Local atom-number fluctuations in quantum gases at finite temperature

Klawunn, M.; Recati, Alessio; Pitaevskiĭ, Lev P.; Stringari, S.

doi:10.1103/physreva.84.033612

Cited by 54 publications

(109 citation statements)

References 22 publications

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“…Therefore, the quantum contribution becomes negligible as ∆ → ∞, and the thermodynamic prediction of Eq. (1) is recovered [25]. For our parameters, the contribution of Eq.…”

Section: Nearly Ideal Bose Gasmentioning

confidence: 99%

“…Although the two-body correlation function g (2) is dominated by quantum fluctuations in this regime, we have shown that the variance δN 2 is still dominated by thermal excitations. To resolve quantum fluctuations one would need to access wavelengths smaller than the phonon thermal wavelengthh 2 /mk B T l ξ [25], which is in the submicron range for our parameters. Our work opens up further opportunities in the study of 1D Bose gases, such as better understanding of the mechanisms of thermalisation and the role of three-body correlations.…”

Section: Nearly Ideal Bose Gasmentioning

confidence: 99%

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Sub-Poissonian Fluctuations in a 1D Bose Gas: From the Quantum Quasicondensate to the Strongly Interacting Regime

et al. 2011

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We report on local, in situ measurements of atom number fluctuations in slices of a onedimensional Bose gas on an atom chip setup. By using current modulation techniques to prevent cloud fragmentation, we are able to probe the crossover from weak to strong interactions. For weak interactions, fluctuations go continuously from super-to sub-Poissonian as the density is increased, which is a signature of the transition between the sub-regimes where the two-body correlation function is dominated respectively by thermal and quantum contributions. At stronger interactions, the super-Poissonian region disappears, and the fluctuations go directly from Poissonian to subPoissonian, as expected for a 'fermionized' gas.PACS numbers: 03.75. Hh, 67.10.Ba Fluctuations witness the interplay between quantum statistics and interactions and therefore their measurement constitutes an important probe of quantum manybody systems. In particular, measurement of atom number fluctuations in ultracold quantum gases has been a key tool in the study of the Mott insulating phase in optical lattices [1], isothermal compressibility of Bose and Fermi gases [2][3][4][5], magnetic susceptibility of a strongly interacting Fermi gas [6], scale invariance of a twodimensional Bose gas [7], generation of atomic entanglement in double-wells [8], and relative number squeezing in pair-production via binary collisions [9,10].While a simple account of quantum statistics can change the atom number distribution, in a small volume of an ideal gas, from a classical-gas Poissonian to superPoissonian (for bosons) or sub-Poissonian (for fermions) distributions, many-body processes can further modify the correlations and fluctuations. For example, threebody losses may lead to sub-Poissonian fluctuations in a Bose gas [11,12]. Even without dissipation, the intrinsic interatomic interactions can also lead to sub-Poissonian fluctuations, such as in a repulsive Bose gas in a periodic lattice potential, where the energetically costly atom number fluctuations are suppressed. This effect has been observed for large ratios of the on-site interaction energy to the inter-site tunnelling energy [13,14], with the extreme limit corresponding to the Mott insulator phase [15,16]. The same physics, accounts for sub-Poissonian fluctuations observed in double-well experiments [8,17]. Sub-Poissonian fluctuations of the total atom number have been also realised via controlled loading of the atoms into very shallow traps [18].In this work, we observe for the first time subPoissonian atom number fluctuations in small slices of a single one-dimensional (1D) Bose gas with repulsive interactions, where each slice approximates a uniform system. Taking advantage of the long scale density varia- Nearly ideal Bose gasQuasi-condensate tion due to a weak longitudinal confinement, we monitor -at a given temperature -the atom number fluctuations in each slice as a function of the local density. For a weakly interacting gas, the measured fluctuations are super-Poissonian at low densities, and t...

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“…Therefore, the quantum contribution becomes negligible as ∆ → ∞, and the thermodynamic prediction of Eq. (1) is recovered [25]. For our parameters, the contribution of Eq.…”

Section: Nearly Ideal Bose Gasmentioning

confidence: 99%

Section: Nearly Ideal Bose Gasmentioning

confidence: 99%

Sub-Poissonian Fluctuations in a 1D Bose Gas: From the Quantum Quasicondensate to the Strongly Interacting Regime

et al. 2011

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“…In practice the smallest spot sizes obtained are comparable to the healing length (typically ∼1 μm). The size of the cell relative to the physical length scales of the system (e.g., thermal wavelength and healing length) is crucial in determining the measurement results [23].…”

Section: Introductionmentioning

confidence: 99%

“…Recent work [23] has addressed how this can be done in uniform systems. Here we consider the extension to the trapped system.…”

Section: Introductionmentioning

confidence: 99%

Finite-resolution fluctuation measurements of a trapped Bose-Einstein condensate

2013

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We consider the fluctuations in atom number that occur within finite-sized measurement cells in a trapped Bose-Einstein condensate. These approximate the fluctuation measurements made in current experiments with finite-resolution in situ imaging. A numerical scheme is developed to calculate these fluctuations using the quasiparticle modes of a cylindrically symmetric three-dimensionally trapped condensate with either contact or dipole-dipole interactions. We use this scheme to study the properties of a pancake-shaped condensate using cylindrical cells. The extension of the theory to washer-shaped cells with azimuthal weighting is made and used to discriminate between the low-energy roton modes in a dipolar condensate according to their projection of angular momentum. Our results are based on the Bogoliubov approach valid for zero and small finite temperatures.

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“…Experimental in situ investigations of atomnumber fluctuations have already probed quantum fluctuations in one dimension [45], the universality of the Berezinkskii-Kosterlitz-Thouless transition [10] and the Hanbury Brown-Twiss effect [46] in Bose gases. Furthermore, recent Theoretical studies pave the way for experi-ments to utilize number fluctuations to investigate spinor condensates [47] and roton excitations in dipolar condensates [48][49][50].…”

Section: Introductionmentioning

confidence: 99%

Scaling of fluctuations in a trapped binary condensate

2015

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We demonstrate that measurements of number fluctuations within finite cells provide a direct means to study susceptibility scaling in a trapped two-component Bose-Einstein condensate. This system supports a second-order phase transition between miscible (co-spatial) and immiscible (symmetry-broken) states that is driven by a diverging susceptibility to magnetic fluctuations. As the transition is approached from the miscible side the magnetic susceptibility is found to depend strongly on the geometry and orientation of the observation cell. However, a scaling exponent consistent with that for the homogenous gas (γ = 1) can be recovered, for all cells considered, as long as the fit excludes the region in the immediate vicinity of the critical point. As the transition is approached from the immiscible side, the magnetic fluctuations exhibit a non-trivial scaling exponent γ 1.30. Interestingly, on both sides of the transition, we find it best to extract the exponents using an observation cell that encompasses half of the trapped system. This implies that relatively low-resolution in situ imaging will be sufficient for the investigation of these exponents. We also investigate the gap energy and find exponents νz = 0.505 on the miscible side and, unexpectedly, νz = 0.60(3) for the immiscible phase.

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Local atom-number fluctuations in quantum gases at finite temperature

Cited by 54 publications

References 22 publications

Sub-Poissonian Fluctuations in a 1D Bose Gas: From the Quantum Quasicondensate to the Strongly Interacting Regime

Sub-Poissonian Fluctuations in a 1D Bose Gas: From the Quantum Quasicondensate to the Strongly Interacting Regime

Finite-resolution fluctuation measurements of a trapped Bose-Einstein condensate

Scaling of fluctuations in a trapped binary condensate

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