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

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.

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

Science ◽

10.1126/science.aaw4465 ◽

2019 ◽

Vol 366 (6472) ◽

pp. 1496-1499 ◽

Cited By ~ 13

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.

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

Science ◽

10.1126/science.abe9869 ◽

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.

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

Archive for Rational Mechanics and Analysis ◽

10.1007/s00205-021-01616-9 ◽

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.

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

Physical Review A ◽

10.1103/physreva.72.063604 ◽

2005 ◽

Vol 72 (6) ◽

Cited By ~ 44

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

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Effects of three-body atomic interaction and optical lattice on solitons in quasi-one-dimensional Bose-Einstein condensate

Pramana ◽

10.1007/s12043-009-0039-2 ◽

2009 ◽

Vol 72 (2) ◽

pp. 445-450

Author(s):

Sk. Golam Ali ◽

B. Talukdar ◽

Aparna Saha

Keyword(s):

Optical Lattice ◽

Einstein Condensate ◽

Atomic Interaction ◽

One Dimensional ◽

Bose Einstein Condensate ◽

Three Body ◽

Bose Einstein

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Phase separation in spin-orbit-angular-momentum coupling Bose–Einstein condensate systems

Modern Physics Letters B ◽

10.1142/s0217984920502413 ◽

2020 ◽

Vol 34 (23) ◽

pp. 2050241

Author(s):

Jin Xu ◽

Jinbin Li

Keyword(s):

Angular Momentum ◽

Phase Separation ◽

Coupling Strength ◽

Interaction Strength ◽

Einstein Condensate ◽

Three Dimensions ◽

Pitaevskii Equation ◽

Spin Orbit ◽

Bose Einstein Condensate ◽

Bose Einstein

We study the phase separation in three-component spin-orbit-angular-momentum coupled Bose–Einstein condensate with spin-1 in three dimensions. Different types of phase-separation are acquired upon an increase of the coupling strength, magnetic gradient strength, spin-dependent interaction strength and particle number above a critical value. Increasing the value of coupling strength and other related parameters shows distinct behaviors which are produced by repulsion for large strengths of spin-orbit angular-momentum (SOAM) coupling. The present investigation is carried out through a numerical Crank–Nicolson method of the underlying mean-field Gross–Pitaevskii equation.

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Entropy Production Within a Pulsed Bose–Einstein Condensate

Zeitschrift für Naturforschung A ◽

10.1515/zna-2016-0073 ◽

2016 ◽

Vol 71 (10) ◽

pp. 875-881 ◽

Cited By ~ 1

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.

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