Entangled photons produced by a three-level atom in free-space

Nicolas Gisin, John Rarity, Gregor Weihs

Samad Roshan Entezar

The coherent control of the entanglement between a three-level atom located within a three-dimensional (3D) anisotropic photonic band gap (PBG) material, with one transition frequency near the edge of the PBG, and its radiation field is demonstrated. As a result of quantum interference and photon localization, the entanglement can be decreased or increased depending on the relative phase between the control laser coupling, the two upper levels and the pump laser pulse used to create an excited state of the atom in the form of a coherent superposition of the two upper levels. Unlike the free-space case, the steady-state entanglement is strongly dependent on the externally prescribed initial conditions. This non-zero steady-state entanglement is achieved by virtue of the localization of light in the vicinity of the emitting atom.

Guo-Hui Yang, Ling Zhou

Gessler Hernandez, Jiepeng Zhang, Yifu Zhu

We report an experimental study of the collective coupling of three-level atoms with a cavity mode and a free-space laser field. The measurement of the cavity transmission with a weak probe field coupled into the cavity mode reveals three spectral peaks: two sidebands and a central peak, which is produced by the coherent interaction of the free-space field with individual atoms and the collective interaction of the multiple atoms with the cavity mode. The experimental results agree with a simple calculation based on the classical light transmission through a cavity containing multiple atoms coherently driven by a free-space laser.

Amaal M. Ali, Natasha Bastien, Wendy-Ann Gibbons +2 more

Nicolas Sangouard, Jean-Daniel Bancal, Philipp Müller +2 more

An obvious way to entangle two atoms located at remote locations is to produce a pair of entangled photons half-way between the two atoms, to send one photon to each location and to subsequently map the photonic entanglement into the atoms. The efficiency of this process is, however, fundamentally limited due to overall transmission losses. We propose a method to herald the success of the mapping operation in free space without destroying nor revealing the stored quantum state. Interestingly for a Bell test, the heralding signal does not open the detection loophole provided the measurement choice is performed once the heralding is obtained only. We show through a detailed feasibility study that this approach could provide an attractive alternative to Bell tests where the atom–atom entanglement is created from atom–photon entanglement using an entanglement swapping operation.