Time-resolved two-photon correlations in parametric downconversion (A)

Saikat Sarkar, Roger Andrews, Edward R. Pike

Chung Ki Hong

Stephen R. Friberg, C. K. Hong, L. Mandeļ

When a laser beam interacts with a nonlinear crystal, some of the incident photons fission into two lower frequency signal and idler photons through the process of spontaneous parametric downconversion. It is shown that, as a result of the strong positive correlation between signal and idler photons, the normalized intensity cross-correlation function λ12(τ) should be inversely proportional to the downconverted light intensity and ideally should be given by the inverse of the mean number of photons counted in the resolving time. This unusual relationship, which is a reflection of the quantum mechanical character of the downconverted optical field, has been confirmed in photoelectric counting measurements. The experiment makes use of the light from an argon-ion laser oscillating at 351.1 nm interacting with an 8-cm long crystal of KDP. The downconverted light is extracted at 633.5 and 788.0 nm in two directions that satisfy the phase-matching condition and is allowed to fall on two counting photomultipliers. The output pulses are fed to a time-to-digital converter that yields the cross-correlation function.

Boris L. Glebov, Jingyun Fan, Alan L. Migdall

We present a realistic numerical simulation of a source of number-squeezed photon states employing a cavity-based parametric downconversion (PDC) process. A cavity containing the PDC medium is pumped repeatedly. The cavity recycles only one of the PDC output modes, allowing it to be amplified with each subsequent pump pulse. A photon number resolved (PNR) measurement is made on the other PDC output mode following each pump pulse. Once the PNR measurements indicate that the target number of photons has accumulated in the cavity, the pumping is stopped and the resulting photon state is released. The photon number uncertainty in the resulting state is ~3 dB below that of a mean-equivalent coherent state and furthermore the probability of generating the target photon number is similarly increased.

Lorenzo M. Procopio, Óscar Rosas-Ortiz, Víctor Velázquez +4 more

Alexander V. Sergienko, Yanhua H. Shih, Morton H. Rubin

A two-photon wave packet (a biphoton) produced by type-II parametric downconversion is studied in a simple beam-splitting experiment for its natural shape in space–time. The measured triangular shape of a two-photon correlation function is the signature of a rectangular-shaped biphoton. Inserting a birefringent sample into the beam causes a displacement of the vertex of the notch pattern, which can be used to measure the optical delay between the ordinary and the extraordinary rays in the sample with femtosecond resolution.