Simultaneous generation of two spin-wave–photon entangled states in an atomic ensemble

Abstract

The generation and storage of entangled photons play important roles in quantum information technique. Spontaneous Raman scattering (SRS) in atomic ensembles provides a promising method to generate entangled photons capable of storage. In the past experiments, a spin-wave-photon entangled state is produced via SRS in an atomic ensemble, with which a pair of entangled photons is obtained. Here, we report a scheme of simultaneously generating two spin-wave-photon entangled states in an atomic ensemble by collecting Stokes photons at two different directions. Based on the obtained two atom-photon entangled sources, we generate a three-photon GHZ polarization-entangled state and conditionally prepare a polarization-entangled photon pair, respectively. 2The entangled photon pairs are the crucial resources in linear optical quantum computations (LOQC) and quantum communications (QC) [1][2][3][4][5].However, the probabilistic generations of entangled photons limit their applications in the real world [1,[6][7]. For solving this problem, a promising scheme is to effectively store the entangled photons in atomic or solid-state ensembles for a desired time [1][2][3][4][5].Spontaneous Raman scattering (SRS) in an atomic ensemble can emit a single photon and simultaneously create a single spin-wave excitation [8][9][10][11][12][13][14][15][16][17][18][19][20].The emitted photon can be directly stored in atomic ensembles via EIT with a larger storage efficiency up to 20-50% [11][12][13]. The correlation between the emitted photons and the spin-wave excitations forms the physical fundament of generating the spin-wave-photon (atom-photon) entanglement [3]. In past experiments [13][14][15][16][17], an atom-photon entangled state has been generated from a cold atomic ensemble, with which a pair of entangled photons is obtained.However, in some quantum information protocols, the three-qubit GHZ state[18] and on-demand entanglement source [19] are required, whose preparation relies on the simultaneous generations of two or more entangled photon pairs capable of storages.On the other hand, although the quantum repeater node [17] has been experimentally demonstrated by using two atom-photon entangled states simultaneously generated from two cold atomic ensembles, the storage 2 3 3 lifetime of the entanglement is very short (~ 6 µs), which is not enough for the long-distance quantum communication [17]. For solving this problem, we can firstly produce a pair of polarization-entangled photons in a heralded or conditional manner, and then mapped the entanglement into atomic-ensemble memories via the long-lived (1-ms) EIT quantum storage scheme [20].In this letter, we present an experimental demonstration of the simultaneous generation of two atom-photon entangled states in a cold atomic ensemble via SRS induced by a write laser pulse. In contrast to past experiments [13,[16][17], which achieved the high-fidelity atom-photon entanglement by encoding the photonic qubit in two spatial modes of a single photon, the presented experiment empl...

Long-lived and multiplexed atom-photon entanglement interface with feed-forward-controlled readouts

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Generation of polarization-entangled photon pairs in a cold atomic ensemble

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Sedimentary response and restoration of paleoshoreline of Taiyuan-Shanxi Formations in North China basin

“…Based on Spontaneous Raman Scattering (SRS) of cold atom ensemble, the atom-photon quantum entanglement has been generated [7][8][9][10][11][12]. Quantum entanglement experiments have also been experimentally prepared in many matters, such as ion, quantum dots and other different quantum systems [13][14][15][16][17][18][19][20][21]. Riedmatten's group [22] demonstrated a heralded single photon source with controllable read pulse duration emission time based on a cold atomic ensemble, which can generate photons with temporal durations varying over three orders, which can used for other different quantum systems.…”