Presented by:
Iman Marvian
Date:
Wednesday 25th July 2018 - 09:00 to 09:45
Venue:
INI Seminar Room 1
Abstract:
The role of coherence in quantum thermodynamics has been
extensively studied in the recent years and it is now well-understood that
coherence between different energy eigenstates is a resource independent of
other thermodynamics resources, such as work. A fundamental remaining open
question is whether the laws of quantum mechanics and thermodynamics allow the
existence a "coherence distillation machine", i.e. a machine that, by
possibly consuming work, obtains pure coherent states from mixed states, at a
nonzero rate. This question is related to another fundamental question:
Starting from many copies of noisy quantum clocks which are (approximately)
synchronized with a reference clock, can we distill synchronized clocks in pure
states, at a non-zero rate? In this paper we study quantities called
"coherence cost" and "distillable coherence", which
determine the rate of conversion of coherence in a standard pure state to
general mixed states, and vice versa, in the context of quantum thermodynamics.
We find that the coherence cost of any state (pure or mixed) is determined by
its Quantum Fisher Information (QFI), thereby revealing a novel operational
interpretation of this central quantity of quantum metrology. On the other
hand, we show that, surprisingly, distillable coherence is zero for typical
(full-rank) mixed states. Hence, we establish the impossibility of coherence
distillation machines in quantum thermodynamics, which can be compared with the
impossibility of perpetual motion machines or cloning machines. To establish
this result, we introduce a new additive quantifier of coherence, called the
"purity of coherence", and argue that its relation with QFI is
analogous to the relation between the free and total energies in
thermodynamics.
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