Probing the Roton Excitation Spectrum of a Stable Dipolar Bose Gas

Petter, D.; Natale, G.; Bijnen, Rick van; Patscheider, A.; Mark, Manfred J.; Chomaz, Lauriane; Ferlaino, Francesca

doi:10.1103/physrevlett.122.183401

Cited by 135 publications

(118 citation statements)

References 59 publications

(128 reference statements)

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“…Figure 1 shows the calculated excitation spectrum for ground-states in the regular BEC, the supersolid, and the ID phases for a Dy (upper row) and Er (lower row) quantum gas. In the BEC regime close to the supersolid transition (a, b), the spectrum of excitations shows a single excitation branch with the characteristic phonon-maxonroton dispersion of a BEC [42][43][44][45][46], as recently measured [47]. When the roton fully softens (at a s = a * s ), the ground-state becomes density modulated with a wave number close to the roton one, k rot .…”

supporting

confidence: 59%

Excitation Spectrum of a Trapped Dipolar Supersolid and Its Experimental Evidence

et al. 2019

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We study the spectrum of elementary excitations of a dipolar Bose gas in a three-dimensional anisotropic trap across the superfluid-supersolid phase transition. Theoretically, we show that, when entering the supersolid phase, two distinct excitation branches appear, respectively associated with dominantly crystal and superfluid excitations. These results confirm infinite-system predictions, showing that finite-size effects play only a small qualitative role, and connect the two branches to the simultaneous occurrence of crystal and superfluid orders. Experimentally, we probe compressional excitations in an Er quantum gas across the phase diagram. While in the Bose-Einstein condensate regime the system exhibits an ordinary quadrupole oscillation, in the supersolid regime, we observe a striking two-frequency response of the system, related to the two spontaneously broken symmetries. arXiv:1907.01986v2 [cond-mat.quant-gas]

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confidence: 59%

Excitation Spectrum of a Trapped Dipolar Supersolid and Its Experimental Evidence

et al. 2019

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“…and β ijk represents the integrals defined in Eq. (17). The dipolar contribution to M is obtained by taking the second partial derivative of the expression on the RHS of Eq.…”

Section: Linearization Of the Thomas-fermi Stationary Solutionsmentioning

confidence: 99%

“…More recently the production of dysprosium and erbium BECs, which feature considerably stronger dipolar interactions than Cr BECs, has led to the discovery of an increasingly diverse range of exotic phenomena [10,11]. Examples of these include self-bound dipolar droplets [12][13][14][15] and the experimental confirmation of the presence of roton modes [16,17] and the supersolid phase [18][19][20]. Many of these have been found to be explicitly dependent on the role of beyond-mean-field quantum fluctuations in stabilizing a strongly dipolar BEC [21,22].…”

Section: Introductionmentioning

confidence: 99%

Vortex lattice formation in dipolar Bose-Einstein condensates via rotation of the polarization

et al. 2019

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The behaviour of a harmonically trapped dipolar Bose-Einstein condensate with its dipole moments rotating at angular frequencies lower than the transverse harmonic trapping frequency is explored in the co-rotating frame. We obtain semi-analytical solutions for the stationary states in the Thomas-Fermi limit of the corresponding dipolar Gross-Pitaevskii equation and utilise linear stability analysis to elucidate a phase diagram for the dynamical stability of these stationary solutions with respect to collective modes. These results are verified via direct numerical simulations of the dipolar Gross-Pitaevskii equation, which demonstrate that dynamical instabilities of the corotating stationary solutions lead to the seeding of vortices that eventually relax into a triangular lattice configuration. Our results illustrate that rotation of the dipole polarization represents a new route to vortex formation in dipolar Bose-Einstein condensates. arXiv:1906.08664v2 [cond-mat.quant-gas]

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“…As the oscillation period of the out-of-phase mode is much longer than the droplet lifetime, which is limited by three-body losses 8 , it is currently not feasible to use a standard spectroscopic method 23,29 to detect the Goldstone mode. However, the low excitation energy of the out-of-phase Goldstone mode leads to its excitation within the energy bandwidth of the dynamical formation process.…”

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The low-energy Goldstone mode in a trapped dipolar supersolid

Guo¹,

Böttcher²,

Hertkorn³

et al. 2019

Nature

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A supersolid is a counter-intuitive state of matter that combines the frictionless flow of a superfluid with the crystal-like periodic density modulation of a solid 1, 2 . Since the first prediction in the 1950s 3 , experimental efforts to realize this state have focussed mainly on Helium, where supersolidity remains elusive 4 . Recently, supersolidity has also been studied intensively in ultracold quantum gases, and some of its defining properties have been induced in spin-orbit coupled Bose-Einstein condensates (BECs) 5 and BECs coupled to two crossed optical cavities 6, 7 . However, the periodicity of the crystals in both systems is fixed to the wavelength of the applied periodic optical potentials. Recently, hallmark properties of a supersolid -the periodic density modulation and simultaneous global phase coherence -have been observed in arrays of dipolar quantum droplets 8-10 , where the crystallization happens in a self-organized manner due to intrinsic interactions. In this letter, we prove the genuine supersolid nature of these droplet arrays by directly observing the low-energy Goldstone mode. The dynamics of this mode is reminiscent of the effect of second sound in other superfluid systems 11,12 and features an out-ofphase oscillation of the crystal array and the superfluid density. This mode exists only due to the phase rigidity of the experimentally realized state, and therefore confirms the genuine superfluidity of the supersolid. arXiv:1906.04633v1 [cond-mat.quant-gas]

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Probing the Roton Excitation Spectrum of a Stable Dipolar Bose Gas

Cited by 135 publications

References 59 publications

Excitation Spectrum of a Trapped Dipolar Supersolid and Its Experimental Evidence

Excitation Spectrum of a Trapped Dipolar Supersolid and Its Experimental Evidence

Vortex lattice formation in dipolar Bose-Einstein condensates via rotation of the polarization

The low-energy Goldstone mode in a trapped dipolar supersolid

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