Two-level Atomic System Research Articles

Temperature dependence of optical phase transitions in a system of two-level atoms and photons interacting inside a nonlinear cavity

Temperature dependence of optical phase transitions in a system of two-level atoms and photons interacting inside a nonlinear cavity

Theoretical model for correlations between two symmetric Four-Wave Mixing processes in an atomic two-level system

The dependence of the correlations between two symmetric four-wave mixing (FWM) signals on detuning is discussed through a simple theoretical model. The model consists of an ensemble of two-level atoms interacting with two electric fields in the semi-classical approach. Using the density matrix formalism, stochastic equations for the component of coherence responsible for the FWM processes are obtained. Here, the stochastic nature of the problem arises from the phase of the fields. Through Ito’s calculus, the stochastic differential equations are solved and the dependence of the cross-correlation function G(2) on the detuning of one field is analyzed. The emergence of Rabi oscillations in the G(2) function, consistent with previous experimental findings, is observed. What is more, for weak detuning, there is a crossover from the correlation to the anticorrelation regime, the latter persisting for a relatively large range of detuning. This paper could be of interest for the optimization of the experimental parameters for the correlations between FWM signals.

Dynamics of quantum coherence and non-classical correlations between non-interacting two 2-level atoms in thermal baths

This paper delves into the exploration of quantum resources within a two-qubit system composed of two 2-level atoms connected to distinct thermal baths. Various quantifiers are employed to evaluate different aspects of the system’s quantum characteristics. Specifically, the [Formula: see text]-norm and relative entropy of coherence ([Formula: see text] and [Formula: see text]) are utilized to gauge quantum coherence, while local quantum Fisher information (LQFI) is used to quantify non-classical correlations within the system. The findings suggest that the amount of quantum correlations and coherence decline as the spontaneous emission rate [Formula: see text] and the mean thermal photon number n increase. However, it is observed that manipulating parameters defining the initial state of the two-level atoms system can enhance non-classical correlations and quantum coherence between the two atoms. Additionally, it is noted that these three key metrics entirely vanish in the asymptotic limit of time. Our research underscores the importance of precisely adjusting the parameters of the initial system state, which is prepared in an extended Werner-like state (EWL), to protect quantum resources shared between the two atoms from environmental influences.

Exploring optical tomography dynamics for a dissipative coherent cavity in interaction with two-level atomic system

In this paper, we explore the optical tomography and quantum coherence dynamics for a coherent cavity field interacting with a two-level atom via intensity dependent coupling. We derive a specific solution to the master equation for the Jaynes–Cummings model, considering cavity damping. This solution reveals how the atom coherent-cavity interactions can produce new coherent states when the initial dissipative cavity-field state is coherent state or even coherent state. The effects of the atom-coherent-cavity interactions and the cavity damping, on the dynamics of the initial coherent state optical tomography and coherence is examined. In addition to the nonclassical properties, the atom-cavity interactions have a remarkable capacity to form distinct cavity field states linked to certain optical tomography distributions. Additionally, we investigate the maximal optical tomography dynamics for coherent state and even coherent state considering a range of cavity damping and detuning values.

Measuring Unruh radiation from accelerated electrons

Detecting thermal Unruh radiation from accelerated electrons has presented a formidable challenge due not only to technical difficulties but also for lack of conceptual clarity about what is actually seen by a laboratory observer. We give a summary of the current interpretations along with a simpler heuristic description that draws on the analogy between the Unruh effect and radiation from a two-level atomic system. We propose an experiment to test whether there is emission of thermal photons from an accelerated electron.

