scholarly journals Dissipation-induced structural instability and chiral dynamics in a quantum gas

Science ◽  
2019 ◽  
Vol 366 (6472) ◽  
pp. 1496-1499 ◽  
Author(s):  
Nishant Dogra ◽  
Manuele Landini ◽  
Katrin Kroeger ◽  
Lorenz Hruby ◽  
Tobias Donner ◽  
...  
Keyword(s):  
Structural Instability ◽  
Einstein Condensate ◽  
Quantum Gas ◽  
Body System ◽  
Many Body ◽  
Dynamical Phase ◽  
Dispersive Effect ◽  
Bose Einstein Condensate ◽  
Nonstationary State ◽  
Bose Einstein

Dissipative and unitary processes define the evolution of a many-body system. Their interplay gives rise to dynamical phase transitions and can lead to instabilities. In this study, we observe a nonstationary state of chiral nature in a synthetic many-body system with independently controllable unitary and dissipative couplings. Our experiment is based on a spinor Bose gas interacting with an optical resonator. Orthogonal quadratures of the resonator field coherently couple the Bose-Einstein condensate to two different atomic spatial modes, whereas the dispersive effect of the resonator losses mediates a dissipative coupling between these modes. In a regime of dominant dissipative coupling, we observe the chiral evolution and relate it to a positional instability.

scholarly journals Polaron Problems in Ultracold Atoms: Role of a Fermi Sea across Different Spatial Dimensions and Quantum Fluctuations of a Bose Medium

Atoms ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 18
Author(s):  
Hiroyuki Tajima ◽  
Junichi Takahashi ◽  
Simeon Mistakidis ◽  
Eiji Nakano ◽  
Kei Iida
Keyword(s):  
Spectral Function ◽  
Einstein Condensate ◽  
Three Dimensions ◽  
Quantum Gas ◽  
Many Body ◽  
Bose Einstein Condensate ◽  
Spatial Dimensions ◽  
Three Body ◽  
Bose Einstein ◽  
The Impact

The notion of a polaron, originally introduced in the context of electrons in ionic lattices, helps us to understand how a quantum impurity behaves when being immersed in and interacting with a many-body background. We discuss the impact of the impurities on the medium particles by considering feedback effects from polarons that can be realized in ultracold quantum gas experiments. In particular, we exemplify the modifications of the medium in the presence of either Fermi or Bose polarons. Regarding Fermi polarons we present a corresponding many-body diagrammatic approach operating at finite temperatures and discuss how mediated two- and three-body interactions are implemented within this framework. Utilizing this approach, we analyze the behavior of the spectral function of Fermi polarons at finite temperature by varying impurity-medium interactions as well as spatial dimensions from three to one. Interestingly, we reveal that the spectral function of the medium atoms could be a useful quantity for analyzing the transition/crossover from attractive polarons to molecules in three-dimensions. As for the Bose polaron, we showcase the depletion of the background Bose-Einstein condensate in the vicinity of the impurity atom. Such spatial modulations would be important for future investigations regarding the quantification of interpolaron correlations in Bose polaron problems.

scholarly journals Observation of a non-Hermitian phase transition in an optical quantum gas

Science ◽  
2021 ◽  
Vol 372 (6537) ◽  
pp. 88-91
Author(s):  
Fahri Emre Öztürk ◽  
Tim Lappe ◽  
Göran Hellmann ◽  
Julian Schmitt ◽  
Jan Klaers ◽  
...  
Keyword(s):  
Phase Transition ◽  
Einstein Condensate ◽  
Quantum Gases ◽  
Exceptional Point ◽  
Einstein Condensation ◽  
Quantum Gas ◽  
Many Body ◽  
Lattice Systems ◽  
Bose Einstein Condensate ◽  
Bose Einstein

Quantum gases of light, such as photon or polariton condensates in optical microcavities, are collective quantum systems enabling a tailoring of dissipation from, for example, cavity loss. This characteristic makes them a tool to study dissipative phases, an emerging subject in quantum many-body physics. We experimentally demonstrate a non-Hermitian phase transition of a photon Bose-Einstein condensate to a dissipative phase characterized by a biexponential decay of the condensate’s second-order coherence. The phase transition occurs because of the emergence of an exceptional point in the quantum gas. Although Bose-Einstein condensation is usually connected to lasing by a smooth crossover, the observed phase transition separates the biexponential phase from both lasing and an intermediate, oscillatory condensate regime. Our approach can be used to study a wide class of dissipative quantum phases in topological or lattice systems.

