Atomic Decay Rate Research Articles

Spontaneous Emission of an Excited Atom in a Dusty Unmagnetized Plasma Medium

Investigation of spontaneous decay of an excited atom in dusty unmagnetized plasma is presented in this paper. The transverse contribution to the decay rate is normally associated with spontaneous emission. The rate of spontaneous emission can be obtained by Fermi’s golden rule. In this calculation, the transverse contribution to dielectric permittivity and Green function technique are used. Calculation of the decay rate of atoms is applicable to understand the particular structure of the vacuum state of the electromagnetic field.

Cavity QED of a leaky planar resonator coupled to an atom and an input single-photon pulse

In contrast to the free-space evolution of an atom governed by a multimode interaction with the surrounding electromagnetic vacuum, the evolution of a cavity-QED system can be characterized by just three parameters: (i) atom-cavity coupling strength $g$, (ii) cavity relaxation rate $\ensuremath{\kappa}$, and (iii) atomic decay rate into the noncavity modes $\ensuremath{\gamma}$. In the case of an atom inserted into a planar resonator with an input beam coupled from the outside, it has been shown by Koshino [Phys. Rev. A 73, 053814 (2006)] that these three parameters are determined not only by the atom and cavity characteristics, but also by the spatial distribution of the input pulse. By an ab initio treatment, we generalize the framework of Koshino and determine the cavity-QED parameters of a coupled system of atom, planar (leaky) resonator, and input single-photon pulse as functions of the lateral profile of the pulse and the length of resonator. We confirm that the atomic decay rate can be suppressed by tailoring appropriately the lateral profile of the pulse. Such an active suppression of atomic decay opens an attractive route towards an efficient quantum memory for long-term storage of an atomic qubit inside a planar resonator.

Reduction of the radiative decay of atomic coherence in squeezed vacuum

Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the ordinary vacuum level, allowing measurements that surpass the standard quantum limit in sensitivity. The effects of such 'squeezed states' of light on matter were first considered in a prediction of the radiative decay rates of atoms in squeezed vacuum. Despite efforts to demonstrate such effects in experiments with natural atoms, a direct quantitative observation of this prediction has remained elusive. Here we report a twofold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum. The artificial atom is effectively a two-level system formed by the strong interaction between a superconducting circuit and a microwave-frequency cavity. A Josephson parametric amplifier is used to generate quadrature-squeezed electromagnetic vacuum. The observed twofold reduction in the decay rate of the atom allows the transverse coherence time, T2, to exceed the ordinary vacuum decay limit, 2T1. We demonstrate that the measured radiative decay dynamics can be used to reconstruct the Wigner distribution of the itinerant squeezed state. Our results confirm a canonical prediction of quantum optics and should enable new studies of the quantum light-matter interaction.

Efficient Scheme for Implementing the Deutsch-Jozsa Algorithm in Cavity QED

A scheme is proposedfor implementing a two-qubit quantum logic gate and realizing the Deutsch-Jozsa algorithm in cavity QED. In the scheme a three-level atom interacts with highly detuned cavity modes. The gate is not affected by the atomic decay rates because of the metastable lower levels are involved in the gate operations. The Deutsch-Jozsa algorithm is easily realized with current experimental techniques.

A quasi-continuous superradiant Raman laser with < 1 intracavity photon

Steady-state collective emission from ensembles of laser cooled atoms has been proposed as a method for generating sub-millihertz linewidth optical lasers, with potential for broad impacts across science and technology. We have built a model system that tests key predictions for such active oscillators using a Raman laser with laser cooled atoms as the gain medium. The laser operates deep in the bad-cavity, or superradiant, regime of laser physics, where the cavity decay rate is much greater than the atomic coherence decay rate. Specifically, we demonstrate that a system of 106 87Rb atoms trapped in a 1D standing wave optical lattice can spontaneously synchronize and collectively emit a quasi-continuous coherent optical output, even when the intracavity field contains on average < 1 photon.

CONTROLLING SINGLE-PHOTON TRANSPORT IN A ONE-DIMENSIONAL RESONATOR WAVEGUIDE BY INTERATOMIC DIPOLE–DIPOLE INTERACTION

Controlling single-photon transport in a one-dimensional resonator waveguide can be realized by the interatomic dipole–dipole interaction (DDI). Our numerical results show that the effects of the DDI act as that of a positive detuning. Because of the DDI, the period of the transmission spectrum changes, and its amplitude increases for stronger DDI intensity. We also discuss the influences of the DDI on the transport in low-energy and high-energy regimes. Besides, a cooperation dissipation, induced by the two atoms coupling to a common reservoir, can lead to the increase of the atomic total decay rates and the decrease of the reflection amplitude of the incident photon.

Difference between radiative transition rates in atoms and antiatoms

We demonstrate that CP violation results in a difference of the partial decay rates of atoms and antiatoms. The magnitude of this difference is estimated.

