Quantum teleportation and entanglement swapping for systems of arbitrary spin

Quantum teleportation plays an important role in quantum information science. In order to obtain the effect of quantum teleportation of a quantum state by using an entangled resource, the fidelity of teleporting the quantum state should be calculated. Braunstein and Kimble[Phys. Rev. Lett. 80 869 (1998)] derived a formula of calculating the fidelity of quantum teleportation for Gaussian entangled resource and any input state to be teleported. Then, the point is how to calculate the quantum teleportation fidelity for any entangled resource. In this paper, werealize this purpose by using the entangled state representation. First, we derive the Weyl expansion of any density operator by using the completeness relation between coherent state and P-representation. Then using the orthogonal property of entangled state representation and the traditional Kimble-Braunstein scheme of quantum teleportation, we further derive the mean density operator of the output state, which means that we establish the relation between the output density operator and the characteristic functions of the input state to be teleported and the entangled resources. The characteristic function of the output state is also derived which is in the concise form relating these two characteristic functions above. Then we further obtain a new formula for calculating the quantum teleportation fidelity for the coherent state input and any two-mode entangled resource. It is shown that the fidelity of teleportation can be easily calculated when the Q-function of the normally ordering form of entangled resource is known. This is a convenient way of obtaining the fidelity of teleportation. As its applications, some Gaussian and non-Gaussian entangled states are examined to teleport the coherent state, whose results are correct.

Classical secret sharing proposed by Shamir used classical computational power in classical cryptography to achieve secret key sharing, but with the advent of quantum systems, computational power can be overruled. To ensure a secure secret sharing scheme independent of computational power, a scheme independent of computational complexity is needed to achieve security. This paper will provide a protocol dependent on inherent secure nature of quantum cryptography (quantum no cloning theorem and quantum measurement rule). A secure multiparty quantum secret sharing scheme has been proposed to ensure that no one can eavesdrop or extract any share of the secret message via inherent security provided by quantum entanglement swapping and quantum teleportation. Entanglement swapping is a process that allows two non-interacting quantum systems to be entangled. Whereas, Quantum teleportation allows a party to send a qubit to another entangled party without sending the qubit over the channel. Moreover, in order to ensure security against possible active attacks, sender himself will generate and distribute EPR pairs to be used in the scheme. Result will be a secure multiparty QSS scheme which will be secure against internal and external eavesdropping, masquerading and brute-force attacks.

Quantum teleportation and entanglement swapping represent pivot concepts in quantum information science. Here, we show that entangled photon pairs generated on-demand by quantum-dots can be used to implement successfully quantum teleportation and entanglement swapping protocols.

Recent discovery of the fine-grained entropy formula in gravity succeeded in reconstructing the Page curves that are compatible with unitary evolution. The formula of generalized entropy derived from the gravitational path integration, nevertheless, does not provide a concrete insight on how information comes out from a black hole. In this paper, we start from a qubit model and provide a quantum informational interpretation of entanglement islands. We propose an identification of entanglement islands with quantum measurements and remark on the parallel between the black hole information problem and the old problem of quantum measurements. We show that the Page curve can still be realized even if information is lost so that the information paradox can be explained as one manifestation of measurement problem. We show that such interpretation is necessary for a quantum informational model if smooth horizons and bulk reconstruction are assumed, and demonstrate explicitly that Page curves of solvable 2D gravity can be obtained through teleportation and entanglement swapping. We argue that the similarities between the black hole information problem and the measurement problem suggest links in the origins of the two problems.

Any set of states which cannot be perfectly distinguished by local operations\nand classical communication (LOCC) alone, can always be locally distinguished\nusing quantum teleportation with enough entanglement resource. However, in\nquantum information theory, entanglement is a very valuable resource, so it\nleaves the following open question: how to accomplish this task more\nefficiently than teleportation, that is, design the local discrimination\nprotocol using less entanglement resource. In this paper, we first present two\nprotocols to locally distinguish a set of unextendible product bases (UPB) in\n$5\\otimes 5$ by using different entanglement resource. Then, we generalize the\ndistinguishing methods for a class of UPB in $d\\otimes d$, where $d$ is odd and\n$d\\geqslant 3$. Furthermore, for a class of UPB in $d\\otimes d$, where $d$ is\neven and $d\\geqslant 4$, we prove that these states can also be distinguished\nby LOCC with multiple copies of low-dimensional entanglement resource. These\nresults offer rather general insight into how to use entanglement resource more\nefficiently, and also reveal the phenomenon of less nonlocality with more\nentanglement.\n

It is shown that quantum teleportation and entanglement swapping can be easily derived from Einstein-Podolsky-Rosen correlations and special relativity. This raises the question of what is really teleported in a teleportation experiment. It is also shown that the behavior of two photons that arrive together at a beam splitter can be seen as a particular case of a nonlocal effect in which they arrive ``together'' at two different beam splitters.

