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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:Coherence distillation machines are impossible in
quantum thermodynamics - Iman Marvian (Duke Univer
sity)
DTSTART;TZID=Europe/London:20180725T090000
DTEND;TZID=Europe/London:20180725T094500
UID:TALK108310AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/108310
DESCRIPTION:The role of coherence in quantum thermodynamics ha
s been extensively studied in the recent years and
it is now well-understood that coherence between
different energy eigenstates is a resource indepen
dent of other thermodynamics resources\, such as w
ork. A fundamental remaining open question is whet
her the laws of quantum mechanics and thermodynami
cs allow the existence a "coherence distillation m
achine"\, i.e. a machine that\, by possibly consum
ing work\, obtains pure coherent states from mixed
states\, at a nonzero rate. This question is rela
ted to another fundamental question: Starting from
many copies of noisy quantum clocks which are (ap
proximately) synchronized with a reference clock\,
can we distill synchronized clocks in pure states
\, at a non-zero rate? In this paper we study quan
tities called "coherence cost" and "distillable co
herence"\, which determine the rate of conversion
of coherence in a standard pure state to general m
ixed states\, and vice versa\, in the context of q
uantum thermodynamics. We find that the coherence
cost of any state (pure or mixed) is determined by
its Quantum Fisher Information (QFI)\, thereby re
vealing a novel operational interpretation of this
central quantity of quantum metrology. On the oth
er hand\, we show that\, surprisingly\, distillabl
e coherence is zero for typical (full-rank) mixed
states. Hence\, we establish the impossibility of
coherence distillation machines in quantum thermod
ynamics\, which can be compared with the impossibi
lity of perpetual motion machines or cloning machi
nes. To establish this result\, we introduce a new
additive quantifier of coherence\, called the "pu
rity of coherence"\, and argue that its relation w
ith QFI is analogous to the relation between the f
ree and total energies in thermodynamics.
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:INI IT
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