Vol 39, No 6 (2018)
- Year: 2018
- Articles: 11
- URL: https://journals.rcsi.science/1071-2836/issue/view/15514
Article
Quantum and Classical Correlations for Interacting and Noninteracting Qubits in Contact with Different Environments
Abstract
We study the time evolution of the classical and quantum correlations for interacting and noninteracting two-qubit systems under the influence of noncorrelated and correlated environmental models. We discuss the dependence of different physical quantifiers on the environment parameters. Interestingly, we examine the effects of the initial state and different system parameters on the evolution of correlations of the system of qubits in contact with different kinds of environments. We show how the interaction among qubits can protect and preserve the correlation loss during the time evolution for various environmental models. Moreover, we examine the competition between the dissipative and coherent effects in different kinds of correlations dynamics of the system of qubits. Our study gives a deeper understanding on the correlations for a wide variety of the environment models, which is rather significant in different tasks of quantum optics and information.
Quantum Dynamical Behavior of the Morse Oscillator: the Wigner Function Approach
Abstract
We explore the quantum dynamical behavior of the Morse oscillator in the phase space using the Wigner function. For an initial wave packet excited with Gaussian probability distribution, we calculate the associated Wigner function and compute its time evolution. By calculating the marginal probabilities, we study the formation of quantum carpets both in the position space and in the momentum space. In addition, in view of these probabilities, we present the time evolution of the position and momentum expectation values. The structure of quantum carpets and the time-evolved expectation values mimic the emergence of quantum revivals and fractional revivals.
A Necessary Condition for Quantum Adiabaticity Applied to the Adiabatic Grover Search
Abstract
Numerous sufficient conditions for adiabaticity of the evolution of a driven quantum system have been known for quite a long time. In contrast, necessary adiabatic conditions are scarce. Recently a practicable necessary condition well suited for many-body systems has been proved. Here we tailor this condition for estimating run times of adiabatic quantum algorithms. As an illustration, the condition is applied to the adiabatic algorithm for searching in an unstructured database (adiabatic Grover search algorithm). We find that the thus obtained lower bound on the run time of this algorithm reproduces \( \sqrt{N} \) scaling (with N being the number of database entries) of the explicitly known optimum run time. This is in contrast to the poor performance of the known sufficient adiabatic conditions, which guarantee adiabaticity only for a run time on the order of O(N), which does not constitute any speedup over the classical database search. This observation highlights the merits of the new adiabatic condition and its potential relevance to adiabatic quantum computing.
Error Estimation at the Information Reconciliation Stage of Quantum Key Distribution
Abstract
Quantum key distribution (QKD) offers a practical solution for secure communication between two distinct parties via a quantum channel and an authentic public channel. In this work, we consider different approaches to the quantum bit error rate (QBER) estimation at the information reconciliation stage of the post-processing procedure. For reconciliation schemes employing low-density parity-check (LDPC) codes, we develop a novel syndrome-based QBER estimation algorithm. The algorithm suggested is suitable for irregular LDPC codes and takes into account punctured and shortened bits. Testing our approach in a real QKD setup, we show that an approach combining the proposed algorithm with conventional QBER estimation techniques allows one to improve the accuracy of the QBER estimation.
EIT Ground State Cooling Scheme of 171Yb+ Based on the 2S1/2→2P1/2 Cooling Transition
Abstract
We propose a method for EIT ground state cooling of 171Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).
Process Window for Nd:YAG Laser Welding of Super Duplex Stainless Steel
Abstract
Super duplex stainless steel (SDSS), an advanced duplex stainless steel with higher alloying concentration, is employed widely in acidic atmospheres. In this study, we make an attempt to develop a process window for the pulsed mode Nd:YAG laser welding of SDSS, as reference maps, to identify the range of process parameters viz., laser power, welding speed, defocusing distance, and pulse frequency for obtaining a defect free full penetration welds. The eminence of the welds, based on the macrostructure, microstructure, and tensile strength, is reported. We obtain a complete penetration weld devoid of undercut, crating at the top and minimum heat affected zone (HAZ) with a overlapping factor of 80–90% and heat input at 100–200 J/mm. The experimental settings prevailing inside the preferred region of the process window exhibit a higher tensile strength as well.
