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Science China Physics Mechanics and Astronomy

Existence and construction of simultaneous cloning machines for mixed states

Zhihua Guo, HuaiXin Cao, ShiXian Qu

Published Oct 24, 2014• 3 citations
Publisher
DOI
10.1007/s11433-014-5619-6

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It is a well-known fact that the no-cloning theorem forbids the creation of identical copies of an arbitrary unknown quantum state.In other words,there does not exist a quantum cloning machine that can clone all quantum states.However,it is possible to clone given quantum states under certain conditions,for instance,k distinct pure states|ψ1,|ψ2,...,|ψk can be cloned simultaneously if and only if they are orthogonal.This paper discusses the existence and construction of simultaneous cloning machines for mixed states.It is proved that k distinct mixed statesρ1,ρ2,...,ρkof the n-dimensional quantum system Cncan be cloned simultaneously,that is,there exists a quantum channel Φ on MnMn and a state Σ in Mn,such that Φ(ρiΣ)=ρiρi for all i,if and only ifρiρj=0(i j).Also,the constructing procedure of the desired simultaneous cloning machine is given.
Using the reduced density operator of quantum state to study the deletion and clone of quantum information.Testify that there no exists quantum deleting machine which makes the deleted states and the blank states be correlated;also we can not construct a machine to perfectly delete arbitrary mixed quantum states.At last,we consider the problem of cloning and deleting of mixed quantum states in the case of probabilistic form,provide a sufficient and necessary condition in the form of probability with a unification formula.By using the results obtained,the processing of quantum information can be further comprehended and has aspiring significance for quantum computer.
The efficacies of maximally and that of non-maximally entangled mixed states as teleportation channels have been studied. A new class of non-maximally entangled mixed states have been proposed also. Their advantages as quantum teleportation channels over existing non-maximally entangled mixed states have been verified. The mixed states can also be generated using quantum cloning machines. We have also studied how one can utilize the mixed entangled states obtained as output from a state independent quantum cloning machine in teleportation and dense coding. Mixed states can also be used in secret sharing. A new protocol of secret sharing has been devised where four parties are involved. One of them is honest by nature and the other is dishonest. The dishonest one has two associates who are also involved in the protocol. It has been shown how the honest party, by using quantum cloning machine, can prevent the dishonest party from communicating the secret message to his accomplices. A relation has been established among entanglement of the initially prepared state, entanglement of the mixed state received by the recipients of the dishonest one after honest party applies the cloning scheme and the cloning parameters of the cloning machine. The usefulness of tri-partite and four-partite entangled states in controlled dense coding has been discussed. The thesis concludes with the summary and possible courses of future works.