Atom-cavity System Research Articles

Manipulation and improvement of multiphoton blockade in a cavity-QED system with two cascade three-level atoms

We present a study of manipulating the multiphoton blockade phenomenon in a single mode cavity with two ladder-type three-level atoms. Combining the cavity QED with electromagnetically induced transparency technique, we show that it is possible to actively manipulate the photon blockade when two atoms are in phase radiations. As a result, the two-photon blockade can be changed to three-photon blockade by changing the control field Rabi frequency. In the case of out-phase radiations, we show that the three-photon blockade can be improved with enhanced mean photon number. In addition, we show that the nonclassical field with sub-Poissonian distribution can be changed to the classical field with super-Poissonian distribution by tuning the Rabi frequency of the control field. The results presented in this work open up the possibility for achieving a two-photon gateway operation, which could be used in network of atom-cavity systems to control the quantum property of photons leaking from the cavity.

Emergent limit cycles and time crystal dynamics in an atom-cavity system

We propose an experimental realization of a time crystal using an atomic Bose-Einstein condensate in a high finesse optical cavity pumped with laser light detuned to the blue side of the relevant atomic resonance. By mapping out the dynamical phase diagram, we identify regions in parameter space showing stable limit cycle dynamics. Since the model describing the system is time-independent, the emergence of a limit cycle phase indicates the breaking of continuous time translation symmetry. Employing a semiclassical analysis to demonstrate the robustness of the limit cycles against perturbations and quantum fluctuations, we establish the emergence of a time crystal.

Cavity quantum electrodynamics with atom-like mirrors.

It has long been recognized that atomic emission of radiation is not an immutable property of an atom, but is instead dependent on the electromagnetic environment1 and, in the case of ensembles, also on the collective interactions between the atoms2-6. In an open radiative environment, the hallmark of collective interactions is enhanced spontaneous emission-super-radiance2-with non-dissipative dynamics largely obscured by rapid atomic decay7. Here we observe the dynamical exchange of excitations between a single artificial atom and an entangled collective state of an atomic array9 through the precise positioning of artificial atoms realized as superconducting qubits8 along a one-dimensional waveguide. This collective state is dark, trapping radiation and creating a cavity-like system with artificial atoms acting as resonant mirrors in the otherwise open waveguide. The emergent atom-cavity system is shown to have a large interaction-to-dissipation ratio (cooperativity exceeding 100), reaching the regime of strong coupling, in which coherent interactions dominate dissipative and decoherence effects. Achieving strong coupling with interacting qubits in an open waveguide provides a means of synthesizing multi-photon dark states with high efficiency and paves the way for exploiting correlated dissipation and decoherence-free subspaces of quantum emitter arrays at the many-body level10-13.

Shortcuts to adiabatic passage for the generation of maximally entangle states in a distributed atom-cavity system

We propose an efficient scheme to generate maximally entangled states between two three-level atoms in multi-cavity systems via shortcuts to the adiabatic technique. Two atoms are trapped in spatially separated cavities which are linked through direct coupling and optical fiber coupling, respectively. Time-dependent lasers which are tactfully designed radiate the atoms to drive the evolution rapidly. A determinate analysis solution for this distributed maximally entangled state is achieved by controlling the detuning between the cavity mode and laser fields. Numerical simulations show that the shortcut scheme permits the decoherence which arises from the noisy environment and spontaneous emission to some extent. Meanwhile, the scheme tolerates the imprecision of the experimental parameters, such as evolution time, laser parameters and so on. Our research provided a fast, analytical and feasible technology in non-locality quantum entanglement preparation in quantum electronic dynamics.

Measuring spatially extended density profiles using atom-cavity collective strong coupling to higher-order modes

The collective strong coupling of rubidium atoms in a magneto-optical trap (MOT) to the Laguerre-Gaussian (LG) modes of a Fabry-P\'erot cavity is investigated. Bright and dark $^{85}\mathrm{Rb}$ MOT atoms are prepared at the geometric center of the cavity, and the vacuum Rabi splitting (VRS) of the collectively coupled atom-cavity system is measured for ${\mathrm{LG}}_{l0}$ ($l=0,1,2,3$) modes. The atom number coupled to the cavity mode depends on the overlap of the atomic density distribution and the specific spatial mode function, which is reflected in the measured VRS spectrum. The known mode function and the measured VRS can then be used to test whether the atomic density distribution in the experiment is Gaussian or uniform. A simple theoretical model for this process is described, and the experimental measurements are found to be in close agreement with the model.

