Random lasing of CsPbBr_3 perovskite thin films pumped by modulated electron beam

Aiming at the application requirements of information optics,this Letter proposed a perovskite quantum dot random lasing pumping method suitable for high-speed modulation.At the same time,the luminescence characteristics of perovskite quantum dot films under electron beam pumping conditions are analyzed,and the random lasing mechanism of electron beam pumping CsPbBr3 quantum dot films is revealed.Finally,it is confirmed that perovskite quantum dots are easy to realize random lasing under electron beam pumping conditions.     

Pumping Lemma for Quantum Automata

Not all lattice-valued quantum automata possess the pumping property in its strict form. However the pumping lemma can be generalized, and all lattice-valued quantum automata possess the generalized pumping property.     

Optical pumping of the electronic and nuclear spin of single charge-tunable quantum dots

We present a comprehensive examination of optical pumping of spins in individual GaAs quantum dots as we change the net charge from positive to neutral to negative with a charge-tunable heterostructure. Negative photoluminescence polarization memory is enhanced by optical pumping of ground state electron spins, which we prove with the first measurements of the Hanle effect on an individual quantum dot. We use the Overhauser effect in a high longitudinal magnetic field to demonstrate efficient optical pumping of nuclear spins for all three charge states of the quantum dot.     

Dimerization,trimerization and quantum pumping

We study one-dimensional topological models with dimerization and trimerization and show that these models can be generated using interaction or optical superlattice. The topological properties of these models are demonstrated by the appearance of edge states and the mechanism of dimerization and trimerization is analyzed. Then we show that a quantum pumping process can be constructed based on each one-dimensional topological model. The quantum pumping process is explicitly demonstrated by the instantaneous energy spectrum and local current. The result shows that the pumping is assisted by the gapless states connecting the bands and one charge is pumped during a cycle, which also defines a nonzero Chern number. Our study systematically shows the connection of one-dimensional topological models and quantum pumping, and is useful for the experimental studies on topological phases in optical lattices and photonic quasicrystals.     

Impact of Interacting Quantum Coherence via Decays and Incoherent Pumping on Transient and Steady-State Behaviors of Absorption

The effects from quantum coherence via decays and incoherent pumping on the lasing without inversion(LWI) are investigated in a four-level system.By analyzing the transient and steady-state behaviors of the absorption,we find that the gain occurs when both spontaneously generated coherence(SGC) and coherence induced by incoherent pumping(IPC) are considered.We attribute the occurrence of the gain to the interaction of quantum coherence via decays and incoherent pumping.     

基于钠硼铝硅酸盐玻璃的PbSe量子点红外单模光纤激光

根据实验制备的钠硼铝硅酸盐PbSe量子点玻璃及其透射电子显微镜(TEM)图、吸收谱和发射谱,计算机数值模拟了以PbSe量子点作为激活增益介质的红外单模光纤激光。应用遗传算法,通过数值求解粒子数速率方程和激光谐振腔振荡方程,优化计算了量子点光纤激光器(QDFL)的最佳抽运波长、光纤长度、掺杂浓度及出射镜反射率。结果表明:饱和抽运功率为2 W,在1676nm激光波长处,QDFL最大输出功率可达1.36 W,抽运效率达68%。与通常的掺稀土离子(Yb3+、Er3+)的光纤激光器相比,QDFL具有抽运效率高、激励阈值低、掺杂密度可调、光纤饱和长度短等特点。由于量子点辐射波长的尺寸依赖特性,容易形成多波长激射或波长可调的新型激光器。     

Quantum pump for spin and charge transport in a Luttinger liquid

We study two different parametric pumps--one for pumping spin currents, the other for charge currents--in interacting quantum wires. We find that, as a function of pumping frequency, the spin or charge pumped per cycle has a nonuniversal crossover--depending on pumping details--between two universal fixed point values of 0 and twice the electronic spin or charge quantum number. The direction of flow between these two fixed points depends on whether the interactions are repulsive or attractive, while the quantization itself is a signature of interactions.     

