Coherent dynamics and complete population depletion of a special three-level quantum system.

Non-Markovian dynamics of a three-level system is studied with the help of stochastic Schrodinger equation (SSE). We derive a new form of SSE for a three-level system driven by four independent Ornstein-Uhlenbeck stochastic noises. The main advantage of the suggested SSE is the ensuring of the complete positivity of the reduced density operator. We demonstrate significant influence of the non-Markovian noises on the dynamics of the three-level quantum system.

In this work, we exploit the idea of composite pulses to achieve robust\npopulation inversion in a three-level quantum system. The scheme is based on\nthe modulation of the coupling strength, while the other physical parameters\nremain unchanged. The composite pulses sequence is designed by vanishing\nhigh-order error terms, and can compensate the systematic errors to any desired\norder. In particular, this scheme keeps a good performance under the\ndisturbance of waveform deformations. This trait ensures that population\ninversion can be nearly obtained even when the pulse sequence has a short jump\ndelay. As an example, we employ the designed composite pulse sequence to\nprepare the W state in a robust manner in the superconducting circuits. The\nnumerical results show that the fidelity can still maintain a high level in a\ndecoherence environment.\n

This study investigates the quantum dynamics of three-level Stark-shifted atomic systems under the influence of a Nonlinear Kerr Medium (NLKM), focusing on the interplay between Quantum Fisher Information (QFI), Von Neumann Entropy (VNE), and photon-mediated interactions. By analyzing the temporal evolution of QFI (quantifying parameter estimation precision) and VNE (measuring quantum entanglement (QE), we demonstrate how Kerr nonlinearity (chi), Stark shifts (beta), phase (phi), and photon numbers govern system behavior. Key findings reveal that lower chi values (e.g., chi =0.3) induce oscillatory QFI decay and rapid VNE growth, driven by atomic motion and NLKM interactions, with QFI peaks inversely correlated to VNE dips. Higher chi (text{1,3}) stabilizes both metrics, suppressing decoherence and entanglement fluctuations. Elevated photon numbers enhance stability by strengthening field-atom correlations, reducing oscillation amplitudes (particularly at low chi), and mitigating quantum fluctuations. The Stark effect (SE) amplifies energy-level shifts, while phase adjustments introduce asymmetries in quantum interference. These results highlight the system’s tunability via chi , beta . phi, and photon density. They position it as a versatile platform for quantum metrology and information processing, where precision, entanglement stability, and photon-mediated coherence are critical. Kerr interactions suppress long-time coherence and entanglement, while when chi =0, Stark shifts can induce mild, transient quantum correlations. These dynamics are essential for controlling entanglement in cavity QED systems, especially when precise metrological performance is desired.

Nuclear coherent population transfer (NCPT) plays an important role in the exploration and application of atomic nuclei. How to achieve high-fidelity NCPT remains so far challenging. Here, we investigate the complete population transfer of nuclear states. We first consider a cyclic three-level system, based on the mixed-state inverse engineering scheme by adding additional laser fields in an open three-level nuclear system with spontaneous emission. We find the amplitude of the additional field is related to the ratio of the pump and Stokes field amplitudes. As long as an appropriate additional field is selected, complete transfer can be achieved even when the intensities of the pump and Stokes fields are exceedingly low. The transfer efficiency exhibits excellent robustness with respect to laser peak intensity and pulse delay. We demonstrate the effectiveness through examples such as $^{229}\mathrm{Th}, ^{223}\mathrm{Ra}, ^{113}\mathrm{Cd}$, and $^{97}\mathrm{Tc}$, which have a long lifetime excited state, as well as $^{187}\mathrm{Re}, ^{172}\mathrm{Yb}, ^{168}\mathrm{Er}$, and $^{154}\mathrm{Gd}$ with a short lifetime excited state. Focusing on the case without additional coupling, we further reduce the three-level system to an effective two-level problem. We modify the pump and Stokes pulses by using counterdiabatic driving to implement high-fidelity population transfer. The schemes open up new possibilities for controlling nuclear states.

A systematic scheme is proposed to numerically estimate the quantum speed limit and temporal shape of optimal control in two-level and three-level quantum systems with bounded amplitude. For the two-level system, two quantum state transitions are studied as illustration. Comparisons between numerical and analytical results are made, and deviations are significantly small. For the three-level system, two critical time points are determined with high accuracy, and optimal controls are obtained for different durations. The shape of optimized control field is simple and does not switch frequently, thus are easy to implement in experiment. In addition, we compare our method with the chopped random basis (CRAB), and the performance of our method is much better than that of CRAB. Our scheme is of importance in estimating the quantum speed limit and optimal control for cases in which analytical solution is absent.

