2,078 research outputs found
Amending coherence-breaking channels via unitary operations
The coherence-breaking channels play a significant role in quantum
information theory. We study the coherence-breaking channels and give a method
to amend the coherence-breaking channels by applying unitary operations. For
given incoherent channel , we give necessary and sufficient conditions
for the channel to be a coherence-breaking channel and amend it via unitary
operations. For qubit incoherent channels that are not
coherence-breaking ones, we consider the mapping and present
the conditions for coherence-breaking and channel amendment as well.Comment: 8 page
Two-copy Quantum Teleportation
We investigate two-copy scenario of quantum teleportation based on Bell
measurements. The detailed protocol is presented and the general expression of
the corresponding optimal teleportation delity is derived, which is given by
the two-copy fully entangled fraction that is invariant under local unitary
transformations. We prove that under a speci c case of the protocol, which is
signi cant for improving the optimal delity, the set of states with their
two-copy fully entangled fractions bounded by a threshold value that required
for useful two-copy teleportation is convex and compact. Hence the witness
operators exist to separate states that are useful for two-copy teleportation
from the rest ones. Moreover, we show that the optimal delity of two-copy
teleportation surpasses that of the original one copy teleportation.Comment: 8 pages, 2 figure
Complex Organic Molecules Formation in Cold Cores on Stochastically Heated Grains
We investigate the roles of stochastic grain heating in the formation of
complex organic molecules (COMs) in cold cores, where COMs have been detected.
Two different types of grain-size distributions are used in the chemical
models. The first one is the MRN distribution, and the second one considers
grain coagulation to study its effects on the chemical evolution in these
environments. The macroscopic Monte Carlo method is used to perform the
two-phase chemical model simulations. We find that (1) grain coagulation can
affect certain gas-phase species, such as CO and NH, in the cold
core environments, which can be attributed to the volatile precursors
originating from the small grains with temperature fluctuations; (2) grains
with radii around 4.6 10 m contribute most to the
production of COMs on dust grains under cold core conditions, while few species
can be formed on even smaller grains with radii less than 2 10
m; (3) COMs formed on stochastically heated grains could help explain the
observed abundances of gas-phase COMs in cold cores.Comment: 15 pages, 10 figures, 3 tables. Accepted by MNRA
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