Vol 37, No 4 (2016)

We propose the discretization of the density matrix as a nonlinear positive map for systems with continuous variables. We use this procedure for calculating the entanglement between two modes through different criteria, such as Tsallis entropy, von Neumann entropy and linear entropy, and the logarithmic negativity. As an example, we study the dynamics of entanglement for the two-mode squeezed-vacuum state in the parametric amplifier and show good agreement with the analytic results. Also we address the loss of information on the system state due to the discretization of the density matrix.

A key element in the architecture of quantum information processing is a reliable physical interface between fields and qubits. Here, we study the population transfer and entanglement for a two-level atomic system interacting with entangled spin coherent states (ESCSs) considering one- and two-mode interactions. The results show that decrease in the spin number provides a periodic behavior of the entanglement exhibiting the sudden death and birth phenomena. For large values of spin, the atom–field system stabilizes at high value of entanglement during the time evolution exhibiting maximum correlations for both cases of one- and two-mode interactions. Finally, we find an interesting correlation between the entanglement and the population transfer during the time evolution. In particular, we show that the population may be used as an indicator of nonlocal correlations in the system under consideration.

We investigate entanglement and mixedness of a superconducting qubit coupled to the damped cavity field. We introduce a new measure for the mixedness and find that the phase damping of the cavity leads to simultaneous long-death of the entropy squeezing, the purity of the qubit states, and the entanglement of the field–qubit system.

We consider the requirements of the energy-control system of the PICO laser facility and describe a design of the calorimeter based on the proposed method of laser-radiation-energy measurements using the calorimeter–sensor thermal response. We present the results of an experimental study of the calorimeter temporal parameters and dynamic analog memory.

We report a Ho:YAG (Ho-doped yttrium aluminum garnet) laser pumped by a dual-end-diode-pumped Tm:YLF (Tm-doped yttrium lithium fluoride) laser to obtain an efficient experimental device with high output-power characteristics. We study the influence of the specific values of the output coupling mirror transmittance, the resonant cavity length, and the radius of curvature of the output coupling mirror on the Ho:YAG laser output characteristics. Under optimum experimental conditions, under which the output coupling mirror transmittance was 30%, the resonant cavity length was 25 mm and the output coupling mirror radius of curvature was 300 mm, and the maximum pumping power of the dual-end-diode-pumped Tm:YLF laser was 15.2 W. We obtain an efficient high-power 2.122-μm laser output of 7.98 W from the Ho:YAG laser. The optical-to-optical conversion efficiency is 52.5%, and the beam quality factor figures are M_x² = 2.89 and M_y² = 2.97.

We report a high peak power, narrow linewidth, stable pulsed Ho:GdVO₄ amplifier based on thuliumdoped fiber, which produces 6.65 W average output power at 2,048 nm and 56.8 kW peak power with 11.7 ns pulse width at 10 kHz repetition rate. We use a simple Q-switched Ho:GdVO₄ laser as a seed laser and a thulium-doped fiber pumped by a 792 nm laser diode as an amplifier. The fiber amplifier provided 6.5 dB gain to the input signal. The spectral linewidth of the Ho:GdVO₄ amplifier remains < 0.5 nm with an M² beam quality of 1.36.

We report a diode-pumped continuous-wave (CW) thin-disk Yb³⁺-doped Sr₅(PO₄)₃F (Yb:S-FAP) laser operating at 985 nm. We achieve a power of 4.34 W at 980 nm in the CW operation regime with a fiber-coupled laser diode emitting 17.2 W at 914 nm. Furthermore, we demonstrate intracavity second-harmonic generation in the continuous-wave mode with a power of 893 mW at 492.5 nm using a BiB₃O₆ (BiBO) nonlinear crystal. The fluctuation of the blue output power was better than 3.57%. The M₂ factors are about 1.15 and 1.18 in the X and Y directions, respectively.