OBSERVATION OF VACUUM FLUCTUATIONS IN A SPINOR BOSE-EINSTEIN CONDENSATE

The nature of the vacuum state and its fluctuations constitutes one of the most fascinating aspects of modern physics. In particular, the parametric amplification of such fluctuations is crucial for phenomena ranging from optical parametric down-conversion¹ to stimulated positronium annihilation,² and boson creation in Universe inflation.³ Spinor Bose-Einstein condensates,^4–7 consisting of atoms with non-zero total spin, provide an optimal system for the investigation of the vacuum state.^8,9 Here we describe the amplification of vacuum fluctuations in gaseous spinor condensates in an unstable spin configuration. We observe strong instability resonances in the spinor condensate,¹⁰ induced by the confinement of the atomic ensemble. On these resonances we conclusively demonstrate that the system can act as a parametric amplifier for vacuum fluctuations,¹¹ providing a new microscope to investigate the vacuum state and a promising method for entanglement and squeezing production in matter waves.