A single-photon server with just one atom

Abstract

Neutral atoms are ideal objects for the deterministic processing of quantum information. Entanglement operations have been performed by photon exchange [1] or controlled collisions.[2] Atom-photon interfaces were realized with single atoms in free space [3,4] or strongly coupled to an optical cavity. [5,6] A long standing challenge with neutral atoms, however, is to overcome the limited observation time. Without exception, quantum effects appeared only after ensemble averaging. Here we report on a single-photon source with one-and-onlyone atom quasi permanently coupled to a high-finesse cavity. Quasi permanent refers to our ability to keep the atom long enough to, first, quantify the photon-emission statistics and, second, guarantee the subsequent performance as a single-photon server delivering up to 300,000 photons for up to 30 seconds. This is achieved by a unique combination of single-photon generation and atom cooling. [7,8,9] Our scheme brings truly deterministic protocols of quantum information science with light and matter [10,11,12,13,14,15,16] Deterministic single-photon sources are of prime importance in quantum information science.[17] Such sources have been realized with neutral atoms, embedded molecules, trapped ions, quantum dots, and defect centres.[18] All these sources are suitable for applications where the indivisibility of the emitted light pulses is essential. For quantum computing or quantum networking, the emitted photons must also be indistinguishable. Such photons have so far only been produced with quantum dots [19] and atoms. [20,21] Another requirement is a high efficiency. This is hard to obtain in free space, as the light collecting lens covers only a fraction of the full 4π solid angle. The efficiency can be boosted by strongly coupling the radiating object to an optical microcavity, as has been achieved with atoms [5,6] and quantum dots. [22] An additional advantage of the cavity is that a vacuum-stimulated Raman adiabatic passage can be driven in a multilevel atom. [23] In this way amplitude, [5,24] frequency, [20] and polarization [25] of the photon can be controlled. It should also make possible to combine partial photon production with internal atomic rotations for the construction of entangled photon states such as W and GHZ states. [15] All these demands together have so far only been achieved with atoms in high-finesse microcavities. A reason is that neutral atoms are largely immune to perturbations, such as electric patch fields close to dielectric mirrors. However, atomic systems have always suffered from a fast atom loss. We have now implemented a cavity-based scheme, see figure 1, with a dipole laser for trapping, a trigger laser for photon generation and a recycling laser for repumping, monitoring and cooling the atom. [8,9] The scheme combines high photon-generation efficiency and long trapping times. The most remarkable features are, first, that the single-photon stream is specified by its intensity correlation function evaluated in realtime during a short time int...

Transfer and teleportation of quantum states encoded in decoherence-free subspace

“…Experimentally, the currently achieved technology of deterministic single-photon source [13] provides potential support for our scheme. As 300,000 high-quality single photons could be generated continuously within 30 sec, a fast implementation of our scheme is available.…”

Teleportation of an arbitrary multipartite state via photonic Faraday rotation

“…Specifically, supposing that the failure rate associated with the decay of the virtual atomic excitation is about 2%, the current dark count rate of the single-photon detector yields the inefficiency of 10 −4 , and other imperfection rate due to photon loss is about 6%, we thus have the success rate to be [(1 − 2%) 2 × 10 −4 × (1 − 6%)] N . Fortunately, thanks to the highly efficient single-photon generator producing 10000 photons every second [23], we may accomplish the teleportation in finite time. For example, a successful teleportation of a two-qubit state takes about three hours.…”

Optimization of periodic single-photon sources based on combined multiplexing

“…Beside the deterministic single-photon sources based on various single quantum emitters such as single atoms [19,20], ions [21,22], molecules [23,24], diamond color centers [25][26][27], and quantum dots [28][29][30], probabilistic single-photon sources offer an alternative way to address this problem. This approach is based on the generation of correlated photon pairs.…”