A semiclassical optics derivation of Einstein’s rate equations

We provide a semiclassical optics derivation of Einstein’s rate equations (ERE) for a two-level system illuminated by a broadband light field, setting a limit on their validity that depends on the spectral properties of the light field. Starting from the optical Bloch equations for individual atoms, the ensemble averaged atomic inversion is shown to follow ERE under two concurrent hypotheses: (i) the decorrelation of the inversion at a given time from the field at later times and (ii) a Markov approximation owing to the short correlation time of the light field. When the latter hypothesis is relaxed, we find effective Bloch equations for the ensemble average in which the atomic polarization decay rate is increased by an amount equal to the width of the light spectrum, which allows its adiabatic elimination for a large enough spectral width. The use of a phase-diffusion model of light allows us to check our results and hypotheses using numerical simulations of the corresponding stochastic differential equations. We take into account both light bandwidth and atomic linewidth, which allows us to discuss the differences existing between rate equations in the limits of large light bandwidth or large atomic linewidth. Only in the former case does one obtain ERE with the correct expression for Einstein’s B coefficient.

Temperature dependence of atomic decay rate induced by the BEC of photons

Bose–Einstein condensation of a weakly interacting photon gas in a two-dimensional optical microcavity is investigated. The effective mass and chemical potential for a photon confined inside this optical microcavity are non-vanishing. A reservoir theory has been used to study the decay rate of a two-level atom in the microcavity, in which photons are in the Bose–Einstein condensate state. It is found that below the critical temperature Tc, the atomic decay rate is a monotonically increasing function of the absolute temperature T.

Linear susceptibilities of a single two-level atom and two two-level atoms inside a coupled resonator waveguide: Green function approach

In this paper, we use the Green function method to determine the linear quantum mechanical susceptibilities of a single two-level atom and two two-level atoms located inside a coupled-resonator optical waveguide (CROW). We first calculate the susceptibility of a single atom in a CROW which has the same form as that of a single atom in free space, except for the modification of the atomic decay rate and the frequency shift. Then, we consider two non-identical, non-interacting two-level atoms inside two separate cavities of the CROW. We find that the susceptibility of this system contains not only the contributions of the two individual atoms, but also the contribution arising from the atom-atom correlation due to the CROW field. This additional contribution leads to an electromagnetically induced transparency-like (EIT-like) phenomenon. Furthermore, we find that the optical response of the atomic systems under consideration can be controlled by tuning the atomic transition frequency. Finally, we study the effects of the dissipation processes, i.e., the spontaneous emission of the atoms and the photon leakage from the CROW, on the optical susceptibility.

Nonlinear superluminality in cold atoms confined in hollow core photonic crystal fiber

We propose a scheme for superluminal propagation of a linearly polarized smooth light pulse in cold atoms trapped inside a hollow-core fiber with intensity-dependent negative group velocity. The tight confinement of the atoms inside the fiber core prevents atom-wall collisions, while the Doppler width is negligible as compared to atomic decay rate. We show that with initially prepared Zeeman coherence, the absorption of light is smaller enough to be ignored, while due to nonlinear dependence on laser intensity more intense parts of the pulse travel slower leading to the formation of the extremely sharp trailing edge and to the lengthening of the leading edge of the pulse. Such a behavior is contrast to the case of nonlinear propagation of the pulse in a medium with normal dispersion where a shock wave is generated. It is highly important that with 104 atoms inside the fiber the large nonlinearities in the medium refractive index can be achieved at extremely low light levels.

Temperature Dependence of Atomic Decay Rate

We investigate the decay rate of an atom in a two-dimensional optical microcavity in which there exists a Bose-Einstein condensation of photons. It is found that below the critical temperature Tc, the atomic decay rate depends on the absolute temperature T. Especially, at absolute zero temperature almost all photons are in the condensate state, and the atom can be approximately treated as if it is in vacuum.

Quantum memory with a single two-level atom in a half cavity

We propose a setup for quantum memory based on a single two-level atom in a half cavity with a moving mirror. We show that various temporal shapes of incident photon can be efficiently stored and readout by shaping the time-dependent decay rate $\gamma(t)$ between the atom and the light. This is achieved uniquely by an appropriate motion of the mirror without the need for additional control laser or atomic level. We present an analytical expression for the efficiency of the process and study its dependence on the ratio between the incident light field bandwidth and the atomic decay rate. We discuss possible implementations and experimental issues, particularly for a single atom or ion in a half cavity quantum optical setup as well as a superconducting qubit in the context of circuit QED.

