Quantum Virtual Cooling. (arXiv:1812.02175v2 [quant-ph] UPDATED)

We propose a quantum information based scheme to reduce the temperature of
quantum many-body systems, and access regimes beyond the current capability of
conventional cooling techniques. We show that collective measurements on
multiple copies of a system at finite temperature can simulate measurements of
the same system at a lower temperature. This idea is illustrated for the
example of ultracold atoms in optical lattices, where controlled tunnel
coupling and quantum gas microscopy can be naturally combined to realize the
required collective measurements to access a lower, virtual temperature. Our
protocol is experimentally implemented for a Bose-Hubbard model on up to 12
sites, and we successfully extract expectation values of observables at half
the temperature of the physical system. Additionally, we present related
techniques that enable the extraction of zero-temperature states directly.

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