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SUMMARY:Coherence distillation machines are impossible in quantum thermody
 namics - Iman Marvian (Duke University)
DTSTART:20180725T080000Z
DTEND:20180725T084500Z
UID:TALK108310@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:The role of coherence in quantum thermodynamics has been exten
 sively studied in the recent years and it is now well-understood that cohe
 rence between different energy eigenstates is a resource independent of ot
 her 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 state
 s\, at a nonzero rate. This question is related to another fundamental que
 stion: Starting from many copies of noisy quantum clocks which are (approx
 imately) synchronized with a reference clock\, can we distill synchronized
  clocks in pure states\, at a non-zero rate? In this paper we study quanti
 ties called "coherence cost" and "distillable coherence"\, 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 quantum thermodynamics. W
 e find that the coherence cost of any state (pure or mixed) is determined 
 by its Quantum Fisher Information (QFI)\, thereby revealing a novel operat
 ional 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 impossibili
 ty of coherence distillation machines in quantum thermodynamics\, which ca
 n be compared with the impossibility of perpetual motion machines or cloni
 ng machines. To establish this result\, we introduce a new additive quanti
 fier 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.  <br><br><br><br>
LOCATION:Seminar Room 1\, Newton Institute
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