Constructive and destructive quantum interference sensitive to quantum vacuum mode structure in a metallic waveguide

Quantum vacuum mode structure can be changed due to length scale fluctuation of the cross section of a metallic waveguide. Such a structure change in vacuum modes (particularly in cutoff vacuum modes) would lead to dramatic enhancement or inhibition of spontaneous emission decay of atoms and, if the waveguide is filled with a dilute atomic vapor consisting of quantum-coherent atoms of a four-level tripod-configuration system, an optical wave propagating inside the waveguide can be coherently manipulated by tunable constructive and destructive quantum interference between two control transitions (driven by two control fields) in a quite unusual way (e.g., the optical response, in which a three-level dark state is involved, is sensitive to the waveguide dimension variations at certain positions of resonance of the atomic spontaneous emission decay rate). Therefore, an intriguing effect that can be employed to designs of new photonic and quantum optical devices could be achieved based on the present mechanisms of quantum-vacuum manipulation and quantum coherence control.

Matter rogue wave in Bose-Einstein condensates with attractive atomic interaction

We investigate the matter rogue wave in Bose-Einstein condensates with attractive interatomic interaction analytically and numerically. Our results show that the formation of rogue wave is mainly due to the accumulation of energy and atoms toward to its central part; and the decay rate of atoms in unstable matter rogue wave can be effectively controlled by modulating the trapping frequency of external potential. The numerical simulation demonstrate that even a small periodic perturbation with small modulation frequency can induce the generation of a near-ideal matter rogue wave. We also give an experimental protocol to observe this phenomenon in Bose-Einstein condensates.

Initial cooperative decay rate and cooperative Lamb shift of resonant atoms in an infinite cylindrical geometry

We obtain in both the scalar and vector photon models the analytical expressions for the initial cooperative decay rate and the cooperative Lamb shift for an ensemble of resonant atoms distributed uniformly in an infinite cylindrical geometry for the case that the initial state of the system is prepared in a phased state modulated in the direction of the cylindrical axis. We find that qualitatively the scalar and vector theories give different results.

Effects of vacuum fluctuation suppression on atomic decay rates

The use of atomic decay rates as a probe of sub-vacuum phenomena will be studied. Because electromagnetic vacuum fluctuations are essential for radiative decay of excited atomic states, decay rates can serve as a measure of the suppression of vacuum fluctuations in non-classical states, such as squeezed vacua. In such states, the renormalized expectation value of the square of the electric field or the energy density can be periodically negative, representing suppression of vacuum fluctuations. We explore the extent to which atomic decays can be used to measure the mean squared electric field or energy density. We consider a scheme in which atoms in an excited state transit a closed cavity whose lowest mode contains photons in a non-classical state. A crucial feature of our analysis is that we do not employ the rotating wave approximation. The change in the decay probability of the atom in the cavity due to the non-classical state can, under certain circumstances, serve as a measure of the mean squared electric field or energy density in the cavity. We make some estimates of the magnitude of this effect, which indicate that an experimental test might be possible, although very challenging.

Spin-forbidden radiative decay rates from the3 3P1,2and3 1P1states of helium

We have calculated atomic helium spontaneous decay rates and absorption oscillator strengths for the spin-forbidden transitions from $3 {}^{3}{P}_{1,2}$ and $3 {}^{1}{P}_{1}$ to all lower ${}^{1}{S}_{0}$ and ${}^{3}{S}_{1}$ states. In particular we found ${A}_{10}=44.33(4) {\mathrm{s}}^{\ensuremath{-}1}$ for the $E$1 transition $3 {}^{3}{P}_{1}$--$1 {}^{1}{S}_{0}$ and 0.1147(1) ${\mathrm{s}}^{\ensuremath{-}1}$ for the $M$2 transition $3 {}^{3}{P}_{2}$--$1 {}^{1}{S}_{0}$.

Quantum interference due to energy shifts and its effect on spontaneous emission

We study the quantum interference in spontaneous emission with the inclusion of counterrotating terms and energy shifts. The energy shifts come from the emission and then reabsorption of virtual photons as well as the real photon emission. We show that the quantum interference resulting from the energy shifts has significant influence on the effective decay rates of the two levels, even when the transition dipole elements are the same and the energy separation of the two levels is small. We also show that the energy shift has substantial influence on the spectrum emitted by the atom. The result is valid in the long time limit. The effect of the energy shift can be observed at the time scale of 1 over the atomic decay rate. We suggest an experiment to test the effect of quantum interference because of energy shifts on the emission spectrum.

Atomic decay near a quantized medium of absorbing scatterers

The decay of an excited atom in the presence of a medium that both scatters and absorbs radiation is studied with the help of a quantum-electrodynamical model. The medium is represented by a half-space filled with a randomly distributed set of non-overlapping spheres, which consist of a linear absorptive dielectric material. The absorption effects are described by means of a quantized damped-polariton theory. It is found that the effective susceptibility of the bulk does not fully account for the medium-induced change in the atomic decay rate. In fact, surface effects contribute to the modification of the decay properties as well. The interplay of scattering and absorption in the total decay rate is discussed.