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SUMMARY:Port-based teleportation stretching of adaptive protocols and cond
 itional channel simulation - Riccardo Laurenza
DTSTART:20181129T141500Z
DTEND:20181129T151500Z
UID:TALK113170@talks.cam.ac.uk
CONTACT:Johannes Bausch
DESCRIPTION:When we combine quantum channel simulation with quantum telepo
 rtation\, we obtain remarkable results regarding the natural limitations t
 hat quantum mechanics imposes on the optimal performance of any quantum ta
 sk performed over quantum channels. Usually these ultimate limits are very
  difficult to address since the strategies employed to assess them are ver
 y general and involve adaptive\, i.e. feedback-assisted\, quantum operatio
 ns\, where feedback from the output is used to update the input. In this s
 cenario\, we first show that port-based teleportation for channel simulati
 on can be exploited to devise a reduction procedure (dubbed stretching)\, 
 by means of which the output of an adaptive protocol over arbitrary quantu
 m channels is decomposed in terms of the tensor product of multicopies of 
 the channel’s Choi state. When we specify this technique for quantum cha
 nnel discrimination\, we are able to derive a universal computable lower b
 ound on the probability of the error affecting the discrimination between 
 two arbitrary finite-dimensional quantum channels. We then show that our m
 ethodology can be applied also to quantum metrology\, where we characteriz
 e the Heisenberg scaling as a direct consequence of port-based teleportati
 on. In the second part of this talk we present a different design of quant
 um channel simulation that relies on a suitable control system and allows 
 to simulate average quantum channels which are expressed in terms of ensem
 ble of channels\, even when these channel-components cannot be simulated t
 hrough teleportation. We then derive relative-entropy-of-entanglement uppe
 r bounds for private communication over various channels as the amplitude 
 damping channel\, non-Gaussian mixtures of bosonic lossy channels and the 
 dephrasure channel.
LOCATION:MR4\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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