Spontaneous Emission Of Photons Research Articles

On the relationship between the intensity of zero-point fluctuations of an electromagnetic field (ZPFs) and the magnitude of an elementary electric charge

The consequences of the idea of stimulation of spontaneous emission of photons and scattering of particles in quantum electrodynamics by zero-point fluctuations of an electromagnetic field (ZPFs) are considered. It is shown that this idea leads to a connection between the magnitude of the elementary electric charge and the intensity of the ZPFs, leads to the idea of the stochastic nature of the electromagnetic interaction in time, and due to this, to the possibility of “classical” passage of particles through a potential barrier.

Liquid scintillation counting at the limit of detection in biogeosciences.

Liquid scintillation is widely used to quantify the activity of radioisotopes. We present an overview of the technique and its application to biogeosciences, particularly for turnover rate measurements. Microbial communities and their metabolism are notoriously difficult to analyze in low energy environments as biomass is exceedingly sparse and turnover rates low. Highly sensitive methods, such as liquid scintillation counting, are required to investigate low metabolic rates and conclusively differentiate them from the background noise of the respective analyzer. We conducted a series of experiments to explore the effects of luminescence, measurement time and temperature on scintillation measurements. Luminescence, the spontaneous emission of photons, disproportionally affects samples within the first few hours after sample preparation and can be minimized by following simple guidelines. Short measurement times will negatively affect liquid scintillation analysis or if background noise makes up a significant proportion of the detected events. Measurement temperature affected liquid scintillation analysis only when the temperature during the measurement reached approximately 30°C or higher, i.e. the liquid scintillation analyzer was placed in an environment without temperature control, but not in cases where chemicals were stored at elevated temperatures prior to measurement. Basic understanding on the functionality of a liquid scintillation analyzer and simple precautions prior to the measurement can significantly lower the minimum detection limit and therefore allow for determination of low turnover rates previously lost in the background noise.

On the statistical background of quantum mechanics: generalities and a concrete example

We revisit our description of randomness in quantum processes that began in collaboration of Jean Ginibre. The calculations were performed on a worked example: the fluorescence of a single two-level atom pumped by a resonant laser field. This pump laser is described classically (by a function, not an operator). Our aim is first to built a Kolmogorov-type equation (K-equation) for the atomic state, so that the two parameters θ, φ that define this density matrix are random functions of time, therefore the atomic density matrix is a random density matrix. Such an approach, initiated for gas kinetics, was not yet applied to quantum phenomena, whereas it is especially tailored to very quick events well separated (in time) like the quantum jumps observed in spontaneous emission of photons by an atom. Here, we try to clarify the basis of our statistical approach leading to the K-equation below, and we present the main results deduced from it. We explain finally that our approach can be interpreted in terms of Everett’s theory of many-worlds, because at every emission a new history begins for the atom, with two nonoverlapping wave functions.

Superradiant Droplet Emission from Parametrically Excited Cavities.

Superradiance occurs when a collection of atoms exhibits a cooperative, spontaneous emission of photons at a rate that exceeds that of its component parts. Here, we reveal a similar phenomenon in a hydrodynamic system consisting of a pair of vibrationally excited cavities, coupled through their common wave field, that spontaneously emit droplets via interfacial fracture. We show that the droplet emission rate of two coupled cavities is higher than the emission rate of two isolated cavities. Moreover, the amplified emission rate varies sinusoidally with distance between the cavities, as is characteristic of superradiance. We thus present a hydrodynamic phenomenon that captures several essential features of superradiance in optical systems.

Dynamical effects from anomalies: Modified electrodynamics in Weyl semimetals

We discuss the modified quantum electrodynamics from a time-reversal-breaking Weyl semimetal coupled with a $U(1)$ gauge (electromagnetic) field. A key role is played by the soft dispersion of the photons in a particular direction, say $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{z}$, due to the Hall conductivity of the Weyl semimetal. Due to the soft photon, the fermion velocity in $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{z}$ is logarithmically reduced under renormalization group flow, together with the fine-structure constant. Meanwhile, fermions acquire a finite lifetime from spontaneous emission of the soft photon, namely, the Cherenkov radiation. At low-energy $E$, the inverse of the fermion lifetime scales as ${\ensuremath{\tau}}^{\ensuremath{-}1}\ensuremath{\sim}E/\mathrm{PolyLog}(E)$. Therefore, even though fermion quasiparticles are eventually well-defined at very low energy, over a wide intermediate energy window the Weyl semimetal behaves like a marginal Fermi liquid. Phenomenologically, our results are more relevant for emergent Weyl semimetals, where the fermions and photons all emerge from strongly correlated lattice systems. Possible experimental implications are discussed.

