Condensate fluctuations of interacting Bose gases within a microcanonical ensemble

Wang, Jianhui; He, Jizhou; Ma, Yong-li

doi:10.1103/physreve.83.051132

Cited by 13 publications

(3 citation statements)

References 35 publications

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“…It has been shown that the fluctuations of an interacting condensate, in the limit of large atom numbers, are up to two times smaller than the ones of the non-interacting gas [19]. The Bogoliubov approximation has been applied for the problem of fluctuations in the canonical [19][20][21][22][23][24] and then in the microcanonical ensemble [25,26]. However, this approach only holds for low temperatures and weak interactions.…”

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confidence: 99%

Microcanonical and canonical fluctuations in atomic Bose-Einstein condensates – Fock state sampling approach

et al. 2023

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The fluctuations of the atom number between a Bose-Einstein condensate and the surrounding thermal gas have been the subject of a long standing theoretical debate. This discussion is centered around the appropriate thermodynamic ensemble to be used for theoretical predictions and the effect of interactions on the observed fluctuations. Here we introduce the so-called Fock state sampling method to solve this classic problem of current experimental interest for weakly interacting gases. A suppression of the predicted peak fluctuations is observed when using a microcanonical with respect to a canonical ensemble. Moreover, interactions lead to a shift of the temperature of peak fluctuations for harmonically trapped gases. The absolute size of the fluctuations furthermore depends on the total number of atoms and the aspect ratio of the trapping potential. Due to the interplay of these effect, there is no universal suppression or enhancement of fluctuations.

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confidence: 99%

Microcanonical and canonical fluctuations in atomic Bose-Einstein condensates – Fock state sampling approach

et al. 2023

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“…is obtained through the exact microcanonical method [33]. We change the traditional MCE system with (N , V, E) to a closed system with (N , V, E(N , V, T )) to withdraw the adiabatic wall at t = 0 instantaneously.…”

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confidence: 99%

Thermodynamic Anomalies of Small Quantum Systems Within a New Approach to Statistical Physics

Zhou

Tang

2014

J Low Temp Phys

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Based on a new statistical theory, we investigate the thermodynamic anomalies of small quantum systems, such as the negative specific heat (NSH) and negative entropy (NE) within the generalized canonical ensemble. We consider the systembath heat exchange and "uncompensated heat" in the thermodynamical level which is independent on the details of the system-bath coupling. For ideal finite systems, we calculate two thermodynamic quantities, i.e., the experimental specific heat and the entropy. The results show that the NSH and NE exist in quantum thermodynamics, particularly at low temperatures for small systems. They agree with the results of the reduced partition function theory and reveal that the finite boundary effects of the uncompensated heat and heat exchange of small quantum systems dominate the nonequilibrium irreversible processes. Keywords Small quantum system · Negative specific heat · Negative entropy Thermodynamics and the traditional statistical-mechanical interpretation are originally developed for large systems in the equilibrium state. However, the theories are not sufficient to describe the thermodynamical properties of small quantum systems [1-3]. There are increasing findings of anomalies presented experimentally in these systems [4][5][6][7][8][9]. These experimental results [6,10,11] turn up the existence of negative specific heat (NSH) and negative entropy (NE) [12]. But the specific heat is necessarily positive both in the standard Boltzmann-Gibbs statistical theories of the canonical ensemble (CE) and grand-canonical ensemble (GCE) and in the exact CE theory on the

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“…A prominent example is a quantum heat engine which may use an isolated finite system as its working substance to produce work [6]. In an isolated finite system [26] as well as quantum mechanics, the concept of energy (rather than temperature) is well-defined. Recently, a quantum-mechanical (QM) Carnot cycle working between two energy baths instead of heat baths has been generalized and studied intensively [10,13,27] since it was first proposed by Bender et al [9].…”

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confidence: 99%

Quantum-mechanical engine models and their efficiencies

Wang¹,

Ma²,

He³

2013

Preprint

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Based on quantum thermodynamic processes, we make a quantum-mechanical (QM) extension of the typical heat engine cycles, such as the Carnot, Brayton, Otto, and Diesel cycles, etc. The temperature is not included in these QM engine cycles, as lies in the fact that the concept of energy is well-defined in quantum mechanics, temperature a priori is not. These QM engine cycles are implemented by an ideal or interacting system with an arbitrary number of particles confined in an arbitrary power-law trap. As a result, a relation between the quantum adiabatic exponent and trap exponent is found. The efficiency of a given QM engine cycle is similar to that of its classical counterpart, thereby identifying the universality of the efficiency.

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Condensate fluctuations of interacting Bose gases within a microcanonical ensemble

Cited by 13 publications

References 35 publications

Microcanonical and canonical fluctuations in atomic Bose-Einstein condensates – Fock state sampling approach

Microcanonical and canonical fluctuations in atomic Bose-Einstein condensates – Fock state sampling approach

Thermodynamic Anomalies of Small Quantum Systems Within a New Approach to Statistical Physics

Quantum-mechanical engine models and their efficiencies

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