Multiple-scale analysis of open quantum systems

In this work, we present a multiple-scale perturbation technique suitable for the study of open quantum systems, which is easy to implement and in few iterative steps allows us to find excellent approximate solutions. For any time-local quantum master equation, whether markovian or non-markovian, in Lindblad form or not, we give a general procedure to construct analytical approximations to the corresponding dynamical map and, consequently, to the temporal evolution of the density matrix. As a simple illustrative example of the implementation of the method, we study an atom-cavity system described by a dissipative Jaynes-Cummings model. Performing a multiple-scale analysis we obtain approximate analytical expressions for the strong and weak coupling regimes that allow us to identify characteristic time scales in the state of the physical system.

Few-photon Fock-state wave packet interacting with a cavity-atom system in a waveguide: Exact quantum state dynamics

In the paper, we employ a wavefunction approach to investigate the evolution of a two-photon wave packet propagating in a one-dimensional waveguide coupled to the Jaynes-Cummings (JC) system. We derive and solve, both analytically and numerically, a set of equations of motion governing the quantum state of the system. That allows us to provide real-time analysis of the evolution of the wave packet two-photon joint spectrum (2PJS) and the excitation dynamics of the JC system in the course of its interaction with the two-photon pulse. We demonstrate that the 2PJS and the spectrum of the wave packet scattered from the JC system experience transformation for nonzero atom-cavity couplings. Moreover, using Schmidt decomposition, we show that the scattered photons feature frequency entanglement contrary to the incident ones which are not entangled.

Cavity-enhanced optical controlling based on three-wave mixing in cavity-atom ensemble system.

Cavity-enhanced optical controlling is experimentally observed with a low-control laser power in a cavity-atom ensemble system. Here, the three-level atoms are coupled with two optical modes of a Fabry-Perot cavity, where a new theoretical model is developed to describe the effective three-wave mixing process between spin-wave and optical modes. By adjusting either temperature or cavity length, we demonstrate the precise frequency tuning of the hybrid optical-atomic resonances. When the doubly-resonant condition is satisfied, the probe laser can be easily modulated by a control laser. In addition, interesting non-Hermitian physics are predicted theoretically and demonstrated experimentally, and all-optical switching is also achieved. Such a doubly-resonant cavity-atom ensemble system without a specially designed cavity can be used for future applications, such as optical signal storage and microwave-to-optical frequency conversion.

Time evolution of entanglement and trace distance in an atom-cavity system described with random walk and non-random walk states

An atom-cavity system consists of an atom or group of atoms inside a cavity. When an atom in cavity is stimulated by a laser pump, it is affected by the atom-field interaction shows the qusi- random walk behavior. This can change the entanglement and trace distance of system. In this work, the change entanglement and trace distance of system in two different cases -namely- the random walk and non-random walk is considered. The descriptive system is a two-level atom in the electrodynamics cavity based on the Jayne’s-Cummings model, which is stimulated by two longitudinal and transverse laser pumps. The results show that the consideration of the random walk case for the atom changes in the amount of entanglement can be seen as the phenomenon of sudden death and birth of entanglement. It results in its rate of changes to be increased. In contrast to the non-random walk case, this rate is increased and decreased more quickly compared to the random walk case. The maximum amount of entanglement in each case is the same, but the minimum in random walk case is less than that of non-random walk case.

