Experimental entanglement purification of arbitrary unknown states

Pan, Jian-Wei; Gasparoni, Sara; Ursin, Rupert; Weihs, Gregor; Zeilinger, Anton

doi:10.1038/nature01623

Cited by 485 publications

(409 citation statements)

References 27 publications

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“…The experimentally feasible protocol given in Refs. [37,38] also requires collective operations at both ends. There is a further difference of the entanglement swapping protocol considered in this paper, with entanglement distillation protocols [32].…”

Section: F a Kind Of Superadditivity For Werner Statesmentioning

confidence: 99%

Entanglement swapping of noisy states: A kind of superadditivity in nonclassicality

Sen

Brukner

et al. 2005

Phys. Rev. A

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We address the question as to whether an entangled state that satisfies local realism will give a violation of the same, after entanglement swapping in a suitable scenario. We consider such possibility as a kind of superadditivity in nonclassicality. Importantly, it will indicate that checking for violation of local realism, in the state obtained after entanglement swapping, can be a method for detecting entanglement in the input state of the swapping procedure. We investigate various entanglement swapping schemes, which involve mixed initial states. The strength of violation of local realism by the state obtained after entanglement swapping, is compared with the one for the input states. We obtain a kind of superadditivity of violation of local realism for Werner states, consequent upon entanglement swapping involving Greenberger-Horne-Zeilinger state measurements. We also discuss whether entanglement swapping of specific states may be used in quantum repeaters with a substantially reduced need to perform the entanglement distillation step.

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Section: F a Kind Of Superadditivity For Werner Statesmentioning

confidence: 99%

Entanglement swapping of noisy states: A kind of superadditivity in nonclassicality

Sen

Brukner

et al. 2005

Phys. Rev. A

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“…Essential to the scalability of the DLCZ scheme are the long lived collective excitations, which represent a quantum memory. Without such quantum memory, the overhead scales exponentially with the channel length.Although entanglement swapping [7] and entanglement purification [8] have been experimentally demonstrated with linear optics, it is difficult to achieve the high fidelity quantum memory. Significant experimental advances have been made to implement the DLCZ-scheme [3] both with ultra-cold atomic clouds [9,10,11,12,13,14] and hot vapors in buffer gas cells [15,16,17].…”

mentioning

confidence: 99%

Collisional decoherence during writing and reading quantum states

et al. 2007

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Collisions, even though they do not limit the lifetime of quantum information stored in ground state hyperfine coherences, they may severely limit the fidelity for quantum memory when they happen during the write and read process. This imposes restrictions on the implementation of Raman type quantum processes in thermal vapor cells and their performance as a quantum memory. We study the effect of these collisions in our experiment.PACS numbers: 32.80. Qk , 03.67.Hk, 03.65.Yz In recent years, significant experimental advances have been achieved in the field of quantum communication (QC) [1,2]. However, photon loss and detector noise limit direct QC to moderate distances (up to 100 km in quantum cryptography). In 2001, Duan, Lukin, Cirac and Zoller (DLCZ) proposed a practical quantum repeater [3,4] based on writing and reading single excitations in atomic ensembles using Raman type processes. A joint projective measurement of individual photons emitted from two separated atomic ensembles leads to qubittype entanglement of collective excitations in both ensembles, which combined with entanglement swapping [5] and entanglement purification [6] allows to create entanglement over (arbitrary) long distances. Essential to the scalability of the DLCZ scheme are the long lived collective excitations, which represent a quantum memory. Without such quantum memory, the overhead scales exponentially with the channel length.Although entanglement swapping [7] and entanglement purification [8] have been experimentally demonstrated with linear optics, it is difficult to achieve the high fidelity quantum memory. Significant experimental advances have been made to implement the DLCZ-scheme [3] both with ultra-cold atomic clouds [9,10,11,12,13,14] and hot vapors in buffer gas cells [15,16,17]. While ultracold ensembles require substantial technological effort, vapor cells provide comparatively easy experimental access. Moreover atomic clock experiments have shown that with the correct coating of cell walls and the use of buffer gas the ground state coherence can be preserved for up to > 10 8 collisions [18] leading to very narrow line widths.In this paper, we demonstrate however that the mapping process between light fields and atomic coherence is strongly influenced by collisions. This severely limits the fidelity of the DLCZ-scheme and a quantum memory in hot atomic ensembles.The mapping process between light fields and atomic coherence is essential to the DLCZ scheme [3]. Single excitations are written in an atomic ensemble Raman transitions in a three level λ-configuration: (ground states FIG. 1: (color online) a) Experimental setup: Two control lasers (write and read) are combined at a Wollastone prism (WP) and intersect inside a magnetically shielded 87 Rb vapor cell with Neon buffer gas. The weak signal fields (Stokes and Anti-Stokes) are separated from the control beams at a second polarizer. After spectral filtering, the signal photons are detected by fiber coupled avanlanche photo diode (APD). b) Simplified level sche...

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“…Purification of two mode entangled states has been shown experimentally for qubits [20,21] and in the continuous variable (CV) regime [22,23]. (CV-entanglement purification is especially challenging [24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Quantum state engineering, purification, and number-resolved photon detection with high-finesse optical cavities

et al. 2010

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We propose and analyze a multi-functional setup consisting of high finesse optical cavities, beam splitters, and phase shifters. The basic scheme projects arbitrary photonic two-mode input states onto the subspace spanned by the product of Fock states |n |n with n = 0, 1, 2, . . .. This protocol does not only provide the possibility to conditionally generate highly entangled photon number states as resource for quantum information protocols but also allows one to test and hence purify this type of quantum states in a communication scenario, which is of great practical importance. The scheme is especially attractive as a generalization to many modes allows for distribution and purification of entanglement in networks. In an alternative working mode, the setup allows of quantum non demolition number resolved photodetection in the optical domain.

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Experimental entanglement purification of arbitrary unknown states

Cited by 485 publications

References 27 publications

Entanglement swapping of noisy states: A kind of superadditivity in nonclassicality

Entanglement swapping of noisy states: A kind of superadditivity in nonclassicality

Collisional decoherence during writing and reading quantum states

Quantum state engineering, purification, and number-resolved photon detection with high-finesse optical cavities

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