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We add a missing element to the set of directly computable scenarios of light-matter-interaction within classical numerical Maxwell solvers, i.e., light scattering from hybrid systems of resonators and individual Fourier-limited emitters. In particular, individual emitters are incorporated as tiny polarizable and resonant spherical scatterers. This emitter model is based on well-known extremal properties of Mie modes. The spherical emitter is made from an artificial Drude metal with ϵ (ω) = ϵ b − ω p 2 / ( ω 2 + i Γ ω) . By tuning ϵb and ωp we adjust the resonance frequency and the Fourier-limited linewidth and by adjusting Γ we may add non-radiative damping or dephasing. This approach automatically reproduces the ideal text book coherent scattering cross-section of Fourier-limited two level quantum systems of σ0 = 3λ2/(2πϵout) which is not possible with typically used Lorentz permittivities which only mimic optical resonances. Further, the emitter's linewidth adopts to the surrounding optical local density of states (LDOS). To demonstrate this we successfully benchmark our approach with prominent examples from the literature. [ABSTRACT FROM AUTHOR]

Fabrication of dielectrics at low temperature is required for temperature-sensitive detectors. For superconducting detectors, such as transition edge sensors and kinetic inductance detectors, AlMn is widely studied due to its variable superconducting transition temperature at different baking temperatures. Experimentally only the highest baking temperature determines AlMn transition temperature, so we need to control the wafer temperature during the whole process. In general, the highest process temperature happens during dielectric fabrication. Here, we present the cryogenic microwave performance of Si 3 N 4 , SiN x and α -Si using ICPCVD at low temperature of 75 ∘ C. The dielectric constant, internal quality factor and TLS properties are studied using Al parallel plate resonators. [ABSTRACT FROM AUTHOR]

The operation of a two-level gas laser is theoretically studied in schemes with single- and double-sided transversal diode pumping Some analytical formulas, which describe the operation of a two-level gas laser with single- and double-sided diode pumping and make it possible to find any laser energy characteristics and optimal working medium and pumping radiation parameters necessary for maximally efficient laser operation, are derived for the case when the outer mirror has a not very low reflection coefficient. It is shown that the generation efficiency of a two-level gas laser can be increased by 11–20 by switching from single-sided to double-sided pumping. [ABSTRACT FROM AUTHOR]

The dynamics of the Rosen–Zener transition (RZT) in interacting two-level systems within nonreciprocal systems is examined, where nonreciprocity stems from asymmetric couplings between energy levels. For the linear case, an analytical expression for the RZT probability is derived. In the nonlinear scenario, numerical experiments are utilized to investigate the impact of various initial states and scanning periods on transition probabilities under adiabatic conditions. Additionally, an equivalent classical Hamiltonian is formulated to elucidate the origin of transition asymmetry under different initial state conditions. The influence of energy level detuning on the RZT is explored, leading to the suggestion of new applications for studying parameters of two-level systems related to nonlinearity and nonreciprocity. This opens avenues for potential Rosen–Zener–Stückelberg interferometry implementations.

In practice, both comprehensive hospital (e.g. AAA hospital) and primary hospital (e.g. community hospital) can exist in healthcare system, where the comprehensive hospital can provide a guaranteed service, but the waiting time of patients is relatively long. By contrast, the primary hospital is less congested, but the patients cannot be treated if the illness is found to be severe. Then the trade-off between efficiency (primary hospital) and quality (comprehensive hospital) should be considered. In this paper, we consider a resource allocation problem in a public service system with multi-type service providers and patients. To capture the interactions between the multi-type hospitals, a queueing-game-theoretical model is established. And we obtain the following results. First, the socially optimal reimbursement policy is obtained, and the sensitivities of parameters are examined, which indicate that, somewhat interestingly, both the optimal budget to primary hospital and the maximal social welfare are non-monotone in the effectiveness parameter or the joining probability of patients. Second, by comparing the socially optimal strategy with individually equilibrium strategy, we find that individual behaviour of patients does not necessarily lead to systems more congested than what is socially desirable. Third, we demonstrate the robustness of our model by extending it to a three-level system and a system with multiple parallel primary hospitals. [ABSTRACT FROM AUTHOR]