Influence of the Stark Shift and Field Nonclassicality on the Dynamics of Non-classical Correlations of N two-level Atomic System

Influence of the Stark Shift and Field Nonclassicality on the Dynamics of Non-classical Correlations of N two-level Atomic System

The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines

The long-standing paradox of the linear polarization signal of the Na i D1 line was recently resolved by accounting for the atom’s hyperfine structure and the detailed spectral structure of the incident radiation field. That modeling relied on the simplifying angle-averaged (AA) approximation for partial frequency redistribution (PRD) in scattering, which potentially neglects important angle–frequency couplings. This work aims at evaluating the suitability of a PRD-AA modeling for the D1 and D2 lines through comparisons with general angle-dependent (AD) PRD calculations in both the absence and presence of magnetic fields. We solved the radiative transfer problem for polarized radiation in a 1D semiempirical atmospheric model with microturbulent and isotropic magnetic fields, accounting for PRD effects and comparing PRD-AA and PRD-AD modelings. The D1 and D2 lines are modeled separately as a two-level atomic system with hyperfine structure. The numerical results confirm that a spectrally structured radiation field induces linear polarization in the D1 line. However, the PRD-AA approximation greatly impacts the Q/I shape, producing an antisymmetric pattern instead of the more symmetric PRD-AD one while presenting a similar sensitivity to magnetic fields between 10 and 200 G. Under the PRD-AA approximation, the Q/I profile of the D2 line presents an artificial dip in its core, which is not found for the PRD-AD case. We conclude that accounting for PRD-AD effects is essential to suitably model the scattering polarization of the Na i D lines. These results bring us closer to exploiting the full diagnostic potential of these lines for the elusive chromospheric magnetic fields.

Efficient broadband polarization retarder via shortcuts to adiabaticity.

The use of two-level atomic systems in quantum optics allows for the design of highly efficient and broadband achromatic retarders through the application of adiabatic passage and composite pulse techniques. In this work, we propose shortcuts to adiabaticity to improve broadband polarization retarders with shorter lengths. We achieve this by inversely engineering the relative refractive indices and further optimizing them with respect to the perturbation of input wavelength. Our results are compared with adiabatic and composite protocols, demonstrating that our method provides the advantage of integrating efficiency and robustness.

Transmission and Reflection properties of the incident Light via SW coherent laser field

The relative phase of the applied lights has been used to explore the position dependence of the transmitted and reflected light from a defective dielectric medium. The duplicated two-level atomic system that makes up the dielectric medium interacts with a position-dependent standing wave (SW) coupling light and a weak probe laser field. We found that identical behaviors can be produced for the transmitted and reflected light in various directions due to the relative phase of the applied light. Furthermore, we understood that the transmitted and reflected spectra of the incident light become asymmetric for the asymmetric profile of the coupling light, and that these circumstances will cause the probing field to be amplified. In this instance, we found that altering the relative phase of the applied lights can modify the position of the subluminal and superluminal light.

Quantum correlations beyond entanglement between two moving atoms interacting with a coherent cavity

Studying the ability of atom-photon interactions, especially in two two-level atomic systems, to generate quantum information resources has recently become an important research topic in quantum information science. Therefore, this paper explores the ability of two moving atoms coupling with a coherent field through a two-photon transition to generate atomic quantum correlations by using local quantum uncertainty (LQU), local quantum Fisher information (LQFI) as well as logarithmic negativity (LN). Schrödinger equation is used to obtain the time evolution of the atom-cavity-atom interactions with an initial coherent cavity state and an initial atomic uncorrelated pure state. The generation of atomic LQU, LQFI, and LN correlations are exactly examined under the unitary interaction parameter effects, including the atom-cavity coupling strengths, the cavity field half-wave number, and the initial coherent state intensity. The atom-cavity-atom interaction parameters lead to notable changes in the amplitudes, speed, and regularity of the LQU, LQFI, and LN dynamics, which can be enhanced by increasing the initial coherent intensity. The cavity field half-wave number leads to generating atomic quantum correlations with regular oscillatory behavior. The sudden death-birth phenomenon of the logarithmic negativity depends on the atom-cavity-atom interaction and the atomic location parameter.

Modeling Dielectric Loss in Superconducting Resonators: Evidence for Interacting Atomic Two-Level Systems at the Nb/Oxide Interface

While several experiments claim that two-level system (TLS) defects in amorphous surfaces and interfaces are responsible for energy relaxation in superconducting resonators and qubits, none can provide quantitative explanation of their data in terms of the conventional noninteracting TLS model. Here a model that interpolates between the interacting and noninteracting TLS loss tangent is proposed to perform numerical analysis of experimental data and extract information about TLS parameters and their distribution. As a proof of principle, the model is applied to TESLA cavities that contain only a single lossy material in their interior, the niobium-niobium oxide interface. The best fits show interacting TLSs with a sharp modulus of electric dipole moment for both thin ($5\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$) and thick ($100\phantom{\rule{0.2em}{0ex}}\mathrm{nm}$) oxides, indicating that the TLSs are ``atomic'' instead of ``glassy.'' The proposed method can be applied to other devices with multiple material interfaces and substrates, with the goal of elucidating the nature of TLSs causing energy loss in resonators and qubits.