Ultrafast interband pumping of quantum‐cascade structures: A feasibility study of a THz pulse amplifier

Gain spectra of a three‐well GaAs/AlGaAs quantum‐cascade structure under interband pumping by ultrashort optical pulses are studied within the framework of the density matrix theory. A mathematical model for intersubband kinetics is derived taking into account many‐body interactions and ultrafast interband optical pumping. It is found that pulsed interband pumping leads to an increase in intersubband gain by an order of magnitude, which is characterised by 1 ps rise time and 8 ps recovery time under pumping by 100 fs pulses with a peak intensity of 100 MW/cm². Possible implementations of the concept are highlighted. The results uncover a new possibility for ultrafast switching of the material gain in quantum‐cascade structures.     

Influence of pumping laser bandwidth on the quantum fluctuation chracteristic of a non-degenerate optical parametric amplifier

Usually the quantum fluctuation characteristic of a non-degenerate optical parametric amplifier is analysed under the assumption of monochromatic pumping. However, in experiments, a driving beam with finite bandwidth is used to obtain the non-degenerate signal and idler beam amplifications. On account of that, we derive an analytical solution for the non-degenerate optical parametric amplification system with finite bandwidth laser pumping, and evaluate the associated quantum fluctuation. Finally, the application of the V1 criterion to bipartite entanglement is discussed.     

Controlled flow of spin-entangled electrons via adiabatic quantum pumping

We propose a method to dynamically generate and control the flow of spin-entangled electrons, each belonging to a spin singlet, by means of adiabatic quantum pumping. The pumping cycle functions by periodic time variation of localized two-body interactions. We develop a generalized approach to adiabatic quantum pumping as traditional methods based on a scattering matrix in one dimension cannot be applied here. We specifically compute the flow of spin-entangled electrons within a Hubbard-like model of quantum dots, discuss possible implementations, and identify parameters that can be used to control the singlet flow.     

Effects of absorption saturation in colloidal quantum dots as fluorophores for multiphoton fluorescence microscopy

It is shown that colloidal semiconductor nanocrystals (quantum dots), which are promising fluorophores for multiphoton fluorescence microscopy, exhibit a two-photon absorption saturation effect at moderate powers (not exceeding 10 mW) of femtosecond pumping radiation. An analytical expression for the power of two-photon fluorescence of quantum dots as a function of the average pumping power is obtained. With this expression, the deviation of the found dependence from the quadratic law is explained by two factors, i.e., a large two-photon absorption cross section of quantum dots and their slow (compared to the typical pumping pulse-repetition period) relaxation to an unexcited state. Using an LSM 510 Carl Zeiss laser scanning microscope equipped with a Ti:Sa tunable femtosecond laser, a series of model experiments is performed to reveal the saturation effect in a solution of commercially available quantum dots. Good agreement is obtained between the measured dependence of the power of two-photon fluorescence on the average pump power and the theoretical calculation results. It is also experimentally demonstrated that, under fluorescence saturation conditions, the spatial resolution of the method of multiphoton fluorescence microscopy is lost; this effect is analyzed numerically.     

Quantum efficiency and signal bandwidth of thallium atomic line filters

We derive a new, simplified method for the computation of trapping effects in coupled three-level atomic systems. The linearity of the Holstein radiation trapping equation allows the reduction of the general rate equation to the solution of the basic two-level Holstein equation and to an algebraic eigenvalue problem. The method is applied to the numerical simulation of the quantum efficiency and the signal bandwidth of thallium atomic line filters. With a pumping scheme that achieves population inversion between the ground state and the metastable state, 90% quantum efficiency and 10 MHz signal bandwidth can be achieved, while in noninverting pumping schemes, even quite high pump intensities result in less than 60% quantum efficiency and 8 MHz signal bandwidth. A tradeoff between quantum efficiency, signal bandwidth and pump power is possible.     