Developing coherent excitation methods for quantum emitters ensuring high brightness, optimal single‐photon purity and indistinguishability of the emitted photons has been a key challenge in the past years. While various methods have been proposed and explored, they all have specific advantages and disadvantages. This study investigates the dynamics of the recent swing‐up scheme as an excitation method for a two‐level system and its performance in single‐photon generation. By applying two far red‐detuned laser pulses, the two‐level system can be prepared in the excited state with near‐unity fidelity. The successful operation and coherent character of this technique are demonstrated using a semiconductor quantum dot (QD). Moreover, the multi‐dimensional parameter space of the two laser pulses is explored to analyze its impact on excitation fidelity. Finally, the performance of the scheme as an excitation method for generating high‐quality single photons is analyzed. The swing‐up scheme itself proves effective, exhibiting nearly perfect single‐photon purity, while the observed indistinguishability in the studied sample is limited by the influence of the inevitable high excitation powers on the semiconductor environment of the quantum dot. [ABSTRACT FROM AUTHOR]

We investigated the mixed state geometric phase of a two-level system which is coupled to a bosonic reservoir in both weak and strong coupling regimes, and driven by a classical field. Besides, we extended the direct-drive model to the indirect-drive model by incorporating an additional qubit. In the direct-drive model, the geometric phase undergoes corresponding alterations through the amplification of the classical field strength. Moreover, the combination of the classical driving and the strong coupling between the two-level system and the bosonic reservoir significantly changes the geometric phase. Furthermore, we elucidate the asymmetric effect of the detuning between the two-level system and the Lorentzian spectrum on the geometric phase, while achieving stability in the geometric phase regardless of the detuning value by appropriately adjusting the classical driving strength. In the indirect-drive model, intriguing phenomena arise, such as different behaviors of the geometric phase and the restoration of the symmetric effects of the detuning. The explicit dynamics of the geometric phase has been numerically analyzed by investigating the time-dependent factor of the reduced density matrix. Finally, the energy flow of the entire system was clarified by utilizing quasimode theory and visualizing the temporal evolution of the Bloch vector. [ABSTRACT FROM AUTHOR]

We consider the process of transition of a two-level system to the excited state with subsequent photon emission in the presence of a laser pulse with a high degree of unipolarity. Within the framework of quantum electrodynamics, we obtain analytical expressions for the differential probability of the process depending on the temporal scales of the problem: laser pulse duration, excited-state lifetime, inverse transition frequency, and inverse frequency of the photon emitted. Besides, we calculate the total absorption probability by integrating over the three-dimensional photon momentum and summing over polarizations. We compare the results obtained for unipolar and bipolar (many-cycle) pulses. [ABSTRACT FROM AUTHOR]

Superconducting resonators are widely used in many applications such as qubit readout for quantum computing, and kinetic inductance detectors. These resonators are susceptible to numerous loss and noise mechanisms, especially the dissipation due to two‐level systems (TLS) which become the dominant source of loss in the few‐photon and low temperature regime. In this study, capacitively‐coupled aluminum half‐wavelength coplanar waveguide resonators are investigated. Surprisingly, the loss of the resonators is observed to decrease with a lowering temperature at low excitation powers and temperatures below the TLS saturation. This behavior is attributed to the reduction of the TLS resonant response bandwidth with decreasing temperature and power to below the detuning between the TLS and the resonant photon frequency in a discrete ensemble of TLS. When response bandwidths of TLS are smaller than their detunings from the resonance, the resonant response and thus the loss is reduced. At higher excitation powers, the loss follows a logarithmic power dependence, consistent with predictions from the generalized tunneling model (GTM). A model combining the discrete TLS ensemble with the GTM is proposed and matches the temperature and power dependence of the measured internal loss of the resonator with reasonable parameters. [ABSTRACT FROM AUTHOR]

In this paper, we investigate quantum speed limits (QSLs) of a two-level system in the colored environments which are described by stochastic processes. We present QSL can be affected by the correlation time, the partitions of the constituent elements of the two-level system in different colored environments: the Ornstein–Uhlenbeck environment, simple fluctuating bottleneck environment, and the Dichotomic (two-state) environment. The investigations provide us a potential way to manipulate the quantum speed limit time (QSLT) of the quantum system in the colored environments. Our results could provide different insights on quantum control technologies of QSL and decoherent dynamics for the quantum computation.