Symmetries in cavity models: Beyond the rotating wave approximation

The interaction of confined atoms with a single mode radiation field is the main subject in the theory of cavity quantum electrodynamics. The constraints imposed by the cavity on matter and radiation fields give rise to collective phenomena. One possible outcome is the enhanced and coherent spontaneous emission of photons by the atoms: the superradiance. As predicted by Dicke, conservation laws are essential in superradiance and are derived from the matter-interaction Hamiltonian. Here, we consider N two-level ultracold atoms interacting with a single mode bosonic field, in the Dicke Hamiltonian, and trapped inside a non-dissipative optical cavity. Numerical and analytical results derived from finite size regime indicate the matter–radiation coupling strength, λ, is insufficient to draw the complete picture of the system. Instead, they support the relevance of U(1) symmetry, which prompts the study of (i) particle and angular momentum conservation, (ii) the constraints imposed to correlation functions and (iii) the influence of symmetries in the system dynamics. Further exploring the U(1) and rotational symmetries permits a simple interpretation of antirotating contributions as spin–orbit operators. As application, we show two species of ultracold clouds develop interactions due to antirotating operators.

Technological implementation of a photonic Bier-Glas cavity

In this paper, we introduce a novel quantum photonic device, which we term photonic Bier-Glass cavity. We discuss its fabrication and functionality, which is based on the coupling of integrated In(Ga)As quantum dots to a broadband photonic cavity resonance. By design, the device architecture uniquely combines the Purcell enhancement of a photonic micropillar structure with broadband photonic mode shaping of a vertical, tapered waveguide, making it an interesting candidate to enable the efficient extraction of entangled photon pairs. We detail the epitaxial growth of the heterostructure and the necessary lithography steps to approach a GaAs-based photonic device with a height exceeding 15 $\mu$m, supported on a pedestal that can be as thin as 20 nm. We present an optical characterization, which confirms the presence of broadband optical resonances, in conjunction with amplified spontaneous emission of single photons.

Multimode semiconductor laser gyroscope and factors determining its operation

We report the results of a study of a multimode semiconductor laser gyroscope (MSLG) with a long fibre-optic ring cavity (RC) and alternating frequency dithering formed by a lithium niobate phase modulator, and discuss the factors that determine the device operation. The fundamental limitations in MSLG operation are phase fluctuations and the multimode nature of radiation. Phase fluctuations caused by spontaneous emission of photons in a semiconductor optical amplifier (SOA) result in a slow drop in the beat amplitude. However, its complete decay does not occur due to the periodic and short-term lock-in phenomenon, which leads to the equalisation of the fluctuation levels in pairs of counterpropagating waves (PCPWs) that form the RC modes, and, thereby, to the restoration of the beat amplitude. The limitations associated with the multimode lasing regime are overcome due to the fact that the emission spectrum consists of a small number of narrow lines, and the positions of the antinodes and nodes of standing waves in the SOA field distribution coincide or are close. Both factors lead to the mode locking in spectral lines and, as a consequence, to synchronisation of PCPW beats at the device output. The mechanism of the formation of these factors is not yet clear.

Achieving Atom Localization in Noise Spectrum from a Loop Three Level Atom

A scheme for achieving atom localization in the noise spectrum in phase quadrature of resonance fluorescence from a three-level A atom is suggested. We add a microwave field to the lower energy states in the three-level A atom localization scheme, and form a three-level loop atom system. When spontaneous emission photons are detected, by changing the relative phase between the three nonresonant fields, the atom is located in one of two half wavelengths, so the probability of atomic localization is 50%. We also see that the intensity and the detuning of the microwave field affect intensively localization probability. Compared with the scheme based on electromagnetically induced transparency, the detection probability of atoms in the sub wavelength range is only 25%, and the resonance condition is useless.

Theoretical balance model of the ytterbium-doped fiber amplifier

Based on conservation laws, kinetic equations for changes in ion populations in different energy states are written down, as well as equations how optical radiation intensity (and power) is changing in the optical fiber core is sequentially derived. Physical limitations of the given approach are also considered. A comparison of the results of a numerical analysis of the formation of luminescence in the ytterbium-doped optical fiber (with different representations of the probability of “survival” of spontaneous emission photons) with experimental data is presented.

