Spontaneous Emission Of Radiation Research Articles

Underground Tests of Quantum Mechanics by the VIP Collaboration at Gran Sasso

Modern physics lays its foundations on the pillars of Quantum Mechanics (QM), which has been proven successful to describe the microscopic world of atoms and particles, leading to the construction of the Standard Model. Despite the big success, the old open questions at its very heart, such as the measurement problem and the wave function collapse, are still open. Various theories consider scenarios which could encompass a departure from the predictions of the standard QM, such as extra-dimensions or deformations of the Lorentz/Poincaré symmetries. At the Italian National Gran Sasso underground Laboratory LNGS, we search for evidence of new physics proceeding from models beyond standard QM, using radiation detectors. Collapse models addressing the foundations of QM, such as the gravity-related Diósi–Penrose (DP) and Continuous Spontaneous Localization (CSL) models, predict the emission of spontaneous radiation, which allows experimental tests. Using a high-purity Germanium detector, we could exclude the natural parameterless version of the DP model and put strict bounds on the CSL one. In addition, forbidden atomic transitions could prove a possible violation of the Pauli Exclusion Principle (PEP) in open and closed systems. The VIP-2 experiment is currently in operation, aiming at detecting PEP-violating signals in Copper with electrons; the VIP-3 experiment upgrade is foreseen to become operative in the next few years. We discuss the VIP-Lead experiment on closed systems, and the strong bounds it sets on classes of non-commutative quantum gravity theories, such as the θ–Poincaré theory.

Synergistic interplay between photoisomerization and photoluminescence in a light-driven rotary molecular motor

Photoactuators and photoluminescent dyes utilize light to perform mechanical motion and undergo spontaneous radiation emission, respectively. Combining these two functionalities in a single molecule would benefit the construction of advanced molecular machines. Due to the possible detrimental interaction between the two light-dependent functional parts, the design of hybrid systems featuring both functions in parallel remains highly challenging. Here, we develop a light-driven rotary molecular motor with an efficient photoluminescent dye chemically attached to the motor, not compromising its motor function. This molecular system shows efficient rotary motion and bright photoluminescence, and these functions can be addressed by a proper choice of excitation wavelengths and solvents. The moderate interaction between the two parts generates synergistic effects, which are beneficial for lower-energy excitation and chirality transfer from the motor to the photoluminescent dye. Our results provide prospects towards photoactive multifunctional systems capable of carrying out molecular rotary motion and tracking its location in a complex environment.

Novel CSL bounds from the noise-induced radiation emission from atoms

We study spontaneous radiation emission from matter, as predicted by the Continuous Spontaneous Localization (CSL) collapse model. We show that, in an appropriate range of energies of the emitted radiation, the largest contribution comes from the atomic nuclei. Specifically, we show that in the energy range Esim 10,-,10^{5} keV the contribution to the radiation emission from the atomic nuclei grows quadratically with the atomic number of the atom, overtaking the contribution from the electrons, which grows only linearly. This theoretical prediction is then compared with the data from a dedicated experiment performed at the extremely low background environment of the Gran Sasso underground National Laboratory, where the radiation emitted form a sample of Germanium was measured.As a result, we obtain the strongest bounds on the CSL parameters for r_Cle 10^{-6} m, improving the previous ones by more than an order of magnitude.

Spontaneous quantum superradiant emission in atomic Bose-Einstein condensates subject to a synthetic vector potential

We theoretically investigate the spontaneous quantum emission of phonon pairs by superradiant processes in an atomic Bose-Einstein condensate subject to a synthetic vector potential. Within the analog gravity perspective, this effect corresponds to the spontaneous emission of radiation from the ergosurface of rotating black holes. A general input-output formalism is built and used to characterize the spectral and correlation properties of the emission. Experimentally accessible signatures of the emission are pointed out in the correlation functions of the atomic gas.

Frustules of Amphora sp. as a photonic crystal with photoluminescent CdS nanoparticles.

Diatom frustules have species-specific patterns of pores, striae, pores, and nanopores, periodically arranged on its silica surface, as sets of cavities that modify the vacuum electromagnetic density of states. Therefore, frustules may be considered photonic crystals; the interaction with light-emitting sources inside the pores may potentially result in enhancement or inhibition of their spontaneous radiative emission rate and frequencies. In this work, we studied the photoluminescence of cadmium sulfide nanoparticles (CdS-NP) deposited inside frustule cavities that conveyed evidence of cavity-NP interaction. We synthesized CdS-NP, a semiconductor compound achieving quantum dots small enough to impose confinement effects to the electronic states. CdS-NP and their clusters were physiosorbed onto the surface, striae, and predominantly inside the pores of the cleansed frustules of Amphora sp. A broad peak with a maximum intensity at 437 nm (2.84 eV) was recorded after excitation with a 375 nm light source, showing a large blue shift and signal amplification of the CdS-NP photoluminescence when these were embedded inside the pores of the silica frustule. Using the Brus equation, we estimated a NP size of 4.1 ± 0.2 nm for the CdS-NP snuggly packed inside the smaller pores of the frustule, of 10 ± 0.7 nm in average diameter, The emission Purcell enhancement factor for an emitting atom in a cavity was calculated. The obtained Q factor (c. 5) was smaller than typical Q factors for designed semiconductor cavities of similar dimensions, an expected situation if it is assumed that the pores are open-ended cavities.