Coherent population transfer in quantum systems is of fundamental importance in many fields spanning atomic and molecular collision dynamics, information processing for qubit systems. Stimulated Raman nonadiabatic passage technique, when implemented in an externally driven three-level system, provides an efficient approach for realizing accelerated population transfer while maintaining robust quantum coherence, without the rotating wave approximation. However, previous protocols employ multiple pulses and imply that Rabi frequencies have a few oscillations during dynamical evolution. In this paper, under two-photon resonance, we utilize the gauge transformation method to inversely design a Λ-configuration three-level system that can be solved exactly. By invoking a <inline-formula><tex-math id="M2">\begin{document}$SU(3)$\end{document}</tex-math></inline-formula> transformation, we establish the connection between Schrödinger representation and gauge representation with which the effective Hamiltonian is an Abelian operator. Subsequently, we construct the desired Hamiltonian and further investigate its dynamic behavior. The result demonstrate that, by imposing appropriate boundary conditions on the control parameters, high-fidelity population transfer can be achieved in ideal evolution. In addition, for the practical case with pulse truncation and intermediate state decay, the fidelities of specific models can reach about <inline-formula><tex-math id="M3">\begin{document}$99.996\%$\end{document}</tex-math></inline-formula> and for <inline-formula><tex-math id="M4">\begin{document}$99.983\%$\end{document}</tex-math></inline-formula>. Compared to other existing nonadiabatic quantum control schemes, we show that the present scheme has the distinctive advantages. Firstly, instead of introducing an additional microwave field, we achieve the desired quantum control by applying only a few sets of Stokes and pump pulses. Moreover this approach does not exhibit Rabi oscillations in the dynamic process, nor does it present singularities in the pulse itself.

Modeling the evolution of a system using stochastic dynamics typically implies increasing subjective uncertainty in the adopted state of the system and its environment as time progresses, and stochastic entropy production has been developed as a measure of this change. In some situations, the evolution of stochastic entropy production can be described using an Itô process, but mathematical difficulties can emerge if diffusion in the system phase space happens to be restricted to a subspace of a lower dimension. This situation can arise if there are constants of the motion, for example, or more generally when there are functions of the coordinates that evolve without noise. More simply, difficulties can emerge if there are more coordinates than there are independent noises. We show how the problem of computing the stochastic entropy production in such a situation can be overcome. We illustrate the approach using a simple case of diffusion on an ellipse. We go on to consider an open three-level quantum system modeled within a framework of Markovian quantum state diffusion. We show how a nonequilibrium stationary state of the system, with a constant mean rate of stochastic entropy production, can be established under suitable environmental couplings.

Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light harvesting complex, we explore the influence of including correlations in inter-chromophore couplings between different chromophore dimers that share a common chromophore. We find that the relative sign of the different correlations can have profound influence on decoherence time and energy transfer rate and can provide sensitive control of relaxation in these complex quantum dynamical open systems.

In this paper we study the coherent transient property of a &Lambda;-three-level system (&Omega;_<i>d</i> = 0) and a quasi- &Lambda; -four-level system (&Omega;_<i>d</i>&gt;0). Optical switching of the probe field can be achieved by applying a pulsed coupling field or rf field. In &Lambda; -shaped three-level system, when the coupling field was switched on, there is a almost total transparency of the probe field and the time required for the absorption changing from 90% to 10% of the maximum absorption is 2.9_&Gamma;0 (_&Gamma;0 is spontaneous emission lifetime). When the coupling field was switched off, there is an initial increase of the probe field absorption and then gradually evolves to the maximum of absorption of the two-level absorption, the time required for the absorption of the system changing from 10% to 90% is 4.2_&Gamma;0. In four-level system, where rf driving field is used as switching field, to achieve the same depth of the optical switching, the time of the optical switching is 2.5_&Gamma;0 and 6.1_&Gamma;0, respectively. The results show that with the same depth of the optical switching, the switch-on time of the four-level system is shorter than that of the three-level system, while the switch-off time of the four-level system is longer. The depth of the optical switching of the four-level system was much larger than that of the three-level system, where the depth of the optical switching of the latter is merely 14.8% of that of the former. The speed of optical switching of the two systems can be increased by the increase of Rabi frequency of coupling field or rf field.

Localization of cold [formula omitted] atom simulated by a three-level quantum system within half-wavelength domain

This study investigates the quantum information dynamics of a multi-level atomic system interacting with an SU(1;1) quantum system, focusing on atomic inversion, entropy, coherence, and skew information. The system is specified as a two-level and three-level Λ-type configuration, incorporating multi-mode SU(1;1) quantum systems and the Stark effect. Numerical simulations are performed to solve the time-dependent density matrix equations under varying shift, intensity, and Stark parameters. Results show that increasing the shift stabilizes inversion but raises statistical uncertainty, while greater field intensity amplifies entropy. The Stark amplitude suppresses decoherence and improves quantum information retention. Negativity is used to quantify entanglement between the first two SU(1;1) modes, showing that stronger Stark shifts stabilize entanglement and coherence. Three-level systems consistently outperform two-level ones in preserving coherence and entanglement due to enhanced interference and spectral separation. Eigenvalue analysis reveals the nonlinear structure of three-level systems, explaining their robustness. These findings are supported by recent experiments in SU(1;1) interferometry and Stark-tuned quantum systems, offering insights for quantum sensing, computation, and communication.

