On the observation of nonclassical excitations in Bose-Einstein condensates

Abstract

In the recent experimental and theoretical literature well-established nonclassicality criteria from the field of quantum optics have been directly applied to the case of excitations in matter-waves. Among these are violations of Cauchy-Schwarz inequalities, Glauber-Sudarshan P-nonclassicality, sub-Poissonian number-difference squeezing (also known as the two-mode variance) and the criterion of nonseparability. We review the strong connection of these criteria and their meaning in quantum optics, and point out differences in the interpretation between light and matter waves. We then calculate observables for a homogenous Bose-Einstein condensate undergoing an arbitrary modulation in the interaction parameter at finite initial temperature, within both the quantum theory as well as a classical reference. We conclude that to date in experiments relevant for analogue gravity, nonclassical effects have not conclusively been observed and conjecture that additional, noncommuting, observables have to be measured to this end.

11 pages, 1 figure

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• Assessing degrees of entanglement of phonon states in atomic Bose gases through the measurement of commuting observables
• Low frequency analogue Hawking radiation: The Bogoliubov-de Gennes model
• Controlling and observing nonseparability of phonons created in time-dependent 1D atomic Bose condensates
• Momentum correlations as signature of sonic Hawking radiation in Bose-Einstein condensates
• On the Limits of Experimental Knowledge
• Vorticity in analogue spacetimes
• The influence of spacetime curvature on quantum emission in optical analogues to gravity
• Thermal noise in BEC-phononic gravitational wave detectors
• Analytical description of quantum emission in optical analogues to gravity
• Analogue Quantum Simulation: A New Instrument for Scientific Understanding
• Towards a Gordon form of the Kerr spacetime
• On the role of interactions in trans-sonically flowing atomic condensates
• Density correlations from analogue Hawking radiation in the presence of atom losses
• Quantifying two-mode entanglement of bosonic Gaussian states from their full counting statistics
• Analogue quantum simulation of the Hawking effect in a polariton superfluid