Anomalous fluctuations of Bose-Einstein condensates in optical lattices

• URL: http://arxiv.org/abs/2507.21001v1
• Date: Mon, 28 Jul 2025 17:11:33 GMT
• Title: Anomalous fluctuations of Bose-Einstein condensates in optical lattices
• Authors: Zahra Jalali-Mola, Niklas Käming, Luca Asteria, Utso Bhattacharya, Ravindra W. Chhajlany, Klaus Sengstock, Maciej Lewenstein, Tobias Grass, Christof Weitenberg,
• Abstract summary: We study the condensate particle number fluctuations in an optical lattice BEC across the phase transition.<n>We find strongly anomalous fluctuations, where the variance of the condensate number $delta N_rm BEC2$ scales with the total atom number as $N1+gamma$<n>Our study highlights the importance of the trap geometry on the character of fluctuations and on fundamental quantum mechanical properties.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Fluctuations are fundamental in physics and important for understanding and characterizing phase transitions. In this spirit, the phase transition to the Bose-Einstein condensate (BEC) is of specific importance. Whereas fluctuations of the condensate particle number in atomic BECs have been studied in continuous systems, experimental and theoretical studies for lattice systems were so far missing. Here, we explore the condensate particle number fluctuations in an optical lattice BEC across the phase transition in a combined experimental and theoretical study. We present both experimental data using ultracold $^{87}$Rb atoms and numerical simulations based on a hybrid approach combining the Bogoliubov quasiparticle framework with a master equation analysis for modeling the system. We find strongly anomalous fluctuations, where the variance of the condensate number $\delta N_{\rm BEC}^2$ scales with the total atom number as $N^{1+\gamma}$ with an exponent around $\gamma_{\rm theo}=0.74$ and $\gamma_{\rm exp}=0.62$, which we attribute to the 2D/3D crossover geometry and the interactions. Our study highlights the importance of the trap geometry on the character of fluctuations and on fundamental quantum mechanical properties.

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