An Intracavity-Triggered Passively-Switched Nd:YVO4 Laser
Abstract
We demonstrate an intracavity-triggered passively Q-switched Nd:YVO4 laser within a diode-end-pumped configuration. We employ a Cr4+:YAG saturable absorber as the passive Q switch and an Nd:LiYF4 (YLF) laser as the laser triggering of the Q-switched laser. Since we use the same Cr4+:YAG crystal and output coupler with the Nd:YVO4 laser, the Cr4+:YAG Q switch is triggered inside the Nd:YLF laser cavity. As a result, the timing jitter in standard deviation of Nd:YVO4 laser can be reduced to 16 ns.
Using Laser Measuring and SFM Algorithm for Fast 3D Reconstruction of Objects
Abstract
Effective measurement of the reflective or transparent surface of an object has always been a disadvantage in laser scanning modeling. We propose a fast and complete three-dimensional (3D) reconstruction method for small static objects using laser scanning and the structure from motion (SFM) algorithm. Meanwhile, a complete reconstruction workflow is designed and a multi-angle 3d reconstruction system is set up. To generate the complete point cloud model of the object, the SFM algorithm is used to reconstruct the surface part of the object, the data for which cannot be obtained by the laser measuring instrument. The experimental results show that this method not only improves the speed, accuracy, integrity, and visual effect of 3D reconstruction of small objects, but also extends the scope of 3D reconstruction of laser measurement.
Injection-Seeded 500 Hz Repetition Rate High Peak Power Single-Frequency Nd:YAG Laser for Mid-Infrared Generation
Abstract
We develop an injection-seeded single-frequency neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with 500 Hz repetition rate and high peak power. The laser construction is designed as seed injection and master oscillator power amplifier (MOPA) including single-frequency master oscillator, extra-cavity frequency doubling crystal, and round-trip power amplifier. The master oscillator can emit 1,064 nm laser of 8.4 mJ with 6.8 ns pulse width at the pump energy equal to 23 mJ. A green laser energy of 1.1 mJ is obtained by setting the proper temperature of the LBO crystal. The pulse energy of 1,064 nm laser decreases to 6.5 mJ after passing through the LBO crystal and rises to 25.3 mJ after a round-trip power amplifier corresponding to the extraction efficiency of 29%. The final output pulse width is 6.5 ns, representing a peak power of 3.9 MW. The 1,064 nm laser beam quality factor M2 of the master oscillator and the amplified one are 1.3 and 1.5, respectively. The laser will be used to generate mid-infrared where the 532 nm laser with narrow pulse width is to pump sheet optical parametric oscillator (OPO) and the 1,064 nm laser with high peak power to pump the OPO.
High-Pulse-Energy Passively Q-Switched 1,123 nm Laser with a Nd:GdYAG Mixed Garnet as Laser Medium
Abstract
We demonstrate a diode-pumped passively Q-switched Nd:GdYAG mixed garnet laser at 1,123 nm. A Cr4+:YAG crystal with an initial transmission of 97% is used as the saturable absorber. The maximum average output power is 1.05 W at an absorbed pumping power of 8.12 W. A single-pulse energy can reach up to 78.9 μJ, with a corresponding pulse repetition rate of 13.3 kHz.
A Novel 1,066 nm Nd:Gd0.69Y0.3NbO4 Passively Q-Switched Pulse-Burst Laser
Abstract
We demonstrate for the first time a Cr4+:YAG passively Q-switched 1066 nm pulse-burst laser under 879 nm direct pump with a novel Nd:Gd0.69Y0.3NbO4 crystal. The output laser characteristics with different pump repetition rates and different Cr4+:YAG initial transmission are studied. Without the Cr4+:YAG, we obtain a maximum output energy of 2.55 mJ at an absorbed pump energy of 5.79 mJ with the highest 48% slope efficiency. The pulse-burst laser contains a maximum of 7 pulses for a Cr4+:YAG initial transmission of 55% and a pump repetition rate of 1 kHz. The single-pulse energy and narrowest pulse width reach 160 μJ and 5.5 ns at 38.2 kHz, with a peak power of 32 kW.