in an optical lattice for heavy atoms with a small filling factor. We also find that this novel system is sufficiently stable with respect to molecular relaxation into deep bound states and to the process of trimer formation.

cond-mat.stat-mech↗