Quantum teleportation and superdense coding through the composite W-Bell channel

The states of triqubit systems have an important category W states. A class of asymmetric W states |W _n 〉₁₂₃ were proposed by Agrawal and Pati (Phys Rev A 74:062320, 2006). We introduce an entangled system composed of the |W _n 〉₁₂₃ states and Bell pairs and show its utility for perfect teleportation and superdense coding.     

Quantum secure direct communication with optimal quantum superdense coding by using general four-qubit states

From the perspective of quantum circuit, a construction framework and a measurement framework of a general kind of four-qubit states are sketched, respectively. By utilizing the properties of this kind of states, a quantum secure direct communication (QSDC) protocol is put forward, which adopts the idea of optimal quantum superdense coding to achieve a maximal efficiency and high resources capacity. The security of the proposed protocol is discussed in detail and it is proved to be secure theoretically. Moreover, the sufficient and necessary condition of which multipartite states are suitable for optimal quantum superdense coding in quantum secure direct communication is figured out.     

Simultaneous perfect teleportation of three 2-qubit states

In this paper we show that simultaneous transfer of certain 2-qubit states by three different senders to three different receivers is possible with the help of a single shared entanglement resource. The multi-task is accomplished through a single protocol. There is a supervisor in the type of teleportation process we present here. All the senders perform their quantum measurements in the GHZ-type basis. The protocol is substantially simplified due to the fact that in each measurement of the senders, fifty percent of the basis elements appear. This also leads to an increased efficiency of our protocol which we calculate here. The type of protocol is perfect teleportation protocol.     

Continuous-variable quantum network coding for coherent states

As far as the spectral characteristic of quantum information is concerned, the existing quantum network coding schemes can be looked on as the discrete-variable quantum network coding schemes. Considering the practical advantage of continuous variables, in this paper, we explore two feasible continuous-variable quantum network coding (CVQNC) schemes. Basic operations and CVQNC schemes are both provided. The first scheme is based on Gaussian cloning and ADD/SUB operators and can transmit two coherent states across with a fidelity of 1/2, while the second scheme utilizes continuous-variable quantum teleportation and can transmit two coherent states perfectly. By encoding classical information on quantum states, quantum network coding schemes can be utilized to transmit classical information. Scheme analysis shows that compared with the discrete-variable paradigms, the proposed CVQNC schemes provide better network throughput from the viewpoint of classical information transmission. By modulating the amplitude and phase quadratures of coherent states with classical characters, the first scheme and the second scheme can transmit \(4{\log _2}N\) and \(2{\log _2}N\) bits of information by a single network use, respectively.     

Analysis of quantum linear systems’ response to multi-photon states

The purpose of this paper is to present a mathematical framework for analyzing the response of quantum linear systems driven by multi-photon states. Both the factorizable (namely, no correlation among the photons in the channel) and unfactorizable multi-photon states are treated. Pulse information of a multi-photon input state is represented in terms of tensor, and the response of quantum linear systems to multi-photon input states is characterized by tensor operations. Analytic forms of output correlation functions and output states are derived. The proposed framework is applicable no matter whether the underlying quantum dynamic system is passive or active. Examples from the physics literature are used to illustrate the results presented.     

Efficient schemes for the quantum teleportation of a sub-class of tripartite entangled states

In this paper we propose two schemes for teleportation of a sub-class of tripartite states, the first one with the four-qubit cluster state and the second one with two Bell pairs as entanglement channels. A four-qubit joint measurement in the first case and two Bell measurements in the second are performed by the sender. Appropriate unitary operations on the qubits at the receiver’s end along with an ancilla qubit result in the perfect teleportation of the tripartite state. Analysis of the quantum circuits employed in these schemes reveal that in our technique the desired quantum tasks are achieved with lesser quantum cost, gate count and classical communication bits compared with other similar schemes.     

Generating and using truly random quantum states in Mathematica

The problem of generating random quantum states is of a great interest from the quantum information theory point of view. In this paper we present a package for Mathematica computing system harnessing a specific piece of hardware, namely Quantis quantum random number generator (QRNG), for investigating statistical properties of quantum states. The described package implements a number of functions for generating random states, which use Quantis QRNG as a source of randomness. It also provides procedures which can be used in simulations not related directly to quantum information processing.Program summaryProgram title: TRQSCatalogue identifier: AEKA_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEKA_v1_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 7924No. of bytes in distributed program, including test data, etc.: 88 651Distribution format: tar.gzProgramming language: Mathematica, CComputer: Requires a Quantis quantum random number generator (QRNG, http://www.idquantique.com/true-random-number-generator/products-overview.html) and supporting a recent version of MathematicaOperating system: Any platform supporting Mathematica; tested with GNU/Linux (32 and 64 bit)RAM: Case dependentClassification: 4.15Nature of problem: Generation of random density matrices.Solution method: Use of a physical quantum random number generator.Running time: Generating 100 random numbers takes about 1 second, generating 1000 random density matrices takes more than a minute.     

