Ondrej Haderka

Quantum random number generator

Since reflection or transmission of a quantum particle on a beamsplitter is inherently random quantum process, a device built on this principle does not suffer from drawbacks of neither pseudo-random computer generators or classical noise sources. Nevertheless, a number of physical conditions necessary for high quality random numbers generation must be satisfied. Luckily, in quantum optics realization they can be well controlled. We present an easy random number generator based on the division of weak light pulses on a beamsplitter. The randomness of the generated bit stream is supported by passing the data through series of 15 statistical test. The device generates at a rate of 109.7 kbit/s.

Testing operational phase concepts in quantum optics

An experimental comparison of several operational phase concepts is presented. In particular, it is shown that statistically motivated evaluation of experimental data may lead to a significant improvement in phase fitting upon the conventional procedure of Noh et al (1993 Phys. Rev. Lett. 71 2579). The analysis is extended to the asymptotic limit of large intensities, where a strong evidence in favour of multi-dimensional estimation procedures has been found.

Surface Spontaneous Parametric Down-Conversion

Surface spontaneous parametric down-conversion is predicted as a consequence of continuity requirements for electric- and magnetic-field amplitudes at a discontinuity of chi;{(2)} nonlinearity. A generalization of the usual two-photon spectral amplitude is suggested to describe this effect. Examples of nonlinear layered structures and periodically poled nonlinear crystals show that surface contributions to spontaneous down-conversion can be important.

Generation of sub-Poissonian non-Gaussian states from multimode twin beams by photon-number-resolving detectors

We generate sub-Poissonian non-Gaussian conditional states from pulsed multimode twin beams by measuring with photon-number-resolving detectors. Links among twin-beam non-classicality and the properties of the conditional states are discussed.

Photon-Number Entanglement in Twin Beams Generated in Spontaneous Parametric Down-Conversion

Joint signal-idler photon-number distribution and quantum phase-space quasi-distributions are measured for light generated in intense spontaneous parametric down-conversion. Entanglement in the signal- and idler-photon numbers is observed.

Quantum cryptography based on realistic single-photon source

A photon source based on postselection from entangled photon pairs produced by parametric frequency down-conversion is suggested and applied in quantum cryptography. Its ability to provide good approximations of single-photon states is examined. Use of this source for quantum key distribution is discussed. Advantages of this quantum-key-distribution system are clarified.

Phase estimation in quantum optics

An experimental comparison of several operational phase concepts is presented. In particular, it is shown that statistically motivated evaluation of experimental data may lead to a significant improvement in phase fitting upon the conventional Noh, Fourgeres and Mandel procedure. The analysis is extended to the asymptotic limit of large intensities, where a strong evidence in favor of multi- dimensional procedures has been found.

Photon source for quantum cryptography using postselection from entangled quantum states

A realistic model for a photon source based on postselection from correlated photon pairs produced by parametric frequency down-conversion is suggested. Its efficiency in producing approximation of single photon states is examined. The application of such source in quantum key distribution schemes is discussed and comparison with currently used sources of photons is given. Future prospects of this type of photon source are outlined.

Experimental implementation of quantum cryptography

Quantum cryptography is a quickly developing field that brings direct applications of fundamentals of quantum theory. In this paper we present a brief review of the tasks and problems faced by classical cryptography and we point out the benefits of quantum cryptography to their solution. An overview of the experimental achievements and an outline of the principle of quantum key distribution are given. Various experimental approaches are compared. The quantum cryptographic device built by the authors is described and its use for mutual identification system is presented.