Symmetry-broken momentum distributions induced by matter-wave diffraction during time-of-flight expansion of ultracold atoms

Weinberg, Malte; Jürgensen, Ole; Ölschläger, C.; Lühmann, Dirk-Sören; Sengstock, K.; Simonet, Juliette

doi:10.1103/physreva.93.033625

Cited by 7 publications

(6 citation statements)

References 29 publications

(49 reference statements)

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“…Moreover, in a recent experiment with the same system as in Ref. [17], the diffraction was modified by eliminating one spin population from the lattice just before the atoms were released [21]. The consequent elimination of the asymmetry signal is consistent with our suggested explanation.…”

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confidence: 84%

Signatures of spatial inversion asymmetry of an optical lattice observed in matter-wave diffraction

et al. 2016

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The structure of a two-dimensional honeycomb optical lattice potential with small inversion asymmetry is characterized using coherent diffraction of 87 Rb atoms. We demonstrate that even a small potential asymmetry, with peak-to-peak amplitude of ≤ 2.3% of the overall lattice potential, can lead to pronounced inversion asymmetry in the momentum-space diffraction pattern. The observed asymmetry is explained quantitatively by considering both Kapitza-Dirac scattering in the RamanNath regime, and also either perturbative or full-numerical treatment of the band structure of a periodic potential with a weak inversion-symmetry-breaking term. Our results have relevance for both the experimental development of coherent atom optics and the proper interpretation of timeof-flight assays of atomic materials in optical lattices. DOI: 10.1103/PhysRevA.93.063613 In x-ray crystallography, the diffraction of light is analyzed to determine the exact crystalline structure of a material. Similarly, with the availability of ultracold sources of coherent matter waves of atoms, one can use atomic diffraction to characterize potentials experienced by the atoms. Of particular interest are the optical lattice potentials produced by periodic patterns of light intensity and polarization, formed by the intersection of several coherent plane waves of light or by direct imaging. Lattice potentials of various geometries and dimensionalities, some incorporating atomic-spin dependence and gauge fields, have been produced or proposed for the purpose of creating synthetic atomic materials by placing quantum-degenerate atoms within them [1][2][3]. Just as in condensed matter, the characteristics of such synthetic atomic materials derive from the nature of the optical crystal upon which they are based. Matter-wave crystallography therefore becomes a vital tool in the study of such synthetic quantum matter [4].A key first step in determining the structure of a lattice is the assignment of its point-group and space-group symmetries. The violation of a symmetry is identified in x-ray crystallography by a difference in the intensities of diffraction spots [5]. Following such work, here we detect the inversion asymmetry of an optical lattice by observing significant asymmetries in the diffraction of a coherent matter wave from the potential. For this, we produce a spin-polarized 87 Rb Bose-Einstein condensate at rest, and then impose for a variable pulse duration the two-dimensional honeycomb optical lattice potential produced by three light beams intersecting at equal angles [6]. The resulting Kapitza-Dirac diffraction is quantified by imaging the gas after it is allowed to expand freely. By tuning the pulse time and working with a deep optical lattice, we produce highly visible (over 50% contrast) * Electronic address: dmsk@berkeley.edu inversion asymmetry in the populations of the first-order diffraction peaks even while the inversion-asymmetric part of the potential is ≤ 2.3% of the overall lattice potential. This observation highlights the extre...

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confidence: 84%

Signatures of spatial inversion asymmetry of an optical lattice observed in matter-wave diffraction

et al. 2016

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“…This requires a negligible influence of collisions on the time evolution. We achieve this by releasing the gas from the vertical confinement [47,48] as well as flashing on a light pulse propagating along the z-direction which rapidly ejects atoms in state | ↑ [26,28,49,50]. This projects the wave function of atoms in state | ↓ onto free particle states and allows us to extract the occupation f (k) of the interacting system using the matter wave focusing technique described above.…”

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confidence: 99%

Two-Dimensional Homogeneous Fermi Gases

et al. 2018

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We report on the experimental realization of homogeneous two-dimensional (2D) Fermi gases trapped in a box potential. In contrast to harmonically trapped gases, these homogeneous 2D systems are ideally suited to probe local as well as nonlocal properties of strongly interacting many-body systems. As a first benchmark experiment, we use a local probe to measure the density of a noninteracting 2D Fermi gas as a function of the chemical potential and find excellent agreement with the corresponding equation of state. We then perform matter wave focusing to extract the momentum distribution of the system and directly observe Pauli blocking in a near unity occupation of momentum states. Finally, we measure the momentum distribution of an interacting homogeneous 2D gas in the crossover between attractively interacting fermions and bosonic dimers.

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“…It is interesting to note although Gross-Pitaevskii equation has an intrinsic mean-field nature, the quantities analysed to investigate localisation phenomena, namely the density distribution across the lattice and the ground state spectra, indeed exhibit signatures associated to the lattice geometry. Additionally, the information displayed in the ground state spectra in the reciprocal space can be compared with direct experimental measurements in ultracold systems via time of flight measurements 89 . Further investigations of transport phenomena can be addressed with the approach followed in the present work.…”

Section: Model: Weakly Interacting Ultracold Atoms In 2d Disordered Lmentioning

confidence: 99%

“…Due to the intrinsic mean-field nature of the Gross-Pitaevskii equation, the quantities that characterize the localization phenomena, namely the average localization length and the energy spectrum, do not capture strong finite size effects. However, the information displayed in the energy spectra in the reciprocal space can be compared with direct experimental measurements in ultracold systems 41 . Further investigations of transport phenomena can be addressed with the approach followed in the present work.…”

Section: Summary Of Findings and Outlookmentioning

confidence: 99%

Localisation of weakly interacting bosons in two dimensions: disorder vs lattice geometry effects

González-García¹,

Caballero-Benítez²,

Paredes

2019

Sci Rep

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We investigate the effects of disorder and lattice geometry against localisation phenomena in a weakly interacting ultracold bosonic gas confined in a 2D optical lattice. The behaviour of the quantum fluid is studied at the mean-field level performing computational experiments, as a function of disorder strength for lattices of sizes similar to current experiments. Quantification of localisation, away from the Bose glass phase, was obtained directly from the stationary density profiles through a robust statistical analysis of the condensate component, as a function of the disorder amplitude. Our results show a smooth transition, or crossover, to localisation induced by disorder in square and triangular lattices. In contrast, associated to its larger tunneling amplitude, honeycomb lattices show absence of localisation for the same range of disorder strengths and same lattice amplitude, while also exhibiting partial localisation for large disorder amplitudes. We also conclude that the coordination number z have a partial influence on how fast this smooth transition occurs as the system size increases. Signatures of disorder are also found in the ground state energy spectrum, where a continuous distribution emerges instead of a distribution of sharp peaks proper to the system in the absence of disorder.

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Symmetry-broken momentum distributions induced by matter-wave diffraction during time-of-flight expansion of ultracold atoms

Cited by 7 publications

References 29 publications

Signatures of spatial inversion asymmetry of an optical lattice observed in matter-wave diffraction

Signatures of spatial inversion asymmetry of an optical lattice observed in matter-wave diffraction

Two-Dimensional Homogeneous Fermi Gases

Localisation of weakly interacting bosons in two dimensions: disorder vs lattice geometry effects

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