G. O. Rytikov

Macroscopic pure state of light free of polarization noise.

The preparation of completely nonpolarized light is seemingly easy; an everyday example is sunlight. The task is much more difficult if light has to be in a pure quantum state, as required by most quantum-technology applications. The pure quantum states of light obtained so far are either polarized or, in rare cases, manifest hidden polarization; even if their intensities are invariant to polarization transformations, higher-order moments are not. We experimentally demonstrate the preparation of the macroscopic singlet Bell state, which is pure, is completely nonpolarized, and has no polarization noise. Simultaneous fluctuation suppression in three Stokes observables below the shot-noise limit is demonstrated, opening perspectives for noiseless polarization measurements. The state is shown to be invariant to polarization transformations. This robust highly entangled isotropic state promises to fuel important applications in photonic quantum technologies.

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.

COMPARATIVE TEST OF TWO METHODS OF QUANTUM EFFICIENCY ABSOLUTE MEASUREMENT BASED ON SQUEEZED VACUUM DIRECT DETECTION

We realize and test in experiment a method recently proposed for measuring absolute quantum efficiency of analog photodetectors. Similar to the traditional (Klyshko) method of absolute calibration, the new one is based on the direct detection of two-mode squeezed vacuum at the output of a traveling wave OPA. However, in the new method, one measures the difference-photocurrent variance rather than the correlation function of photocurrents (number of coincidences), which makes the technique applicable for high-gain OPA. In this work we test the new method versus the traditional one for the case of photon-counting detectors where both techniques are valid.

Multiphoton nonclassical correlations in entangled squeezed vacuum states

Photon-number correlation measurements are performed on bright squeezed vacuum states using a standard Bell-test setup, and quantum correlations are observed for conjugate polarization-frequency modes. We further test the entanglement witnesses for these states and demonstrate the violation of the separability criteria, which infers that all the macroscopic Bell states, containing typically

Generation of Entangled States in Polydomain Potassium-Dihydrophosphate Crystals

10^6

Generation of bright squeezed vacuum in the Karassiov states

photons per pulse, are polarization entangled. The study also reveals the symmetry of macroscopic Bell states with respect to local polarization transformations.

Possibility Investigation of Experimental Verification of General Bell Inequality Violation for Polarization Scalar Light Based Realization

It is shown experimentally that polarized entangled two-photon states in a pair of frequency modes can appear in the process of the spontaneous parametric down conversion in ferroelectric crystals with a quasi-regular domain structure (such as potassium dihydrophosphate). Entanglement measures and polarization characteristics of these states are determined.

Entanglement of macroscopic Bell states

We suggest an experimental procedure allowing one to prepare squeezed vacuum in a special type of generalized Bell states, first introduced by V.P. Karassiov. We present the first results on the experimental generation of such states and observation of their polarization properties.

Preparation and measurement of biphotons in given polarization state

We discuss the fundamental problems of nonclassical correlations and microscopic entanglement experimental observation possibility for multiphoton quantum light beams. Optical beams of multiphoton nonclassical light are of practical interest due to possibility of applications in quantum metrology and quantum informatics. Quantum macroscopic states of light are the significant information carrier in practical realization of quantum computing algorithms, quantum dense coding, quantum key distribution, quantum teleportation and other cases of quantum communications. And quantum macroscopic light beam can be used as high sensitive probe field in special type spectroscopy and in light sources and detectors etalonless calibration.