An atom and a photon

Claude N. Cohen-Tannoudji, J. Dupont-Roc, G. Grynberg

Qin Wu, Mao-Fa Fang, Yao-Hua Hu

We have investigated the evolution of the atomic quantum entropy and the entanglement of atom–photon in the system with competing k -photon and l -photon transitions by means of fully quantum theory, and examined the effects of competing photon numbers ( k and l ), the relative coupling strength between the atom and the two-mode field ( λ/g ), and the initial photon number of the field on the atomic quantum entropy and the entanglement of atom–photon. The results show that the multiphoton competing transitions or the large relative coupling strength can lead to the strong entanglement between atoms and photons. The maximal atom–photon entanglement can be prepared via the appropriate selection of system parameters and interaction time.

Valérian Giesz, Niccolò Somaschi, Gaston Hornecker +12 more

In a quantum network based on atoms and photons, a single atom should control the photon state and, reciprocally, a single photon should allow the coherent manipulation of the atom. Both operations require controlling the atom environment and developing efficient atom-photon interfaces, for instance by coupling the natural or artificial atom to cavities. So far, much attention has been drown on manipulating the light field with atomic transitions, recently at the few-photon limit. Here we report on the reciprocal operation and demonstrate the coherent manipulation of an artificial atom by few photons. We study a quantum dot-cavity system with a record cooperativity of 13. Incident photons interact with the atom with probability 0.95, which radiates back in the cavity mode with probability 0.96. Inversion of the atomic transition is achieved for 3.8 photons on average, showing that our artificial atom performs as if fully isolated from the solid-state environment.

Michèle Leduc, Nicolas Treps

Wolfgang Demtröder

Matthias Steiner, Victor Leong, Mathias Alexander Seidler +2 more

Summary form only given. Is an atom more likely to scatter a photon with an exponentially rising or decaying temporal profile? We try to answer this question experimentally and investigate the scattering of heralded photons from a single atom in free-space. We use a single Rubidium atom trapped in optical tweezers and prepared in the groundstate of a cyclic dipole transition as a textbook-like two-level system. A time-ordered photon pair source, in conjunction with an asymmetric cavity, generates heralded single photons with an exponentially decaying or rising temporal profile. The heralded photons are resonant with the atomic transition and have a bandwidth comparable to the atomic linewidth. The photons are strongly focused onto the atom by a large numerical aperture lens. We study the scattering dynamics by measuring the atomic emission and the reduction in the number of transmitted photons. We perform the scattering experiment for photons with exponentially decaying and rising temporal envelopes and find that the atomic dynamics depend on the temporal profile of the photon. The atomic absorption is shorter but has a higher maximum for the rising photon than for the the decaying one. Interestingly, the overall probability that the photon is scattered by the atom is similar for decaying and rising photons.