Arkadiusz Orłowski

Decoherence of entangled states in two-mode cavities

Decoherence of the Schrodinger-cat states in two-mode cavities are discussed. The cat states are assumed to be produced by the measurement of the energy of a three-level atom which have passed through the cavity. The evolution of the field density matrix is obtained from the Lindblad form of the dissipater at zero temperature. It is shown that the decoherence time of the two-mode cat states critically depends on the degree of entanglement. Implications for decoherence of entanglement in the macroscopic scales are discussed.

Facts and Myths of Enigma: breaking stereotypes

In spite of a relatively large number of publications about breaking Enigma by the Allies before and during the World War II, this subject remains relatively unknown not only to the general public, but also to people professionally involved in cryptological research. For example, the story of Enigma is rarely a part of a modern textbook on cryptology or a modern course on cryptography and network security. There exist multiple reasons for this situation. First, there are still a few unresolved issues, resulting from conflicting reports, the lack of reliable sources, and a long period required for declassifying documents related to any cryptological activity during the World War II. Secondly, the issue is highly political, and there is little consensus in weighing the contribution of all involved countries. Thirdly, many contemporary cryptologists honestly believe that there is little to learn from the analysis of old cryptosystems, because of the tremendous progress in theory and practice of cryptography and a little similarity between old and modern ciphers. In this paper we confront these opinions by presenting a look at the current state of knowledge about cryptological methods and devices used to break Enigma. We introduce all major players involved in these activities, and we make an effort to weigh their original contributions. Finally, we show that the story of Enigma can still provide contemporary cryptographers with many useful lessons regarding the way of organizing and building any large-scale security system.

Optimization of investment management in Warsaw stock market

Abstract Application of simple prescriptions of technical analysis on the Warsaw Exchange Market (GPW) has been analyzed using several stocks belonging to WIG20 group as examples. Only long positions have been considered. Three well-known technical-analysis indicators of the market have been investigated: the Donchian channels, the Relative Strength Index, and Moving Average Convergence-Divergence indicator. Optimal values of parameters of those indicators have been found by „brute force“ evaluation of (linear) returns. It has been found that trading based on both Donchian channels and Relative Strength Index easily outperform the „buy and hold“ strategy if supplied with optimal values of parameters. However, those optimal values are by now means universal in the sense that they depend on particular stocks, and are functions of time. The optimal management of capital in the stock market strongly depends on the time perspective of trading. Finally, it has been argued that the criticism of technical analysis which is often delivered by academic quantitative financial science is unjustified as based of false premises.

Spontaneous emission in a Fabry–Perot cavity: frequency modulation and collective effects

The spontaneous emission of radiation from two two-level atoms in a Fabry–Perot cavity is considered. The transition frequency of the atoms is assumed to be modulated. It is shown that the frequency modulation leads to radical change of the spontaneous emission dynamics, including the decoherence properties of the entangled atomic states. Two ingredients are necessary in order to achieve this. Firstly, the modulation should be able to periodically detune the atoms from the resonance with the cavity. Secondly, the dynamics of spontaneous emission is efficiently modified if a resonant condition between the modulation frequency and modulation depth is fulfilled. Thus, frequency modulation can be used to dynamically control the collective effects in spontaneous emission in cavities.

Anderson Localization of Electromagnetic Waves in Confined Disordered Dielectric Media

Scattering of electromagnetic waves from various kinds of obstacles is rich of interesting and sometimes unexpected phenomena. Already for two scatterers placed together well within a wavelength an extremely narrow proximity resonance can appear [10]. For many randomly distributed scatters we may expect that, for same range of parameters, Anderson localization can show up.

Novel Quantum Effects in Light Scattering from Cold Trapped Atoms

Both far off-resonance and resonant scattering of light from single atoms trapped by 3D harmonic potentials has thoroughly been studied. Novel effects are predicted for different physical regimes. We have shown that dynamics of the atomic center-of-mass strongly influences the scattering cross section. Possibility of using spectrum of the scattered light in far-off-resonance regime to nondestructively measure the temperature of ultracold atoms is advocated: off-resonance scattering can be used as an ‘optical thermometer’. The realistic Compton-like regime in resonant scattering has been investigated in detail. Another interesting quantum effect in resonant regime, which has not been discussed here due to the lack of space, is the time resolved scattering, showing up when the atom can remain in the excited state long enough to make many trips back and forth in the trap before emitting a photon. The possibility of the experimental observation of the predicted effects is now being scrutinized.

From Proximity Resonances to Anderson Localization

This paper serves as a guide for a tour from proximity resonances to Anderson localization. It can be quite a long trip. To see a proximity resonance it is enough to have just two scatteres placed very close together. To observe Anderson localization we need, in general, an infinite number of scatterers. It is hard to count from two to infinity within ten pages. Therefore we will have to stop somewhere in between. We are able to manage 1000 scatterers and, fortunately, this number seems to be large enough to justify some reasonable conclusions.