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Aurélien Perrin

Publications and source records attributed to Aurélien Perrin.

At least 19 recordsLinked to original sources

Soliton turbulence of a strongly driven one-dimensional Bose gas

We study the out-of-equilibrium dynamics of a weakly interacting one-dimensional Bose gas in a box trap, subjected to a drive realized by a periodically oscillating linear potential. After a transient regime, the gas reaches a quasi-steady state, characterized by the presence of several solitons. At weak driving amplitude, the solitons are only weakly perturbed by one another, while at strong driving amplitude a regime analogous to turbulence is reached, where the solitons are strongly intertwined with each other. We show that a hallmark of both regimes can be found in the momentum distribution, which displays a power-law decay $n(k) \sim k^{-2}$ at weak driving amplitude and $n(k) \sim k^{-α}$ with a power-law exponent $α\in [7,9]$ at large amplitude. We further characterize each of the two regimes by following the space-time maps and characterizing the solitons using the inverse scattering transform. The protocol analyzed in this study is amenable to experimental realization in current experimental setups.

cond-mat.quant-gas

Microwave spectroscopy of ultracold-sodium least-bound molecular states

We have performed microwave spectroscopy of sodium least-bound molecular states, improving the precision of the knowledge of their energies at zero magnetic field by almost three orders of magnitude. Our experimental observations give us access also to states submitted to predissociation, a phenomenon where a bound molecular state can naturally decay into the continuum. Our findings are compared to numerical calculations based on the latest interpolation of sodium interaction potentials and show good agreement, with slight discrepancies in the zero-field energy of the molecular states, suggesting a need for small adjustment of the interaction potentials.

physics.atom-ph

Fast manipulation of a quantum gas on an atom chip with a strong microwave field

We report on an experimental platform based on an atom chip encompassing a coplanar waveguide which enables the manipulation of a quantum gas of sodium atoms with strong microwave fields. We describe the production with this setup of a very elongated degenerate quantum gas with typically 10^6 atoms, that can be prepared all along the cross-over from the three-dimensional to the one-dimensional regime, depending on the atom number and trapping geometry. Using the microwave field radiated by the waveguide, we drive Rabi oscillations between the hyperfine ground states, with the atoms trapped at various distances from the waveguide. At the closest position explored, the field amplitude exceeds 5 G, corresponding to a Rabi frequency on the strongest transition larger than 6 MHz. This enables fast manipulation of the atomic internal state.

cond-mat.quant-gas

Thermal melting of a vortex lattice in a quasi two-dimensional Bose gas

We report the observation of the melting of a vortex lattice in a fast rotating quasi-two dimensional Bose gas, under the influence of thermal fluctuations. We image the vortex lattice after a time-of-flight expansion, for increasing rotation frequency at constant atom number and temperature. We detect the vortex positions and study the order of the lattice using the pair correlation function and the orientational correlation function. We evidence the melting transition by an abrupt change in the decay of orientational correlations, associated to a proliferation of dislocations. Our findings are consistent with the hexatic to liquid transition in the KTHNY scenario for two-dimensional melting.

cond-mat.quant-gas

Comparison of time profiles for the magnetic transport of cold atoms

We have compared different time profiles for the trajectory of the centre of a quadrupole magnetic trap designed for the transport of cold sodium atoms. Our experimental observations show that a smooth profile characterized by an analytical expression involving the error function minimizes the transport duration while limiting atom losses and heating of the trapped gas. Using numerical calculations of single atom classical trajectories within the trap, we show that this observation can be qualitatively interpreted as a trade-off between two types of losses: finite depth of the confinement and Majorana spin flips.

cond-mat.quant-gas

Expansion of a quantum gas in a shell trap

We report the observation of the controlled expansion of a two-dimensional quantum gas confined onto a curved shell-shaped surface. We start from the ellipsoidal geometry of a dressed quadrupole trap and introduce a novel gravity compensation mechanism enabling to explore the full ellipsoid. The zero-point energy of the transverse confinement manifests itself by the spontaneous emergence of an annular shape in the atomic distribution. The experimental results are compared with the solution of the three-dimensional Gross-Pitaevskii equation and with a two-dimensional semi-analytical model. This work evidences how a hidden dimension can affect dramatically the embedded low-dimensional system by inducing a change of topology.

cond-mat.quant-gas

Detailed study of a transverse field Zeeman slower

We present a thorough analysis of a Zeeman slower for sodium atoms made of permanent magnets in a Halbach configuration. Due to the orientation of the magnetic field, the polarisation of the slowing laser beam cannot be purely circular leading to optical leakages into dark states. To circumvent this effect, we propose an atomic state preparation stage able to significantly increase the performances of the Zeeman slower. After a careful theoretical analysis of the problem, we experimentally implement an optical pumping stage leading to an increase of the magneto-optical trap loading rate by 3.5. Such method is easy to set up and could be extended to other Zeeman slower architectures.

physics.atom-ph

Supersonic rotation of a superfluid: a long-lived dynamical ring

We present the experimental realization of a long-lived superfluid flow of a quantum gas rotating in an anharmonic potential, sustained by its own angular momentum. The gas is set into motion by rotating an elliptical deformation of the trap. An evaporation selective in angular momentum yields an acceleration of rotation until the density vanishes at the trap center, resulting in a dynamical ring with 350 hbar angular momentum per particle. The density profile of the ring corresponds to the one of a quasi two-dimensional superfluid, with a linear velocity reaching Mach 18 and a rotation lasting more than a minute.

cond-mat.quant-gas

Probing superfluidity in a quasi two-dimensional Bose gas through its local dynamics

