273 research outputs found
Probabilistic cloning and identification of linearly independent quantum states
We construct a probabilistic quantum cloning machine by a general
unitary-reduction operation. With a postselection of the measurement results,
the machine yields faithful copies of the input states. It is shown that the
states secretly chosen from a certain set can be
probabilistically cloned if and only if , , and are linearly-independent. We
derive the best possible cloning efficiencies. Probabilistic cloning has close
connection with the problem of identification of a set of states, which is a
type of outcome measurement on linearly independent states. The
optimal efficiencies for this type of measurement are obtained.Comment: Extension of quant-ph/9705018, 12pages, latex, to appear in Phys.
Rev. Let
Novel cloning machine with supplementary information
Probabilistic cloning was first proposed by Duan and Guo. Then Pati
established a novel cloning machine (NCM) for copying superposition of multiple
clones simultaneously. In this paper, we deal with the novel cloning machine
with supplementary information (NCMSI). For the case of cloning two states, we
demonstrate that the optimal efficiency of the NCMSI in which the original
party and the supplementary party can perform quantum communication equals that
achieved by a two-step cloning protocol wherein classical communication is only
allowed between the original and the supplementary parties. From this
equivalence it follows that NCMSI may increase the success probabilities for
copying. Also, an upper bound on the unambiguous discrimination of two
nonorthogonal pure product states is derived. Our investigation generalizes and
completes the results in the literature.Comment: 22 pages; the presentation is revised, and some typos are correcte
Probabilistic cloning with supplementary information
We consider probabilistic cloning of a state chosen from a mutually
nonorthogonal set of pure states, with the help of a party holding
supplementary information in the form of pure states. When the number of states
is 2, we show that the best efficiency of producing m copies is always achieved
by a two-step protocol in which the helping party first attempts to produce m-1
copies from the supplementary state, and if it fails, then the original state
is used to produce m copies. On the other hand, when the number of states
exceeds two, the best efficiency is not always achieved by such a protocol. We
give examples in which the best efficiency is not achieved even if we allow any
amount of one-way classical communication from the helping party.Comment: 6 pages, no figure
Probabilistic cloning with supplementary information contained in the quantum states of two auxiliary systems
In probabilistic cloning with two auxiliary systems, we consider and compare
three different protocols for the success probabilities of cloning. We show
that, in certain circumstances, it may increase the success probability to add
an auxiliary system to the probabilistic cloning machine having one auxiliary
system, but we always can find another cloning machine with one auxiliary
system having the same success probability as that with two auxiliary systems.Comment: 18 page
The roles of quantum correlations in quantum cloning
In this paper, we study the entanglement and quantum discord of the output
modes in the unified state-dependent cloning and probabilistic
quantum cloning. The tripartite entanglement among the output modes and the
quantum cloning machine is also considered. We find that the roles of the
quantum correlations including the bipartite and tripartite entanglement and
quantum discord strongly depend on the quantum cloning machines as well as the
cloned state. In particular, it is found that this quantum cloning scheme can
be realizable even without any quantum correlation.Comment: Accepted by Eur. Phys. J.
Unambiguous Discrimination Between Linearly Dependent States with Multiple Copies
A set of quantum states can be unambiguously discriminated if and only if
they are linearly independent. However, for a linearly dependent set, if C
copies of the state are available, then the resulting C particle states may
form a linearly independent set, and be amenable to unambiguous discrimination.
We obtain necessary and sufficient conditions for the possibility of
unambiguous discrimination between N states given that C copies are available
and that the single copies span a D dimensional space. These conditions are
found to be identical for qubits. We then examine in detail the linearly
dependent trine ensemble. The set of C>1 copies of each state is a set of
linearly independent lifted trine states. The maximum unambiguous
discrimination probability is evaluated for all C>1 with equal a priori
probabilities.Comment: 12 Pages RevTeX 4, 1 EPS figur
A generalized no-broadcasting theorem
We prove a generalized version of the no-broadcasting theorem, applicable to
essentially \emph{any} nonclassical finite-dimensional probabilistic model
satisfying a no-signaling criterion, including ones with ``super-quantum''
correlations. A strengthened version of the quantum no-broadcasting theorem
follows, and its proof is significantly simpler than existing proofs of the
no-broadcasting theorem.Comment: 4 page
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