<i>Colloquium</i>: Bulk Bogoliubov excitations in a Bose-Einstein condensate

Ozeri, Roee; Katz, Nadav; Steinhauer, Jeff; Davidson, Nir

doi:10.1103/revmodphys.77.187

Cited by 196 publications

(223 citation statements)

References 62 publications

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“…This spectrum should not only show a phononlike behavior 9,10 but also the appearance of a negative energy dispersion, often called "ghost branch," resulting from the prevalence of parametric processes in the excitation of the quantum fluid. 11 Such a negative energy resonance has been first observed by Vogels et al with condensates of sodium atoms in a magnetic trap. 12 Recently, the Bogoliubov dispersion has been investigated in the solid state in a coherent polariton gas, 13 and the ghost dispersion branch has finally been observed.…”

Section: Introductionmentioning

confidence: 87%

Four-wave mixing excitations in a dissipative polariton quantum fluid

et al. 2012

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The Bogoliubov transformation of a polariton quantum fluid has recently been revealed in the four-wave mixing response of a driven microcavity polariton gas. In this work, we investigate the modifications that the dual nature of microcavity polaritons produce on the excitations of this particular half-light-half-matter quantum fluid. We discuss in particular the Bogoliubov character of the excitations of a lower polariton superfluid when it coexists with upper polaritons. We show unique effects resulting from the interplay between polariton decay and Bogoliubov transformation such as the modification of the Bogoliubov dispersion or the slowing down of the four-wave mixing dynamics.

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Section: Introductionmentioning

confidence: 87%

Four-wave mixing excitations in a dissipative polariton quantum fluid

et al. 2012

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“…In a companion paper [10], we show that the frequencies of these hydrodynamic modes can be measured using two-photon Bragg spectroscopy, a standard tool used to study excitations in trapped, ultracold quantum gases [11].…”

Section: Discussionmentioning

confidence: 99%

“…In a companion paper [10], we show how these twofluid modes can be measured using standard two-photon Bragg scattering techniques [11]. Extending the variational method described in this paper, we show the density response function has resonances at the breathing and dipole mode frequencies.…”

Section: Introductionmentioning

confidence: 99%

Variational theory of two-fluid hydrodynamic modes at unitarity

Taylor

Liu

et al. 2008

Phys. Rev. A

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We present the results of a variational calculation of the frequencies of the low-lying Landau two-fluid hydrodynamic modes in a trapped Fermi superfluid gas at unitarity. Landau's two-fluid hydrodynamics is expected to be the correct theory of Fermi superfluids at finite temperatures close to unitarity, where strong interactions give rise to collisional hydrodynamics. Two-fluid hydrodynamics predicts the existence of in-phase modes in which the superfluid and normal fluid components oscillate together, as well as out-of-phase modes where the two components move against each other. We prove that at unitarity, the dipole and breathing in-phase modes are locally isentropic. Their frequencies are independent of temperature and are the same above and below the superfluid transition. The out-of-phase modes, in contrast, are strongly dependent on temperature and hence, can be used to test the thermodynamic properties and superfluid density of a Fermi gas at unitarity. We give numerical results for the frequencies of these new modes as function of temperature in an isotropic trap at unitarity.

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“…Kk, 03.75.Mn, 32.80.Qk, 71.70.Ej Since the achievement of Bose-Einstein condensation (BEC) in dilute atomic gases, the investigation of collective excitations has been a key tool to gain insight into this unusual state of matter [1]. For most atomic species used in BEC experiments the interactions between the ultracold atoms can be described by isotropic, short-range s-wave scattering, which leads to the well-known linear phonon excitation spectrum at low momentum.…”

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confidence: 99%

Measurement of collective excitations in a spin-orbit-coupled Bose-Einstein condensate

et al. 2014

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We measure the collective excitation spectrum of a spin-orbit coupled Bose-Einstein condensate using Bragg spectroscopy. The spin-orbit coupling is generated by Raman dressing of atomic hyperfine states. When the Raman detuning is reduced, mode softening at a finite momentum is revealed, which provides insight towards a supersolid-like phase transition. We find that for the parameters of our system, this softening stops at a finite excitation gap and is symmetric under a sign change of the Raman detuning. Finally, using a moving barrier that is swept through the BEC, we also show the effect of the collective excitation on the fluid dynamics.PACS numbers: 03.75. Kk, 03.75.Mn, 32.80.Qk, 71.70.Ej Since the achievement of Bose-Einstein condensation (BEC) in dilute atomic gases, the investigation of collective excitations has been a key tool to gain insight into this unusual state of matter [1]. For most atomic species used in BEC experiments the interactions between the ultracold atoms can be described by isotropic, short-range s-wave scattering, which leads to the well-known linear phonon excitation spectrum at low momentum. However, if long-range interactions, such as dipolar interactions, are present, the collective excitation spectrum of a BEC can exhibit a more complex structure: in addition to the typical low energy phonon spectrum, a roton-like structure can appear. It is characterised by a shoulder in the spectrum, which for certain parameters can turn into a parabolic minimum at a finite momentum [2][3][4][5].Interestingly, a similar parabolic minimum at a finite momentum can also exist in spin-orbit coupled (SOC) systems. In cold atomic gases, spin-orbit coupling can be implemented by Raman dressing of two or more atomic hyperfine states, which play the role of different (pseudo-)spins. The Raman lasers are arranged in such a way that a Raman transition between the states is accompanied by a change of momentum [6][7][8][9][10][11]. Since the Raman coupling strength and the detuning from the Raman resonance can be independently adjusted in an experiment, this provides a very flexible platform to engineer interesting dispersion relations and test spin-orbit coupled physics (for a review, see, e.g., [12][13][14][15]). In the single-particle picture, the effect of the Raman dressing is to displace two copies of the parabolic dispersion originating from the kinetic energy of the particle in opposite directions in momentum space. The Raman coupling opens a gap at the crossing of these two parabolas so that the resulting single-particle dispersion has the form of a double well in momentum space. The double well can be biased towards either minimum by changing the Raman detuning. When the Raman detuning or the Raman coupling exceed a critical value, one of the minima disappears and a single well dispersion results. * engels@wsu.eduIn the presence of nonlinear effects stemming from the s-wave scattering between the atoms in a Raman dressed BEC, the double well structure continues to exist. In a biased double wel...

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Colloquium: Bulk Bogoliubov excitations in a Bose-Einstein condensate

Cited by 196 publications

References 62 publications

Four-wave mixing excitations in a dissipative polariton quantum fluid

Four-wave mixing excitations in a dissipative polariton quantum fluid

Variational theory of two-fluid hydrodynamic modes at unitarity

Measurement of collective excitations in a spin-orbit-coupled Bose-Einstein condensate

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