scholarly journals Derivation of the Landau–Pekar Equations in a Many-Body Mean-Field Limit

2021 ◽  
Vol 240 (1) ◽  
pp. 383-417
Author(s):  
Nikolai Leopold ◽  
David Mitrouskas ◽  
Robert Seiringer
Keyword(s):  
Mean Field ◽  
Einstein Condensate ◽  
Back Reaction ◽  
Many Body ◽  
Field Limit ◽  
Mean Field Limit ◽  
Phonon Field ◽  
Bose Einstein Condensate ◽  
Weakly Couple ◽  
Bose Einstein

AbstractWe consider the Fröhlich Hamiltonian in a mean-field limit where many bosonic particles weakly couple to the quantized phonon field. For large particle numbers and a suitably small coupling, we show that the dynamics of the system is approximately described by the Landau–Pekar equations. These describe a Bose–Einstein condensate interacting with a classical polarization field, whose dynamics is effected by the condensate, i.e., the back-reaction of the phonons that are created by the particles during the time evolution is of leading order.

scholarly journals Nonperturbative dynamical many-body theory of a Bose-Einstein condensate

2005 ◽  
Vol 72 (6) ◽  
Author(s):  
Thomas Gasenzer ◽  
Jürgen Berges ◽  
Michael G. Schmidt ◽  
Marcos Seco
Keyword(s):  
Einstein Condensate ◽  
Many Body ◽  
Many Body Theory ◽  
Bose Einstein Condensate ◽  
Bose Einstein ◽  
Body Theory

scholarly journals Entropy Production Within a Pulsed Bose–Einstein Condensate

2016 ◽  
Vol 71 (10) ◽  
pp. 875-881 ◽  
Author(s):  
Christoph Heinisch ◽  
Martin Holthaus
Keyword(s):  
Einstein Condensate ◽  
Many Body ◽  
Initial State ◽  
Site Model ◽  
Bose Einstein Condensate ◽  
Body Dynamics ◽  
Adiabatic Motion ◽  
The Many ◽  
Bose Einstein ◽  
Loss Of Coherence

AbstractWe suggest to subject anharmonically trapped Bose–Einstein condensates to sinusoidal forcing with a smooth, slowly changing envelope, and to measure the coherence of the system after such pulses. In a series of measurements with successively increased maximum forcing strength, one then expects an adiabatic return of the condensate to its initial state as long as the pulses remain sufficiently weak. In contrast, once the maximum driving amplitude exceeds a certain critical value there should be a drastic loss of coherence, reflecting significant heating induced by the pulse. This predicted experimental signature is traced to the loss of an effective adiabatic invariant, and to the ensuing breakdown of adiabatic motion of the system’s Floquet state when the many-body dynamics become chaotic. Our scenario is illustrated with the help of a two-site model of a forced bosonic Josephson junction, but should also hold for other, experimentally accessible configurations.

scholarly journals Many-body dissipative flow of a confined scalar Bose-Einstein condensate driven by a Gaussian impurity

2018 ◽  
Vol 98 (1) ◽  
Author(s):  
G. C. Katsimiga ◽  
S. I. Mistakidis ◽  
G. M. Koutentakis ◽  
P. G. Kevrekidis ◽  
P. Schmelcher
Keyword(s):  
Einstein Condensate ◽  
Many Body ◽  
Dissipative Flow ◽  
Bose Einstein Condensate ◽  
Bose Einstein

scholarly journals Anharmonicity-induced criticality of collective excitation in a trapped Bose–Einstein condensate

2018 ◽  
Vol 32 (31) ◽  
pp. 1850345
Author(s):  
Qun Wang ◽  
Bo Xiong
Keyword(s):  
Collective Mode ◽  
Collective Excitation ◽  
Einstein Condensate ◽  
Low Energy ◽  
Many Body ◽  
Bose Einstein Condensate ◽  
Large Numbers ◽  
Many Body Systems ◽  
Repulsive Forces ◽  
Bose Einstein

We investigate the low-energy excitations of a dilute atomic Bose gas confined in a anharmonic trap interacting with repulsive forces. The dispersion law of both surface and compression modes is derived and analyzed for large numbers of atoms in the trap, which show two branches of excitation and appear two critical values, where one of them indicates collective excitation which would be unstable dynamically, and the other one indicates the existing collective mode with lower frequency under anharmonic influence than that in harmonic trapping case. Our work reveals the key role played by the anharmonicity and interatomic forces which introduce a rich structure in the dynamic behavior of these new many-body systems.

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