We study theoretically the nonadiabatic geometric phase of a doubly driven two-level system with an additional relative phase between the two driving modes introduced in. It is shown that the time evolution of the system strongly depends on this relative phase. The condition for the system returning to its initial state after a single period is given by the means of the Landau–Zener–Stückelberg–Majorana destructive interference. The nonadiabatic geometric phase accompanying a cyclic evolution is shown to be related to the Stokes phase as well as this relative phase. By controlling the relative phase, the geometric phase can characterize two distinct phases in the adiabatic limit. [ABSTRACT FROM AUTHOR]

Graphene flakes acting as photonic nanoantennas may sustain strong electromagnetic field localization and enhancement. To exploit the field enhancement, quantum emitters such as atoms or molecules should be positioned in such close proximity to the flake that electron tunneling might influence the optical and electronic properties of the system. However, tunneling is usually not considered if the optical coupling mechanism between quantum emitters and nanoantennas is at focus. This work presents a framework for describing the electron dynamics in hybrid systems consisting of graphene nanoflakes coupled both electronically and optically to adatoms and subject to external illumination. Our framework combines the single-particle tight-binding approach with a nonlinear master equation formalism that captures both optical and electronic interactions. We apply the framework to demonstrate the impact of electron tunneling between the adatom and the flake on emblematic quantum optical phenomena: degradation of coherent Rabi oscillations and quenching of Purcell spontaneous emission enhancement in two-level adatoms in proximity of triangular graphene nanoflakes.

The saturation effect during the excitation of a two-level system by laser pulses is investigated in the framework of two approaches: excitation probability based on Karplus–Schwinger spectral profile and exact solution of Bloch equations. Simple analytical expression for the excitation probability by exponential pulse is derived. The excitation spectra obtained using this expression were compared with the result of solving the Bloch equations for various values of the pulse duration and the Rabi frequency, which describes the strength of the electromagnetic interaction. It is shown that in the case of long pulses, there is a satisfactory correspondence between the two approaches, but in short-pulse limit and strong saturation, the probability description based on Karplus–Schwinger spectral profile and perturbation theory does not provide satisfactory results. [ABSTRACT FROM AUTHOR]

We propose an exact solution to a linear two-level system with the existence of a special hyperbolic secant external field and elucidate its transition dynamics. We then extend the model to the nonlinear case and show that the nonlinearity will significantly affect the transition dynamics. As nonlinearity increases, Landau–Zener–Stückelberg–Majorana interference fringes can be constructive and the up energy level in the adiabatic limit splits into three levels. For fast-sweeping fields, we derive an analytic expression for dynamics transition under the stationary phase approximation and find that transition probability will be blocked as the nonlinearity intensity is much larger than the external field frequency, which agrees with the numerical result. [ABSTRACT FROM AUTHOR]

OBJECTIVES The aim of this study is to examine and underline the problems regarding the issue in the National Physical Education Leader’s qualification framework which revised in 2015 and provide guidelines for developing a new qualifications framework and revising the written examination subjects. METHODS To Implement an integrated qualifications framework, it’s important to make a decision after listening to various opinions such as the number of levels to be changed, the qualification requirements (testing qualifications) after changing the level system, the academic settings/level of sports, the eligibility requirements between levels. For the structure of the qualification framework integration, integrating it into the two-level or three- level system has the greater advantage in various aspects and it may minimize controversy. CONCLUSIONS The qualification framework should be integrated into the two-level or three-level system, and the selection of the written examination subjects should be revised. To consider the sequence of the courses and learning contents for the National Physical Education Leader qualifications, the following written examination subjects should be included as the compulsory subjects for the three-level, twolevel, or one-level systems respectively: exercise physiology, exercise mechanics, sports psychology, and health education; physical education measurement and evaluation, health and fitness evaluation, exercise prescription, and pathophysiology; and prevention and treatment of sports injuries and training theory. One of the innovative strategies to improve the current exam contents, the following written examination subjects should be eliminated such as sports education, sports ethics, Korean sports history, and sports sociology or significantly reduce the number of questions to be asked. Another strategy is to determine the eligibility qualifications according to standard guidelines on the knowledge, skills, and attitudes required for each job area by subject and position according to the qualification system, such as the secondary education teachers exam or the certified nutritionist certification exam, and select exam contents and numbers of the question in each subject according to the essential knowledge and skills. It is also worth considering the question of different ratios.

We present a hybrid spinning whispering-gallery-mode (WGM) optomechanical system, where the mechanical resonator is not only coupled to the WGM cavity via radiation pressure but also coupled to a two-level system (TLS) via the Jaynes–Cummings coupling. If the WGM cavity is spinning along the clockwise or counterclockwise direction, the cavity field can undergo different Sagnac effect. The transmission spectra experience the conversion from optomechanically induced transparency (OMIT) to Fano resonance by controlling the resonator-TLS coupling, the rotational direction of the WGM cavity, and the cavity-pump detuning. Furthermore, both the OMIT and Fano resonance in the transmission spectra can induce the transparency windows accompanied by the rapid normal phase dispersion, which results in the tunable delayed or accelerated probe light transmission. The numerical results indicate that the OMIT leads to slow light, while Fano resonances generate the conversion from fast to slow light (or slow to fast light), and the parameters of the resonator-TLS coupling, the Sagnac frequency shift, the pump field frequency, and the cavity-pump detuning together determine the fast and slow light effect based on the hybrid spinning optomechanical system.