Interaction of photons with a coupled atom-cavity system through a bidirectional time-delayed feedback

In this paper, we have developed a method for describing the dynamics of an arbitrary quantum system under a bidirectional time-delayed feedback loop. For this purpose, we have described the evolution in terms of the time propagation of the quantum system of interest without feedback together with several identical systems, which represent the history of the quantum system under study. This technique provides a numerically efficient solution for describing a system's dynamics in the case of significant time delays in which direct investigation of the state of the reservoirs becomes numerically intractable. Using this method, we have studied two scenarios of multiple scatterings of photons incident on a cavity with a two-level atom positioned inside it, coupled to two waveguides that are connected at their ends. In the first scenario, two photons impinge on the cavity through separate waveguides with a delay between them. We have demonstrated that the maximum difference between the two output photon numbers occurs when the delay between the incident photons becomes close to the inverse of their linewidth. In the second scenario, multiple photons impinge on the cavity through the same waveguide and go through multiple interactions. We have shown that, for a fixed atom-cavity coupling rate, the transmission rate enhances as the number of photons increases and have quantified this enhancement. The developed method enables us to study a broad range of nonlinear dynamics in complex quantum networks.

Light-Induced Coherence in an Atom-Cavity System.

We demonstrate a light-induced formation of coherence in a cold atomic gas system that utilizes the suppression of a competing density wave (DW) order. The condensed atoms are placed in an optical cavity and pumped by an external optical standing wave, which induces a long-range interaction mediated by photon scattering and a resulting DW order above a critical pump strength. We show that the light-induced temporal modulation of the pump wave can suppress this DW order and restore coherence. This establishes a foundational principle of dynamical control of competing orders analogous to a hypothesized mechanism for light-induced superconductivity in high-T_{c} cuprates.

Thermalization and Heating Dynamics in Open Generic Many-Body Systems.

The last decade has witnessed remarkable progress in our understanding of thermalization in isolated quantum systems. Combining the eigenstate thermalization hypothesis with quantum measurement theory, we extend the framework of quantum thermalization to open many-body systems. A generic many-body system subject to continuous observation is shown to thermalize at a single trajectory level. We show that the nonunitary nature of quantum measurement causes several unique thermalization mechanisms that are unseen in isolated systems. We present numerical evidence for our findings by applying our theory to specific models that can be experimentally realized in atom-cavity systems and with quantum gas microscopy. Our theory provides a general method to determine an effective temperature of quantum many-body systems subject to the Lindblad master equation and thus should be applicable to noisy dynamics or dissipative systems coupled to nonthermal Markovian environments as well as continuously monitored systems. Our work provides yet another insight into why thermodynamics emerges so universally.

Measuring acceleration using the Purcell effect

We show that a two-level atom resonantly coupled to one of the modes of a cavity field can be used as a sensitive tool to measure the proper acceleration of a combined atom-cavity system. To achieve it we investigate the relation between the transition probability of a two-level atom placed within an ideal cavity and study how it is affected by the acceleration of the whole. We indicate how to choose the position of the atom as well as its characteristic frequency in order to maximize the sensitivity to acceleration.

The effects of atom–cavity coupling constant on physical observables for different transitions

The aim of this work is to investigate the changing effects of the atom–cavity coupling constant on an atom–cavity system. A three-level atom in the Λ configuration with q-photon transition between levels 2 and 3 is confined in a single-mode Fabry–Pérot optical cavity. To solve the master equation of this system in the steady-state by using the appropriate physical quantities, the matrix continued fractions method for recurrence equations is applied. The behavior of physical observables including atom–field correlation, mean photon number, and second-order coherence function is discussed. The effect of altering the atom–cavity coupling constant for different transitions on these observables is fully considered. The results of calculations show that by increasing this coupling constant, the range of atom–cavity correlation becomes longer, the maximum value of the output mean photon number from the cavity remains almost constant, the broadening in the curves of the mean photon number increases and the lasing process is amplified in the system. Finally, the transformation of the three-level atom into a two-level one under several specific conditions in a four-photon transition case has been studied. The obtained results of the two-level atomic pattern are adequately confirmed by the simulations related to the three-level atom.

Lie algebraic approach to a nonstationary atom-cavity system

In this work we study the generation of photons inside an ideal cavity with resonantly oscillating boundaries in the presence of a two-level atom. We make use of Lie algebraic techniques to obtain an approximate time-evolution operator and evaluate not only the resonant and dispersive regimes but also explore different regions of parameters. We have found a very good agreement between our approximate results and those obtained by numerical means.

