Quantum critical region of ultracold Bose gases exhibiting universal density-probability distribution after free expansion
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| Number of Parts | 62 | |
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| License | CC Attribution 3.0 Unported: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
| Identifiers | 10.5446/38777 (DOI) | |
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Transcript: English(auto-generated)
00:06
It is well known that for a system with completely random phase fluctuations in two or three dimensions, the density probability distribution is always exponential. This unique behavior, for example, can be observed for a light wave having phase fluctuations with two freedoms.
00:26
In this work, we will give the first experimental demonstration of this exponential density probability distribution with matter waves. In our experiment, a one-dimensional optical lattice with periodic potentials was applied along the axis direction of a cigar-shaped condensate.
00:49
After a time of free expansion, the atomic density was recorded by a CCD camera. From the atomic density, we extract the density probability distribution and make compare with the exponentially decaying curve.
01:06
We found that the density probability distribution matches the exponential shape when lattice depth is high enough. For the 1D optical lattice system, the Bose gas in each lattice wave becomes quasi-2D,
01:23
and quasi-2D gas should undergo the BKD transition at critical temperature. About this critical temperature, the unbinding of bound vertices will lead to strong spatial phase fluctuations within the single step condensate. Of course, there also exists another kind of phase fluctuations,
01:44
that is, the relative phase fluctuations between the different lattice waves. In the phase diagram, the BKD transition line divides the quantum critical region into two parts, the type I and type II. We focus on type I QC region, taking into account the intersight and intersight phase fluctuations.
02:07
We calculated the density probability distribution, and found that it does follow an exponential rule. In superfluid region or type II QC region, only intersight phase fluctuations exists,
02:22
and the exponential rule is not obeyed according to our theoretical model. Our experiments have justified that the exponential rule is varied once the system enters type I quantum critical region. We also numerically simulated the density distribution in three regions.
02:44
The results for superfluid and type I QC regions are in good agreement with the experiment. In summary, we have demonstrated an exponential density probability distribution of ultra-cold quantum critical Bose gases in a one-dimensional optical lattice by experiment.
03:04
We have also given a simple theoretical model to explain the observed universal behavior. Thank you for your attention.