In this paper we investigate non-Markovian evolution of a two-level system (qubit) in a bosonic bath under influence of an external classical fluctuating environment. The interaction with the bath has the Lorentzian spectral density, and the fluctuating environment (stochastic field) is represented by a set of Ornstein-Uhlenbeck processes. Each of the subenvironments of the composite environment is able to induce non-Markovian dynamics of the two-level system. By means of the numerically exact method of hierarchical equations of motion, we study steady states of the two-level system, evolution of the reduced density matrix and the equilibrium emission spectra in dependence on the frequency cutoffs and the coupling strengths of the subenvironments. Additionally, we investigate the impact of the rotating wave approximation (RWA) for the interaction with the bath on accuracy of the results.

The dynamics of the Rosen–Zener transition (RZT) in interacting two-level systems within nonreciprocal systems is examined, where nonreciprocity stems from asymmetric couplings between energy levels. For the linear case, an analytical expression for the RZT probability is derived. In the nonlinear scenario, numerical experiments are utilized to investigate the impact of various initial states and scanning periods on transition probabilities under adiabatic conditions. Additionally, an equivalent classical Hamiltonian is formulated to elucidate the origin of transition asymmetry under different initial state conditions. The influence of energy level detuning on the RZT is explored, leading to the suggestion of new applications for studying parameters of two-level systems related to nonlinearity and nonreciprocity. This opens avenues for potential Rosen–Zener–Stückelberg interferometry implementations. • Nonreciprocity Impact : Nonreciprocal parameter adds imaginary spectrum, impacts RZT dynamics. • Transition Probabilities : Analytical RZT probabilities for weak/strong nonreciprocity; nonlinear numerical study. • Asymmetric Transitions : Asymmetric RZT due to initial states in nonreciprocal systems. • Nonlinearity Effects : Alters RZT dynamics under nonreciprocity. [ABSTRACT FROM AUTHOR]

The carrier–phonon interaction in semiconductor quantum dots (QDs) can greatly affect the optical preparation of the excited state. For resonant excitation used in the Rabi preparation scheme, the polaron is formed accompanied by the emission of a phonon wave packet, leading to a degradation of preparation fidelity. In this article, phonon wave packets for different coherent excitation schemes are analyzed. One example is the adiabatic rapid passage scheme relying on a chirped excitation. Herein, also a phonon wave packet is emitted, but the preparation fidelity can still be approximately unity. A focus is on the phonon impact on a recently proposed swing‐up scheme, induced by two detuned pulses. Similar to the Rabi scheme, a degradation and a phonon wave packet emission are found, despite the detuning. If the swing‐up frequency coincides with the maximum of the phonon spectral density, a series of wave packets is emitted yielding an even stronger degradation. The insight gained from our results further helps in designing an optimal preparation scheme for QDs. [ABSTRACT FROM AUTHOR]

The thermodynamics of light absorption is analysed using, as model system, a two-level molecular system characterised by mirror symmetry between its absorption and emission spectra. This means that the structure of the HOMO-1 and HOMO (highest occupied molecular orbital) ground state and the LUMO, LUMO + 1 (lowest unoccupied molecular orbital) excited states are nearly identical in their vibronic structures. This is a good model for many dyes and, in particular, for chlorophyll molecules, the main chromophore presents in the photosynthetic apparatus of plants. When a photon is absorbed by this two-level system, a transition from the HOMO ground state to the LUMO excited state occurs. Then, the system rapidly relaxes to an equilibrium distribution over the excited state sublevels and this equilibrium distribution is defined by the temperature of the bath that contains the molecule. In the described scenario, taking into account the changes in internal energy and the partition function before and after the photon absorption event, it is demonstrated that no entropy change occurs upon electronic transition from the ground state to the excited state, upon photon absorption. Furthermore, the idea that the photon-induced electronic transition can be described in terms of system heating is considered. We conclude that photon energy cannot be considered as heat. Instead, when thermal excitation is taken into account, the increased system temperature leads inexorably to entropy changes. [ABSTRACT FROM AUTHOR]