Construction of general quantum channel for quantum teleportation

We investigate teleportation and controlled teleportation of an arbitrary $N$ -qubit state by using a multipartite entanglement channel. By establishing one-to-one correspondence between an $N$ -qubit quantum state and a high-dimension quantum state, we construct a general quantum channel for quantum teleportation and controlled teleportation of an arbitrary $N$ -qubit state. Furthermore, we generalize the definition of bipartite maximally entangled state for a multi-qubit system, and show that our teleportation protocols can be utilized not only to construct a variety of genuine multipartite entangled states, but also to identify and explore the capability of multipartite entanglement for quantum teleportation and controlled teleportation.     

Faithful teleportation via multi-particle quantum states in a network with many agents

An efficient scheme is proposed for faithful teleportation of an arbitrary unknown multi-particle state via multi-particle quantum states, in which the teleportation is completely deterministic providing that one can successfully construct a group of EPR pairs. Our scheme can effectively avoid possible destruction of the unknown state to be teleported, which however may occur in existing probabilistic teleportation schemes. In addition, we develop a scheme for establishing a faithful quantum channel for both indirect and direct teleportation multi-particle system, which can be applied in a teleportation network where intermediate agents exist between a sender and a receiver. Compared to the indirect construction of the faithful channel, the required auxiliary particle resources, local operations and classical communications in the direct construction scheme are considerably reduced.     

Schemes for teleportation of quantum gates

Quantum teleportation is a computational primitive that allows non-local quantum communication and quantum computation. In this work, we present two schemes for quantum gate teleportation. The first scheme shows under what conditions an n-qudit gate can be teleported using a generalization of Gottesman-Chuang procedure [Nature 402, 390 (1999)]. The second scheme shows that quantum gate teleportation can be transformed in the teleportation of a single-qudit.     

From n-qubit multi-particle quantum teleportation modelling to n-qudit contextuality based quantum teleportation and beyond

This paper further generalizes the modelling framework for contextuality based quantum teleportation to n-dimensional quantum states, or n-qudits (quantum odd-prime based units) which holds considerable promise for even higher mathematical abstraction. The proposed generalization extends the two states in the qubit model, to n states and this n could tend towards infinity. We are heading towards point-sized loops or fine-grained particles of nature, which have been rejected out of hand by string theorists. It is not physical reality when measured from the sense of Planck’s length of 10^?35 metres, but finer-grained particles than Planck’s length 10^?35 metres may exist, although, they are not matter anymore. We argue that why stop at degree of freedom of three, but instead pursue quantum odd-prime based units with higher degree n such as 5, 7, 11, 13, 17 and so on till n^th degree of freedom even tending to infinity. String theorists admit its multiple landscapes with higher degrees of freedom which points its uniqueness both for particles finer than 10^?35 metres as well as distances greater than 10¹⁰ light years. Modern research by physicists and mathematicians including Roger Penrose, Max Tegmark, Nick Bostrom and Herbert Bernstein provides scientific basis to this work.     

Quantum teleportation and dense coding via topological basis

By means of Temperley–Lieb Algebra and topological basis, we make a new realization of topological basis, and get sixteen complete orthonormal topological basis states which are all maximally entangled for four quasi-particles. Then we present an explicit protocol for teleporting an arbitrary two-qubit state via a topological basis entanglement channel. We also show that four bits of classical information can be encoded into a topological basis state by two-particle unitary operations.     

Minimum assured fidelity and minimum average fidelity in quantum teleportation of single qubit using non-maximally entangled states

We study use of non-maximally entangled states (NME) in quantum teleportation (QT) of single qubit. We find that if NME states are written in the form ${| E \rangle =\sum_{j,k} {E_{jk} | j \rangle | k \rangle}}$ , where (j, k) = 0 and 1, and maximally entangled Bell-basis is used in measurement by the sender, the ??Minimum Assured Fidelity?? (the minimum value of fidelity for all possible information states) for QT is 2C/(1?+?C), where C is the concurrence of ${| E \rangle }$ given by C?=?2|det (E)| and E is the matrix defined by the coefficients E _jk . We also find the average of fidelity over various results of Bell-state measurement and its minimum value over all possible information states and discuss it for some special cases. We also show that, to evaluate quality of imperfect QT, minimum assured fidelity is a better measure than concurrence or minimum average fidelity.     

