Quantum Electronics

The work is dedicated to the further development of a compact quantum frequency standard based on a rubidium gas cell with a mixture of buffer gases. The results of frequency measurements and analysis of short-term frequency instability obtained on a laboratory prototype of a microwave rubidium atomic frequency standard (RAFS) with pulsed optical pumping (POP) are presented. The main in magnitude contributions to the overall frequency instability of the RAFS with POP are estimated. Short-term frequency instability expressed in terms of the Allan deviation and measured at averaging times τ up to several tens of seconds, σ_y(τ) = 2.5×10⁻¹³τ^−1/2, coincides satisfactorily with the calculated value of σ_y(τ) = 2.1×10⁻¹³τ^−1/2.

A frequency chain for converting the frequency of an optical clock based on ultracold ⁸⁷Sr atoms is updated for its comparison with the frequency of microwave standards from the State Primary Standard of time and frequency units and the national time scale, GET 1-2018. The results of the corresponding experiments are reported and analysed. An instrumental complex for reproducing and keeping the time and frequency units and the national time scale of the primary standard is described; this complex includes an optical clock based on strontium atoms and microwave standards of new generation. The order of the atomic time scale generation with application of optical clocks is also determined.

We examine the possibilities of refining an asymptotic description and quantitative calculations of the effects induced by thermal blackbody radiation (BBR) of the environment on the Rydberg states of atoms. Numerical values are calculated and asymptotic expressions are proposed for simplified estimates of natural lifetimes and threshold photoionisation cross sections for Rydberg states of rubidium and caesium atoms with large values of the principal quantum number, n ⩾ 20, and small orbital momenta, l = 0, 1, 2, 3. Based on analytical expressions, we present numerical estimates for the contributions of photoionisation probabilities to the BBR-induced broadening of the Rydberg energy level, as well as the contributions of continuum integrals to thermally induced shifts in the Rydberg-state energy levels.

We present a brief review of experimental work on the investigation of stimulated low-frequency Raman scattering of light in systems of submicron and nanosized particles of various physical nature.

We investigate displacement measurements of up to 17 μm on a heterodyne laser interferometer laboratory model. The measurement error for small (up to 200 nm) linear displacements is found to be 270 pm at a 10-s averaging time. The results obtained can be used for developing a space laser interferometric system for the global Earth's gravity field mapping.

We consider main methods for detecting single photons used in quantum communications, including the quantum key distribution (QKD) technology. Two most promising single photon detectors (SPDs) based on superconducting nanowires and on a single-photon avalanche diode are described. The most effective SPD designs are presented and their advantages and disadvantages are analysed from the point of view of the possibility of their use in QKD devices. The results of the work of various scientific groups conducting research on QKD are discussed, which makes it possible to trace the trends in the global technological development of this industry over the past five years.

This paper considers abnormal blocking of a guided mode propagating in a silicon optical waveguide with periodic tunnelling inserts. Using an independent two-dimensional analysis by the method of lines (MoL) and direct simulation by the finite-difference time-domain (FDTD) method, we have identified additional signal blocking bands, unrelated to Bragg conversion to backward guided modes of the parent silicon waveguide. These bands are due to the conversion of the incident wave energy to a leaky quasi-mode of the periodically segmented structure, which subsequently transfers the energy to the ambient medium in the form of radiation modes. A distinctive feature of this phenomenon is resonant coupling of the guided mode of the strip waveguide with its radiation modes, which is due to the weak tunnel coupling with the periodically segmented structure. This structure does not support independent guided propagation, so the energy stored in it is re-emitted to space. The abnormal blocking effect may find application in optical telecommunications elements and in the fabrication of optical sensors.

We report a numerical and experimental study of the laser beam propagation through a suspension of polystyrene microspheres in distilled water, showing the presence of higher-order centrally symmetric aberrations for the scatterer concentrations in the range from 1.3 × 10⁵ to 10⁶ mm⁻³ and analysing the dependence of the scattered light wavefront distortion on the concentration of particles in a turbid medium. The study has also shown the effectiveness of the compensation of the wavefront aberrations of a scattered laser beam using a bimorph adaptive mirror.

We consider image recording and reproduction using a reversed stimulated echo hologram, with a recording medium exposed to pulses of nonresonant electromagnetic standing waves. It is shown that the spatial intensity distribution in a stimulated echo hologram response depends on the electric field strength of nonresonant standing waves, which makes it possible to control reconstructed images.

Using a free electron laser developed in Novosibirsk, we have studied the reflection of monochromatic (λ = 130 μm) surface plasmon-polaritons (SPPs) from a plane mirror attached to a waveguiding surface. It is found that 100 % SPP reflection occurs not only in the perpendicular position of the mirror relative to the surface, but also when the mirror is deflected from the normal by the angle α being smaller than the limiting angle α* proportional to the SPP wave vector. When the mirror is deflected by the angle greater than α*, SPPs on a perfectly smooth surface must transform into a bulk wave, while, in the experiment, the SPP reflection coefficient decreases gradually to zero with increasing α, which is a manifestation of dispersion of the wave vector of monochromatic SPPs, caused by their scattering on the inhomogeneities of a real surface.