A. N. Penin

High-visibility multiphoton interference of Hanbury Brown–Twiss type for classical light

Difference-phase (or Hanbury Brown\char21{}Twiss type) intensity interference of classical light is considered in higher orders in the intensity. It is shown that, while the visibility of sum-phase (NOON-type) interference for classical sources drops with the order of interference, the visibility of difference-phase interference has opposite behavior. For three-photon and four-photon interference of two coherent sources, the visibility can be as high as 81.8% and 94.4%, respectively. High-visibility three-photon and four-photon interference of space-time and polarization types has been observed in experiment, for both coherent and pseudothermal light.

Statistical reconstruction of qutrits

We discuss a procedure of measurement followed by the reproduction of the quantum state of a three-level optical system - a frequency- and spatially degenerate two-photon field. The method of statistical estimation of the quantum state based on solving the likelihood equation and analyzing the statistical properties of the obtained estimates is developed. Using the root approach of estimating quantum states, the initial two-photon state vector is reproduced from the measured fourth moments in the field . The developed approach applied to quantum states reconstruction is based on the amplitudes of mutually complementary processes. Classical algorithm of statistical estimation based on the Fisher information matrix is generalized to the case of quantum systems obeying Bohrs complementarity principle. It has been experimentally proved that biphoton-qutrit states can be reconstructed with the fidelity of 0.995-0.999 and higher.

Possibility of absolute calibration of analog detectors by using parametric downconversion: a systematic study

Prompted by the need for various studies ranging from quantum information to foundations of quantum mechanics, we systematically study the possibility of the absolute calibration of analog photodetectors based on the properties of parametric amplifiers. Our results show that such a method can be effectively developed with interesting possible applications in metrology.

Spontaneous parametric down-conversion

Spontaneous parametric down-conversion (SPDC) in media with no inversion center and the use of this phenomenon in the spectroscopy of natural oscillation states of a crystal lattice (i.e., optical phonons) are retrospectively described. We think that the SPDC spectroscopy method is estimated inappropriately and hope to again attract the attention of readers to one of the most interesting quantum phenomena of nonlinear optics that has no classical analog. The capabilities of SPDC spectroscopy will certainly be used in both fundamental science and technology of new materials.

Absolute meter of photodetector quantum efficiency based on the parametric down-conversion effect

The quantum phenomena of parametric down conversion have been used for absolute measurement of the photodetector quantum efficiency of ultra-low-light radiation ranging from 10 -12 to 10 -15 W, which is equivalent to photon fluxes of 10 7 to 10 4 s -1 . The process of parametric down conversion gives rise to highly correlated (in time and space) photon flux pairs. We describe the method, experimental investigation, and a new device involving the measurement of the coincidence rate of photodetection of these two correlated beams of light. The coincidence is lowered by a nonunit quantum efficiency of either detection. This fact was used for the definition of the absolute value of both photodetectors quantum efficiencies.

Mapping of periodically poled crystals via spontaneous parametric down-conversion

A new method for characterization of periodically poled crystals is developed based on spontaneous parametric down-conversion. The method is demonstrated on crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled structures, obtained directly under the Czochralski growth procedure and designed for application of 1.064 μmpumped OPO in the mid-infrared range. Infrared dispersion of refractive index, effective working periods and wavelengths of OPO were determined by special treatment of frequency-angular spectra of spontaneous parametric down-conversion in the visible range. Two-dimensional mapping via spontaneous parametric down-conversion is proposed for characterizing spatial distribution of bulk quasi-phase matching efficiency across the input window of a periodically poled sample.

Parametric Frequency Conversion in Layered Nonlinear Media

Frequency-angular distributions of signal wave intensity are calculated for spontaneous parametric down-conversion and parametric frequency conversion in spatially nonuniform nonlinear media. Wave reflection from interfaces is taken into account, and both regular and irregular nonuniform distributions of second-order nonlinear susceptibility are considered. A unified approach using a scattering matrix and a generalized Kirchhoff law is applied in calculations of spontaneous and stimulated processes in dissipative nonlinear media. Interference of electromagnetic zero-point fluctuations of the vacuum, nonlinear interference, and nonlinear diffraction are examined for media with various absorptive properties. Theoretical foundations are developed for diagnostics of nonuniform distributions of the second-order susceptibility, based on measurement of the line profiles of nonlinear signals.

Generation and detection of terahertz radiation by means of periodically and aperiodically poled crystals

The nonlinear optical methods for generating and detecting terahertz radiation using periodically and aperiodically poled crystals in the quasi-phase-matching mode are analyzed. Two radically different versions of optical pumping are considered: a quasi-continuous mode and pumping by Fourier-limited femto-second pulses. General relations are obtained, which determine the spectra of generated and detected waves through the optical pumping parameters and the crystal generator and crystal detector nonlinear transfer functions. It is shown that, by choosing the optimal spatial modulation of the crystal nonlinear susceptibility, one can control the shape of the generation and detection spectra. An optical scheme is proposed and the optimal parameters of domain structures for quasi-phase-matched generation and frequency-matched detection of forward and backward terahertz waves under quasi-continuous-wave optical pumping are reported.

Absolute calibration of photodetectors: photocurrent multiplication versus photocurrent subtraction

We report testing of the new absolute method of photodetector calibration based on the difference-signal measurement for two-mode squeezed vacuum by comparison with the traditional absolute method based on coincidence counting. Using low-gain parametric downconversion, we have measured the quantum efficiency of a counting detector by both methods. The difference-signal method was adapted for the counting detectors by taking into account the dead-time effect.

Two methods for detecting nonclassical correlations in parametric scattering of light

Two methods for studying nonclassical correlations at the output of a two-mode parametric amplifier—first, the measurement of normalized Glauber correlation functions and, second, the measurement of the variance of the photon-number difference in conjugate modes—are compared. It is shown theoretically and experimentally that the corresponding quantities, the normalized correlation function, and the noise reduction factor have significantly different dependences on the main system parameters such as the parametric gain, optical losses, photo-detector quantum efficiency, and the detected angular and frequency bands.