Quantumness of a two-level system which interacts with one of two environments in an indefinite way is studied in terms of violation of the temporal steering inequalities, where the indefiniteness is created by a coherent superposition of two environments. Two models of two-level system and environment are applied. One is a dephasing spin-boson model with the Ohmic-like spectral density and the other is a zero-temperature dissipative spin-boson model with the Lorentzian spectral density. It is shown that a coherent superposition of the two environments can enhance the quantumness of the two-level system. The parameter regions in which the indefiniteness is effective for enhancing the quantumness are clarified. [ABSTRACT FROM AUTHOR]

We investigate high-order harmonics spectra radiated from a two-level model system driven by strong, ultrabroadband, half- and single-cycle pulses, which are shorter than the inverse of the transition frequency. In this driving regime, the plateau in frequency spectra typical for radiation from strongly driven systems, has noticeable modulation in amplitude due to interference between waves of same frequency and emitted at different time instants. Specifically, there are characteristic 'dip' structures at a set of frequencies in the radiation spectra, where the corresponding amplitudes are suppressed by several orders of magnitude. Understanding these structures is required for applications such as the generation of attosecond pulse, where the number of composing modes and their relative phases are important. Therefore, we demonstrate a systematic way to find frequencies at which the dips are formed. To further illustrate the interference mechanism, we extract the phase information with the help of time-frequency distribution functions, namely the Husimi and Wigner functions. In particular, we found that the negativity structure of the Wigner function corresponds to each dip frequency and that the information regarding the type of interference is encoded in the pattern of the negative region of the Wigner function. Since such time-frequency Wigner function can actually be measured, we envisage utilizing its negativity structure to extract the phase information between radiation components emitted at time points within a subcycle timescale. This should provide an efficient tool for understanding and designing photonic applications, including short-wavelength coherent light sources. [ABSTRACT FROM AUTHOR]

A polycrystalline sample of the Sn20.5□3.5As22I8 clathrate was synthesised by a standard ampoule method from elements. Temperature dependencies of the heat capacity Cp(T) and unit cell parameter a(T) experimentally studied at the temperatures of 2–300 K revealed abnormal behaviour of CP(T) and a(T) dependencies at the lowest (2–30 K) and elevated (200–300 K) temperatures. This was attributed to disorder in the clathrate crystal structure due to significant number of vacancies in the clathrate host matrix. The dependencies studied were analysed within the Debye–Einstein approach taking into account soft atomic potential theory, vibrations of two-level system (TLS) at the lowest temperatures, and anharmonicity of lattice vibration at elevated temperatures, which allows determining parameters of different contributions to thermodynamic characteristics of the studied clathrate. A comparison of the temperature dependence of Grüneisen parameter, which was determined from experimental data, with the temperature dependence of the calculated Grüneisen mode parameters revealed specific modes that have a decisive influence on the anomalous behaviour of the thermodynamic characteristics of the title clathrate in different parts of the studied temperature range. The dimensionless Grüneisen parameter reaches γ = 4 at moderately high temperatures, which indicates a significant degree of structural disorder and its influence on thermodynamic properties of clathrates and correlates well with low thermal conductivity of the title clathrate. [ABSTRACT FROM AUTHOR]

The saturation effect during the excitation of a two-level system by laser pulses is investigated in the framework of two approaches: excitation probability based on Karplus–Schwinger spectral profile and exact solution of Bloch equations. Simple analytical expression for the excitation probability by exponential pulse is derived. The excitation spectra obtained using this expression were compared with the result of solving the Bloch equations for various values of the pulse duration and the Rabi frequency, which describes the strength of the electromagnetic interaction. It is shown that in the case of long pulses, there is a satisfactory correspondence between the two approaches, but in short-pulse limit and strong saturation, the probability description based on Karplus–Schwinger spectral profile and perturbation theory does not provide satisfactory results.