Global quantum discord and von Neumann entropy in multipartite two-level atomic systems

We have computed the global quantum discord (GQD) and von Neumann entropy (VNE) of multipartite two-level atomic systems interacting with a single-mode Fock field. We use Tavis–Cumming model. We have explored how quantum correlations and quantum entanglement evolve with time in such systems. The quantum system is prepared initially in a mixed state and different parameters are varied to see how they affect the information processing in the system. The dynamical character of the GQD and VNE show an interplay between classical and nonclassical correlations. Photons in this model play an important role to assist the GQD and VNE and we observed that the effects of the field on the GQD and VNE reside in the time evolution of the system indicating that both atom and field states have become entangled. The GQD is assisted in a nonlinear fashion with the number of photons in the system. The GQD and VNE show linear behavior with each other in the dynamics of the system. The effects of intrinsic decoherence on the dynamics of the GQD and VNE are also studied. We have extrapolated the results for a large photon number on the system. We have studied the effect of the change in the size of the system on the maximum value of GQD and VNE and we have estimated the scaling coefficients for this behavior.

Rotational mirror–mirror entanglement via dissipative atomic reservoir in a double-Laguerre–Gaussian-cavity system

We propose a new scheme to prepare macroscopic entanglement between two rotating mirrors using dissipative atomic reservoir in a double-Laguerre–Gaussian-cavity system. The two-level atomic system driven by a strong field, acts as a single pathway of Bogoliubov dissipation to push the two original cavity modes into the desirable entangled state under the near-resonant conditions. Successively, the photon–photon entanglement can be transferred to mirror–mirror entanglement through the exchange of orbital angular momentum. In essence, the macroscopic entanglement is originated from the dissipative atomic reservoir rather than the radiation torque, thereby it is usually robust against environmental noises. The present scheme provides a feasible way to realize stable entanglement between spatially separated mirrors with high capacity, which may find potential applications in remote quantum communications.

Dynamics of quantum correlations in two 2-level atoms coupled to thermal reservoirs

In this paper, we examine the dynamics of quantum correlations in two noninteractive two-level atoms coupled to two separate identical thermal reservoirs. The two atoms are initially produced in a Gisin state, which is a blend of a maximally entangled two-qubit state and a separable mixed state. Quantum entanglement is measured by logarithmic negativity, while the nonclassical correlations are characterized by trace distance discord and local quantum uncertainty. Using the mean photon number of reservoirs and spontaneous emission rates of atoms as inputs, we explore how these quantum resources behave. Consequently, we demonstrate that the dynamics of quantum entanglement and quantum correlations depend upon the parameters driving the system. Significantly, we further demonstrate that specific parameters may be tweaked to preserve the quantum resources in the system. The results give a full grasp of the quantum features of such a two-level atomic system, showing capabilities to construct quantum technology.

A fast, high-order numerical method for the simulation of single-excitation states in quantum optics

We consider the numerical solution of a nonlocal partial differential equation which describes the phenomenon of collective spontaneous emission in a two-level atomic system containing a single photon. We reformulate the problem as an integro-differential equation for the atomic degrees of freedom, and describe an efficient solver for the case of a Gaussian atomic density. The problem of history dependence arising from the integral formulation is addressed using sum-of-exponentials history compression. We demonstrate the solver on two systems of physical interest: in the first, an initially-excited atom decays into a photon by spontaneous emission, and in the second, a photon pulse is used to an excite an atom, which then decays.

