The interference of light scattered by two distant nonidentical atoms

Julian Grond, W. Pötz, Ataç İmamoğlu

A scheme for probabilistic entanglement generation between two distant single electron doped quantum dots, each placed in a high-$Q$ microcavity, by detecting strong coherent light which has interacted dispersively with both subsystems and experienced Faraday rotation due to the spin selective trion transitions is discussed. In order to assess the applicability of the scheme for distant entanglement generation between atomic qubits proposed by T. D. Ladd et al. [New J. Phys. 8, 184 (2006)] to two distant quantum dots, one needs to understand the limitations imposed by hyperfine interactions of the quantum dot spin with the nuclear spins of the material and by nonidentical quantum dots. Feasibility is displayed by calculating the fidelity for Bell state generation analytically within an approximate framework. The fidelity is evaluated for a wide range of parameters and different pulse lengths, yielding a trade-off between signal and decoherence, as well as a set of optimal parameters. Strategies to overcome the effect of nonidentical quantum dots on the fidelity are examined and the time scales imposed by the nuclear spins are discussed, showing that efficient entanglement generation is possible with distant quantum dots. In this context, effects due to light hole transitions become important and have to be included. The scheme is discussed for one- as well as for two-sided cavities, where one must be careful with reflected light which carries spin information. The validity of the approximate method is checked by a more elaborate semiclassical simulation which includes trion formation.

Lothar Frommhold, Michael H. Proffitt

P. Cañizares, T. Görler, Juan Pablo Paz +2 more

The spatial coherence of an atomic wavepacket can be detected in scattered photons, even when the center-of-mass motion is in the quantum coherent superposition of two distant, nonoverlapping wavepackets. Spatial coherence manifests itself in the power spectrum of the emitted photons, whose spectral components can exhibit interference fringes as a function of the emission angle. The contrast and the phase of this interference pattern provide information about the quantum state of the center of mass of the scattering atom.

Thomas Wellens, Tobias Geiger, Vyacheslav Shatokhin +1 more

We deduce the coherent backscattering signal from two distant laser-driven atoms using single-atom equations. The background and interference components of the double scattering spectrum obtained by this alternative approach agree exactly with the results of the standard master equation treatment. In contrast to the master equation, however, the new approach is suitable for the generalization to a large number of atomic scatterers.

Wolfgang Vogel, Sascha Wallentowitz