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arXiv:quant-ph/0506168 · Journal of Optics B Quantum and Semiclassical Optics

Local versus nonlocal cloning in a noisy environment

Alessandro Ferraro, Matteo G. A. Paris

Published Nov 15, 2005• 3 citations
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Abstract

We address the distribution of quantum information among many parties in the presence of noise. In particular, we consider how to optimally send to m receivers the information encoded into an unknown coherent state. On one hand, a local strategy is considered, consisting in a local cloning process followed by direct transmission. On the other hand, a telecloning protocol based on nonlocal quantum correlations is analyzed. Both the strategies are optimized to minimize the detrimental effects due to losses and thermal noise along the propagation. The comparison between the local and the nonlocal protocol shows that telecloning is more effective than local cloning for a wide range of noise parameters. Our results indicate that nonlocal strategies can be more robust against noise than local ones, thus being suitable candidates to play a major role in quantum information networks.

DOI
10.1088/1464-4266/7/12/013

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We address the distribution of quantum information among many parties in the presence of noise. In particular, we consider how to optimally send to m receivers the information encoded into an unknown coherent state. On one hand, a local strategy is considered, consisting in a local cloning process followed by direct transmission. On the other hand, a telecloning protocol based on nonlocal quantum correlations is analyzed. Both the strategies are optimized to minimize the detrimental effects due to losses and thermal noise along the propagation. The comparison between the local and the nonlocal protocol shows that telecloning is more effective than local cloning for a wide range of noise parameters. Our results indicate that nonlocal strategies can be more robust against noise than local ones, thus being suitable candidates to play a major role in quantum information networks.
We address the generation, propagation, and application of multipartite continuous variable entanglement in a noisy environment. In particular, we focus our attention on the multimode entangled states achievable by second-order nonlinear crystals---i.e., coherent states of the SU(m,1)\mathrm{SU}(m,1)SU(m,1) group---which provide a generalization of the twin-beam state of a bipartite system. The full inseparability in the ideal case is shown, whereas thresholds for separability are given for the tripartite case in the presence of noise. We find that entanglement of tripartite states is robust against thermal noise, both in the generation process and during propagation. We then consider coherent states of SU(m,1)\mathrm{SU}(m,1)SU(m,1) as a resource for multipartite distribution of quantum information and analyze a specific protocol for telecloning, proving its optimality in the case of symmetric cloning of pure Gaussian states. We show that the proposed protocol also provides the first example of a completely asymmetric $1\ensuremath{\rightarrow}m$ telecloning and derive explicitly the optimal relation among the different fidelities of the mmm clones. The effect of noise in the various stages of the protocol is taken into account, and the fidelities of the clones are analytically obtained as a function of the noise parameters. In turn, this permits the optimization of the telecloning protocol, including its adaptive modifications to the noisy environment. In the optimized scheme the clones' fidelity remains maximal even in the presence of losses (in the absence of thermal noise), for propagation times that diverge as the number of modes increases. In the optimization procedure the prominent role played by the location of the entanglement source is analyzed in details. Our results indicate that, when only losses are present, telecloning is a more effective way to distribute quantum information than direct transmission followed by local cloning.
We first classify the quantum clone into irreversible and reversible types from the perspective of quantum-information distribution. We propose a scheme of continuous-variable reversible telecloning, which broadcast the information of an unknown state without loss from a sender to several spatially separated receivers exploiting multipartite entanglement as quantum channels. In this scheme, the quantum information of an unknown state is distributed into MMM optimal clones and $M\ensuremath{-}1$ anticlones using 2M2M2M-partite entanglement. For the perfect quantum-information distribution that is optimal cloning, 2M2M2M-partite entanglement is required to be a maximum two-party entanglement.
The distribution of the quantum states to remote receivers is an indispensable technology in quantum communication, quantum networks, and quantum information processing. Perfect distribution does not allow any quantum information loss of the distributed quantum state. Quantum telecloning, which is made up of quantum cloning and quantum teleportation, is a remote quantum information distribution protocol. Here, we experimentally demonstrate unconditional $1\ensuremath{\rightarrow}3$ quantum telecloning of coherent states, and the fidelities of the cloned states are $0.64\ifmmode\pm\else\textpm\fi{}0.01, 0.64\ifmmode\pm\else\textpm\fi{}0.01$, and $0.49\ifmmode\pm\else\textpm\fi{}0.01$, respectively. No information about the unknown state is lost during the telecloning process by exploiting the quadripartite entangled modes as an auxiliary resource. Deterministic $1\ensuremath{\rightarrow}3$ quantum telecloning has great potential for applications in advanced quantum technology.
We show that perfect quantum teleportation can be achieved with mixed photon polarization states when nonlocal memory effects influence the dynamics of the quantum system. The protocol is carried out with a pair of photons, whose initial maximally entangled state is destroyed by local decoherence prior to teleportation. It is demonstrated that the presence of strong nonlocal memory effects, which arise from initial correlations between the environments of the photons, allow to restore perfect teleportation. We further analyze how the amount of initial correlations within the environment affects the fidelity of the protocol, and find that for a moderate amount of correlations the fidelity exceeds the one of the previously known optimal teleportation protocol without memory effects. Our results show that memory effects can be exploited in harnessing noisy quantum systems for quantum communication and that non-Markovianity is a resource for quantum information tasks.
Abstract Quantum state transfer is the act of transferring quantum information from one system in a quantum network to another without physically transporting carriers of quantum information, but instead engineering a Hamiltonian such that the state of the sender is transferred to the receiver through the dynamics of the whole network. A generalization of quantum state transfer called quantum routing concerns simultaneous transfers between multiple pairs in a quantum network, imposing limitations on its structure. This study considers transfer of Gaussian states over noisy quantum networks with modular structure, which have been identified as a suitable platform for quantum routing. Two noise models are compared, affecting either the network topology or the network constituents, studying their effects on both the transfer fidelities and the network properties. The two models are found to affect different features of the network allowing for the identification and quantification of the noise. These features are then used as a guide toward different strategies for the compensation of the noise, and to examine how the compensation strategies perform. The results show that in general, modular networks are more robust to noise than monolithic ones.