D. N. Klyshko

Polarization state of a biphoton: Quantum ternary logic

Polarization state of biphoton light generated via collinear frequency-degenerate spontaneous parametric down-conversion is considered. A biphoton is described by a three-component polarization vector, its arbitrary transformations relating to the SU(3) group. A subset of such transformations, available with retardation plates, is realized experimentally. In particular, two independent orthogonally polarized beams of type-I biphotons are transformed into a beam of type-II biphotons. Polarized biphotons are suggested as ternary analogs of two-state quantum systems (qubits).

Polarized biphotons as “optical quarks”

The transformation properties and the measurable parameters of a quasimonochromatic optical field consisting of two photons with the same directions of propagation and average frequency are analyzed. Like quarks, such a field possesses SU(3) symmetry.

Fourth-order interference between independent biphotons

The interference of biphotons emitted during collinear parametric scattering from two spatially separated regions is investigated experimentally and theoretically. It is shown that in this case the phase of the interference is determined by the pump wavelength and there is no need to equalize the optical paths for radiation from different regions.

Parametric photometer: a device for standardless nondestructing measurement of radiation spectral brightness

Utilization of the parametric down—conversion provides a unique possibility of absolute standardless brightness calibration ofhigh—temperature visible, infrared and near UV radiation. The calibration method has been suggested in Moscow State University in 1977 and then was applied there to experimental measurements of radiation spectral brightness for laser and luminiscence sources of visible range and filament lamps radiating in IR range. The method is based on the comparison between two signals: the signal p, corresponding to the measured radiation parametric up-conversion and the noise signal P corresponding to parametric scattering of the pump; this noise signal is observed both in the presence of the measured radiation at the converters idler channel entrance and in the absence of it. The noise signal intensity is determined by the effective brightness of zero vacuum fluctuations at the idler frequency which equals to one photon per mode, or, in the energetic units, Bvac = hc2/A, where h is the Plank constant, c —the light velocity, )2 —the idler wavelength. Measuring the ratio of signals P P + P and P at the exit of the crystal—converter at frequency w = wo — w (w0 being the pump frequency, and w —the frequency of the flux being calibrated), one can calculate the absolute value N of energetic brightness spectral density for the radiation which fills the idler channel of the converter: N = k[(P/P )— 1] in the units photon/mode or B = BvacN in the energetic units (here icis a correction coefficient describing the non-ideal transparency of the converting crystal). No additional standard sources or detectors are required here; the method uses as a reference the effective value of zero vacuum fluctuations brightness. The reference effective brightness temperature depends on the radiation wavelegth: T0 = hc/Ak in 2, k being the Boltzmann constant, so that for A2 10 p Tvac 2000 K, and for 0.5 Tvac 40 000 K. In this work the accuracy of the method is analysed and the resolution for different schemes of the parametric photometer is calculated.

Absolute measurements of radiation sources spectral brightness and detectors quantum efficiency

In this paper we present schemes of experimental setups for the radiation spectral brightness measurements in the range of 0.6 - 5 (mu) for N varying from 10-1 to 102 (if, for example, (lambda) equals 1 (mu) , this range of N corresponds to the brightness temperature range from 6 (DOT) 103 to 106 K), and for photomultipliers quantum efficiency measurements in the range of 0.4 - 5 (mu) with a dynamical range 10 - 1012 photon/sec and accuracy not worse than 1%. The new measurement methods are based on the utilization of the parametric light scattering phenomenon which is a spontaneous decay of laser pump photons in correlated photon pairs in crystals with quadratic nonlinear susceptibility. The first of two methods allows measurement of the radiation spectral brightness N in absolute units (photons per mode) in visible and infrared range. The quantity N is related to the energetic brightness spectral density B through the equation B equals (hc2/(lambda) 5)N, where h is the Plank constant, c - the light velocity, (lambda) - the wavelength. The method is absolute and does not require any reference source or detector of radiation. Quantum noise of a parametric down-convertor, caused by the zero vacuum fluctuations with an effective brightness Nvac equals 1 photon per mode, is the reference in this case. The second method concerns the quantum efficiency of photodetectors determination, and it is based on the connection between the statistics of photocurrent and the radiation which causes it. The parametric scattering is a unique source of rather intensive and directed radiation flow consisting of photon pairs. Such a flow can be used to determine the absolute quantum efficiency of photodetectors.

Quantum teleportation of a photon's polarization using an optical gate

The possibility to copy the unknown polarization of a photon to another photon is considered. The initial idea of quantum teleportation by measuring the Bell operator, describing the polarization, correlations of two photons, seems to be practically unrealizable and the corresponding experiments have been interpreted incorrectly. An alternative method using the optical gate is proposed.

Observation of two-photon virtual interference and diffraction

Observations of unusual diffraction and interference by two-photon correlation measurements are reported. The signal and idler beams produced by spontaneous parametric down conversion are sent in different directions, and detected by two distant point-like photon counting detectors. A double-slit or a single-slit is inserted into the signal beam. Interference- diffraction patterns are observed in coincidences by scanning the detector in the idler beam.