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.
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.
Entanglement manipulation, and especially Entanglement Swapping is at the heart of current work on quantum information processing, purification and quantum teleportation. We will discuss how it may be generalized to multiparticle systems and how this enables multi-user quantum cryptographic protocols to be developed. Our scheme allows us to establish multiparticle entanglement between particles which belong to distant users in a communication network through a prior distribution of Bell state singlets followed by local measurements. We compare our method for generating entanglement with existing schemes using simple quantum networks, and highlight the advantages and applications in cryptographic conferencing and in reading messages from more than one source through a single quantum measurement. We also discuss how entanglement leads to the idea of ‘telecloning’, in which a teleportation-like protocol can be found which reproduces the output of an optimal quantum cloning machine. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Recently, there is much interest in the study of quantum teleportation. Its marvelous security property makes it particularly attractive as potential means for future communication. Uncertain principal and no-cloning theories of quantum mechanics forbid exact copy of quantum states. To solve the problem, quantum teleportation devides message state into two parts: classical message and quantum message which are transmitted through relevant classical and quantum channels from a sender Alice to a distant receiver Bob, respectively. According to both message states, Bob can recover the original message state with certain possibility. Utilizing the general quantum teleportation protocol, in this scheme, a new method is presented by which multi-qubit quantum information can be teleported in a much easier way. It has been extended to teleportation of an arbitrary N-qubit state via entanglement swapping and probabilistic teleportation is investigated as well, which has a more general meaning. N non-maximally entangled triplet GHZ states (Greenberger-Home-Zeilinger), taking the place of the previous EPR states (Einstein-Podolsky-Rosen), serve as quantum channels, which avoids introducing extra auxiliary qubit. In order to complete the teleportation, Alice has to devide all qubits into N parts and make Bell-State measurement on qubit pair (i, x(subscript i)) and tell Bob the measurement result through classical channel, then Bob perform some simple local operations on qubits (y(subscript i), z(subscript i)) to finish teleporting the i-th qubit. Conditioned on N-times similar repeat, Bob can faithfully reconstruct the initial state. Results show that, in this method, the identification difficulty of entangled states is considerably reduced, the new method is more feasible in technique. And the total possibility of successful teleportation is (The equation is abbreviated). As a special case, teleportation of an arbitrary two-qubit state is proposed.
In this thesis, we have proposed some novel thought experiments involving foundations of quantum mechanics and quantum information theory, using quantum entanglement property. Concerning foundations of quantum mechanics, we have suggested some typical systems including two correlated particles which can distinguish between the two famous theories of quantum mechanics, i.e. the standard and Bohmian quantum mechanics, at the individual level of pair of particles. Meantime, the two theories present the same predictions at the ensemble level of particles. Regarding quantum information theory, two theoretical quantum communication schemes including quantum dense coding and quantum teleportation schemes have been proposed by using entangled spatial states of two EPR particles shared between two parties. It is shown that the rate of classical information gain in our dense coding scheme is greater than some previously proposed multi-qubit protocols by a logarithmic factor dependent on the dimension of Hilbert space. The proposed teleportation scheme can provide a complete wave function teleportation of an object having other degrees of freedom in our three-dimensional space, for the first time. All required unitary operators which are necessary in our state preparation and Bell state measurement processes are designed using symmetric normalized Hadamard matrix, some basic gates and one typical conditional gate, which are introduced here for the first time.
We present a mathematical formulation of old teleportation protocol (original teleportation protocol introduced by Bennett et al.) for mixed state and study in detail the role of mixedness of the two-qubit quantum channel in a teleportation protocol. We show that maximally entangled mixed state described by the density matrix of rank-4 will be useful as a two-qubit teleportation channel to teleport a single qubit mixed state when the teleportation channel parameter p1 > 1/2. Also we discuss the case when p1 ≤ 1/2.
Abstract In a controlled quantum secure direct communication (Controlled QSDC) protocol between three parties, the sender sends the encoded secured message to one of the two receivers, which can be decoded only when the other receiver agrees to cooperate. A lot of studies have been done on it using the three-qubit GHZ state, and only a few works have involved the W state. In this work, we introduce a controlled QSDC protocol exploiting a three-qubit W class of state shared between three parties, Alice (Sender), Bob (Controller), and Charlie (Receiver). In the proposed protocol, the shared state parameters and the secret are linked in such a way that it is very difficult to factor them. We will show that these parameters can be factored out easily if the receiver uses a quantum cloning machine (QCM) and thus can retrieve the secret. We find that the protocol is probabilistic and have calculated the probability of success of the protocol. Further, we establish the relation between the success probability and the efficiency of the QCM. In general, we find that the efficiency of the constructed QCM is greater than or equal to 1 3 , but we have shown that its efficiency can be enhanced when the parameters of the shared state are used as the parameters of the QCM. Moreover, we derived the linkage between the probability of success and the amount of entanglement in the shared W class of state. We analyzed the obtained result and found that even a less entangled W class of state can also play a vital role in the proposed controlled QSDC scheme.
Quantum mechanical objects can exhibit correlations with one another that are fundamentally at odds with the paradigm of classical physics; one says that the objects are ‘entangled’. In the last few years, entanglement has come to be studied not only as a marvel of nature but as a potential resource, particularly as a resource for certain unusual kinds of communication. This paper reviews two such uses of entanglement, called ‘teleportation’ and ‘dense coding’. Teleportation is the direct, though not instantaneous, transfer of a quantum state from one object to another over a distance. Dense coding is the effective doubling of the information–carrying capacity of a quantum particle through prior entanglement with a particle at the receiving end. The final section of the paper presents various quantitative measures of entanglement and considers novel features that arise when entanglement is shared among three objects.