Generation of an Attosecond Pulse Based on Collective Spontaneous Radiation Emission of a Layer of Three-Level Atoms Excited by a Pair of Unipolar Pulses

A method of coherent controlling the polarization of a medium has been proposed recently for the generation of extremely short pulses. The method is based on the excitation of atomic polarization oscillations and their subsequent stop using a pair of ultrashort pulses. The so-called stopped pulse of the polarization of a medium, which arises in the interval between its excitation and deexcitation, can be a source of an extremely short radiation pulse. In this work, the above-indicated possibility of generation of an isolated attosecond ultraviolet pulse in a three-level resonant medium whose parameters correspond to a hydrogen atom excited by a pair of unipolar X-ray pulses is considered theoretically. In this case, the generation mechanism is of the antenna-type, that is, it is caused by the collective spontaneous emission of pre-phased atoms in the absence of a noticeable decay of their free polarization.

Superradiant and stimulated-superradiant emission of bunched electron beams

We outline the fundamental coherent radiation emission processes from a bunched charged particles beam. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles, a pre-bunched electron beam can emit spontaneously coherent radiation proportional to the number of particles - squared, through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke's). The coherent SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated-superradiance (ST-SR) in the presence of a seed injected radiation field. In this review, these coherent radiation emission processes for both single bunch and periodically bunched beams are considered in a model of radiation mode expansion. The general model of coherent spontaneous emission is extended to the nonlinear regime, particularly for undulator (wiggler) interaction: Tapering-Enhanced Stimulated Superradiant Amplification (TESSA). Processes of SP-SR and TESSA take place in tapered wiggler seed-injected FELs. In such FELs, operating in the X-Ray regime, these processes are convoluted with other effects. However these fundamental emission concepts are useful guidelines for the strategy of wiggler tapering efficiency and power enhancement. Based on this model, we review previous theories and experiments on coherent radiation sources based on SP-SR (coherent undulator radiation, synchrotron radiation, Smith-Purcell radiation etc.), in the THz regime and on-going works on tapered wiggler efficiency-enhancement concepts in all optical frequency regimes up to X-Rays.

Capturing vacuum fluctuations and photon correlations in cavity quantum electrodynamics with multitrajectory Ehrenfest dynamics

We describe vacuum fluctuations and photon-field correlations in interacting quantum mechanical light-matter systems by generalizing the application of mixed quantum classical dynamics techniques. We employ the multitrajectory implementation of Ehrenfest mean-field theory, traditionally developed for electron-nuclear problems, to simulate the spontaneous emission of radiation in a model quantum electrodynamical cavity-bound atomic system. We investigate the performance of this approach in capturing the dynamics of spontaneous emission from the perspective of both the atomic system and the cavity photon field through a detailed comparison with exact benchmark quantum mechanical observables and correlation functions. By properly accounting for the quantum statistics of the vacuum field, while using mixed quantum classical (mean-field) trajectories to describe the evolution, we identify a surprisingly accurate and promising route towards describing quantum effects in realistic correlated light-matter systems.

Exotic molecules consisting of an antiproton and a hydrogen atom

A theoretical study is conducted on the stability of exotic antiproton-hydrogen molecular anions ($\overline{p}\mathrm{H}$), which in the separated atom limit correlate with $\overline{p}+\mathrm{H}(n=2)$ ($n$ being the principal quantum number). The $\overline{p}\mathrm{H}$ molecule in the electronic ground state is highly unstable due to pair annihilation and autodetachment ($\ensuremath{\rightarrow}\overline{p}p+e$). However, if the $\overline{p}\mathrm{H}$ molecule is electronically excited, the molecular stability can be drastically improved. Since the excited states of the $\mathrm{H}$ atom have accidental degeneracy, the asymptotic form of the Born-Oppenheimer potential curve of $\overline{p}+\mathrm{H}(n=2)$ behaves as $1/{R}^{2}$ ($R$ being the relative distance), which can play a critical role in the bonding and stability of the molecule. It is found that the $\overline{p}\mathrm{H}$ molecule in the first electronic excited state and in a high rotational state is sufficiently stable and has a lifetime dominated by spontaneous radiative emission ($\ensuremath{\rightarrow}\overline{p}+\mathrm{H}+h\ensuremath{\nu}$). The $\overline{p}\mathrm{H}$ system is dynamically similar to ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$, which had been commonly considered to be unstable due to autodetachment. However, recent measurements of ion-beam sputtering unambiguously verified the existence of long-lived ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$ molecules in high rotational states. This suggests that the $\overline{p}\mathrm{H}$ molecules may actually be created if one employs experimental means such as the chemical sputtering of hydrogen-rich targets with $\overline{p}$ beams.