In this paper we propose a new protocol for multiparty secret key sharing by using quantum entanglement swapping. Quantum Entanglement swapping is a process that allows two non-interacting quantum systems to be entangled. Further, to increase the security level and to make sure that the users are legitimate, authentication for both parties will be required by a trusted third party. In this protocol, a trusted third party will authenticate the sender and the receiver and help them forming a secret key. Furthermore, the proposed protocol will perform entanglement swapping between the sender and the receiver. The result from the entanglement swapping will be an Einstein-Podolsky-Rosen (EPR) pair that will help them in forming and sending the secret key without having the sender to send any physical quantum states to the receiver. This protocol will provide the required authentication of all parties to the trusted party and it will provide the required secure method in transmitting the secret key.

Quantum teleportation is one of the most basic quantum protocols, which transfers an unknown quantum state from one location to another through local operation and classical communication by using shared quantum entanglement without physical transfer of the information carrier. And it has been widely used in various quantum information protocols such as entanglement swapping, quantum repeaters, quantum gate teleportation, quantum computation based on measurement, and quantum teleportation networks, which have important application value in quantum computation and quantum information. Quantum teleportation is a naturally bipartite process, in which an unknown quantum state can only be transmitted from one node to another. With the further development of quantum information research, it is necessary to transfer quantum states or quantum information among more and more nodes. Multipartite quantum protocols are expected to form fundamental components for larger-scale quantum communication and computation. A bipartite quantum teleportation should be extended to a multipartite protocol known as a quantum teleportation network. In this paper, a multifunctional quantum teleportation network is proposed theoretically. We first propose a special method of constructing four-partite quantum resources in continuous variables (CVs), and based on this, construct two different types of CV quantum teleportation networks. One type of network contains just one quantum teleportation process consisting of a sender, a receiver and two controllers. In this type of network, the unknown quantum state can be recovered at any other node according to the requirement after the measurement in the input node, which enriches the transfer direction and transfer mode of the unknown quantum state. And meanwhile, the two controllers can control the transfer of a quantum state from the sender to the receiver by restricting the sender and receiver’s access to their information, which makes the quantum teleportation network controllable. The other type of network has two quantum teleportation processes, each containing only a sender, a receiver and no controllers, which increases the number of quantum states that can be transmitted. Then we analyze the dependence of the fidelity of each quantum teleportation network on different physical parameters, and compare the characteristics, advantages and disadvantages among different types of quantum teleportation networks. The scheme for constructing a multifunctional quantum teleportation network in this paper shows some advantages, such as the greater number of quantum nodes, diversity of types, simple operation procedure. And all these advantages provide a broader application prospect for establishing larger and more complex quantum information networks in the future and quicken the pace of the application of quantum information.

One scheme that aids in this distribution is entanglement concentration. This converts a large number of less entangled pairs into a smaller number of more entangled pairs using only local operations @3#. The concentrated pairs can then be used to perform the communication protocol faithfully. One such protocol, quantum teleportation @2#, exploits priorly shared entanglement to transfer an unknown ~or even partially unknown @4#! quantum state to a distant location. Teleporting one particle of an entangled pair results in the exchange of entangled partners across a distance, a process known as ‘‘entanglement swapping’’ @2,5#. Two of the particles that become entangled have not directly interacted at any stage, and, therefore, the swapping can be used as a means of entanglement distribution. Both teleportation and entanglement swapping have been experimentally demonstrated @6,7#, in the domain of microscopic systems. Demonstrations of such schemes with macroscopic objects would be of fundamental interest. An increasingly controllable macroscopic quantum system is a Bose-Einstein condensed state of a trapped dilute gas @8#. Bose condensates have already been used to demonstrate quantum features, such as superposition, in the macroscopic domain @9#. More recently, there have also been suggestions for creating specific types of entangled atomic beams, and multiparticle entangled states from Bose condensates @10#. In this paper, we propose a method for achieving entanglement swapping, using techniques that are experimentally feasible. This opens up the possibility of entanglement-aided communications using Bose condensates. We also show that a theoretical proposal for entanglement concentration by entanglement swapping, @11#, may be implemented, using exactly the same measurements. We begin by presenting a general entanglement swapping protocol for Bose condensates. We consider four condensates labeled by the modes a,b,c, and d ~see Fig. 1!. Modes a and b are entangled with a total number of n atoms uc ab& 15 ( p50 n

