



01232nas a2200157   4500008004100000245005300041210005300094260001500147490000800162520078900170100001800959700002100977700002100998700001801019856003701037       2011                        eng d00aEntanglement can completely defeat quantum noise0 aEntanglement can completely defeat quantum noise  c2011/12/150 v1073 a  We describe two quantum channels that individually cannot send any
information, even classical, without some chance of decoding error. But
together a single use of each channel can send quantum information perfectly
reliably. This proves that the zero-error classical capacity exhibits
superactivation, the extreme form of the superadditivity phenomenon in which
entangled inputs allow communication over zero capacity channels. But our
result is stronger still, as it even allows zero-error quantum communication
when the two channels are combined. Thus our result shows a new remarkable way
in which entanglement across two systems can be used to resist noise, in this
case perfectly. We also show a new form of superactivation by entanglement
shared between sender and receiver.
1 aChen, Jianxin1 aCubitt, Toby, S.1 aHarrow, Aram, W.1 aSmith, Graeme  uhttp://arxiv.org/abs/1109.0540v101195nas a2200157   4500008004100000245009000041210006900131260001500200300001600215490000700231520070200238100002100940700001800961700002100979856003701000       2011                        eng d00aSuperactivation of the Asymptotic Zero-Error Classical Capacity of a  Quantum Channel0 aSuperactivation of the Asymptotic ZeroError Classical Capacity o  c2011/12/01  a8114 - 81260 v573 a  The zero-error classical capacity of a quantum channel is the asymptotic rate
at which it can be used to send classical bits perfectly, so that they can be
decoded with zero probability of error. We show that there exist pairs of
quantum channels, neither of which individually have any zero-error capacity
whatsoever (even if arbitrarily many uses of the channels are available), but
such that access to even a single copy of both channels allows classical
information to be sent perfectly reliably. In other words, we prove that the
zero-error classical capacity can be superactivated. This result is the first
example of superactivation of a classical capacity of a quantum channel.
1 aCubitt, Toby, S.1 aChen, Jianxin1 aHarrow, Aram, W.  uhttp://arxiv.org/abs/0906.2547v3