Том 37, № 6 (2016)

We show the star-product quantization procedure for spin-1/2 particles (qubits) employing the construction of a pair of operators – dequantizers and quantizers. We present an explicit description of all minimal systems of such dequantizers and quantizers and discuss their relation to the probability representation of spin states where the fair probability distribution is identified with the spin states. We give some examples and discuss the possibility of constructing a symplectic structure in the finite-dimensional phase space.

We present a comparative study of the dynamics of entanglement and quantum discord in a bipartite system in the presence of mixed classical noises. In particular, the joint effects of three different types of classical noises, namely, random telegraphic noise (RTN), Ornstein–Uhlenbeck noise (OU), and static noise, are studied by combining them in two different ways. In each case, one marginal system is coupled with random telegraphic noise, and the other marginal system is coupled with either OU or static noise. We make a comparison between the behaviors of both correlations in the two setups. In the weak coupling regime, the qualitative behavior of entanglement is unaffected by switching the coupling of only one marginal system from OU to static noise, and vice versa. However, the behavior of quantum discord strongly depends on whether it is coupled with OU or static noise. On the other hand, in the strong coupling regime, the static noise is more fatal to the survival of both correlations as compared to the other two noises.

We study quantum information properties of a seven-level system realized by a particle in a onedimensional square-well trap and discuss the features of encodings of seven-level systems in a form of three-qubit or qubit–qutrit systems. We use the three-qubit encoding of the system in order to investigate the subadditivity and strong subadditivity conditions for the particle’s thermal state. We employ the qubit–qutrit encoding to suggest a single qudit algorithm for calculating the parity of a bit string. The results obtained indicate on the potential resource of multilevel systems for realization of quantum information processing.

We develop a laser utilizing second harmonic generation that exhibits both high single-pulse energy and high beam quality. The system starts with a double-arched laser-diode-array stagger-pumped electro-optic Q-switched Nd:YAG with a thermal lensing compensated convex-concave resonator. The 1,064 nm output beam is then frequency doubled in an extracavity KTP double-crystal assembly that offsets birefringence walk-off. We obtain a maximum single-pulse energy of 72.7 mJ at 532 nm with 176 mJ at 1,064 nm. The corresponding optical-to-optical conversion efficiency is 41.3%, and the pulse width is 9.2 ns at a repetition rate of 20 Hz. The beam quality factor M² is 1.83 in both horizontal and vertical directions at the maximum output energy, and the energy stability is better than 3% across half an hour.

Direct writing technique is usually used in femtosecond-laser two-photon micromachining. The size of the scanning step has important influence on the surface quality and machining efficiency of microdevices. According to the mechanism of two-photon polymerization combining the distribution function of the light intensity and the free-radical-concentration theory, we establish the mathematical model of coverage of solidification unit and analyze the effect of coverage on the machining quality and efficiency of microdevices. Using the principle of exposure equivalence, we also obtain the analytic expression of the relationship between the surface-quality characteristic parameters of microdevices and the scanning step and carry out the numerical simulation and experiment. The results show that the scanning step has little influence on the surface quality of the line when it is much smaller than the size of the solidification unit. However, when the scanning step is gradually increasing, the smoothness of the line surface is reduced rapidly, and the surface quality becomes worse drastically. For stereo-device processing with different slopes, we propose a kind three-dimensional continuous-variable scanning method and provide the calculation expression of the scanning step. From the experimental example of fabricating a spherical structure, we show that, compared with the fixed-step scanning method, the continuous-variable scanning-step method should be used to improve the surface quality of microdevices.