In this paper, we review the theory of open quantum systems and macroscopic quantum electrodynamics, providing a self-contained account of many aspects of these two theories. The former is presented in the context of a qubit coupled to a electromagnetic thermal bath, the latter is presented in the context of a quantization scheme for surface-plasmon polaritons (SPPs) in graphene based on Langevin noise currents. This includes a calculation of the dyadic Green's function (in the electrostatic limit) for a Graphene sheet between two semi-infinite linear dielectric media, and its subsequent application to the construction of SPP creation and annihilation operators. We then bring the two fields together and discuss the entanglement of two qubits in the vicinity of a graphene sheet which supports SPPs. The two qubits communicate with each other via the emission and absorption of SPPs. We find that a Schrödinger cat state involving the two qubits can be partially protected from decoherence by taking advantage of the dissipative dynamics in graphene. A comparison is also drawn between the dynamics at zero temperature, obtained via Schrödinger's equation, and at finite temperature, obtained using the Lindblad equation. [ABSTRACT FROM AUTHOR]

We investigate the analytical solution of a two-level system subject to a monochromatical, linearly polarized external field that was first published in 2007. In particular, we derive an explicit expression for the quasienergy. Moreover, we calculate the time evolution of a typical two-level system over a full period by evaluating series solutions of the confluent Heun equation. This is possible without invoking the connection problem of this equation since the complete time evolution of the system under consideration can be reduced to that of the first quarter-period. As a physical application we consider the work performed on a two-level system. [ABSTRACT FROM AUTHOR]

One of the most powerful and potentially useful methods of time-dependent matrix differential equations is the Magnus expansion. In this work, we applied the Magnus expansion for Schrödinger and master equations of a dissipative two-level system interacting with a time-dependent π pulse. Two different models of dissipative two-level systems are considered, namely (i) the system decays from two considered levels into some other levels with given decay rates; (ii) the system decays from its excited level to its ground level. The obtained approximate solutions of a time dynamics by the first-order Magnus expansion are well consistent with the results of numerical calculations obtained by the fourth-order Runge-Kutta method.

Decoherence of a two-level system is studied when it interacts with one of two environments via a dephasing coupling, where the environments are treated as classical and quantum systems. The situation is considered in which the environment that actually interacts with the two-level system is determined by a state of an ancillary two-level system. When information conveyed by the ancillary two-level system is discarded, the reduced dynamics of the relevant two-level system is described by a statistical mixture of two dephasing channels, which shows mixing-induced non-Markovianity. When projective measurement is performed on the ancillary two-level system to extract some information, the diagonal elements of the reduced state of the two-level system depend on time in spite of the dephasing process. Furthermore, it is found that the coherence of the two-level system can exceed its initial value. The parameter region is clarified in which the measurement on the ancillary two-level system can improve the coherence of the relevant two-level system. In particular, when the two environments are equivalent and the ancillary two-level system is in the maximally coherent state, the coherence of the two-level system can be always enhanced by measurement. [ABSTRACT FROM AUTHOR]

Relaxation processes are studied for a two-level system which is placed under the influenced by a superposition of two environments. Two cases are treated: one is that the two-level system interacts with the environment via both linear dissipative coupling and pure dephasing coupling in the Markovian limit and the other uses an exactly solvable single-excitation spin-boson model. In both the cases, an ancillary two-level system determines which environment of the two actually interacts with the relevant two-level system. In the Markovian limit, the reduced time-evolution of the two-level system is characterized by the longitudinal relaxation time T 1 and the transversal relaxation time T 2 which satisfy the inequality 2 T 1 ≥ T 2 . If the strict inequality 2 T 1 > T 2 is fulfilled, the coherence of the two-level system can be definitely enhanced by the environmental superposition effect. If the equality 2 T 1 = T 2 holds, it can be improved probabilistically. On the other hand, in the exactly solvable model, although the non-Markovian effect is observed in the reduced time-evolution, the coherence can be improved only probabilistically since the model does not include a pure dephasing coupling. [ABSTRACT FROM AUTHOR]

The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical pumping. It is shown that, when the photon mean free path in a resonantly absorbing medium is smaller than the characteristic size of this medium or comparable to it, the spontaneous radiation may become an additional pump source. The contribution of spontaneous photons to the kinetics of level has been considered within two approaches. The first approach consists of solution of the radiation transfer equation within the diffusion approximation. The second approach is related to solution of the Biberman–Holstein equation. [ABSTRACT FROM AUTHOR]

We consider two two-level particles (qubits) as the working substances of measurement-based quantum heat engines. A measurement-based quantum heat engine is similar to a quantum Otto heat engine other than a quantum isochoric process is replaced by the quantum measurement. We discuss two identical Bosons case and two interacting particles case, respectively. For two Bosons, we find the efficiency is same to a single-particle case but the work output is enhanced. It tends to classical-like result in low temperature regime and exhibits strong quantum effects in high temperature regime, which is counterintuitive. For two interacting qubits, we show the work done is always suppressed by the coupling. The efficiency can be improved under certain conditions in local measurement case and is same to a single-particle case when Bell measurement is done. [ABSTRACT FROM AUTHOR]

