Nonlinear crystals are typically used when interaction of different frequencies of light is requested. In classical optics these nonlinear phenomena are used for second-harmonic generation, sum-frequency generation, optical parametric amplification and many other effects. In quantum optics, dealing with optical interaction on the level of individual photons, the most prominent process is spontaneous parametric down-conversion (SPDC),<sup>1</sup> where the crystal is pumped by intensive laser light and the crystal can mediate the splitting of a pump photon to a photon pair. The two generated photons are typically called signal and idler.<p> </p>Influence of magnetic field on these nonlinear processes was not thoroughly tested yet. This topic deserves intensive study both from theoretical and experimental point of view, because the magnetic field can decrease the symmetry of the nonlinear crystal and so it may allow to use new types of phase-matching conditions. We started to test the SPDC process in BBO crystals. Nonlinear magneto-optic tensor of this material is not known and we can hardly predict it. According to our first theoretical derivations the efficiency of the nonlinear processes has to oscillate when rotating the magnetic-field orientation.
We report on the organization and realization of the Joint International Physics Summer School - Optics" devoted to High-School students. The idea of the School is to teach Physics through high-level experimental activities, suitably supported by introductory lectures and complemented by data analysis. The School is also open to the participation of a number of teachers, as an opportunity of refreshing their knowledge and increasing their experimental skills. Students and teachers are directly involved in the experimental activities. The aim of the activity is to stimulate students curiosity and interest and help them decide whether a future job career in Science could be suited for them. The School is organized in two weeks: the first in June-July in Como (Italy) at the Department of Science and High Technology and the second at the end of August in Olomouc (Czech Republic) at the Joint Laboratory of Optics. Two editions of the Summer School took place in 2013 and 2014 (overall 40 students and 3 teachers from Italy, 9 students from Czech Republic) and the third one will be in 2015. The first week of the School is devoted to introductory lectures (theoretical and experimental) to consolidate students' and teachers' knowledge of basic optics. The second week is devoted to several advanced experiments in linear, nonlinear, classical and quantum optics, performed in research laboratories. During the last day of the School, students are required to give a presentation of the results obtained during the experimental sessions.
We present experimental characterization of periodically-poled KTP waveguide studying the process of second harmonic generation. Spatial and spectral properties of three types of the nonlinear processes (Type 0, I, and II) have been observed simultaneously utilizing the first, second, and third harmonics of the spatial nonlinear modulation. Experimental results have been interpreted using a model based on scalar finite elements method, which has been adopted in order to calculate spatial mode profiles, propagation constants, and frequencies of the interacting fields. Correlations between spatial and spectral properties of the fundamental and second- harmonic fields have been revealed. Individual nonlinear processes can be switched on and off combining spatial and spectral filtering. Also the influence of waveguide parameters to the second-harmonic spectra has been addressed.
An overview of current commercial and emerging approaches to single-photon-sensitive detection is given. Special
attention is devoted to the detectors providing photon-number resolution with respect to their application in quantum
optics and quantum information. Besides detectors offering photon-number resolution intrinsically, also multiplexing
detectors are treated. A comparison of the detector technologies is presented.
The fundamental research of the parametrical fluorescence is discussed. We start with the mathematical model.
We have included the final size of nonlinear crystal, the chirped pump pulse of Gaussian elliptical beam in the
model. We have verified the numerical results experimentally. We have used two different methods. First one
used ICCD camera, and second one, scan by Hong-Ou-Mandel interferometer.
If there are correlations between two qubits then the results of the measurement on one of them can help to predict measurement results on the other one. It is an interesting question what can be predicted about the results of two complementary
projective measurements on the first qubit. To quantify these predictions the complementary knowledge excesses are used.
A non-trivial constraint restricting them is derived. For any mixed state and for arbitrary measurements the knowledge excesses are bounded by a factor depending only on the maximal violation of Bell's inequalities. This result is experimentally verified on two-photon Werner states prepared by means of spontaneous parametric down-conversion.
We present our experimental realization of a quantum random number generator (RNG) based on the quantum random process of division of light pulse on a fiber coupler. Our prototype consists of fiber optics elements: a pigtailcd laser diode, two mechanical attenuators, a fiber coupler, and two single photon detectors. The RNG contains all necessary electronics for the generation of light pulses, synchronized reading of detectors' states, processing of these results, and transfer of data to a host computer. The connection to the computer is done via a 25-pin parallel port, that makes our device easy to use with any personal computer (PC). The RNG can be operated in four different modes, that arc selected by the PC. The zeroth mode is just for the device control, the first mode serves for appropriate setting of generation efficiency, the second mode is designed for raw data sequence generation at a rate of 114 kByte/s, and the last mode provides balanced data sequence at a rate of 28 kByte/s utilizing von Ncumann's extraction procedure. This procedure is used to gain a properly balanced ratio between '0's and '1's. The balanced data sequence generated by the RNG in the third mode passes all kinds of tests we arc using [for example 15 tests proposed by G. Marsaglia, WWW: http://stat.fsu.edu/ geo/diehard.html 1. The raw data sequence can be used for purposes that do not need properly balanced data, because raw data passes tests that arc not inspecting the sequence balance.
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.