869 research outputs found
Quantum observer and Kolmogorov complexity: a model that can be tested
Different observers do not have to agree on how they identify a quantum
system. We explore a condition based on algorithmic complexity that allows a
system to be described as an objective "element of reality". We also suggest an
experimental test of the hypothesis that any system, even much smaller than a
human being, can be a quantum mechanical observer.Comment: 11 pages. Section 6 on experimental tests added in version
Renormalized entropy of entanglement in relativistic field theory
Entanglement is defined between subsystems of a quantum system, and at fixed
time two regions of space can be viewed as two subsystems of a relativistic
quantum field. The entropy of entanglement between such subsystems is
ill-defined unless an ultraviolet cutoff is introduced, but it still diverges
in the continuum limit. This behaviour is generic for arbitrary finite-energy
states, hence a conceptual tension with the finite entanglement entropy typical
of nonrelativistic quantum systems. We introduce a novel approach to explain
the transition from infinite to finite entanglement, based on coarse graining
the spatial resolution of the detectors measuring the field state. We show that
states with a finite number of particles become localized, allowing an
identification between a region of space and the nonrelativistic degrees of
freedom of the particles therein contained, and that the renormalized entropy
of finite-energy states reduces to the entanglement entropy of nonrelativistic
quantum mechanics.Comment: 5 pages, 1 figur
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