Bose-Einstein Condensate Mimics Early Universe Particle Production, Validates Theory

The earliest moments of the universe, a period of rapid expansion known as inflation, remain a subject of intense scrutiny for cosmologists. Understanding how quantum fluctuations in this epoch seeded the structures we observe today requires recreating, or at least simulating, the conditions of that primordial era. Researchers at Université Paris-Saclay, RIKEN, and the Institut Pprime, led by Clothilde Lamirault, Charlie Leprince, and including Victor Gondret, Quentin Marolleau, Jean-René Rullier, Scott Robertson, Denis Boiron, Christoph I. Westbrook, Amaury Micheli, Léa Camier, and Rui Dias, report the observation of entanglement in a cold atom system designed to mimic the process of ‘preheating’, a critical stage immediately following inflation where particle production occurs. Their work, detailed in a forthcoming publication titled ‘Observation of entanglement in a cold atom analog of cosmological preheating’, demonstrates the emergence of correlated particle pairs from vacuum fluctuations within a Bose-Einstein condensate, providing a novel experimental platform to investigate the dynamics of the early universe and the transition from quantum to classical behaviour. The team’s observations confirm the expected origin of these excitations and offer a pathway to explore the more complex, interaction-dominated regimes of cosmological particle production.

Researchers successfully simulate aspects of the very early universe, specifically the period immediately following the Big Bang known as preheating, utilising a Bose-Einstein condensate. This state of matter, achieved by cooling bosons to temperatures close to absolute zero, allows for the observation of quantum phenomena on a macroscopic scale. The experiment replicates the behaviour of the ‘inflaton field’, a hypothetical scalar field proposed to drive the rapid expansion of the universe in its earliest moments. By oscillating the condensate, scientists effectively mimic the dynamics of this field and the subsequent creation of particles.

Crucially, the observed excitations within the condensate originate from quantum vacuum fluctuations, a fundamental concept in quantum field theory where even seemingly empty space possesses inherent energy and temporary particle-antiparticle pairs. This confirms a key prediction of inflationary cosmology, which posits that the seeds of all structure in the universe arose from these primordial fluctuations. The experiment provides direct, albeit analogue, evidence supporting this theoretical framework.

Characterisation of the correlations between the created quasiparticles, which are collective excitations within the condensate behaving as effective particles, employed both entanglement witnesses and auto-correlation measurements. Entanglement witnesses detect quantum entanglement, a uniquely quantum correlation, while auto-correlation measurements reveal the degree to which the particles are correlated with themselves at different points in time. These measurements, performed as a function of hold time (Δt, the duration the condensate is allowed to evolve) and modulation depth (A, the amplitude of the oscillation), revealed variations in the positive and negative velocity sidebands, indicating the distribution of particle velocities.

Over time, the initial quantum correlations diminish, signifying a transition from a regime dominated by purely quantum effects to one where interactions between the individual atoms comprising the condensate become more significant. This shift provides a valuable opportunity for future research, potentially allowing scientists to investigate the interplay between quantum field theory and many-body physics. The setup represents a novel platform for studying fundamental aspects of both quantum field theory and cosmology within a controlled laboratory environment, offering a complementary approach to astronomical observations and theoretical modelling.