Linearized version of the Riccati-type differential equation for the ratio of population amplitudes in a laserdriven two-level system is used to calculate analytically the induced electric dipole moment. The formula found for the dipole moment is valid for weak excitations by smooth-shape pulses of arbitrary off-resonant frequencies, i.e., those producing neither exact one-photon nor odd multiphoton resonances. For a given pulse shape, the formula allows to express the Fourier components of the induced dipole moment as functions of both laser frequency and intensity and to find the field-dependent refractive index of the system versus laser frequency. [ABSTRACT FROM AUTHOR]

The interest in unipolar pulses in optics is related to the possibility of their efficient action on quantum objects. In this work, we study the interaction of a short rectangular unipolar pulse with a two-level resonant medium under conditions that the pulse duration is shorter than the relaxation times of the medium. It is paradoxical that the polarization and the population difference of the medium oscillate not at the Rabi frequency, but, rather, at a frequency that is proportional to the sum of the squared frequency of the resonant transition of the medium and the squared Rabi frequency of the pulse. This phenomenon is similar to the Stark effect, which consists of a shift of the transition frequencies of a medium in a constant external electric field. The possibility of generating radiation at frequencies that exceed the resonant transition frequency of the medium upon its excitation by a rectangular unipolar pulse is discussed. [ABSTRACT FROM AUTHOR]

In this paper, the influence of dispersion and polarization on the electronic probability density, the transition frequency and the longitudinal optical (LO) phonon spontaneous emission rate in the two-parameter asymmetric Gaussian confinement (AGC) potential two-level system with the electric field are studied by using the Pekar-type variational method. Numerical results show that the selecting the two-parameter AGC potential to describe the restricted effects of electron in quantum dot can more accurately reveal the quantization characteristics of of the wave property of electronic states, the statistical regularity of electron motion and LO phonons spontaneous emission rate. The influence of the electric field, dispersion and electron -phonon coupling of materials on the probability distribution, transition frequency and LO spontaneous emission rate in the two-level system cannot be ignored. [ABSTRACT FROM AUTHOR]

Here, the population transfer between two specific levels of Cesium atomunder the influence of chirped laser source has been numerically investigated. The maingoal of this study is the engineering of the population transfer between the 62S1/2 and 62P1/2levels of Cesium which is corresponding to its D1 transition line using a chirped lasersource. Constructing the system Hamiltonian, as well as the initial and boundaryconditions, the time-dependent Schrödinger equations are numerically solved and thepopulation versus time for different physical parameters has been investigated. The finalpopulation of each state is calculated and discussed for changing the parameters such aslaser intensity, laser frequency and chirping parameter. The results show that using thechirped laser source with tuned parameters, we can arbitrarily control the population oflevels.

This review is devoted to the study of effects of quantum optics in nanostructures. The mechanisms by which the rates of radiative and nonradiative decay are modified are considered in the model of a two-level quantum emitter (QE) near a plasmonic nanoparticle (NP). The distributions of the intensity and polarization of the near field around an NP are analyzed, which substantially depend on the polarization of the external field and parameters of plasmon resonances of the NP. The effects of quantum optics in the system NP + QE plus external laser field are analyzed—modification of the resonance fluorescence spectrum of a QE in the near field, bunching/antibunching phenomena, quantum statistics of photons in the spectrum, formation of squeezed states of light, and quantum entangled states in these systems.

A two-level system interacting with a phonon bath is studied using a variational method with an improved trial wave function. It is shown that our results for the ground state energy are in general lower than those obtained by other similar variational methods. It is also demonstrated that there are two possible ground states for the system, one for smaller values of the tunneling matrix element and the other for larger values of it and the system undergoes a localization-delocalization transition as the tunneling matrix element is increased beyond a critical value. Though, in general, there is no dispute about the existence of this transition, the nature of the transition is still not very clear. In the present work, we show, in contrast to the other variational results, that localization-delocalization transition is always smooth in conformity the exact numerical results. [ABSTRACT FROM AUTHOR]

A systematic study is made of the efficiency of a uniformly suitable approximation for describing the Rabi quantum model beyond the rotating wave model. The correlation characteristics of the electromagnetic field in a resonator are calculated and the physical effects owing to the counter-rotating terms in the Hamiltonian are examined. [ABSTRACT FROM AUTHOR]

