Atom-field Interaction Research Articles

Rapid Production of Many-Body Entanglement in Spin-1 Atoms via Cavity Output Photon Counting.

We propose a simple and efficient method for generating metrologically useful quantum entanglement in an ensemble of spin-1 atoms that interacts with a high-finesse optical cavity mode. It requires straightforward preparation of N atoms in the m_{F}=0 sublevel, tailoring of the atom-field interaction to give an effective Tavis-Cummings model for the collective spin-1 ensemble, and a photon counting measurement on the cavity output field. The photon number provides a projective measurement of the collective spin length S, which, for the chosen initial state, is heavily weighted around values S≃sqrt[N], for which the corresponding spin states are strongly entangled and exhibit Heisenberg scaling of the metrological sensitivity with N, as quantified by the quantum Fisher information.

Quasiprobability Distribution Functions from Fractional Fourier Transforms

We show, in a formal way, how a class of complex quasiprobability distribution functions may be introduced by using the fractional Fourier transform. This leads to the Fresnel transform of a characteristic function instead of the usual Fourier transform. We end the manuscript by showing a way in which the distribution we are introducing may be reconstructed by using atom-field interactions.

One-Mode Wigner Quasi-Probability Distribution Function for Entangled Coherent States Generated by Beam Splitter and Cavity QED

In this paper, we use the displacement operator together with parity operation to construct the superposition of two coherent states. By transmitting this superposition from 50–50 beam splitter the two-mode qubit-like entangled coherent state (ECS) is generated. Moreover, we introduce a controllable method for producing qutrit-like ECS using atom–field interaction in cavity QED and beam splitter. We will show that the distances of peaks of Wigner functions for reduced density matrices of two-mode ECS's are entanglement sensitive and can be witnesses of entanglement. To confirm the results we use concurrence measure to compare bipartite entanglement of ECS's with the behaviour of peaks of Wigner functions. Moreover, we investigate decoherence effects on Wigner function, arising from transmitting ECS's through noisy channels.

Non-Wiener Dynamics of Open Systems for Nonzero Number Density of Surrounding Photons

We propose a collective decay model for a localized ensemble of identical atoms in a vacuum broadband electromagnetic field with a nonzero photon number density considering second-order terms in the atom–field interaction constant. The model is based on the stochastic differential equation for the evolution operator for the atomic ensemble and surroundings, which is controlled by the main quantum random processes and independent classical Wiener processes. It is shown that in some cases, nonzero photon number density does not influence the suppression of collective emission of atoms, and its existence is manifested as an additional mechanism of redistribution of atoms over collective sublevels.

High-precision three-dimensional atom localization via Kerr nonlinearity

Recently, there have been many schemes for achieving high-dimensional atom localization via measuring the first-order linear susceptibility. Here, we present a new scheme for high-precision three-dimensional (3D) atom localization in a three-level atomic system based on the Kerr nonlinearity, which refers to the real part of the third-order nonlinear susceptibility. Due to the space-dependent atom-field interaction, the position information of the atom can be determined by measuring Kerr nonlinearity in 3D space. Interestingly, by properly varying the parameters of the system, we find that there is only a small sphere in 3D space, which means the probability of finding the atom at a particular position can be 100%. Our scheme not only shows a new way to achieve high-precision and high-efficiency 3D atom localization but also provides some potential applications in high-dimensional atom nanolithography.

Surface plasmon laser with two hole arrays as cavity mirrors

Surface plasmon propagation and scattering on structured metal–dielectric interfaces are important tools for field confinement and enhanced atom–field interaction. In this paper, we demonstrate a new type of surface plasmon (SP) lasing that more closely resembles the usual mirror-based laser, in a geometry that comprises a central 50-μm-long flat region between two metal hole arrays that serve as reflecting mirrors. The lasing mode shows features of double-slit interference modulated by the radiation pattern of, and selection rules set by, the scattering of SPs on the 2D hole arrays. Our results also provide information on the group velocity of surface plasmons and their scattering and penetration in hole arrays.

The von Neumann Entropy for Mixed States.

The Araki–Lieb inequality is commonly used to calculate the entropy of subsystems when they are initially in pure states, as this forces the entropy of the two subsystems to be equal after the complete system evolves. Then, it is easy to calculate the entropy of a large subsystem by finding the entropy of the small one. To the best of our knowledge, there does not exist a way of calculating the entropy when one of the subsystems is initially in a mixed state. For the case of a two-level atom interacting with a quantized field, we show that it is possible to use the Araki–Lieb inequality and find the von Neumann entropy for the large (infinite) system. We show this in the two-level atom-field interaction.

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.

