237 research outputs found
Entanglement, non-Markovianity, and causal non-separability
Quantum mechanics, in principle, allows for processes with indefinite causal
order. However, most of these causal anomalies have not yet been detected
experimentally. We show that every such process can be simulated experimentally
by means of non-Markovian dynamics with a measurement on additional degrees of
freedom. Explicitly, we provide a constructive scheme to implement arbitrary
acausal processes. Furthermore, we give necessary and sufficient conditions for
open system dynamics with measurement to yield processes that respect causality
locally, and find that tripartite entanglement and nonlocal unitary
transformations are crucial requirements for the simulation of causally
indefinite processes. These results show a direct connection between three
counter-intuitive concepts: non-Markovianity, entanglement, and causal
indefiniteness.Comment: 14 pages, 8 figure
Spin-chain model of a many-body quantum battery
Recently, it has been shown that energy can be deposited on a collection of
quantum systems at a rate that scales super-extensively. Some of these schemes
for `quantum batteries' rely on the use of global many-body interactions that
take the batteries through a correlated short cut in state space. Here, we
extend the notion of a quantum battery from a collection of a priori isolated
systems to a many-body quantum system with intrinsic interactions.
Specifically, we consider a one-dimensional spin chain with physically
realistic two-body interactions. We find that the spin-spin interactions can
yield an advantage in charging power over the non-interacting case, and we
demonstrate that this advantage can grow super-extensively when the
interactions are long ranged. However, we show that, unlike in previous work,
this advantage is a mean-field interaction effect that does not involve
correlations and that relies on the interactions being intrinsic to the
battery.Comment: 9 pages, 6 figure
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