Two-particle quantum interference in tunnel-coupled optical tweezers

Bosons of a feather flit together Bosons are a type of particle that likes to congregate. This property has a major effect on the behavior of identical bosons. Kaufman et al. demonstrated quantum interference of two bosonic Rb atoms placed in two neighboring quantum wells (see the Perspective by Thompson and Lukin). They prepared the atoms in exactly the same state so that there would be no way to tell them apart except for which well each atom was in. They then monitored the probability of the two atoms still being in separate wells. At certain times, the probability had a characteristic dip signifying that the bosons preferred to be in the same well. Science, this issue p. 306; see also p. 272 Two bosonic rubidium atoms in coupled quantum wells are prepared in a symmetrical state and allowed to interfere. [Also see Perspective by Thompson and Lukin] The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles. Here, we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled 87Rb atoms trapped in two optical tweezers. This controllability allows us to observe signatures of indistinguishability via two-particle interference. Our work establishes laser-cooled atoms in optical tweezers as a promising route to bottom-up engineering of scalable, low-entropy quantum systems.

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