All-optical grating in a V+Ξ configuration using a Rydberg state

We present a theoretical model for controlling the Fraunhofer diffraction patterns of a weak probe field passing through an atomic vapor. In this model a Rydberg state is taken as the uppermost level. The proposed system contains a combined two well-known $V$- and $\mathrm{\ensuremath{\Xi}}$-type configurations which are exposed to a weak probe field and two control fields. The position-dependent feature of the atom-field interaction leads to the periodic transmission spectrum, and various Fraunhofer diffraction patterns are obtained due to the all-optical grating. Also, it is shown that the intensity of the higher-order diffraction can be controlled by tuning the coupling field intensity and the interaction length.

Sub-microwave wavelength localization of Rydberg superatoms

With the interaction among one optical probe field and pairs of standing microwaves in the configuration of Rydberg-dressed electromagnetically induced transparency, we study theoretically the sub-microwave wavelength localization of Rydberg superatoms in two and three dimensions. Composited by an ensemble of Rydberg atoms with strong dipole–dipole interactions, a superatom can be localized within the microwave wavelength through the position-dependent atom–field interaction. By measuring the absorption spectrum from the optical probe field, a single position of Rydberg superatoms with high precision can be obtained, depending on the probe field detuning and phase shifts associated with the standing microwaves.

Optomechanically induced anomalous population inversion in a hybrid system

We consider a two-level atom interacting with a quantized field in an optomechanical cavity and study the population inversion of the atom in this hybrid optomechanical system. Analytical solutions of the excited state population in the hybrid system are derived for various initial states of the cavity field and the mechanical mirror in the limit of weak single-photon coupling regime. Due to the mechanical mirror, the population inversion exhibits anomalous behavior, compared to the results predicted by the Jaynes–Cummings (JC) model. For an initial Fock state cavity field, we show that the atomic population inversion can undergo collapses and revivals induced by the mechanical mirror which is in a Fock state for the resonant atom-field interaction. When the cavity field is far-detuned from the atomic transition, the atom can couple to the mechanical mirror effectively via the JC interaction. In this case, the atomic population inversion can display either full Rabi oscillations or the collapse and revival behavior induced by a Fock state or a coherent state of the mechanical mirror, respectively. We also explore an experimentally more relevant situation when the mechanical mirror is initially in a mixed state. We derive an analytical expression of the excited state population via the unitary evolution for the density operator of the whole system. We find that the population inversion in this case exhibits slower collapse and smaller revival amplitude due to the initial mixture of the mechanical state. For an initial coherent state cavity field, we show that the predicted collapse regime in the original JC model can display nonzero oscillating values. Our analytical predications are further confirmed with numerical calculations in which the dissipation mechanism from the system is included.

Optical qubit generation via atomic postselection in a Ramsey interferometer

We propose a realizable experimental scheme to prepare a superposition of the vacuum and one-photon states using a typical cavity QED-setup. This is different from previous schemes, where the superposition state of the field is generated by resonant atom-field interaction and the cavity is initially empty. Here, we consider only dispersive atom-field interaction and the initial state of the cavity field is coherent. Then, we determine the parameters to prepare the desired state via atomic postselection. We also include the effect of cavity losses and detection imperfections in our analysis, against which this preparation of the optical qubit in a real Fabry–Pérot superconducting cavity is robust. Additionally, we show that this scheme can be used for the preparation of other photon number Fock state superpositions. In summary, our task is achieved with a high fidelity and a postselection probability within experimental reach.

Self-oscillation in the Maxwell–Bloch equations

We elucidated the mechanism of supercritical Hopf bifurcation in the semi-classical Maxwell–Bloch equations for cavity quantum electrodynamics by formulating the atom–field interaction as a feedback control system. It turns out that the existence of self-oscillatory states is a rather unexpected manifestation of the atomic pseudospin precession dynamics born out of the atom–field interaction governed by the driven Jaynes–Cummings Hamiltonian.

Dynamics of a Moving Two-Level Atom Under the Influence of Intrinsic Decoherence

We present a general and fascinating problem of quantum entanglement (QE) that is calculated with the help of quantum Fisher information (QFI) and von Neumann entropy (VNE) for moving two-level atomic systems. We calculate numerically the temporal evolution of the state vector of the entire system under the influence of intrinsic decoherence for a moving two-level atom. We demonstrate that the phase shifts of an estimator parameter, intrinsic decoherence, and the atomic motion play an important and prominent role during the time evolution of the atomic system. We observe that there is a monotonic relation between the atomic quantum Fisher information (QFI) and quantum entanglement (QE) in the absence of atomic motion. We also show that at the revival time the local maximum values of QFI decreases gradually. A periodic behavior of QFI is observed in the presence of atomic motion, which becomes more important and remarkable for two-level atomic systems. Moreover, the atomic quantum Fisher information and entanglement demonstrate an opposite response during the time evolution in the presence of atomic motion. We show that the evolution of entanglement is more susceptible to the intrinsic decoherence; a considerable change occurs in the degree of entanglement when the intrinsic decoherence parameter increases. Intrinsic decoherence in the atom–field interaction represses the nonclassical effects of the atomic systems. Both the entanglement and the quantum Fisher information saturate to their lower levels for longer time scales in the presence of intrinsic decoherence. For larger values of intrinsic decoherence, the sudden death of entanglement is observed.

