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arXiv:quant-ph/0601203 · Physical Review A

Linear optical scheme for error-free entanglement distribution and a quantum repeater

Demetrios A. Kalamidas

Published May 26, 2006• 8 citations
arXivHTMLPDF

Abstract

We present a linear optical scheme for error-free distribution of two-photon polarization-entangled Bell states over noisy channels. The scheme can be applied to an elementary quantum repeater protocol with potentially significant improvements in efficiency and system complexity. The scheme is based on the use of polarization and time-bin encoding of photons and can perform single-pair, single-step purification with currently available technology.

DOI
10.1103/physreva.73.054304

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We present a linear optical scheme for error-free distribution of two-photon polarization-entangled Bell states over noisy channels. The scheme can be applied to an elementary quantum repeater protocol with potentially significant improvements in efficiency and system complexity. The scheme is based on the use of polarization and time-bin encoding of photons and can perform single-pair, single-step purification with currently available technology.
Original quantum repeater protocols based on the single-photon interference suffer from the phase noise of the channel, which makes the long-distance quantum communication infeasible. Fortunately, two-photon interferencelike quantum repeaters can be immune to the phase noise of the channel. However, this type of quantum repeaters may still suffer from polarization disturbance of the channel. Here we propose a quantum repeaters protocol, which is free of the polarization disturbance of the channel based on the invariance of the antisymmetric Bell state $|{\ensuremath{\psi}}^{\ensuremath{-}}⟩=(|H⟩|V⟩\ensuremath{-}|V⟩|H⟩)/\sqrt{2}$ under collective noise. Our protocol is also immune to the phase noise with the Sagnac interferometer configuration. Through single-atom cavity-QED technology and linear optics, this scheme can be implemented easily.
Quantum repeaters create long-distance entanglement between quantum systems while overcoming difficulties such as the attenuation of single photons in a fiber. Recently, an implementation of a repeater protocol based on single qubits in atomic ensembles and linear optics has been proposed [Duan et al., Nature (London) 414, 413 (2001)]. Motivated by rapid experimental progress towards implementing that protocol, here we develop a more efficient scheme compatible with active purification of arbitrary errors. Using similar resources as the earlier protocol, our approach intrinsically purifies leakage out of the logical subspace and all errors within the logical subspace, leading to greatly improved performance in the presence of experimental inefficiencies. Our analysis indicates that our scheme could generate approximately one pair per 3min3\phantom{\rule{0.3em}{0ex}}\mathrm{min}3min over 1280km1280\phantom{\rule{0.3em}{0ex}}\mathrm{km}1280km distance with fidelity $(F\ensuremath{\geqslant}78%)$ sufficient to violate Bell's inequality.
Abstract We propose photonic schemes for the distribution and reconstruction of a two-qubit entangled state using a hybrid entangled state under a noisy quantum channel. First, to generate a hybrid entangled state correlated with polarizations and time-bins, we employ a quantum dot (QD)-cavity system (nonlinear optical gate) and linear optical devices to implement controlled operation. These schemes can achieve the distribution and reconstruction of a two-qubit entangled state from hybrid entanglement by utilizing only linear optical devices without a QD-cavity system (i.e., a nonlinear optical device) for users who want to share an entangled state under a noisy quantum channel. For a feasible realization of the proposed schemes, we analyze the interaction between the photons and QD-cavity system and demonstrate the experimental conditions under which the reliable performance of the QD-cavity system is achieved.
The faithful distribution of entanglement over noisy channels is a vital prerequisite for many quantum technological applications. Quantum information can be encoded in different degrees of freedom (DOF) of photons, where each encoding comes with its own advantages and disadvantages with respect to noise resilience and practicality in manipulation. In this work, we experimentally implement a deterministic entanglement purification protocol that allows us to faithfully distribute entanglement in one DOF over a noisy channel and then remotely transfer it to another DOF for manipulation. In particular, we distribute robust energy-time entanglement and transfer it to polarization entanglement at the communicating parties. The remotely obtained polarization state is independent of the polarization noise during distribution and reaches fidelities to a Bell state of up to $97.6\mathrm{%}$. Our scheme enables robust and efficient polarization entanglement distribution in the presence of arbitrary polarization noise, which is relevant for future large-scale quantum networks.
We present an efficient quantum repeater protocol that uses coupled systems of quantum-dot spins and optical microcavities, in which the spatial entanglement of a photon system can be converted into polarization entanglement of electron spins. The bit-flip and phase-flip errors on the polarization state of each qubit caused by noisy channels can be rejected, without resorting to additional qubits. Two remote parties can obtain the maximally entangled electron-spin state and store it deterministically after the transmission of photons, independent of the noise parameters. The transmission distance of photons will not be limited by the coherence time of memory units in the present protocol, unlike the previous atomic-ensemble-based quantum repeater protocols, and it can be applied directly in long-distance quantum-communication protocols.