Deterministic and Storable Single-Photon Source Based on a Quantum Memory

Abstract

A single photon source is realized with a cold atomic ensemble ( 87 Rb atoms). In the experiment, single photons, which is initially stored in an atomic quantum memory generated by Raman scattering of a laser pulse, can be emitted deterministically at a time-delay in control. It is shown that production rate of single photons can be enhanced by a feedback circuit considerably while the single-photon quality is conserved. Thus our present single-photon source is well suitable for future large-scale realization of quantum communication and linear optical quantum computation.PACS numbers: 03.67. Hk, 32.80.Pj, 42.50.Dv Although weak coherent beams can be used as a pseudo single-photon source, the advent of quantum information processing (QIP) has placed stringent requirements on single photons either on demand or heralded [1]. In particular, secure quantum cryptography [2] and linear optical quantum computing [3] depend on the availability of such single-photon sources. Different approaches have been attempted in the last decade to develop the on-demand single-photon source, such as the implementations with quantum dots [4,5], single atoms and ions [6,7], and color centers [8]. However, all of them are confronted with different challenges. For example, the single-atom implementation provides spectrally narrow single photons with a well defined spatial mode, but the main challenge is the manipulation of single atoms, which requires sophisticated and expensive setups [6]. Although quantum dots present many advantages as potential source of single photons, e.g. high single-photon rate, the requirement of spectral filtering entails inevitable losses. Additionally, it is a major problem for preparing truly identical sources due to inhomogeneities in both the environment of the emitters and the emitters itself [9]. The stability of color centers is excellent, even at room temperature. However, the high peak intensities of a pulsed excitation can lead to complex and uncontrollable dark states [1]. So it has been taken as a formidable task to develop a promising single-photon source.Moreover, an important challenge in distributed QIP is the controllable transfer of quantum state between flying qubit and macroscopic matter. Remarkably, as shown in a recent proposal for long-distance quantum communication with atomic ensembles [10], it is possible to implement both a single-photon source on demand and the controllable transfer of quantum state between photonic qubit and macroscopic matter, provided that proper feedback is applied to achieve the classical feed-forward ability. Such feed-forward ability is a crucial requirement in linear optics QIP [3,10]. In other words, it must be, in principle, possible to detect when an operation has succeeded by performing some appropriate measurement on ancilla photons. This information can then be feed-forwarded for conditional future operations on the photonic qubits to achieve efficient QIP.Recently, significant experimental progresses have been achieved in demonstration of quantum ...

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

“…Up to 8 µs, the fidelity is still above the classical limit. The fidelity drops down mainly because of the decoherence in the collective atomic state 25 .…”

“…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. For example, we could use active feedforward to achieve both a deterministic entanglement source 3-5 and a high-quality single-photon source 25,26 , by which the overall success of the teleportation rate can be greatly increased while the spurious coincidence is suppressed. This, given our present excitation rate of anti-Stokes photons, would require a lifetime of quantum memory up to 1 ms.…”

Mapping photonic entanglement into and out of a quantum memory

“…In the regime of continuous variables, a particularly notable advance has been the teleportation of quantum states between light and matter [14]. For discrete variables with photons taken one by one, important achievements include the efficient mapping of collective atomic excitations to single photons [15,16,17,18,19], the realization of entanglement between a pair of distant ensembles [5,20] In all these cases, progress has relied upon probabilistic schemes following the measurement-induced approach developed in the seminal paper by Duan, Lukin, Cirac and Zoller [4] (DLCZ ) and subsequent extensions. For the DLCZ protocol, heralded entanglement is generated by detecting a single photon emitted indistinguishably by one of two ensembles.…”

“…In the regime of continuous variables, a particularly notable advance has been the teleportation of quantum states between light and matter [14]. For discrete variables with photons taken one by one, important achievements include the efficient mapping of collective atomic excitations to single photons [15,16,17,18,19], the realization of entanglement between a pair of distant ensembles [5,20] and, more recently, entanglement distribution involving two pairs of ensembles [6]. The first step toward entanglement swapping has been made [21] and lightmatter teleportation has been demonstrated [22].…”

An array of integrated atom–photon junctions

“…This atom-chip technology provides a way to miniaturise existing atomic physics devices. In addition, it promises new devices that take advantage of the elementary quantum nature of atoms [7][8][9] [16][17][18] or otherwise attached [19] to a chip. A pair of these fibres looking into each other can be used to detect an atom cloud and can reach close to single atom sensitivity [17].…”