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Scientific Reports

Entanglement concentration for arbitrary four-particle linear cluster states

Tingting Song, Xiaoqing Tan, Tian‐Yin Wang

Published May 10, 2017• 4 citations
Publisher

Abstract

Cluster states, whose model are a remarkably rich structure in measurement-based quantum computation, hold high degree of entanglement, while entanglement is very fragile during the process of transmission because of the inevitable interaction with the environment. We propose two entanglement concentration protocols for four-particle linear cluster states which and are susceptible to the decoherence and the imperfect communication setups. In the first protocol, POVM operators are introduced to maximize the success probability, and the second protocol is based on cross-Kerr nonlinearity which is utilized to check the parity between the original particle and the ancillary particle. Both of the protocols have their own advantages. The first one can be easily realized in experiment by linear optics, while the one with cross-Kerr nonlinearity reach more than 90% success probability by iteration. Since the wide application of cluster states, the two protocols are efficient and valuable to different fields of quantum communication.

DOI
10.1038/s41598-017-02146-9

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Cluster states, whose model are a remarkably rich structure in measurement-based quantum computation, hold high degree of entanglement, while entanglement is very fragile during the process of transmission because of the inevitable interaction with the environment. We propose two entanglement concentration protocols for four-particle linear cluster states which and are susceptible to the decoherence and the imperfect communication setups. In the first protocol, POVM operators are introduced to maximize the success probability, and the second protocol is based on cross-Kerr nonlinearity which is utilized to check the parity between the original particle and the ancillary particle. Both of the protocols have their own advantages. The first one can be easily realized in experiment by linear optics, while the one with cross-Kerr nonlinearity reach more than 90% success probability by iteration. Since the wide application of cluster states, the two protocols are efficient and valuable to different fields of quantum communication.
Multi-particle cluster states play a significant role in quantum information processing. However, due to the inevitable interaction with the environment in the transmission process, the fidelity of entanglement decreases. To distill the perfect cluster states, we present two schemes for arbitrary six-particle cluster states. POVM local unitary operators that are obtained by solving the equation according to the properties of cluster states are used in the first protocol. The second protocol is based on cross-Kerr nonlinearity which is exploited to check parity between original qubit with ancillary single qubit and it can achieve a higher probability of success through iteration. Furthermore, we can generalize the first method to concentrate entanglement on even number of particles. Our protocol will be useful in practical applications.
Abstract Noise in the channel affects the security of cryptography protocols. The obvious solution for quantum protocols is to estimate the transformation of quantum states caused by the noise. Cluster states are the basic structures of quantum cryptography protocols, which are transmitted through the lossy quantum channel during the procedure of the protocols. The entanglement of the cluster states is extremely fragile and easy to be inflected by inevitable interaction with the environment. To ensure the fidelity of cluster states, the entanglement of the states must be concentrated after the transmission. We propose four protocols to concentrate the entanglement of five-photon linear cluster states by linear optics, in two of which only three parties should perform the local POVM operations. All the protocols reach the maximum of successful probability, and furthermore they are implemented by the linear optics alone. The simulation results depict that lots of five-photon linear cluster states could be concentrated via our protocols, and those protocols are robust against the accuracy of the linear optics. Hence, our protocols are valuable in many fields of quantum information and quantum cryptography.
We propose an entanglement concentration protocol to concentrate an arbitrary partially-entangled four-photon cluster state. As a pioneering three-step entanglement concentration scheme, our protocol only needs a single-photon resource to assist the concentration in each step, which makes this protocol more economical. With the help of the linear optical elements and weak cross-Kerr nonlinearity, one can obtain a maximally-entangled cluster state via local operations and classical communication. Moreover, the protocol can be iterated to obtain a higher success probability and is feasible under current experimental conditions.
We present two realistic entanglement concentration protocols (ECPs) for pure partially entangled photons. A partially entangled photon pair can be concentrated to a maximally entangled pair with only an ancillary single photon with a certain probability, while the conventional ECPs require two copies of partially entangled pairs at least. Our first protocol is implemented with linear optics and the second protocol is implemented with cross-Kerr-nonlinearities. Compared with other ECPs, they do not need to know the accurate coefficients of the initial state. With linear optics, it is feasible with current experiments. With cross-Kerr-nonlinearities, it does not require sophisticated single-photon detectors and can be repeated to get a higher success probability. Moreover, the second protocol can get the higher entanglement transformation efficiency and it may be the most economical protocol by far. Meanwhile, both protocols are more suitable for multiphoton system concentration because they need less operations and classical communications. All these advantages make the two protocols useful in current long-distance quantum communications.
We present a protocol for concentrating an arbitrary four-photon entangled state into a maximally entangled state assisted with singled photons. The concentration protocol uses the linear optics and the cross-Kerr nonlinearity based on the post selection principle. Four parties called Alice, Bob, Charlie and Dan in different distant locations can obtain the cluster state from an arbitrary entangled four-photon state with a certain probability. Quantum non-demolition (QND) measurements are available in this protocol. Moreover, this scheme can be steady with a higher success possibility.
We present two two-step practical entanglement concentration protocols for concentrating an arbitrary three-particle less-entangled WWW state into a maximally entangled WWW state assisted with single photons. The first protocol uses the linear optics and the second protocol adopts the cross--Kerr nonlinearity to perform the protocol. In the first protocol, based on the postselection principle, three parties say Alice, Bob, and Charlie in different distant locations can obtain the maximally entangled WWW state from the arbitrary less-entangled WWW state with a certain success probability. In the second protocol, the parties are not required to possess the sophisticated single-photon detectors and the concentrated photon pair can be retained after performing this protocol successfully. Moreover, the second protocol can be repeated to get a higher success probability. Both protocols may be useful in practical quantum-information applications.