Carnot Cycles in a Harmonically Confined Ultracold Gas across Bose–Einstein Condensation

Abstract

Carnot cycles of samples of harmonically confined ultracold 87Rb fluids, near and across Bose–Einstein condensation (BEC), are analyzed. This is achieved through the experimental determination of the corresponding equation of state in terms of the appropriate global thermodynamics for non-uniform confined fluids. We focus our attention on the efficiency of the Carnot engine when the cycle occurs for temperatures either above or below the critical temperature and when BEC is crossed during the cycle. The measurement of the cycle efficiency reveals a perfect agreement with the theoretical prediction (1−TL/TH), with TH and TL serving as the temperatures of the hot and cold heat exchange reservoirs. Other cycles are also considered for comparison.

Entropy and Energy for Non-Mechanical Work at the Bose-Einstein Transition of a Harmonically Trapped Gas Using an Empirical Global-Variable Method

“…In the last year [6], we demonstrated theoretically and experimentally that the efficiency of Carnot cycles is always 1 − T cold /T hot before, across and after BEC, therefore showing that result to hold true in both classical and quantum regimes, as well as in the transition between them. For that end, we have used experimental data and the methodology firstly described on the corresponding author's Master thesis [7], which relied on a formalism called Global-Variable Method [8][9][10], an approach parallel to Local Density Approximation [11] in describing the thermodynamics of inhomogeneous quantum gases (remarkably, the harmonically trapped ones).…”

“…Having V and n, we determine the pressure parameter (P) using Eq. (6). Therefore, we have the four required quantities (N, T, V and P) to describe the thermodynamics of the system, as we discuss in Sec.…”

A quantum Otto engine with shortcuts to thermalization and adiabaticity

“…Currently, there is ongoing research in quantum heat engines and refrigerators [3][4][5][6][7]. Since the pioneering work by Scovil and Schulz-DuBois [8], quantum heat engines have been extensively studied theoretically , and successful experimental demonstrations have been recently reported [40][41][42][43][44][45][46][47]. Despite these theoretical and experimental developments, it is still an open question whether the quantum advantage can lead to Carnot efficiency or better at finite power [48][49][50].…”