Parametric oscillation of electromagnetic waves in momentum band gaps of a spatiotemporal crystal

Photonic crystals have revolutionized the field of optics with their unique dispersion and energy band gap engineering capabilities, such as the demonstration of extreme group and phase velocities, topologically protected photonic edge states, and control of spontaneous emission of photons. Time-variant media have also shown distinct functionalities, including nonreciprocal propagation, frequency conversion, and amplification of light. However, spatiotemporal modulation has mostly been studied as a simple harmonic wave function. Here, we analyze time-variant and spatially discrete photonic crystal structures, referred to as spatiotemporal crystals. The design of spatiotemporal crystals allows engineering of the momentum band gap within which parametric amplification can occur. As a potential platform for the construction of a parametric oscillator, a finite-sized spatiotemporal crystal is proposed and analyzed. Parametric oscillation is initiated by the energy and momentum conversion of an incident wave and the subsequent amplification by parametric gain within the momentum band gap. The oscillation process dominates over frequency mixing interactions above a transition threshold determined by the balance between gain and loss. Furthermore, the asymmetric formation of momentum band gaps can be realized by spatial phase control of the temporal modulation, which leads to directional radiation of oscillations at distinct frequencies. The proposed structure would enable simultaneous engineering of energy and momentum band gaps and provide a guideline for implementation of advanced dispersion-engineered parametric oscillators.

Лучистый тепловой поток от возбужденных атомов в высокочастотном ионном двигателе

The radiant heat flux coming from the discharge plasma on the surfaces of radio frequency ion thrusters is considered. Spontaneous emission of photons is formed when the excitation of plasma atoms and ions is removed. The distributions of the densities of the heat flux brought by radiation to the surface in the thrusters are calculated. The distributions can be used in numerical calculations of temperatures in thrusters design.

Photon generation via the dynamical Casimir effect in an optomechanical cavity as a closed quantum system

We present an analytical and numerical analysis of the particle creation in an optomechanical cavity in parametric resonance. We treat both the electromagnetic field and the mirror as quantum degrees of freedom and study the dynamical evolution as a closed quantum system. We consider different initial states and investigate the spontaneous emission of photons from phonons in the mirror. We find that for initial phononic product states the evolution of the photon number can be described as a non-harmonic quantum oscillator, providing an useful tool so as to estimate the maximum and mean number of photons produced for arbitrary high energies. The efficiency of this mechanism is further analyzed for a detuned cavity as well as the possibility of stimulating the photon production by adding some initial ones to the cavity. We also find relationships for the maximum and mean entanglement between the mirror and the wall in these states. Additionally we study coherent states for the motion of the mirror to connect this model with previous results from quantum field theory with a classical mirror. Finally we study thermal states of phonons in the wall and the equilibration process that leads to a stationary distribution.

Pulsed electron spin resonance spectroscopy in the Purcell regime

In EPR, spin relaxation is typically governed by interactions with the lattice or other spins. However, it has recently been shown that given a sufficiently strong spin-resonator coupling and high resonator quality factor, the spontaneous emission of microwave photons from the spins into the resonator can become the main relaxation mechanism, as predicted by Purcell. With increasing attention on the use of microresonators for EPR to achieve high spin-number sensitivity it is important to understand how this novel regime influences measured EPR signals, for example the amplitude and temporal shape of the spin-echo. We study this regime theoretically and experimentally, using donor spins in silicon, under different conditions of spin-linewidth and coupling homogeneity. When the spin-resonator coupling is distributed inhomogeneously, we find that the effective spin-echo relaxation time measured in a saturation recovery sequence strongly depends on the parameters for the detection echo. When the spin linewidth is larger than the resonator bandwidth, the different Fourier components of the spin echo relax with different characteristic times – due to the role of the resonator in driving relaxation – which results in the temporal shape of the echo becoming dependent on the repetition time of the experiment.

Retaining hypothetical photon mass in atomic spectroscopy models

We revisit the formalism involved in atomic spectroscopy modeling under the assumption that the photon has a finite mass. Starting from the Proca Lagrangian, we build a Hamiltonian suitable for the calculation of line shapes and intensities. Two consequences of finite photon mass are: (i) a dispersion of electromagnetic waves propagating in free space; (ii) the occurrence of a longitudinal polarization state. We illustrate these effects by addressing the spontaneous emission of a massive photon by an excited atom. The Einstein A coefficient and the power spectrum are calculated as an example. If the photon has a finite mass, deviations to standard formulas are showed to occur at energies comparable to the mass energy. A discussion based on the current upper bound estimates for the photon mass is done.

