Observation of Atom Number Fluctuations in a Bose-Einstein Condensate

Abstract

Fluctuations are a key property of both classical and quantum systems. While the fluctuations are well understood for many quantum systems at zero temperature, the case of an interacting quantum system at finite temperature still poses numerous challenges. Despite intense theoretical investigations of atom number fluctuations in Bose-Einstein condensates, their amplitude in experimentally relevant interacting systems is still not fully understood. Moreover, technical limitations have prevented their experimental investigation to date. Here we report the observation of these fluctuations. Our experiments are based on a stabilization technique, which allows for the preparation of ultracold thermal clouds at the shot noise level, thereby eliminating numerous technical noise sources. Furthermore, we make use of the correlations established by the evaporative cooling process to precisely determine the fluctuations and the sample temperature. This allows us to observe a telltale signature: the sudden increase in fluctuations of the condensate atom number close to the critical temperature. arXiv:1812.03064v2 [cond-mat.quant-gas]

Statistical properties of cold bosons in a ring trap

“…Again, we consider noninteracting gas within the framework of canonical ensemble and calculate correla- tion function in exact treatment (with discrete occupations of states) and in classical fields approximation (for details see the Appendix). We have decided to measure the coherence length L φ by half width at half maximum (HWHM) of function (11). Cutoff is chosen to match coherence length obtained from correlation function in ex-act treatment and in classical fields approximation (see Fig.…”

“…It is worth stressing that there are still many open questions in this area, e.g. results are inconclusive, for details see [11].…”

Bose-Einstein condensation and non-extensive statistics

“…Notice that the variance tends to decrease with the value of q. This is an interesting quantitiy, since it can be measured experimentally [30].…”

Finite-Size Effects with Boundary Conditions on Bose-Einstein Condensation

“…The Bose-Einstein condensation (BEC) is a purely quantum-statistical phase transition characterized by the appearance of macroscopic population in ground state below the critical temperature T c , and it plays an important role in condensed matter [1][2][3][4][5][6][7][8][9], optics [10,11], atomic and molecular physics [12][13][14][15], etc. It is emphasized that the transition actually occurs at the thermodynamic limit, or when the discrete level structure is approximated by a continuous density of states [14,[16][17][18][19][20][21].…”