3,189 research outputs found
Implementation of multipartite unitary operations with limited resources
A general method for implementing weakly entangling multipartite unitary
operations using a small amount of entanglement and classical communication is
presented. For the simple Hamiltonian \sigma_z\otimes\sigma_z this method
requires less entanglement than previously known methods. In addition,
compression of multiple operations is applied to reduce the average
communication required.Comment: 7 pages, 4 figures, comments welcom
Interconvertibility of single-rail optical qubits
We show how to convert between partially coherent superpositions of a single
photon with the vacuum using linear optics and postselection based on homodyne
measurements. We introduce a generalized quantum efficiency for such states and
show that any conversion that decreases this quantity is possible. We also
prove that our scheme is optimal by showing that no linear optical scheme with
generalized conditional measurements, and with one single-rail qubit input can
improve the generalized efficiency.Comment: 3 pages, 2 figure
Relations for classical communication capacity and entanglement capability of two-qubit operations
Bipartite operations underpin both classical communication and entanglement
generation. Using a superposition of classical messages, we show that the
capacity of a two-qubit operation for error-free entanglement-assisted
bidirectional classical communication can not exceed twice the entanglement
capability. In addition we show that any bipartite two-qubit operation can
increase the communication that may be performed using an ensemble by twice the
entanglement capability.Comment: 4 page
Countering Quantum Noise with Supplementary Classical Information
We consider situations in which i) Alice wishes to send quantum information
to Bob via a noisy quantum channel, ii) Alice has a classical description of
the states she wishes to send and iii) Alice can make use of a finite amount of
noiseless classical information. After setting up the problem in general, we
focus attention on one specific scenario in which Alice sends a known qubit
down a depolarizing channel along with a noiseless cbit. We describe a protocol
which we conjecture is optimal and calculate the average fidelity obtained. A
surprising amount of structure is revealed even for this simple case which
suggests that relationships between quantum and classical information could in
general be very intricate.Comment: RevTeX, 5 pages, 2 figures Typo in reference 9 correcte
Equivalence of Quantum States under Local Unitary Transformations
In terms of the analysis of fixed point subgroup and tensor decomposability
of certain matrices, we study the equivalence of of quantum bipartite mixed
states under local unitary transformations. For non-degenerate case an
operational criterion for the equivalence of two such mixed bipartite states
under local unitary transformations is presented.Comment: 6 page
NMR C-NOT gate through Aharanov-Anandan's phase shift
Recently, it is proposed to do quantum computation through the Berry's
phase(adiabatic cyclic geometric phase) shift with NMR (Jones et al, Nature,
403, 869(2000)). This geometric quantum gate is hopefully to be fault tolerant
to certain types of errors because of the geometric property of the Berry
phase. Here we give a scheme to realize the NMR C-NOT gate through
Aharonov-Anandan's phase(non-adiabatic cyclic phase) shift on the dynamic phase
free evolution loop.
In our scheme, the gate is run non-adiabatically, thus it is less affected by
the decoherence. And, in the scheme we have chosen the the zero dynamic phase
time evolution loop in obtaining the gepmetric phase shift, we need not take
any extra operation to cancel the dynamic phase.Comment: 5 pages, 1 figur
Faithful remote state preparation using finite classical bits and a non-maximally entangled state
We present many ensembles of states that can be remotely prepared by using
minimum classical bits from Alice to Bob and their previously shared entangled
state and prove that we have found all the ensembles in two-dimensional case.
Furthermore we show that any pure quantum state can be remotely and faithfully
prepared by using finite classical bits from Alice to Bob and their previously
shared nonmaximally entangled state though no faithful quantum teleportation
protocols can be achieved by using a nonmaximally entangled state.Comment: 6 page
On the quantum, classical and total amount of correlations in a quantum state
We give an operational definition of the quantum, classical and total amount
of correlations in a bipartite quantum state. We argue that these quantities
can be defined via the amount of work (noise) that is required to erase
(destroy) the correlations: for the total correlation, we have to erase
completely, for the quantum correlation one has to erase until a separable
state is obtained, and the classical correlation is the maximal correlation
left after erasing the quantum correlations.
In particular, we show that the total amount of correlations is equal to the
quantum mutual information, thus providing it with a direct operational
interpretation for the first time. As a byproduct, we obtain a direct,
operational and elementary proof of strong subadditivity of quantum entropy.Comment: 12 pages ReVTeX4, 2 eps figures. v2 has some arguments clarified and
references update
Evaluation of Processing Tomato Breeding Lines and Cultivars for Mechanical Harvesting and Quality in 1988
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