Resonant intracavity four-wave mixing in a composite atom–cavity system

We experimentally study intracavity four-wave mixing (FWM) using Λ-type, three-level electromagnetically induced transparency (EIT) atoms confined in an optical ring cavity. The original dark-state peak disappears accompanying the generation of intracavity FWM when the coupling light is changed from traveling-wave to standing wave. Additionally, this FWM signal is on resonance with the optical cavity only when the coupling laser is detuned from the atomic resonance center, where the absorption is drastically reduced for both the probe and FWM fields. At last, we do theoretically analysis for the susceptibility of this composite atom–cavity system.

Shortcuts to adiabatic passage for the generation of a maximal Bell state and W state in an atom–cavity system

We propose an efficient scheme to generate the maximal entangle states in an atom–cavity system between two three-level atoms in cavity quantum electronic dynamics system based on shortcuts to adiabatic passage. In the accelerate scheme, there is no need to design a time-varying coupling coefficient for the cavity. We only need to tactfully design time-dependent lasers to drive the system into the desired entangled states. Controlling the detuning between the cavity mode and lasers, we deduce a determinate analysis formula for this quantum information processing. The lasers do not need to distinguish which atom is to be affected, therefore the implementation of the experiment is simpler. The method is also generalized to generate a W state. Moreover, the accelerated program can be extended to a multi-body system and an analytical solution in a higher-dimensional system can be achieved. The influence of decoherence and variations of the parameters are discussed by numerical simulation. The results show that the maximally entangled states can be quickly prepared in a short time with high fidelity, and which are robust against both parameter fluctuations and dissipation. Our study enriches the physics and applications of multi-particle quantum entanglement preparation via shortcuts to adiabatic passage in quantum electronic dynamics.

Monoatomic optical diode based on direction-dependent bistability in the Purcell regime

Until now, single-atom bistability has been widely discussed in strong coupling regime. Here we focus on the scattering property of single atom-cavity coupling system in the Purcell regime, in which optical bistability was not predicted due to adiabatic treatment. In our previous works, we have shown concisely that optical bistability exists in part of the Purcell regime due to the presence of giant single-atom saturation nonlinearity, and the properties of bistable regime rely on the incident direction of input light within asymmetric cavity. Such direction-dependent bistability and its potential application as an efficient optical diode are discussed elaborately in this work. After comprehensive analysis, the thresholds of parameters to discriminate bistable regime from non-bistable regime are presented in detail. The limitation of adiabatic treatment which was widely adopted in the Purcell regime is also surveyed, which shows that only when the selected parameters are far from the bistable regime can the evolution of the cavity field be treated adiabatically. Direction-dependent bistability make it feasible to construct such monoatomic optical diode with high transmission contrast.

Magnetic-field-dependent slow light in strontium atom-cavity system

Realizing and controlling a long-lived slow light is of fundamental importance in physics and may find applications in quantum router and quantum information processing. In this work, we propose a feasible scheme to realize the slow light in a strontium atom-cavity system, in which the value of group delay can be continuously adjusted within a range of different Zeeman splittings and vacuum Rabi frequencies by varying the applied static magnetic field and the atom number instead of a strong coherent field. In our scheme, the major limitations of the slow-light structure, namely, dispersion and loss, can be effectively resolved, and so our scheme may help to achieve the practical application of slow light relevant to the optical communication network.

Concurrence of three Jaynes–Cummings systems

We apply genuine multipartite concurrence to investigate entanglement properties of three Jaynes–Cummings systems. Three atoms are initially put in GHZ-like state and locally interact with three independent cavities, respectively. We present analytical concurrence expressions for various subsystems including three-atom, three-cavity and some atom-cavity mixed systems. We also examine the global system and illustrate the evolution of its concurrence. Except for the sudden death of entanglement, we find for some initial entanglement parameter $$\theta $$ , the concurrence of the global system may maintain unchanged in some time intervals.