Cooperativity and Entanglement of Atom-field States

Abstract

The Jaynes-Cummings model of a single two-level atom interacting with a quantized single-mode coherent field generates at the half-revival time a dynamically disentangled atom-field state. At such times, the field is in asymptotically pure Schrödinger cat state, a macroscopic superposition of distinct field eigenmodes. In this paper we address the problem of field purity when a second atom is allowed to interact with the cavity mode and becomes entangled with the first atom via their mutual cavity field with which they interact. We employ the collective Dicke states to describe the cooperative effects on the entanglement and show that the second atom spoils the purity of the field state except for special cases of the atom-field coupling or of initial conditions.     

Autler-Townes microscopy on a single atom

Abstract

The detection of a spontaneously emitted photon from a threelevel atom, in which the two upper levels are driven by a classical standing light field, yields information about the centre-of-mass position of the atom relative to the nodes of the driving field. We present a pure state treatment of the system and show that the measurement leads to a reduction of the system's wavefunction, which manifests itself in a localization of the atom.     

Permanently disentangled states of atom–field system via spontaneously generated coherence

Abstract

The effect of spontaneously generated coherence on evolution of the entanglement between a driven four-level Y-type atom and its spontaneous emission field is studied. We have shown that the atom will be entangled to its spontaneous emission field due to spontaneously generated coherence and coherent population trapping at the steady state. It is found that the degree of entanglement strongly depends on the initial atomic state. So, it can be controlled by the pumping laser pulses used for preparing an initial atomic system. More interestingly, the atom–field system can be found in a permanently disentangled state for a properly prepared atom.     

The Interaction of Displaced Number State and Squeezed Number State Fields with Two-level Atoms

Abstract

The time-evolution of a single two-level atom in a single-mode high-Q cavity is sensitive to the quantum fluctuations of the cavity radiation field and to its photon statistics: this sensitivity is realizable experimentally in the Rydberg atom micromaser. We study the effects of the interaction of a two-level atom with two new non-classical radiation fields: the squeezed number state and the displaced number state realizable by nonlinear and linear transformations of field number states which have an initially precise occupation number. The time-varying field fluctuations caused by the atomic interaction are described using the Q-function quasi-probability.     

Atomic Dipole Dynamics in the Thermal Quantized Cavity Field

Abstract

We consider the resonant interaction of a two-level atom with a thermal state of the quantized field in a lossless cavity. Non-trivial dynamics of the atomic dipole moment and the field quadrature components arise if the atom is initially prepared in a coherent superposition of its upper and lower states. In particular, the initial thermal field state acquires a well defined phase that corresponds to the initial phase of the superposition atomic state. Population trapping occurs when the intensity grows.     

Preparation of two-mode anticorrelated photon-number state via atom de Broglie wave deflection

Abstract

It is shown that the deflection of an atom de Broglie wave at two adjacent cavities containing non-resonant weak fields can yield a highly entangled quantum state of the atom–field system in which discernible atomic beams are entangled to internal states of the atom and to two-mode photon-number states of the fields. Two-mode anticorrelated entangled photon-number states characterized by the total photon number can be prepared by the detection of the atom in given directions of the propagation.     

Entropy Evolution of the Bimodal Field Interacting with an Effective Two-level Atom Via the Raman Transition

Abstract

The properties of entropy evolution of the bimodal field interacting with an effective two-level atom via the Raman transition are studied. The influences of the initial average photon number and of the atomic coherence on the evolution of the bimodal field entropy are examined. It is shown that the bimodal field is in a pure state only under certain conditions in the early stages of time evolution and later tends to a statistical mixture state with maximum entropy values; the bimodal field remains strongly entangled with the atom.     

Field oscillations in a micromaser with injected atomic coherence

Abstract

The electric field in a lossless, regularly-pumped micromaser with injected atomic coherence can undergo a period-two oscillation in the steady state. The field changes its value after a single atom passes through the micromaser cavity, but returns to its original value after a second atom travels through. We give a simple explanation for this phenomenon in terms of tangent and cotangent states. We also examine the effect of cavity damping on this steady state.     

Atom probe characterisation of high temperature materials

Abstract

An atom probe is capable of quantitatively analysing materials at the atomic level. Modern atom probes are derived from the field ion microscope, and are coupled with time-of-flight mass spectrometers, permitting identification of individual atoms. The introduction of position-sensitive detectors enables the reconstruction of a small volume of the sample owing to simultaneous determination of the x, y, and zcoordinates and the mass to charge ratios of individual atoms. This paper focuses on the application of atom probe techniques to the microstructural analysis of high temperature materials. Illustrations include carbide precipitation in creep resistant power plant steels and analyses of model and commercial multicomponent nickel based superalloys. It is demonstrated that atom probe field ion microscopy and atom probe tomography are valuable techniques in the development and understanding of technologically important alloys for high temperature service.     

The Damped-vacuum-field Jaynes-Cummings Model

Abstract

We study the dynamics of a two-level atom interacting with a single mode of a damped cavity at 0 K when the cavity is initially in the vacuum state and the atom enters it in an arbitrary (pure or mixed) state. A complete analytical solution of this simple model is presented. On the basis of this solution we firstly investigate the pseudo-spin dynamics of the atom and the cavity field, secondly give an illustration of the Araki-Lieb theorem concerning the von Neumann entropies of interacting quantum systems and thirdly demonstrate the generation of entangled states of the atom and cavity field that are of interest in connection with the Bell inequalities.     