Quantum entanglement is the most representative feature of quantum mechanics to classical mechanics. It is the delocalization, non-classical strong correlation among multiple quantum system. It has been developed for nearly one hundred years and a lot of methods of production and applications have been proposed. Aiming at the generation mode of quantum entanglement, this study presents two general preparation methods of quantum entanglement sources, including spontaneous parametric down-conversion (SPDC) and the preparation of quantum entanglement sources based on the four-wave mixing (FWM) effect. The principle, advantages and disadvantages of quantum entanglement sources are analyzed respectively. Finally, the research and application direction of the preparation method of quantum entanglement source are prospected. With the ability of preparation of quantum entanglement source, the application of quantum entanglement developed quickly, (e.g., quantum teleportation, entanglement swapping, quantum key distribution and quantum dense coding in the area of communication), and other area such as quantum computer, quantum imaging, quantum ranging and quantum clock synchronization. These results shed light on guiding further exploration of entanglement fabrication.

Einstein–Podolsky–Rosen correlation and continuous-variable quantum teleportation for the non-Gaussian entangled state with coherent component

A set of orthogonal product states is deemed genuinely nonlocal if they remain locally indistinguishable under any bipartition. In this paper, we first construct a genuinely nonlocal product basis B I(5, 3) in C5⨂C5⨂C5 using a set of nonlocal product states in C3⨂C4 . Then, we obtain a genuinely nonlocal product basis B II(5, 3) by replacing certain states in B I(5, 3) with some superposition states. We achieve perfect discrimination of the constructed genuinely nonlocal product basis, separately employing two EPR states and one GHZ state. Our protocol is more efficient than quantum teleportation.

In view of the problem that there is only one typical Bell basis for QT (Quantum Teleportation), three new GBBs (Generalized Bell Bases) are obtained by transforming unitarily the Hadamard gates with the methods of Pauli gates in the quantum circuit of the traditional Bell basis, and four Bell bases have an identical general formula.Three controlled-QT schemes are proposed based on these GBBs.The changed processes of quantum entangled states during QT in these schemes are derived by using the similar method of the traditional Bell basis.The result analyses of quantum state collapses of controlled-QT show that more two-qubit quantum entanglement resources of Bell states can be available.These schemes can be considered as the beneficial supplements for current QT work with GBS (Generalized Bell State).

Secured Data Aggregation Scheduling in Ubiquitous sensor networks is a major research problem nowadays. Since the sensors communicate wirelessly, they are exposed to a high level of vulnerability from the intruders. Quantum key distribution is a technique that is used nowadays for providing security. Though the secure keys are used for short distances only, it offers many advantages over traditional methods in providing security. Quantum key distribution adopts many methods like entanglement swapping and quantum teleportation. Reversible logic gates like CNOT, Toffoli, and Fredkin are proved to offer many advantages in quantum computing. Also a very little research is carried to provide security to the nodes in ubiquitous sensor networks using quantum cryptography so as to maximize the throughput and utilize the hardware resources effectively. Hence in this paper, we propose an intrusion detection policy for security to sensor nodes using quantum cryptography. The proposed protocol monitors the communication between sensor nodes and uses a simple policy to detect the malicious nodes. In our detection policy we adopted an EPR-pair allocation scheme in terms of the quantum gates like Toffoli and Feynman called SwapGate.

We present a scheme for teleporting multi-qutrit quantum information from a sender to a receiver via the control of many agents in a network. Agents's control parameters are obtained via quantum entanglement swapping. In our scheme, Zhang and Man's QSS protocol [Phys. Rev. A 72 (2005) 022303] based on Bell-state entanglement swapping is generalized to a qutrit case. Our scheme owns the advantage of having higher code capacity and better security than the work [Commun. Theor. Phys. 44 (2005) 847] on controlled teleportation for multi-qubit.