Том 103, № 6 (2016)

The flavor dependence of the medium modification factor R_pp for pp collisions has been studied for a scenario with formation of a small-size quark-gluon plasma (QGP) for RHIC (\(\sqrt s \)= 0.2 TeV) and LHC (\(\sqrt s \)= 2.76 TeV) energies. It has been found that at p_T ~ 10 GeV the pion spectrum is suppressed by ~20–30 (25–35)% for RHIC (LHC), for D (B) mesons the suppression effect is smaller by a factor of ~0.7–0.8 (0.5). The flavor hierarchy R_pp^π < R_pp^D < R_pp^B is held at p_T ≲ 20 GeV for RHIC and at p_T ≲ 70 GeV for LHC. This gives a significant reduction of the heavy-to-light ratios of the nuclear modification factors R_AA as compared to that in the standard scenario without the QGP production in pp collisions.

A theoretical scheme for enhanced Kerr nonlinearity is proposed in a four-level ladder-type atomic system based on double dark resonances (DDRs). We solve the relevant density matrix equations in steady state and utilize the perturbation theory to obtain the analytical expressions for the third order susceptibility of the atomic system. The influence of system parameters on behavior of the first and third order susceptibilities is then discussed. In particular, it is found that an enhanced Kerr nonlinearity with reduced linear and nonlinear absorption is obtained around zero probe detuning under the slow light condition through proper adjusting the laser field intensity and frequency detuning of driving fields. The dressed state analysis is employed to explain the physical origin of the obtained result. The obtained results may be important for all-optical signal processing and quantum information technology.

We report the observation of photovoltage oscillations in back-gated two-dimensional electron systems when tuning the density under incident microwaves and in the absence of a magnetic field. The oscillations are periodic in the inverse of the square root of the density. They originate from the interference of screened bulk plasmons with a linear dispersion. This phenomenon can be exploited to devise a spectrometer-on-a-chip for millimeter waves. The influence of a perpendicular magnetic field is investigated and reveals a transformation of screened bulk plasmons waves into screened edge magnetoplasmons.

It has been shown that, because of the two-orbital character of the subsystem of holes located at oxygen sites and the spatial separation of this subsystem from that of spins at copper ions, the superconducting phase in high-T_c superconductors is stable with respect to the strong Coulomb repulsion of holes located at nearestneighbor oxygen sites if the order parameter has the \({d_{{x^2} - {y^2}}}\) symmetry. This effect is due to the symmetry characteristics of the Coulomb potential, owing to which the equation determining the Cooper pairing in the \({d_{{x^2} - {y^2}}}\) channel does not include this potential.

The phase dynamics of a SQUID consisting of Josephson junctions with topologically nontrivial barriers has been studied. Its comparative analysis with the dynamics of a conventional SQUID has been performed. The current–voltage characteristics have been calculated. The dependence of the return current on the magnetic field has been found. It has been shown that the branch of the current–voltage characteristic corresponding to the resonance frequency in the case of the SQUID with nontrivial barriers is displaced by \(\sqrt 2 \) over voltage. This effect can be used for the detection of Majorana fermions.

Free expansion of Bose–Einstein condensates of rubidium atoms at finite temperatures has been analyzed experimentally and theoretically. It has been shown that the interaction between condensed and noncondensed atoms is manifested most clearly by a decrease in the density of atoms in the center of the expanding cloud as compared to the theoretical prediction for a pure condensate.

An exact solution of the Schrödinger equation has been obtained in the sudden perturbation approximation for the case of the interaction of attosecond and shorter electromagnetic pulses with multielectron atoms. This solution makes it possible to exactly take into account the spatial inhomogeneity of the field of an ultrashort pulse. The result has been presented in an analytical form.

The method of active stabilization of the polarization and other parameters of the optical part of a two-pass fiber optic quantum cryptography has been proposed and implemented. The method allows the completely automated maintenance of the visibility of interference close to an ideal value (V ≥ 0.99) and the reduction of the instrumental contribution to the error in primary keys (QBER) to 0.5%.