Quantum Telecommunication Based on Atomic Cascade Transitions

Abstract

A quantum repeater at telecommunications wavelengths with long-lived atomic memory is proposed, and its critical elements are experimentally demonstrated using a cold atomic ensemble. Via atomic cascade emission, an entangled pair of 1.53 µm and 780 nm photons is generated. The former is ideal for long-distance quantum communication, and the latter is naturally suited for mapping to a long-lived atomic memory. Together with our previous demonstration of photonic-to-atomic qubit conversion, both of the essential elements for the proposed telecommunications quantum repeater have now been realized. PACS numbers: 42.50.Dv,03.65.Ud,03.67.Mn A quantum network would use the resources of distributed quantum mechanical entanglement, thus far largely untapped, for the communication and processing of information via qubits [1,2]. Significant advances in the generation, distribution, and storage of qubit entanglement have been made using laser manipulation of atomic ensembles, including atom-photon entanglement and matter-light qubit conversion [3], Bell inequality violation between a collective atomic qubit and a photon [4], and light-matter qubit conversion and entanglement of remote atomic qubits [5]. In each of these works photonic qubits were generated in the near-infrared spectral region. In related developments, entanglement of an ultraviolet photon with a trapped ion [6] and of a nearinfrared photon with a single trapped atom [7] have been demonstrated. Heterogeneous quantum network schemes that combine single-atom and collective atomic qubits are being actively pursued [8]. However, photons in the ultraviolet to the near-infrared range are not suited for long-distance transmission over optical fibers due to high losses.In this Letter, we propose a telecommunications wavelength quantum repeater based on cascade atomic transitions in either (1) a single atom or (2) an atomic ensemble. We will first discuss the latter case, with particular reference to alkali metals. Such ensembles, with long lived ground level coherences can be prepared in either solid [9] or gas [4] phase. For concreteness, we consider a cold atomic vapor confined in high-vacuum. The cascade transitions may be chosen so that the photon (signal) emitted on the upper arm has telecommunication range wavelength, while the second photon (idler), emitted to the atomic ground state, is naturally suited for mapping into atomic memory. Experimentally, we demonstrate phase-matched cascade emission in an ensemble of cold rubidium atoms using two different cascades: (a) at the signal wavelength λ s = 776 nm, via the 5s 1/2 → 5d 5/2 two-photon excitation, (b) at λ s = 1.53 µm, via the 5s 1/2 → 4d 5/2 two-photon excitation. We observe polarization entanglement of the emitted photon pairs and superradiant temporal profiles of the idler field in both cases.We now describe our approach in detail and at the end we will summarize an alternative protocol for single atoms.Step (A) -As illustrated in Fig. 1(a), the atomic sample is prepared in level |a , e.g., by mean...

Quantum repeaters based on atomic ensembles and linear optics

“…Another interesting possibility for creating non-degenerate photon pairs in ensembles is based on atomic cascade transitions. (Chanelière et al, 2006) have demonstrated an entangled pair of 1530 nm and 780 nm photons generated from an atomic cascade transition in a cold Rb ensemble (see Fig. 29).…”

Correlated photon pairs generated from a warm atomic ensemble

“…Multiple decay paths exist due to the hyperfine splitting of the intermediate state [12,20] that isotope. The continuous (red) line in Fig.…”

Stochastic methods for light propagation and recurrent scattering in saturated and nonsaturated atomic ensembles

“…Strong dipole-dipole interactions may need to be considered to an increasing extent in quantum technologies. For example, collective phenomena, such as superradiant emission, can be important in implementations of quantum memories and quantum interfaces between light and cold atom systems [42]. The advent of metamaterials, arrays of artificially fabricated magnetodielectric resonators whose electromagnetic response and positions are controlled by design, provide a way to exploit cooperative interactions, for example, to focus light or image a system beyond the diffraction limit [43], to produce narrow transmission resonances [44][45][46], or to create a broad area coherent light source driven by an electron beam [47].…”