Patent ID: 6444999
Filing Date: 2002-09-03
Classification: H04B,H04L

Abstract:
A quantum circuit for detecting a quantum state of an optical signal, wherein said quantum state is a Bell state of a polarized photon pair, the directions of polarization of two photons that make up said polarized photon pair being in a fixed relation to each other, and wherein said Bell state of a photon pair is a superposition of the states of said photon pair, each of said states of said photon pair being designated with reference to a set of directions of polarization of individual photons, said quantum circuit comprising:a two-photon absorbing crystal having the crystal symmetry selected so that the two-photon absorbing crystal selectively absorbs a photon pair of a prescribed Bell state in accordance with selection rules based on crystal symmetry; and a two-photon absorption detector that detects absorption of photon pairs by said two-photon absorbing crystal.