Detection of special nuclear material with a transportable active interrogation system

Special nuclear materials hidden in shipping containers are extremely difficult to detect through their faint spontaneous emission of neutrons and photons. R&D efforts focus on active interrogation (AI) techniques, employing external beams of neutrons or high-energy X-rays to first trigger fission reactions and then detect prompt or delayed neutrons and/or photons. Our group created a complete active interrogation system based on detectors developed by the universities of Pisa and Yale and on an ultra-compact linear accelerator (LINAC). The detectors contain liquid droplets that vaporize when exposed to fast neutrons but are insensitive to X-rays. The X-ray generator is based on 9MeV electron LINAC developed by S.I.T. Sordina S.p.A. for intraoperative radiotherapy. The latter is a standing-wave design that does not require external solenoids for electron radial focusing. Copper is used both as X-ray production target and as collimator, which prevents the production of photo-neutrons. In our first tests, we detected depleted uranium, while excluding significant production of contaminant photo-neutrons.

Ghost Spectroscopy with Classical Correlated Amplified Spontaneous Emission Photons Emitted by An Erbium-Doped Fiber Amplifier

We demonstrate wavelength-wavelength correlations of classical broad-band amplified spontaneous emission (ASE) photons emitted by an erbium-doped fiber amplifier (EDFA) in a wavelength regime around 1530 nm. We then apply these classical correlated photons in the framework of a real-world ghost spectroscopy experiment at a wavelength of 1533 nm to acetylene ( C 2 H 2 ) reproducing the characteristic absorption features of the C-H stretch and rotational bands. This proof-of-principle experiment confirms the generalization of an ASE source concept offering an attractive light source for classical ghost spectroscopy. It is expected that this will enable further disseminating ghost modality schemes by exploiting classical correlated photons towards applications in chemistry, physics and engineering.

Coherent gamma photon generation in a Bose–Einstein condensate of [formula omitted]Cs

We have identified a mechanism of collective nuclear de-excitation in a Bose–Einstein condensate of 135Cs atoms in their isomeric state, 135mCs, suitable for the generation of coherent gamma photons. The process described here relies on coherence transfer from the Bose–Einstein condensate to the photon field, leading to collective decay triggered by spontaneous emission of a gamma photon. The mechanism differs from single-pass amplification, which cannot occur in atomic systems due to the nuclear recoil and the associated large shift between absorption and emission lines, nor does it require the large densities necessary for standard Dicke super-radiance. This overcomes the limitations that have been hindering the production of coherent gamma photons in many systems. Therefore, we propose an approach for generation of coherent gamma rays, which relies on a combination of well established techniques of nuclear and atomic physics, and can be realized with currently available technology.

Analogue Hawking radiation in an exactly solvable model of BEC

Hawking radiation, the spontaneous emission of thermal photons from an event horizon, is one of the most intriguing and elusive predictions of field theory in curved spacetimes. A formally analogue phenomenon occurs at the supersonic transition of a fluid: in this respect, ultracold gases stand out among the most promising systems but the theoretical modelling of this effect has always been carried out in semiclassical approximation, borrowing part of the analysis from the gravitational analogy. Here we discuss the exact solution of a one-dimensional Bose gas flowing against an obstacle, showing that spontaneous phonon emission (the analogue of Hawking radiation) is predicted without reference to the gravitational analogy. Long after the creation of the obstacle, the fluid settles into a stationary state displaying the emission of sound waves (phonons) in the upstream direction. A careful analysis shows that a precise correspondence between this phenomenon and the spontaneous emission of radiation from an event horizon requires additional conditions to be met in future experiments aimed at identifying the occurrence of the Hawking-like mechanism in Bose-Einstein condensates.

Quantum feedback cooling of two trapped ions**Project supported by the National Natural Science Foundation of China (Grant Nos. 11504430, 61205108, and 11304387) and the National Key R&D Program of China (Grant No. 2016YFA0301903).

We present a sub-Doppler cooling scheme of a two-trapped-ion crystal by quantum feedback control method. In the scheme, we obtain the motional information by continuously measuring the spontaneous emission photons from one single ion of the crystal, and then apply a feedback force to cool the whole chain down.We derive the cooling dynamics of the cooling scheme using quantum feedback theory and quantum regression theorem. The result shows that with experimentally achievable parameters, our scheme can achieve lower temperature and faster cooling rate than Doppler cooling.