Plasmon coupled super- and sub- radiance from dye shells

Coupled super- and sub- radiant emission of dye fluorescence near the plasmonic surface is shown to be an intrinsic property of the hybrid system. The bi-exponential decay is demonstrated for Au\\SiO2\\ATTO655 core-shell nanoparticles, which persists even when averaging over a broad range of the coupling parameter. The superradiant and subradiant states are distinct and exclusive by the identical permutational symmetry of the atom-field interaction Hamiltonian of the two-level system. Our analytical approach shows that starting from two emitters, coupled for example via the plasmon modes, the symmetry breaking occurs, making detectable the simultaneous existence of the fast super-radiance and the slow sub-radiance. The relaxation in the sub-radiant system occurs mainly due to the interaction with the plasmon modes. Our theory shows that the relaxation leads to the population of the sub-radiant states by dephasing the super-radiant Dicke states giving rise to the bi-exponential decay in agreement with the experiments. Even if we have a group of many coupled emitters or many groups of coupled emitters with different coupling parameters, the averaging will affect the emission among the super-radiant fast transitions and the sub-radiant slow transitions and keep these two group distinct.

Quantum Quantifiers for an Atom System Interacting with a Quantum Field Based on Pseudoharmonic Oscillator States.

We develop a useful model considering an atom-field system interaction in the framework of pseudoharmonic oscillators. We examine qualitatively the different physical quantities for a two-level atom (TLA) system interacting with a quantized coherent field in the context of photon-added coherent states of pseudoharmonic oscillators. Using these coherent states, we solve the model that exhibits the interaction between the TLA and field associated with these kinds of potentials. We analyze the temporal evolution of the entanglement, statistical properties, geometric phase and squeezing entropies. Finally, we show the relationship between the physical quantities and their dynamics in terms of the physical parameters.

Three-dimensional atom localization via spontaneous emission in a four-level atom

We investigate high-precision three-dimensional (3D) atom localization in a coherently-driven, fourlevel atomic system via spontaneous emission. Space-dependent atom-field interactions allow atomic position information to be obtained by measuring spontaneous emission. By properly varying system parameters, atoms within a certain range can be localized with nearly a probability of 100% and a maximal resolution of ~ 0.04λ. This scheme may be useful for the high-precision measurement of the center-of-mass wave functions of moving atoms and in atom nanolithography.

Atom-field interaction in optical cavities: Calibration of the atomic velocities to obtain a list of field states with preselected properties

We investigate statistical properties of a single mode field that interacts with a two-level atom inside an optical cavity. The whole system is described by dispersive Jaynes–Cummings Hamiltonian, both subsystems starting from superpositions of two states. We consider properties of the field states only at the moment each atom is detected in the ground state immediately after it has crossed the cavity. This allows us to get a list of atomic velocities corresponding to field states with preselected properties. The scheme is exemplified for excitation inversion and sub-Poissonian statistics.

Atomic Momentum Diffusion in the Field of Counter-Propagating Stochastic Light Waves

The momentum diffusion of atoms in the field of two counter-propagating stochastic waves, one of which reproduces the other one with a certain time delay, has been studied. It is shown that the parameters of atom-field interaction, at which the light pressure force is maximum, correspond to the increasing momentum diffusion coefficient. In the case of high-intensity field described by the stochastic field model, the momentum diffusion coefficient was found to be proportional to the square root of the field autocorrelation time. The wave function describing the inner state of atoms is modeled, by using the Monte-Carlo method. Numerical calculations are carried out for cesium atoms.

Number state filtered coherent states

Number state filtering in coherent states leads to sub-Poissonian photon statistics. These states are more suitable for phase estimation when compared with the coherent states. Nonclassicality of these states is quantified in terms of the negativity of the Wigner function and the entanglement potential. Filtering of the vacuum from a coherent state is almost like the photon addition. However, filtering makes the state more resilient against dissipation than photon addition. Vacuum state filtered coherent states perform better than the photon-added coherent states for a two-way quantum key distribution protocol. A scheme to generate these states in multi-photon atom–field interaction is presented.