Terahertz spectroscopy with a Josephson oscillator and a SINIS bolometer

The voltage response of a thin-film normal-metal hot-electron bolometer based on a SINIS (superconductor-insulator-normal metal-insulator-superconductor) structure to the radiation of a high-temperature Josephson junction in the terahertz frequency region was measured. Bolometers were integrated with planar log-periodic and double-dipole antennas, and Josephson junctions were integrated with log-periodic antennas. Measurements showed that the Josephson junction at a temperature of 260 mK was overheated by the transport current, so that its electron temperature exceeded 3 K at a bias voltage of 1 mV. The maximum response of a bolometer with a double-dipole antenna was observed at a frequency of 300 GHz, which agreed well with the calculated value. The Josephson radiation was observed at frequencies up to 1.7 THz. The voltage response of a bolometer reached 4×10⁸ V/W, and the total noise-equivalent power reached 1.5×10^?17 W/Hz^1/2.     

On a collective attack on the key in quantum cryptography on two nonorthogonal states

A “collective” attack on the key is considered, and its connection with the classical capacity of a quantum communication channel is analyzed. It has been shown that the allowable error probability for legitimate users to which the secure key can be extracted is less than half the value for “translucent” eavesdropping and individual measurements.     

Spatial-temporal ion structures in the earth’s magnetotail: Beamlets as a result of nonadiabatic impulse acceleration of the plasma

The properties of high-energy ion beams (beamlets) observed in the boundary layer of the plasma sheet of the Earth’s magnetotail during short time intervals (1–2 min) have been considered. Beamlets are induced by nonlinear impulse accelerating processes occurring in the current sheet of the far regions of the geomagnetic tail. Then, moving toward the Earth along the magnetic field lines, they are detected in the magnetotail (in the plasma sheet boundary layer) and in the high-latitude part of the auroral zone in the form of short bursts of high-energy ions (with energies of several tens of keVs). The size of the localization region of the beamlets in the magnetotail and auroral zone has been determined by the epoch-superposition method, and it has been shown that beamlets are concentrated in a narrow region near the plasma sheet boundary, whose latitude size is no more than 0.8δ. This conclusion corroborates the theoretical prediction that the nonadiabatic resonant acceleration of ions occurs in a spatially localized region near the separatrix separating the open magnetic field lines and closed field lines, which contain the hot and isotropic plasmas of the plasma sheet. Based on the CLUSTER multisatellite measurements, the spatial structure of beamlets is analyzed and it has been found that the Alfvén wave arises due to the excitation of fire-hose instability at the instant of the exit of the ion beam from the current sheet to the high-latitude region of the far tail of the Earth’s magnetosphere. The longitudinal (along the magnetic field) and transverse sizes of a beamlet are estimated. It has been found that the beamlet is a dynamic plasma structure whose longitudinal size is several hundred times larger than its transverse size.     

Supersymmetric large extra dimensions and the cosmological constant: an update

This article critically reviews the proposal for addressing the cosmological constant problem within the framework of supersymmetric large extra dimensions (SLED), as recently proposed in hep-th/0304256. After a brief restatement of the cosmological constant problem, a short summary of the proposed mechanism is given. The emphasis is on the perspective of the low-energy effective theory in order to see how it addresses the problem of why low-energy particles like the electron do not contribute too large a vacuum energy. This is followed by a discussion of the main objections, which are grouped into the following five topics: (1) Weinberg’s No-Go Theorem. (2) Are hidden tunings of the theory required, and are these stable under renormalization? (3) Why should the mechanism apply only now and not rule out possible earlier epochs of inflationary dynamics? (4) How big are quantum effects, and which are the most dangerous? and (5) Even if successful, can the mechanism be consistent with cosmological or current observational constraints? It is argued that there are plausible reasons why the mechanism can thread the potential objections, but that a definitive proof that it does depends on addressing well-defined technical points. These points include identifying what fixes the size of the extra dimensions, checking how topological obstructions renormalize and performing specific calculations of quantum corrections. More detailed studies of these issues, which are well within reach of our present understanding of extra-dimensional theories, are currently underway. As such, the jury remains out concerning the proposal, although the prospects for acquittal still seem good. (An abridged version of this article appears in the proceedings of SUSY 2003.)     

Quadratic Integrals of Motion for the Systems of Identical Particles

The dynamical systems of identical particles admitting quadratic integrals of motion are classified. The relevant integrals are explicitly constructed and their relation to separation of variables in Hamilton-Jacobi equation is clarified.     

An interference method for studying a substance in the vicinity of its critical point

An interference method for measuring certain parameters of a substance in the vicinity of the critical state is proposed. The essence of the method is to decipher the interference pattern arising upon grazing incidence of a laser beam on a curved liquid-vapor interface. The deciphering allows one to determine the difference between the refractive indices of the two phases and the scaling factor of the wetting meniscus shape. This, in turn, makes it possible to calculate the critical exponents for the temperature dependences of the surface tension and the difference in the densities of the two phases. The ratio of these critical exponents for xenon, measured in the paper, is 3.81±0.03.     

Recombination of an electron-hole plasma in silicon under the action of femtosecond laser pulses

Experimental data are obtained on the dynamics of conduction-electron relaxation at the stage preceding the melting of a silicon surface layer. The energy of a quantum of probe radiation is smaller than the band gap, making it possible to obtain information about the electron-phonon relaxation processes for an electron concentration of ～ 10²¹ cm^?3 in the conduction band.     

Dynamics in molecular crystals: An application of proton NMR to selectively protonated biphenyl. Do the rings flip together or independently?

The synthesis of a specific isotopomer, C₆D₄H(ortho)-H(ortho)D₄C₆ of biphenyl is reported. The intramolecular dipolar coupling of the protons leads to a well-resolved single-crystal proton nuclear magnetic resonance (NMR) spectrum and allows one to study the dynamics of the phenyl rings in a unique way. At room temperature and above, the most conspicuous dynamical mode consists of 180° ring flips. The present data together with previous measurements of the total flip rate allow us to conclude that the rings flip almost exclusively independently of each other. Between the incommensurate (IC) phase transition of biphenyl at 38 K andT=250 K, the prominent namical mode consists of oscillatory twists ϕ(t) of the two rings. The data allow us to infer the mean square, (φ²), of these twists. (φ²) is found to grow linearly withT for 50<T<200 K. From the slope of (φ²) vs.T the frequency (the wave number[(v)\tilde]\tilde v) is derived. The result is[(v)\tilde] = 20\tilde v = 20 cm⁻¹. ForT<38 K, the spectra give direct evidence of the IC phase transition and its nature (stripelike rather than quiltlike). The temperature dependence of the magnitude of the order parameter of the IC phase is obtained.     

On two functionals connected to the Laplacian in a class of doubly connected domains in space-forms

LetB ₁ be a ball of radiusr ₁ inS ⁿ (ℍⁿ), and letB ₀ be a smaller ball of radiusr ₀ such thatB ₀ ⊂B ₁ . ForS ⁿ we considerr ₁ π. Let u be a solution of the problem- δm = 1 in Ω :=B ₁ /B ₀ vanishing on the boundary. It is shown that the associated functionalJ (Ω) is minimal if and only if the balls are concentric. It is also shown that the first Dirichlet eigenvalue of the Laplacian on Ω is maximal if and only if the balls are concentric.