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It is an open fundamental question how the classical
appearance of our environment arises from the underlying quantum
many-body theory. Experiments explore this question through the creation
of superposition states involving ever larger numbers of constituents.
Atomic Bose-Einstein condensates (BECs) are a promising platform, due
to their typically very well defined many-body state.We present
proposals how entire clouds of cold atoms can be brought into
mesoscopically entangled (or Schroedinger's cat) states in position
space, implying that the cloud as a whole will be in a superposition of
two different places at once.
The first avenue presented involves highly excited Rydberg atoms. Due
to their extreme interactions, these atoms are prone to the generation
of entangled states. This entanglement can then be transferred to
ultra-cold ground state atoms using the
technique of Rydberg dressing, which can give rise to spatial cat
states using dressed dipole-dipole interactions [1] or Rydberg phase
imprinting [2].
However mesoscopically entangled states can also arise among cold
ground state atoms alone, such as in binary collision of bright
solitons. We show that these collisions exhibit intricate many-body
quantum behavior, invalidating mean field theory [3,4]. After collision
the two solitons find themselves in a superposition state of various
constituent atom numbers, positions and velocities, in which all these
quantities are entangled with those of the collision partner. As the
solitons appear to traverse the quantum-classical boundary back and
forth during their scattering process,they emerge as natural probe of
mesoscopic quantum coherence and decoherence phenomena.
[1] “Entangling distant atom clouds through Rydberg dressing”,
S. Möbius, M. Genkin, A. Eisfeld, S. Wüster and J. M. Rost, PRA 87,
051602(R) (2013).
[2] “Phase-Imprinting of Bose-Einstein Condensates with Rydberg
Impurities”,
R. Mukherjee, C. Ates, W. Li and S. Wüster, PRL 115, 040401 (2015).
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