A comparative study of a qutrit (three-level atomic system) coupled to a classical field in a typical Markovian reservoir (free space) and in a photonic band-gap (PBG) crystal is carried out. The aim of the study is to assess the collective impact of structured environment and classical control of the system on the dynamics of quantum coherence, non-Markovianity, and estimation of parameters which are initially encoded in the atomic state. We show that the constructive interplay of PBG material as a medium and classical driving field as a part of system results in a significant enhancement of all the quantum traits of interest, compared to the case when the driven qutrit is in a Markovian environment. Our results supply insights for preserving and enhancing quantum features in qutrit systems which are promising alternative candidates to be used in quantum processors instead of qubits.

Coherent multidimensional optical spectroscopy methods overcome some of the limitations found in their one-dimensional counterparts and allow us, for example, to resolve overlapped spectral features, to separate homogeneous and inhomogeneous broadening, and to track the energy transfer kinetics and coherent dynamics in complex quantum systems. In their most common configurations, signal detection is achieved by optical means, making these techniques widespread in studies of bulk systems but less common in the surface and interface sciences. In this paper, we demonstrate an inherently surface-sensitive two-dimensional coherent spectroscopy scheme, based on photoelectron detection, by studying the interface formed between tris(8-hydroxyquinolinato)aluminium (${\mathrm{Alq}}_{3}$) and a ferromagnetic Co surface. Despite the inhomogeneous linewidth broadening (\ensuremath{\approx}800 meV) in the ensemble of disordered molecules, we resolve two narrow resonances (\ensuremath{\approx}10 meV linewidth) with an energy spacing of \ensuremath{\approx}80 meV. By combining experimental data and simulations, using the Lindblad master equation, we identify these resonances as lowest unoccupied molecular orbital (LUMO) to $\mathrm{LUMO}+1$ transitions in chemically decoupled second-layer ${\mathrm{Alq}}_{3}$ molecules and deduce related optical coherence lifetimes of at least 120 and 240 fs. These observations establish that ${\mathrm{Alq}}_{3}$ molecules in a disordered adsorbate layer exhibit well-defined and rather homogeneous internal electronic transitions, although the absolute energetic positions of the involved states with respect to the substrate reference are significantly affected by the disorder. The results indicate that inhomogeneous line broadening in a disordered ${\mathrm{Alq}}_{3}$ layer and pure dephasing have only a minor impact on optical transitions in individual molecules. This opens interesting opportunities for coherent control schemes and emphasizes the importance of optical coherences for all electron dynamics, even in disordered hybrid metal-molecule interfaces.

The interplay of coherence and decoherence is played out in a three-level quantum system, in which the third level is incoherently coupled to the second one which itself is in coherent interaction with the first level. The study is based on a stochastic scenario in which the coherent, unitary evolution of the system is randomly interrupted by a Poisson-driven pulse sequence. In the absence of an external pulse, the system undergoes coherent, unitary evolution restricted to the subspace spanned by the first level (level 1) and the second level (level 2). The application of a pulse induces transitions between the second and the third level (level 3), thereby introducing non-unitary effects that perturb the otherwise isolated two-level dynamics. The pulses are assumed to have infinitesimal duration, with strengths modeled as random variables that are uncorrelated across different pulses. A representative model for the stochastically-averaged transition (super)operator mimicking the dynamics induced by the application of pulses allows for an analytical derivation of the matrix elements of the averaged density operator, especially, the element pertaining to the first level. When the system is initially in level 1, we obtain in particular the temporal behavior of the stay-put probability, that is, the probability P 1 ( t ) that the system is still in level 1 at time t. As a function of time, the quantity P 1 ( t ) exhibits a coherence-to-decoherence crossover behavior. At short times t ≪ 1 / λ , where λ is the average frequency at which pulses are applied to the system, coherent dynamics dominate. Consequently, P 1 ( t ) displays pronounced Rabi-like oscillations. At long times t ≫ 1 / λ , decoherence effects prevail, leading to an exponential decay of the form P 1 ( t ) − 1 / 3 ∼ exp ⁡ ( − λ t ) . The results are relevant in the context of well-established Rabi oscillations, applicable to molecular beams and magnetic resonance experiments, as well as in more contemporary frameworks including quantum information processing, quantum resetting protocols, and the theory of quantum trajectories.

Wave mixing in a three-level quantum system induced by two-photon resonant pump and one-photon resonant coupling at lower transition has been studied theoretically and experimentally. Resonantly enhanced difference-frequency generation efficiency was observed clearly dependent on the time delay and its sign between the femtosecond pump and probe. The role of the atomic coherences on the amplification without inversion during different sequences of interaction in a closed three-level system has been also stressed. These findings were confirmed experimentally in atomic potassium, where strong parametric amplification, induced by the pump delayed with respect to the probe, has been observed for the first time.