Measuring the pth-Order Correlation Function of Light Field via Two-Level Atoms

In this paper, we present a method for measuring arbitrary-order correlation functions of the light field using a two-level atomic system. Theoretically, light field information should be mapped onto the atomic system after the light interacts with the atom. Therefore, we can measure the atomic system and thus obtain information about the light field. We study two typical models, the p-photon Jaynes–Cummings model, and the p-photon Tavis–Cummings model. In both models, we find that the pth-order correlation function of an unknown light field can be obtained by measuring the instantaneous change of energy of the two-level atoms with the aid of a known reference light field. Moreover, we find that the interactions other than the dipole interactions between light and atoms have no effect on the measurement results.

Enhanced unconventional photon-blockade effect in one- and two-qubit cavities interacting with nonclassical light

The antibunching effect generated in a cavity containing first a single two-level atomic system and then two identical atoms is explored for off-resonant interactions, in strong- and weak-coupling regimes. The cavity is driven by coherent and squeezed sources. Using the second-order correlation function analytically derived in the weak-excitation regime, we show that squeezed light achieves and improves strong antibunching, leading to a photon blockade. This enhancement is due to a destructive quantum interference mechanism induced by the nonclassical light, creating a supplementary transition pathway. The best effect is obtained for equal frequency detunings in the strong-coupling regime. More interestingly, our investigation reveals that the two-atom-cavity system can further improve the antibunching effect compared to the single-atom cavity. It turns out that the additional couplings appearing in the cavity due to the implementation of the two atoms, combined with the squeezed light, could substantially enhance the photon-blockade effect.

Quasienergy operators and generalized squeezed states for systems of trapped ions

Collective many-body dynamics for time-dependent quantum Hamiltonians is investigated for a dynamical system that exhibits multiple degrees of freedom, in this case a combined (Paul and Penning) trap. Quantum stability is characterized by a discrete quasienergy spectrum, while the quasienergy states are symplectic coherent states. We introduce the generators of the Lie algebra of the symplectic group SL(2,R), which we use to build the coherent states (CS) associated to the system under investigation. The trapped ion is treated as a harmonic oscillator (HO) to which we associate the quantum Hamilton function. We obtain the kinetic and potential energy operators as functions of the Lie algebra generators and supply the expressions for the classical coordinate, momentum, kinetic and potential energy, along with the total energy. Moreover, we also infer the dispersions for the coordinate and momentum, together with the asymmetry and the flatness parameter for the distribution. The system interaction with laser radiation is also examined for a system of identical two-level atoms. The Hamilton function for the Dicke model is derived. The optical system is modelled as a HO (trapped ion) that undergoes interaction with an external laser field and we use it to engineer a squeezed state of the electromagnetic (EM) field. We consider coherent and squeezed states associated to both ion dynamics and to the EM field. The approach used enables one to build CS in a compact and smart manner by use of the group theory.

A locally stabilized radial basis function partition of unity technique for the sine–Gordon system in nonlinear optics

This paper develops a localized radial basis function partition of unity method (RBF-PUM) based on a stable algorithm for finding the solution of the sine–Gordon system. This system is one useful description for the propagation of the femtosecond laser optical pulse in a systems of two-level atoms. The proposed strategy approximates the unknown solution through two main steps. First, the time discretization of the problem is accomplished by a difference formulation with second-order accuracy. Second, the space discretization is obtained using the local RBF-PUM. This method authorizes us to tackle the high computational time related to global collocation techniques. However, this scheme has the disadvantage of instability when the shape parameter ɛ approaches to small value. In order to deal with this issue, we adopt RBF-QR scheme that provides the higher accuracy and stable computations for small values ɛ. Two examples are presented to show the high accuracy of the method and to compare with other techniques in the literature.

Effects of counter-rotating-wave terms on the noisy frequency estimation

We investigate the problem of estimating the tunneling frequency of a two-level atomic system embedded in a dissipative environment by employing a numerically rigorous hierarchical equations of motion method. The effect of counter-rotating-wave terms on the attainable precision of the noisy quantum metrology is systematically studied beyond the usual framework of perturbative treatments. We find the counter-rotating-wave terms are able to boost the noisy quantum metrological performance in the intermediate and strong coupling regimes, whether the dissipative environment is composed of bosons or fermions. The result presented in this paper may pave a guideline to design a high-precision quantum estimation scenario under practical decoherence.