Robust Creation of Entanglement between Remote Memory Qubits

Abstract

In this Letter we propose a robust quantum repeater architecture building on the original Duan-Lukin-Cirac-Zoller (DLCZ) protocol [L.-M. Duan, M. D. Lukin, J. I. Cirac, and P. Zoller, Nature (London) 414, 413 (2001)10.1038/35106500]. The architecture is based on two-photon Hong-Ou-Mandel-type interference which relaxes the long-distance stability requirements by about 7 orders of magnitude, from subwavelength for the single photon interference required by DLCZ to the coherence length of the photons. Our proposal provides an exciting possibility for robust and realistic long-distance quantum communication.

Memory-built-in quantum teleportation with photonic and atomic qubits

“…Moreover, as the collective state of atomic ensembles is used to encode an atomic qubit, the teleported state can be easily read out in a controllable time for further quantum information applications. In principle, these distinct advantages make our method robust for scalable quantum communication and computation networks [3][4][5] .A schematic diagram of the set-up of our experiment is shown in Fig. 1.…”

“…The ability to teleport the unknown quantum state of a photonic qubit onto an atomic qubit and then converting it back to a photonic state at a controllable time is essential for the recent quantum-repeater protocols [3][4][5] that address the extremely difficult phase stabilization, as required in an original scheme for long-distance quantum communication 2 . However, we note that owing to the low success probability of teleportation and the short lifetime of quantum memory, significant improvements are still needed for our method to be useful for practical applications.…”

“…In our experiment, we use the polarized photonic qubits as the information carriers and the collective atomic qubits [2][3][4][5]12 (an effective qubit consists of two atomic ensembles, each with 10 6 rubidium-87 atoms) as the quantum memory. In memorybuilt-in teleportation, an unknown polarization state of single photons is teleported onto and stored in a remote atomic qubit via a Bell-state measurement between the photon to be teleported and the photon that is originally entangled with the atomic qubit.…”

Robust quantum repeater with atomic ensembles and single-photon sources

“…A protocol of special importance for long-distance quantum communication with atomic ensemble as local memory qubits and linear optics is proposed in a seminal paper of Duan et al [13]. After that considerable efforts have been devoted along this line [14,15,16,17,18,19,20].In additional to using relatively simple ingredients, DLCZ protocol has built-in entanglement purification and thus is tolerant against photon losses. However, entanglement generation and entanglement connection in the DLCZ protocol is based on a single-photon Mach-Zehnder-type interference, resulting the relative phase in the entangled state of two distant ensembles is very sensitive to path length instabilities [19,21].…”

“…The probability of generating one excitation in two ensembles denoted by p is related to the fidelity of the entanglement, leading to the condition p ≪ 1 to guaranty an acceptable quality of the entanglement. But when p → 0, some experimental imperfections such as stray light scattering and detector dark counts will contaminate the entangled state increasingly [20], and subsequent processes including quantum swap and quantum communication become more challenging for finite coherent time of quantum memory [16].In recent papers [19,21], Chen et al suggest a robust quantum repeater protocol which is insensitive to the path length phase instabilities by using the two-photon Hong-Ou-Mandeltype (HOMT) interference rather than single-photon interference. Sangouard et al [22] developed that protocol by exploiting a more efficient method of generating entangled pairs locally with partial readout of the ensemble-based memories, which makes it generate entanglement most quickly among the previous schemes with the same ingredient.…”