Entangled Photon Pairs: Experiments and Theory

Anton Zeilinger

Hiroki Takesue

Entangled photon pair generation is an important technology for realizing quantum information systems. Among various entangled photon pair sources, a source based on spontaneous four-wave mixing (SFWM) in a silicon wire waveguide (SWW) is now drawing attention. Thanks to the very large third-order nonlinearity in an SWW, we can realize highly efficient SFWM in a short ( ~ 1 cm) waveguide, which will possibly lead to an integrated entanglement source on a silicon chip. In this paper, we review recent progress on SWW-based entanglement sources. This study reviews the basic theory of SFWM, and then describes correlated and entangled photon generation experiments using SWWs and applications to quantum information experiments.

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

Phillip F. Schewe

Pradyumna K. Pathak, Stephen Hughes

We present a formal theory of single quantum dot coupling to a planar photonic crystal that supports quasidegenerate cavity modes and use this theory to describe and optimize entangled-photon pair generation via the biexciton-exciton cascade. In the generated photon pairs, either both photons are spontaneously emitted from the dot or one photon is emitted from the biexciton spontaneously while the other is emitted via the leaky cavity mode. In the strong-coupling regime, the generated photon pairs can be maximally entangled in qualitative agreement with the dressed-state predictions of Johne et al. [Phys. Rev. Lett. 100, 240404 (2008)]. We derive useful analytical formulas for the spectrum of the emitted photon pairs in the presence of exciton and biexciton broadening, which is necessary to connect to realistic experiments and demonstrate the important differences with the approximate dressed-state approach. We also present a method for calculating and optimizing the entanglement between the emitted photons, which can account for postsample spectral filtering. Pronounced entanglement values of greater than 80% are demonstrated using experimentally achievable parameters even without spectral filtering.

K.A. Ispirian, M. K. Ispiryan

Without developing a correct theory, the rate of the production of entangled photon pairs in the X-ray region by high energy electrons is estimated for experimental parameters used in a few experiments on X-ray parametric down conversion. Taking into account the need for X-ray entangled X-ray photons, it is proposed to begin the experimental study of such mechanism of nonlinear X-ray optics before the launch of the X-ray free electron lasers.