Molecular Dynamics Simulation of Thermal Nonequilibrium and Chemical Reaction Processes in Hydrogen Combustion.

Using reactive force field (ReaxFF) and molecular dynamics simulation, we investigate the combustion process of hydrogen-oxygen systems in initial thermal nonequilibrium states with different translational and rovibrational temperatures for oxygen. The system studied in this work contains 300 oxygen molecules and 700 hydrogen molecules with a density of 7 times the air density. For this system, the characteristic relaxation times of oxygen and hydrogen vibrational energies are 0.173 and 0.249 ns, respectively. 0.6% of hydrogen undergoes a chemical reaction with oxygen during the thermal nonequilibrium relaxation stage. For the distribution of translational energy and vibrational energy of oxygen in the thermal nonequilibrium state, the maximum mean error of the statistical distribution in the simulation and the Boltzmann distribution at temperature calculated from the average kinetic energy of molecules is about 2.25 × 10-5. At the same time, it was observed in the simulation that many-body interactions play a certain role in the combustion process. Furthermore, we compare the ignition time and temperature rise behavior of different combustion mechanisms and molecular dynamics simulations starting from the thermal equilibrium state. These results will provide meaningful references for the construction of thermal nonequilibrium combustion chemical reaction mechanisms.

Loss-tolerant and quantum-enhanced interferometer by reversed squeezing processes.

Reversed nonlinear dynamics is predicted to be capable of enhancing the quantum sensing in unprecedented ways. Here, we report the experimental demonstration of a loss-tolerant (external loss) and quantum-enhanced interferometer. Two cascaded optical parametric amplifiers are used to judiciously construct an interferometry with two orthogonal squeezing operation. As a consequence, a weak displacement introduced by a test cavity can be amplified for measurement, and the measured signal-to-noise ratio is better than that of both conventional photon shot-noise limited and squeezed-light assisted interferometers. We further confirm its superior loss-tolerant performance by varying the external losses and comparing with both conventional photon shot-noise limited and squeezed-light assisted configurations, illustrating the potential application in gravitational wave detection.

Generating six pairs of bandwidth-expanded entangled sideband modes via time delay compensation.

Quantum entanglement is an important pillar of quantum information processing. In addition to the entanglement degree, the bandwidth of entangled states becomes another focus of quantum communication. Here, by virtue of a broadband frequency-dependent beam splitter, we experimentally demonstrate six pairs of independent entangled sideband modes with maximum entanglement degree of 8.1 dB. Utilizing a time delay compensation scheme, the bandwidth of independent entangled sideband modes is expanded to dozens of megahertz. This work provides a valuable resource to implement efficient quantum information processing.

Entangled sideband control scheme via frequency-comb-type seed beam.

We report a control scheme of entangled sideband modes without coherent amplitude by employing a frequency-comb-type seed beam. In this scheme, each tooth of the frequency comb serves as a control field for the corresponding downconversion mode. Consequently, all the degrees of freedom can be actively controlled, and the entanglement degrees are higher than 6.7 dB for two pairs of sidebands. We believe that this scheme provides a simple solution for the control of sideband modes, which could be further applied to achieve compact channel multiplexing quantum communications.

Channel likelihood correction for photon-counting array receivers in the presence of dead time and jitters.

This paper presents a modified channel likelihood model for optical communication systems with a photon-counting array receiver where photon-counting events are impaired by undesirable dead time and jitters. After the photon-counting detector detects a photon, the detector will go into a period of dead time under which it cannot detect any incident photons. In this context, the channel will have memory. We derive the channel likelihood in the presence of the detector dead time and the random jitter of the photon arrival. The impact of dead time and jitters on the performance of a pulse-position-modulated (PPM) optical communication system is also investigated. The simulation results indicate that the modified channel likelihood expressions can obtain a more obvious performance gain under the context of a stronger background noise, fewer detection elements, longer dead time and bigger jitter.