Atomic entanglement purification using photonic Faraday rotation

Abstract

We describe an entanglement purification protocol (EPP) for atomic entangled pair using photonic Faraday rotation. It is shown that after the two single photons input-output process in cavity QED, the high quality entangled atomic state can be obtained from the low quality mixed entangled atomic states. Different from other EPPs, the two pairs of mixed states do not need to intact directly. As the photonic Faraday rotation works on the low-Q cavities, this EPP is useful in both quantum communication and computation.PACS numbers: 03.67. Bg, 42.50.Dv I. INTRODUCTIONEntanglement is the important resource in current quantum information processing [1]. For example, quantum teleportaton [2,3], quantum dense coding [4], quantum key distribution [5], quantum state sharing [6][7][8], and quantum direct secure communication [9][10][11], they all require the maximally entangled state to set up the quantum channel. However, the entanglement will inevitably interact with the environment and it will degrade during the process of distribution and storage in the solid system. Entanglement purification is a powerful way for distilling the high quality mixed entangled states in a small ensemble from the low quality mixed states in a large ensembles. In the early works of entanglement purification, they usually used the CNOT gates or similar logic gates, such as the entanglement purification protocol (EPP) proposed by Bennett et. al. [12], the improved EPP proposed by Deustch et. al. [13], the EPP for multipartite entangled systems [14], and so on [15]. In long-distance quantum communication, the photons as the flying qubits are the good candidate for carrying quantum information. So there are many EPPs based on the photons. For example, In 2001, Pan et al. proposed the EPP with the linear optics [16]. In 2003, they realized their protocol in experiment [17]. In 2002, Simon and Pan proposed an EPP using spatial entanglement [18]. In 2008, EPP based on the cross-Kerr nonlinearity was proposed [19]. There are also other EPPs for photonic systems [20-24]. Actually, the flying qubits distribute the entangled states between distance locations, and they should be stored into the solid memory systems for the further application. So there are other EPPs for such solid systems [25-31]. In 2005, Cao et al. proposed an EPP for arbitrary unknown ionic states via linear optics [25]. In the same year, Feng et. al. proposed an EPP with charge detection [26]. In 2006, Reichle et. al. reported their experimental report for purification of two-atom entanglement [27]. In 2011, Wang et al. proposed an EPP for hybrid entangled state using quantum-dot and microcavity coupled system [28].On the other hand, over the pase decades, cavity quantum electrodynamics (QED) has become an important platform for understanding the basic principle of quantum mechanics and quantum information processing [32]. Some excellent experiments, such as the coupling of the trapped atoms with cavity [33], generation of single photons [34], conditional logic gate [35] have b...

Universal quantum gates for atomic systems assisted by Faraday rotation

“…With the Faraday-rotation effect in quantum-dot systems, some interesting tasks can be achieved, such as hyperentangled-Bell-state analysis [52], entanglement concentration [53,54], the construction of CNOT gate [32], and so on. More interestingly, Zhou and Sheng proposed an interesting scheme for entanglement detection [55] and another for entanglement purification [56] with the Faraday-rotation effect in an atomic system. Here, with the development of quantum integrated circuit [57,58], we construct two schemes for Fredkin gate and SWAP gate in an atomic system with the Faraday-rotation effect for the first time.…”

Quantum Private Comparison via Cavity QED

“…[44,[50][51][52]55,61] At present, the physical systems for realizing quantum information processing mainly include cavity quantum electrodynamics (QED), ion trap, nuclear magnetic resonance, quantum dot, superconducting system with Josephson effect, etc. [64] Many works, such as entanglement detection, [65] Bell-state analysis, [66−67] entanglement concentration, [68−71] entanglement purification, [72] entanglement generation [71,73−74] and quantum repeater, [75] have been realized via these physical systems. Cavity QED can guarantee a high level of coherence so that it is an ideal candidate for the experiment of quantum information processing.…”

Optimal multi-photon entanglement concentration with the photonic Faraday rotation

“…The photonic Faraday rotation only works in low-Q cavities and is insensitive to both cavity decay and atomic spontaneous emission. In 2012, based on the photonic Faraday rotation, the group of Peng proposed two entanglement concentration protocols (ECP) for arbitrary atomic state and photonic states, respectively [41], which were improved by our group later [42][43][44][45]. In 2008, Lee et al adopted the atoms as the flying qubits to realize the measurement for the concurrence in a cavity quantum electrodynamics (QED) system [46].…”