Properties of Bose gases with the Raman-induced spin–orbit coupling

Zheng, W. J.; Cui, Xiaoling; Zhai, Hui

doi:10.1088/0953-4075/46/13/134007

Cited by 107 publications

(180 citation statements)

References 26 publications

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“…With the use of a physically straightforward variational method, ground states are demonstrated to include plane wave, stripe, and conventional BEC phases [41,43]. The full phase diagram can be labeled by various parameters, such as δ, Ω, and the nonlinear coefficients g [41,43,115]. Once the ground states are known, their collective excitations can be analyzed using the standard Bogoliubov-deGennes (BdG) equations.…”

Section: Bragg Spectroscopy Indicating Roton-like Excitationmentioning

confidence: 99%

“…Once the ground states are known, their collective excitations can be analyzed using the standard Bogoliubov-deGennes (BdG) equations. It has been shown that the excitation spectrum of a plane wave phase features a rotonlike structure [23,[115][116][117]. The stripe phase, which is a superfluid phase with a broken continuous translational symmetry due to density crystallinity, exhibits an excitation spectrum comprised of two linear phonon modes [47].…”

Section: Bragg Spectroscopy Indicating Roton-like Excitationmentioning

confidence: 99%

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Properties of spin–orbit-coupled Bose–Einstein condensates

et al. 2016

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The experimental and theoretical research of spin-orbit-coupled ultracold atomic gases has advanced and expanded rapidly in recent years. Here, we review some of the progress that either was pioneered by our own work, has helped to lay the foundation, or has developed new and relevant techniques. After examining the experimental accessibility of all relevant spin-orbit coupling parameters, we discuss the fundamental properties and general applications of spin-orbit-coupled Bose-Einstein condensates (BECs) over a wide range of physical situations. For the harmonically trapped case, we show that the ground state phase transition is a Dicke-type process and that spin-orbit-coupled BECs provide a unique platform to simulate and study the Dicke model and Dicke phase transitions. For a homogeneous BEC, we discuss the collective excitations, which have been observed experimentally using Bragg spectroscopy. They feature a roton-like minimum, the softening of which provides a potential mechanism to understand the ground state phase transition. On the other hand, if the collective dynamics are excited by a sudden quenching of the spin-orbit coupling parameters, we show that the resulting collective dynamics can be related to the famous Zitterbewegung in the relativistic realm. Finally, we discuss the case of a BEC loaded into a periodic optical potential. Here, the spin-orbit coupling generates isolated flat bands within the lowest Bloch bands whereas the nonlinearity of the system leads to dynamical instabilities of these Bloch waves. The experimental verification of this instability illustrates the lack of Galilean invariance in the system.

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Section: Bragg Spectroscopy Indicating Roton-like Excitationmentioning

confidence: 99%

Section: Bragg Spectroscopy Indicating Roton-like Excitationmentioning

confidence: 99%

Properties of spin–orbit-coupled Bose–Einstein condensates

et al. 2016

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“…Previous theoretical studies have described roton-like excitations of SOC BECs for the case of vanishing Raman detuning [17,18]. In our experiment, we measure mode softening when, starting from a finite value, the Raman detuning is decreased.…”

mentioning

confidence: 92%

“…Compared to the single-particle spectrum, the second minimum is modified due to the interaction energy, and for small excitation momenta the collective excitation spectrum becomes linear (phonon modes). The resulting dispersion is reminiscent of the phonon-maxon-roton like structure [16][17][18] Moreover, the presence of the nonlinearity leads to several phenomena within the collective excitation spectrum which are absent in the single-particle dispersion. One of the most fundamental of these is the softening of the roton-like modes when the spin-orbit coupling parameters are changed appropriately.…”

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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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“…The phase transition between the plane-wave and the striped phases has a first-order nature. It is charac- * Giovanni.Martone@ba.infn.it terized by the occurrence, on the side of the plane-wave phase, of a roton minimum in the excitation spectrum, whose energy becomes smaller and smaller as one approaches the transition [12][13][14]32]. The presence of the striped phase is one of the most interesting features exhibited by spin-orbit-coupled BECs, due to its direct link to the long sought phenomenon of supersolidity [33], which takes place when two continuous symmetries (gauge and translational invariance) are spontaneously broken.…”

Section: Introductionmentioning

confidence: 99%

Optical-lattice-assisted magnetic phase transition in a spin-orbit-coupled Bose-Einstein condensate

Martone

Ozawa

et al. 2016

Phys. Rev. A

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We investigate the effect of a periodic potential generated by a one-dimensional optical lattice on the magnetic properties of an S = 1/2 spin-orbit-coupled Bose gas. By increasing the lattice strength one can achieve a magnetic phase transition between a polarized and an unpolarized Bloch wave phase, characterized by a significant enhancement of the contrast of the density fringes. If the wave vector of the periodic potential is chosen close to the roton momentum, the transition could take place at very small lattice intensities, revealing the strong enhancement of the response of the system to a weak density perturbation. By solving the Gross-Pitaevskii equation in the presence of a three-dimensional trapping potential, we shed light on the possibility of observing the magnetic phase transition in currently available experimental conditions.

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Properties of Bose gases with the Raman-induced spin–orbit coupling

Cited by 107 publications

References 26 publications

Properties of spin–orbit-coupled Bose–Einstein condensates

Properties of spin–orbit-coupled Bose–Einstein condensates

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

Optical-lattice-assisted magnetic phase transition in a spin-orbit-coupled Bose-Einstein condensate

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