Characterization of light sources for quantum information processing and communication.

by Prof. Konrad Banaszek (Nicolaus Copernicus University, Torun, Poland.)

Monday 26 May 2008, 16:00 → 18:00 Europe/Rome

aula Conversi (Dipartimento di Fisica - Edificio Marconi)

Parametric down-conversion is the basic workhorse in experimental quantum information processing in the optical domain. With progressing sophistication of experiments, the physical characteristics of down-conversion sources gains increasing pratical importance. This talk will review experimental and theoretical activities in this area carried out by our group. The effort focused on fiber-coupled sources for which frequency is the degree of freedom deciding about their usefulness in quantum information experiments. The first work measured the joint spectrum of photon pairs by Fourier transform spectroscopy. The difficulties resulting from the low brightness of the source were overcome by the construction of common-path interferometers that guaranteed stability of the setup over periods of hours. Spectral coherence properties of generated photons were tested in a second work using an original scheme to measure the complete density matrix of a single photon. The off-diagonal elements of the density matrix were determined by detecting two-photon interference with a local oscillator prepared in a double-pulse shape.