We report direct evidence of superfluidity in a quasi two-dimensional Bose gas by observing its dynamical response to a collective excitation. Relying on a novel local correlation analysis, we are able to probe inhomogeneous clouds and reveal their local dynamics. We identify in this way the superfluid and thermal phases inside the gas and locate the boundary at which the Berezinskii--Kosterlitz--Thouless crossover occurs. This new analysis also allows to evidence the coupling of the two fluids which induces at finite temperatures damping rates larger than the usual Landau damping.

cond-mat.quant-gas

A two-dimensional quantum gas in a magnetic trap

We present the first experimental realization of a two-dimensional quantum gas in a purely magnetic trap dressed by a radio frequency field in the presence of gravity. The resulting potential is extremely smooth and very close to harmonic in the two-dimensional plane of confinement. We fully characterize the trap and demonstrate the confinement of a quantum gas to two dimensions. The trap geometry can be modified to a large extent, in particular in a dynamical way. Taking advantage of this possibility, we study the monopole and the quadrupole modes of a two-dimensional Bose gas.

cond-mat.quant-gas

Twin-atom beams

We present highly efficient emission of twin-atom beams into a single transversal mode of a waveguide potential. The source is a one-dimensional degenerate Bose gas in the first radially excited state. We directly measure a suppression of fluctuations in the atom number difference between the beams to 0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after correcting for detection noise. Our results underline the high potential of ultracold atomic gases as sources for quantum matter wave optics and will enable the implementation of schemes previously unattainable with massive particles

cond-mat.quant-gas

Hanbury Brown and Twiss correlations across the Bose-Einstein condensation threshold

Hanbury Brown and Twiss (HBT) correlations, i.e. correlations in far-field intensity fluctuations, yield fundamental information on the quantum statistics of light sources, as highlighted after the discovery of photon bunching. Drawing on the analogy between photons and atoms, similar measurements have been performed for matter-wave sources, probing density fluctuations of expanding ultracold Bose gases. Here we use two-point density correlations to study how coherence is gradually established when crossing the Bose-Einstein condensation (BEC) threshold. Our experiments reveal a persistent multimode character of the emerging matter-wave as seen in the non-trivial spatial shape of the correlation functions for all probed source geometries from nearly isotropic to quasi-one-dimensional (quasi-1D), and for all probed temperatures. The qualitative features of our observations are captured by ideal Bose gas theory, the quantitative differences illustrate the role of particle interactions.

cond-mat.quant-gas

Dynamics of parametric matter wave amplification

We develop a model for parametric amplification, based on a density matrix approach, which naturally accounts for the peculiarities arising for matter waves: significant depletion and explicit time-dependence of the source state population, long interaction times, and spatial dynamics of the amplified modes. We apply our model to explain the details in an experimental study on twin-atom beam emission from a one-dimensional degenerate Bose gas.

cond-mat.quant-gas

Rubidium-87 Bose-Einstein condensate in an optically plugged quadrupole trap

We describe an experiment to produce 87Rb Bose-Einstein condensates in an optically plugged magnetic quadrupole trap, using a blue-detuned laser. Due to the large detuning of the plug laser with respect to the atomic transition, the evaporation has to be carefully optimized in order to efficiently overcome the Majorana losses. We provide a complete theoretical and experimental study of the trapping potential at low temperatures and show that this simple model describes well our data. In particular we demonstrate methods to reliably measure the trap oscillation frequencies and the bottom frequency, based on periodic excitation of the trapping potential and on radio-frequency spectroscopy, respectively. We show that this hybrid trap can be operated in a well controlled regime that allows a reliable production of degenerate gases.

cond-mat.quant-gas

Atomic four-wave mixing via condensate collisions

We perform a theoretical analysis of atomic four-wave mixing via a collision of two Bose-Einstein condensates of metastable helium atoms, and compare the results to a recent experiment. We calculate atom-atom pair correlations within the scattering halo produced spontaneously during the collision. We also examine the expected relative number squeezing of atoms on the sphere. The analysis includes first-principles quantum simulations using the positive P-representation method. We develop a unified description of the experimental and simulation results.

quant-ph

Camparison of the Hanbury Brown-Twiss effect for bosons and fermions

Fifty years ago, Hanbury Brown and Twiss (HBT) discovered photon bunching in light emitted by a chaotic source, highlighting the importance of two-photon correlations and stimulating the development of modern quantum optics . The quantum interpretation of bunching relies upon the constructive interference between amplitudes involving two indistinguishable photons, and its additive character is intimately linked to the Bose nature of photons. Advances in atom cooling and detection have led to the observation and full characterisation of the atomic analogue of the HBT effect with bosonic atoms. By contrast, fermions should reveal an antibunching effect, i.e., a tendency to avoid each other. Antibunching of fermions is associated with destructive two-particle interference and is related to the Pauli principle forbidding more than one identical fermion to occupy the same quantum state. Here we report an experimental comparison of the fermion and the boson HBT effects realised in the same apparatus with two different isotopes of helium, 3He (a fermion) and 4He (a boson). Ordinary attractive or repulsive interactions between atoms are negligible, and the contrasting bunching and antibunching behaviours can be fully attributed to the different quantum statistics. Our result shows how atom-atom correlation measurements can be used not only for revealing details in the spatial density, or momentum correlations in an atomic ensemble, but also to directly observe phase effects linked to the quantum statistics in a many body system. It may thus find applications to study more exotic situations >.

cond-mat.other

Theory for a Hanbury Brown Twiss experiment with a ballistically expanding cloud of cold atoms

We have studied one-body and two-body correlation functions in a ballistically expanding, non-interacting atomic cloud in the presence of gravity. We find that the correlation functions are equivalent to those at thermal equilibrium in the trap with an appropriate rescaling of the coordinates. We derive simple expressions for the correlation lengths and give some physical interpretations. Finally a simple model to take into account finite detector resolution is discussed.

quant-ph