Emission Spectra of a Two-level Atom Under the Presence of Another Two-level Atom

Abstract

We investigate the spectrum of light emitted by a two-level atom interacting with another two-level atom inside an ideal cavity within the frame of generalized Jaynes-Cummings model. The influence of various ratios of the coupling constants of the atoms to the field on the spectrum of the emitted light is studied in detail for the case when the atoms are supposed to be initially in the excited state and the field in a Fock state as well as their superposition.     

Stimulated emission via quantum interference: Scattering of one-photon packets on an atom in a ground state

Abstract

Usually it is assumed that the stimulated emission appears as a consequence of the Bose—Einstein statistics of photons and that to observe this effect at least two excitations have to be initially present in the atom—field system. That is, both the atom and the electromagnetic field have to be excited. In this paper we show that stimulated emission can appear exclusively as a consequence of quantum interference in a system with just a single excitation. Specifically, we consider a single two-level atom which is initially in its lower energy state and it interacts with a single-photon multi-mode wave packet. We show that for a proper choice of the photon-wave packet the atom can exhibit stimulated emission.     

Laser Pulse Shape Effects in Harmonic Generation from a Two-level Atom

Abstract

The harmonic spectrum emitted by a two-level atom driven by a resonant laser field is calculated. The spectrum is seen to depend on the shape of the pulse. In the case of an asymmetric pulse profile, harmonic emission is present also at a relatively low intensity field.     

Production of Macroscopic Schrödinger Cat States from Weak Quantized Cavity Fields Interacting with Atoms Driven by Classical Fields

Abstract

We show that macroscopic superposition (Schrödinger cat) states of a quantized single-mode cavity field can be produced via the interaction of this field with a two-level atom which is driven by a classical field even for small initial intensities of the quantized cavity mode. We show that with a properly chosen driving field an almost pure superposition state with arbitrary amplitudes and phases of component states can be produced.     

Quantum effects in the transient dynamics of a many mode Jaynes-Cummings model

Abstract

Phenomenology and mechanisms of energy exchange, due to induced atomic processes of absorption and emission, are investigated in the evolution of a two-mode Jaynes-Cummings model. One field mode is initially in a highly coherent populated state and the other one is initially empty. The field mode exchanges energy with the atom by two mechanisms, related to very different atomic dynamics, which operate in complementary phases of the system evolution. One mechanism determines the energy exchanges which involve only the populated mode and the atom. The other is responsible for mode-mode photon exchanges and becomes relevant when the first mechanism is quenched. Thus there is no competition between the atomic emission in the empty mode and processes involving the atom and the highly populated mode. Quantum features related to entanglement of atom and field states are discussed. Cooperative effects between the two field modes and their incompatibility with the predictions of neo-classical theory are evidenced.     

N-level Atom Interacting with Single-mode Radiation Field: An Exactly Solvable Model with Multiphoton Transitions and Intensity-dependent Coupling

Abstract

We study the dynamics of an N-level atom coupled in a lossless cavity to a single-mode near-resonant quantized field. The atomic levels are coupled by the multiphoton transitions and the coupling constants between the field and the atomic levels are supposed to be intensity dependent. We find the exact solution for the state vector describing the dynamics of the atom-plus-field system. As an illustration we use the model for studying (i) the time evolution of the atomic occupation probability with the initially coherent field and (ii) the light squeezing, when the cavity field is initially in the vacuum state and the atom is prepared in the atomic ‘coherent state’ (a superposition of atomic states).     

How to catch an atom with single photons

Abstract

We report on trapping a single neutral atom in the standing-wave light field of a high-finesse optical cavity containing one photon on average, a single-photon optical trap, or SPOT for short. This trap has the novel feature that the light field is also used to observe the atom in real time. The oscillatory motion of the trapped atom induces well-resolved oscillations of the light intensity. Periodic structure is visible in the fourth-order intensity correlation function, attributed to long-distance flights of the atom along the standing wave. The finite duration of those flights provides evidence for cavity-mediated cooling of atoms. We discuss the various mechanisms determining the trapping time and compare the results with a quantum-jump Monte Carlo simulation to interpret the observed signals.     

Resonance Fluorescence in a Squeezed Vacuum

Abstract

Fluorescence from a coherently driven two-level atom that is damped by a squeezed vacuum is studied. We show that the mean atomic polarization depends on the relative phases of the squeezed vacuum and the coherent driving field. The fluorescent spectrum is calculated and shows several modifications over the spectrum for normal resonance fluorescence. In particular, the central peak of the Mollow triplet has a linewidth that depends on the phase of the driving field. For strong squeezing this peak can either be much narrower or much broader than the natural linewidth of the atom.     

Spontaneous emission from a three-level atom in two-band photonic crystals

Abstract

We investigate the spontaneous emission from a V three-level atom embedded in two-band isotropic photonic crystals. The dipoles of the two transitions from the two upper levels to the lower level are parallel. Due to the quantum interference between the two transitions and the existence of two bands, the populations in the upper levels display some novel properties, such as anti-trapping and continuous oscillation, which differ from that of a two-level atom (with two bands) and also differ from that if only one band (for three-level atom) is considered. The spontaneous emission field is composed of two parts: localized field and travelling field. The localized field is composed of one or two localized modes, and the travelling field is composed of no, one, two or three propagating modes depending on different conditions. The conditions for different combinations of localized modes and propagating modes are discussed.     

On the Interaction of Two-level Atoms with Superpositions of Coherent States of Light

Abstract

In this paper we study the decoherence process occurring when a field prepared in quantum superpositions of coherent states (Schrödinger cats) interacts with a two-level atom in the framework of the Jaynes-Cummings model. We emphasize the influence of the relative phase in the initial superposition state on the purity of the field during the evolution