Properties of voids in the Local Volume

Current explanation of the overabundance of dark matter subhalos in the Local Group (LG) indicates that there maybe a limit on mass of a halo, which can host a galaxy. This idea can be tested using voids in the distribution of galaxies: at some level small voids should not contain any (even dwarf) galaxies. We use observational samples complete to M_B=-12 with distances less than 8 Mpc to construct the void function (VF): the distribution of sizes of voids empty of any galaxies. There are ~ 30 voids with sizes ranging from 1 to 5 Mpc. We also study the distribution of dark matter halos in very high resolution simulations of the LCDM model. The theoretical VF matches the observations remarkably well only if we use halos with circular velocities larger than 45 +/- 10 km/s. This agrees with the Local Group predictions. Small voids look quite similar to heir giant cousins: the density has a minimum at the center of a void and it increases as we get closer to the border. Thus, both the Local Group data and the nearby voids indicate that isolated halos below 45 +/- 10 km/s must not host galaxies and that small (few Mpc) voids are truly dark.Comment: 5 pages 1 figure. To appear in proceedings of the conference "Galaxies in the Local Volume", Sydney, 8 to 13 July 200

Minimalist design of a robust real-time quantum random number generator

We present a simple and robust construction of a real-time quantum random number generator (QRNG). Our minimalist approach ensures stable operation of the device as well as its simple and straightforward hardware implementation as a stand-alone module. As a source of randomness the device uses measurements of time intervals between clicks of a single-photon detector. The obtained raw sequence is then filtered and processed by a deterministic randomness extractor, which is realized as a look-up table. This enables high speed on-the-fly processing without the need of extensive computations. The overall performance of the device is around 1 random bit per detector click, resulting in 1.2 Mbit/s generation rate in our implementation

Security of entanglement-based QKD with realistic parametric down-conversion sources

The paper analyzes security aspects of practical entanglement-based quantum key distribution (QKD), namely, BBM92 or entanglement-based BB84 protocol. Similar to prepare-and-measure QKD protocols, practical implementations of the entanglement-based QKD have to rely upon non-ideal photon sources. A typical solution for entanglement generation is the spontaneous parametric down-conversion. However, this process creates not only single photon pairs, but also quantum states with more than two photons, which potentially may lead to security deterioration. We show that this effect does not impair the security of entanglement-based QKD systems. We also review the available security proofs and show that properties of the entanglement source have nothing to do with security degradation.Comment: 6 page

Energy level dynamics in systems with weakly multifractal eigenstates: equivalence to 1D correlated fermions

It is shown that the parametric spectral statistics in the critical random matrix ensemble with multifractal eigenvector statistics are identical to the statistics of correlated 1D fermions at finite temperatures. For weak multifractality the effective temperature of fictitious 1D fermions is proportional to (1-d_{n})/n, where d_{n} is the fractal dimension found from the n-th moment of inverse participation ratio. For large energy and parameter separations the fictitious fermions are described by the Luttinger liquid model which follows from the Calogero-Sutherland model. The low-temperature asymptotic form of the two-point equal-parameter spectral correlation function is found for all energy separations and its relevance for the low temperature equal-time density correlations in the Calogero-Sutherland model is conjectured.Comment: 4 pages, Revtex, final journal versio

First Starbursts at high redshift: Formation of globular clusters

Numerical simulations of a Milky Way-size galaxy demonstrate that globular clusters with the properties similar to observed can form naturally at z > 3 in the concordance Lambda-CDM cosmology. The clusters in our model form in the strongly baryon-dominated cores of supergiant molecular clouds. The first clusters form at z = 12, while the peak formation appears to be at z = 3-5. The zero-age mass function of globular clusters can be approximated by a power-law dN/dM ~ M^-2, in agreement with observations of young massive star clusters.Comment: 4 pages, proceedings of the "Multi-Wavelength Cosmology" meeting, June 200

Generic scaling relation in the scalar ϕ4\phi^{4} model

The results of analysis of the one--loop spectrum of anomalous dimensions of composite operators in the scalar $\phi^{4}$ model are presented. We give the rigorous constructive proof of the hypothesis on the hierarchical structure of the spectrum of anomalous dimensions -- the naive sum of any two anomalous dimensions generates a limit point in the spectrum. Arguments in favor of the nonperturbative character of this result and the possible ways of a generalization to other field theories are briefly discussed.Comment: 15 pages, Latex, 50 K