As much of cosmology as is possible

This article traces the development of optical pumping from the ideas first elaborated by Kastler in 1950. It deals with the general characteristics of optical pumping, the optical ‘magnetization’ of gases and vapours, spin exchange, metastability exchange, orientation by collision, multiple quantum resonances, atomic coherences, quantum beats, and dressed atoms: and concludes with a note on laser spectroscopy.     

Effect of Quantum Interference from Incoherent Pumping Field and Spontaneous Emission on Controlling the Optical Bistability and Multi-Stability

Optical bistability (OB) and optical multi-stability (OM) of a four-level Λ-type atomic system with two fold lower levels inside a unidirectional ring cavity is investigated. The effect of quantum interference arising from spontaneous emission and incoherent pumping on OB and OM is discussed. It is found that the threshold of OB and OM can be controlled by quantum interference mechanisms. In addition intensity of coupling field and the rate of an incoherent pumping field on behavior of OB and OM are then discussed.     

Selective optical doping to predict the performance and reveal the origin of photocurrent peaks in quantum dots-in-a-well infrared photodetectors

Resonant optical pumping across the band gap was used as artificial doping in InAs/In_0.15Ga_0.85As/GaAs quantum dots-in-a-well infrared photodetectors. Through efficient filling of the quantum dot energy levels by simultaneous optical pumping into the ground states and the excited states of the quantum dots, the response was increased by a factor of 10. Low temperature photocurrent peaks observed at 120 and 148 meV were identified as intersubband transitions emanating from the quantum dot ground state and the quantum dot excited state, respectively by a selective increase of the electron population in the different quantum dot energy levels.     

Influence of pumping laser bandwidth on the quantum fluctuation chracteristic of non-degenerate optical parametric amplifier

Usually the quantum fluctuation characteristic of the non-degenerate optical parametric amplifier is analysed under the assumption of monochromatic pumping. However, in experiments, the driving beam with finite bandwidth is used to obtain the non-degenerate signal and idler beam amplifications. On account of that, we derive an analytical solution for the non-degenerate optical parametric amplification system with finite bandwidth laser pumping, and evaluate the associated quantum fluctuation. Finally, the application of the V₁ criterion to the bipartite entanglement is discussed.     

Theoretical Study on the Gain and Tuning Characteristics of Miniature Optically Pumped NH3 Submillimeter Laser

The gain and the tuning characteristics of miniature optically pumped super-radiant NH₃ submillimeter-wave gas laser have been studied theoretically based on the quantum density matrix equations. The density matrix equations of three-level quantum system have been solved, and the gain and the output density versus different frequency detuning of submillimeter laser and infrared pumping laser have been calculated respectively by means of iteration method. The characteristic curves corresponding to ideal monochromatic IR pumping model and broadened IR pumping model have been obtained. Meanwhile, the tuning and the nonlinear properties of the system have been revealed.     

Fast topological pumping for the generation of large-scale Greenberger−Horne−Zeilinger states in a superconducting circuit

Topological pumping of edge states in the finite lattice with nontrivial topological phases provides a powerful means for robust excitation transfer, requiring extremely slow evolution to follow an adiabatic transfer. Here, we propose fast topological pumping via edge channels to generate large-scale Greenberger−Horne−Zeilinger (GHZ) states in a topological superconducting circuit with a sped-up evolution process. The scheme indicates a conceptual way of designing fast topological pumping related to the instantaneous energy spectrum characteristics rather than relying on the shortcuts to adiabaticity. Based on fast topological pumping, large-scale GHZ states show greater robustness against on-site potential defects, the fluctuation of couplings and losses of the system in comparison with the conventional adiabatic topological pumping. With experimentally feasible qutrit-resonator coupling strengths and moderate decay rates of qutrits and resonators, fast topological pumping drastically improves the scalability of GHZ states with a high fidelity. Our work opens up prospects for the realization of large-scale GHZ states based on fast topological pumping in the superconducting quantum circuit system, which provides potential applications of topological matters in quantum information processing.