137 research outputs found
From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in Quenched Atomic Superfluids
Sakharov oscillations, conventionally discussed in the context of early
universe evolution and the anisotropy of cosmic microwave background radiation,
is the manifestation of interfering acoustic waves synchronously generated in
an ideal fluid. Here we report the laboratory demonstration of Sakharov
oscillations in a quenched atomic superfluid. We quench the sample by Feshbach
tuning and monitor the subsequent density fluctuations at different time and
length scales by in situ imaging. Sakharov oscillations are identified as the
multi-peak structure in the atomic density power spectrum, resembling that of
the cosmic microwave background. We also observe Sakharov oscillations in the
time domain, from which we extract the energy dispersion of the superfluid, and
determine the sonic horizon of the excitations
Fit-free determination of scale invariant equations of state: application to the 2D Bose gas across the Berezinksii-Kosterlitz-Thouless transition
We present a general "fit-free" method for measuring the equation of state
(EoS) of a scale-invariant gas. This method, which is inspired from the
procedure introduced by Ku et al. [Science 335, 563 (2012)] for the unitary
three-dimensional Fermi gas, provides a general formalism which can be readily
applied to any quantum gas in a known trapping potential, in the frame of the
local density approximation. We implement this method on a weakly-interacting
two-dimensional Bose gas in the vicinity of the Berezinskii-Kosterlitz-Thouless
transition, and determine its EoS with unprecedented accuracy in the critical
region. Our measurements provide an important experimental benchmark for
classical field approaches which are believed to accurately describe quantum
systems in the weakly interacting but non-perturbative regime.Comment: 5 pages, 5 figure
Practical scheme for a light-induced gauge field in an atomic Bose gas
We propose a scheme to generate an Abelian gauge field in an atomic gas using
two crossed laser beams. If the internal atomic state follows adiabatically the
eigenstates of the atom-laser interaction, Berry's phase gives rise to a vector
potential that can nucleate vortices in a Bose gas. The present scheme operates
even for a large detuning with respect to the atomic resonance, making it
applicable to alkali-metal atoms without significant heating due to spontaneous
emission. We test the validity of the adiabatic approximation by integrating
the set of coupled Gross-Pitaevskii equations associated with the various
internal atomic states, and we show that the steady state of the interacting
gas indeed exhibits a vortex lattice, as expected from the adiabatic gauge
field.Comment: 4 pages, 3 figure
Creating a bosonic fractional quantum Hall state by pairing fermions
We numerically study the behavior of spin-- fermions on a
two-dimensional square lattice subject to a uniform magnetic field, where
opposite spins interact via an on-site attractive interaction. Starting from
the non-interacting case where each spin population is prepared in a quantum
Hall state with unity filling, we follow the evolution of the system as the
interaction strength is increased. Above a critical value and for sufficiently
low flux density, we observe the emergence of a twofold quasidegeneracy
accompanied by the opening of an energy gap to the third level. Analysis of the
entanglement spectra shows that the gapped ground state is the bosonic
Laughlin state. Our work therefore provides compelling evidence of a
topological phase transition from the fermionic quantum Hall state at unity
filling to the bosonic Laughlin state at a critical attraction strength
L’effet de la langue maternelle sur la compréhension d’un texte narratif
The purpose of this article is to study the effect of the other mother tongue, the Kabyle, on the narrative text comprehension and especially on the coherent information representation which it vehicles. An experience has been done with three high school learners groups who have read a text by Guy de Maupassant called “Les deux amis”. During a first session, les learners read the French text then produce a first recall. During a second session, two (02) groups read again the same text within one of the two mother tongues, the kabyle and Arabic and the other group, considered as a witness group; read again the text in French. All the groups produce a second recall. The results show that the mother tongue has an effect not only on the number of recall prepositions but also on the coherent comprehensive construction of the studied text. The use of the kabyle in the rereading process helps the activation of the learners former knowledge, thus helping them in the narrative text comprehension
Spin-Injection Spectroscopy of a Spin-Orbit Coupled Fermi Gas
The coupling of the spin of electrons to their motional state lies at the
heart of recently discovered topological phases of matter. Here we create and
detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form
of quantum degenerate matter. We reveal the spin-orbit gap via spin-injection
spectroscopy, which characterizes the energy-momentum dispersion and spin
composition of the quantum states. For energies within the spin-orbit gap, the
system acts as a spin diode. To fully inhibit transport, we open an additional
spin gap, thereby creating a spin-orbit coupled lattice whose spinful band
structure we probe. In the presence of s-wave interactions, such systems should
display induced p-wave pairing, topological superfluidity, and Majorana edge
states
Motion of a Solitonic Vortex in the BEC-BCS Crossover
We observe a long-lived solitary wave in a superfluid Fermi gas of Li
atoms after phase-imprinting. Tomographic imaging reveals the excitation to be
a solitonic vortex, oriented transverse to the long axis of the cigar-shaped
atom cloud. The precessional motion of the vortex is directly observed, and its
period is measured as a function of the chemical potential in the BEC-BCS
crossover. The long period and the correspondingly large ratio of the inertial
to the bare mass of the vortex are in good agreement with estimates based on
superfluid hydrodynamics that we derive here using the known equation of state
in the BEC-BCS crossover
Cascade of Solitonic Excitations in a Superfluid Fermi gas: From Planar Solitons to Vortex Rings and Lines
We follow the time evolution of a superfluid Fermi gas of resonantly interacting [superscript 6]Li atoms after a phase imprint. Via tomographic imaging, we observe the formation of a planar dark soliton, its subsequent snaking, and its decay into a vortex ring, which, in turn, breaks to finally leave behind a single solitonic vortex. In intermediate stages, we find evidence for an exotic structure resembling the Φ soliton, a combination of a vortex ring and a vortex line. Direct imaging of the nodal surface reveals its undulation dynamics and its decay via the puncture of the initial soliton plane. The observed evolution of the nodal surface represents dynamics beyond superfluid hydrodynamics, calling for a microscopic description of unitary fermionic superfluids out of equilibrium.National Science Foundation (U.S.)United States. Army Research Office. Multidisciplinary University Research Initiative on AtomtronicsUnited States. Air Force Office of Scientific Research. Presidential Early Career Award for Scientists and EngineersUnited States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative on Exotic PhasesDavid & Lucile Packard Foundatio
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