Classical communication and non-classical fidelity of quantum teleportation

In quantum teleportation, the role of entanglement has been much discussed. It is known that entanglement is necessary for achieving non-classical teleportation fidelity. Here we focus on the amount of classical communication that is necessary to obtain non-classical fidelity in teleportation. We quantify the amount of classical communication that is sufficient for achieving non-classical fidelity for two independent 1-bit and single 2-bits noisy classical channels. It is shown that on average 0.208 bits of classical communication is sufficient to get non-classical fidelity. We also find the necessary amount of classical communication in case of isotropic transformation. Finally we study how the amount of sufficient classical communication increases with weakening of entanglement used in the teleportation process.     

Probabilistic teleportation via multi-parameter measurements and partially entangled states

In this paper, a novel scheme for probabilistic teleportation is presented with multi-parameter measurements via a non-maximally entangled state. This is in contrast to the fact that the measurement kinds for quantum teleportation are usually particular in most previous schemes. The detail implementation producers for our proposal are given by using of appropriate local unitary operations. Moreover, the total success probability and classical information of this proposal are calculated. It is demonstrated that the success probability and classical cost would be changed with the multi-measurement parameters and the entanglement factor of quantum channel. Our scheme could enlarge the research range of probabilistic teleportation.     

Efficient entanglement concentration for arbitrary less-hyperentanglement multi-photon W states with linear optics

We present an efficient protocol to concentrate arbitrary less-hyperentangled multi-photon W states to the maximally hyperentangled multi-photon W state with parameter-splitting method and linear optics elements. Compared with previous entanglement concentration works, the present protocol does not need two copies of partially entangled states or the ancillary single photon. Moreover, we discuss the feasibility of the setups of the protocol, concluding that the present protocol is feasible with the current technology. Thus, the protocol may be more meaningful in practical quantum information applications.     

Relations between entanglement, Bell-inequality violation and teleportation fidelity for the two-qubit X states

Based on the assumption that the receiver Bob can apply any unitary transformation, Horodecki et al. (Phys Lett A 222:21–25, 1996) proved that any mixed two spin-1/2 state which violates the Bell-CHSH inequality is useful for teleportation. Here, we further show that any X state which violates the Bell-CHSH inequality can also be used for nonclassical teleportation even if Bob can only perform the identity or the Pauli rotation operations. Moreover, we showed that the maximal difference between the two average fidelities achievable via Bob’s arbitrary transformations and via the sole identity or the Pauli rotation is 1/9.     

Improving ancilla states for quantum computation

We analyze the improvement in output state fidelity upon improving the construction accuracy of ancilla states. Specifically, we simulate gates and syndrome measurements on a single qubit of information encoded into the [[7,1,3]] quantum error correction code and determine the output state fidelity as a function of the accuracy with which Shor states (for syndrome measurements) and magic states (to implement T-gates) are constructed. When no syndrome measurements are applied during the gate sequence, we observe that the fidelity increases after performance of a T-gate and improving magic states construction slows the fidelity decay rate. In contrast, when syndrome measurements are applied, loss of fidelity occurs primarily after the syndrome measurements taken after a T-gate. Improving magic state construction slows the fidelity decay rate, and improving Shor state construction raises the initial fidelity but does not slow the fidelity decay rate. Along the way, we show that applying syndrome measurements after every gate does not maximize the output state fidelity. Rather, syndrome measurements should be applied sparingly.     

Quantum broadcast scheme and multi-output quantum teleportation via four-qubit cluster state

In this paper, two theoretical schemes of the arbitrary single-qubit states via four-qubit cluster state are proposed. One is three-party quantum broadcast scheme, which realizes the broadcast among three participants. The other is multi-output quantum teleportation. Both allow two distant receivers to simultaneously and deterministically obtain the arbitrary single-qubit states, respectively. Compared with former schemes of an arbitrary single-qubit state, the proposed schemes realize quantum multi-cast communication efficiently, which enables Bob and Charlie to obtain the states simultaneously in the case of just knowing Alice’s measurement results. The proposed schemes play an important role in quantum information, specially in secret sharing and quantum teleportation.     

Entropy defect and information for two quantum states

An explicit formula is obtained for the entropy defect and the (maximum) information for an ensemble of two pure quantum states; an optimal basis is found, that is, an optimal measurement procedure which enables one to obtain the maximum information. Some results are also presented for the case of two mixed states, described by second-order density matrices (for example, spin polarization matrices). It is shown that in the case of two states the optimal measurement is a direct von Neumann measurement performed in the subspace of the two states.