The interaction force in the four-waving mixing of a two-level atoms system is analyzed. A new rate equation and the formula of the optical force are obtained. By simulation and analysis with MATLAB software, the impulse curve is obtained. The impulse increases with probe-wave detuning increasing and then tends to saturation. When the Ra-bi frequency takes a certain value, the impulse can obtain relative maximum and the relative maximum increases with the Ra-bi frequency increasing. The relation between the most value and the parameters of Ra-bi frequency and probe-wave detuning is also researched. The impulse occurs minimum when probe-wave detuning is zero and Ra-bi frequency is zero, there is no maximum for the impulse, which is close to 0.02 infinitely, the lowest temperature that can be reached is 248 μk. In addition, T 2 /T 1 also has a significant influence on the impulse. • A new rate equation and the formula of the optical force is obtained. • The relation of impulse with Ra-bi frequency and probe-wave detuning was found. • The maximum and minimum values of the impulse are calculated, and the lowest temperature that can be reached is estimated. • Purely radiation damping has a significant influence on the impulse. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study the interaction between a two-level system (qubit) and two continuous-mode photons. Two scenarios are investigated: Case 1, how a two-level system changes the pulse shapes of two input photons propagating in a single input channel; and Case 2, how a two-level system responds to two counterpropagating photons, one in each input channel. The steady-state output field states for both cases are derived analytically in both the time and frequency domains. Numerical simulations demonstrate rich and interesting two-photon scattering phenomena induced by a two-level system. [ABSTRACT FROM AUTHOR]

The impact of a polychromatic field on a two-level medium is considered in the limit of small amplitudes. In the indicated limit, we obtained asymptotic expansions of the polarization spectra of an arbitrary order of smallness. These polarization spectra were compared with the results of the numerical solution of the density matrix equation. Compared to numerical calculation methods, the asymptotic expansion offers an analytical estimation of the contribution of each individual component of a polychromatic field and a description of the intermode interaction. However, with an increase in the intensity of the driving field, the computational efficiency of the method decreases, since, to achieve the required accuracy, it is necessary to increase the order of the asymptotic expansion. [ABSTRACT FROM AUTHOR]

• We obtained a simple, analytic solution of the semiclassical Rabi model in the large, red-detuned regime. • The solution is accurate for arbitrary couplings. • The solution describes accurately the dispersive deep strong-coupling regime. • The trajectory of the Bloch vector and the probability to find the qubit in the excited state are characterized. • Applications to physical situations are discussed. We consider the semiclassical Rabi model in the large, red-detuned regime. Using the method of multiple-scales we obtain a simple, analytic, and approximate solution that describes the evolution of the system accurately for long times and for arbitrary values of the qubit-field coupling. It is used to characterize the probability to find the qubit in the excited state and the trajectory of the associated Bloch vector. Finally, we present physical situations where the results can be applied. [ABSTRACT FROM AUTHOR]

In this paper, we investigate quantum speed limits (QSLs) of a two-level system in the colored environments which are described by stochastic processes. We present QSL can be affected by the correlation time, the partitions of the constituent elements of the two-level system in different colored environments: the Ornstein–Uhlenbeck environment, simple fluctuating bottleneck environment, and the Dichotomic (two-state) environment. The investigations provide us a potential way to manipulate the quantum speed limit time (QSLT) of the quantum system in the colored environments. Our results could provide different insights on quantum control technologies of QSL and decoherent dynamics for the quantum computation. • The stochastic Liouville equation is extended to study the colored environments. • The relation between the quantum speed limit time and the decoherence factor of a two-level system is established. • The quantum speed limit time can be controlled by the initial distribution and the partitions the constituent elements. [ABSTRACT FROM AUTHOR]

To take quantum advantage of collective effects in many-body system, we design an elementary block for building a quantum battery with the optimal number of atoms in a common thermal bath, which is charged collectively by a harmonic driving. Free energy is a novel tool to quantify usable energy in an open system, which includes non-preserved entropy impacts on the stored energy besides the internal energy. The interesting finding is that the free energy variation in the steady state increases non-monotonically, and reaches the maximal value at the optimal number of atoms. It ascribes to the decreasing of the internal energy and the entropy per atom with the increasing of the atoms. In particular, the elementary block with the optimal number of atoms can relax to the optimal steady state with the weak damping of the internal energy due to the strong collective driving. By comparing to each atom parallel charging independently, the optimal battery cell produces lower heat flow to the thermal bath induced by the entropy, which can not be neglected in the dissipative system. The existence of the optimal battery cell provide a guideline for designing a realizable charging scheme.