Efficient Emission Enhancement of Single CdSe/CdS/PMMA Quantum Dots through Controlled Near-Field Coupling to Plasmonic Bullseye Resonators.

A strong increase of spontaneous radiative emission from colloidally synthesized CdSe/CdS/PMMA hybrid particles is achieved when manipulated into plasmonic bullseye resonators with the tip of an atomic force microscope (AFM). This type of antenna provides a broadband resonance, which may be precisely matched to the exciton ground state energy in the inorganic cores. Statistically analyzing the spectral photoluminescence (PL) of a large number of individual coupled and uncoupled CdSe/CdS/PMMA quantum dots, we find an order of magnitude of intensity enhancement due to the Purcell effect. Time-resolved PL shows a commensurate increase of the spontaneous emission rate with radiative lifetimes below 230 ps for the bright exciton transition. The combination of AFM and PL imaging allows for sub-200 nm localization of the particle position inside the plasmonic antenna. This capability unveils a different coupling behavior of dark excitonic states: even stronger PL enhancement occurs at positions with maximum spatial gradient of the nearfield, effectively adding a dipolar component to original quadrupole transitions. The broadband maximization of light-matter interaction provided by our nanoengineered compound systems enables an attractive class of future experiments in ultrafast quantum optics.

State-of-the-art lasers and light treatments for vascular lesions: from red faces to vascular malformations.

Notable milestones in the treatment of vascular lesions have been achieved over the past century. Many cutaneous vascular lesions can be successfully treated with lightbased devices. In this review, we will discuss the treatment of port-wine birthmarks, lymphatic malformations, infantile hemangiomas, rosacea, venous lakes, pyogenic granulomas, cherry angiomas, and angiofibromas using lasers, total reflection amplification of spontaneous emission of radiation, intense pulsed light, and photodynamic therapy. In addition, for several of these diagnoses, we will review medical therapies that can be combined with light-based devices to provide enhanced results.

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.

Inelastic Scattering of a Photon by a Hydrogen-Like Atom

Inelastic scattering of a photon by a bound electron of a hydrogen-like atom is considered. An expression for the cross section of this process, which can take place both without and with a change in the energy of the photon due to atomic transitions, is obtained. Within the framework of the standard technique of Feynman diagrams with a free electron propagator, general expressions for the amplitude and cross section of the process have been obtained. Arguments in favor of the validity of using this representation of the propagator in the calculation of the amplitude in the field of a nucleus are presented. As an accompanying result, an expression for the density matrix of an electron in the field of a nucleus is found in the leading approximation in the small “atomic” expansion parameter (Zα) << 1, α = e 2 / ћc. It is shown that in a real situation at temperatures Т << m e of the equilibrium radiation field this process can be neglected in comparison with spontaneous emission of radiation by a hydrogen-like atom despite the lower power of the parameter (Zα) in its amplitude. As far as is known, this quite important question, framed in such a way, has not been discussed in the literature.

Bosonic Lasing from Collective Exciton Magnetic Polarons in Diluted Magnetic Nanowires and Nanobelts

Exciton magnetic polarons (EMPs) are self-organized magnetic quasiparticles that can be formed by excitons in diluted magnetic semiconductors (DMSs). The optical response of EMPs in DMS microstructures is not yet well understood because it is affected by many competing factors, including spin-dependent exchange interactions, phonon coupling, and collective and nonlinear effects upon the dopant concentration and structural relaxation. Here, we report on lasing from collective EMP states in Co(II)-doped CdS nanowires (NWs) and nanobelts (NBs) that we interpret in terms of bosonic lasing, the spontaneous emission of radiation by a single quantum state macroscopically populated by bosonic quasiparticles. The lasing threshold coincides with the appearance of ferromagnetic domains, indicating an important role of spin ordering in the formation of coherent collective EMPs. These results pave the way to the realization of a new type of bosonic laser, different from exciton-polariton lasers, where formation of the...

STIRAP schemes for atomic Bose-Einstein condensates

In coherent control of Bose-Einstein condensates (BEC) the major limitation to successful high fidelity transfer using optical Raman transitions is spontaneous emission of radiation and the decoherence that this causes. We present a scheme based on stimulated Raman adiabatic passage (STIRAP) designed specifically for Rubidium 87. STIRAP is a method of population transfer that relies on the adiabatic theorem of quantum mechanics. Instead of transferring population between Hamiltonian ground states, one adiabatically evolves the ground states into some desired superposition. We show that one may thereby implement arbitrary rotations of spinor BECs with extremely high fidelities. Our simulations show that given a BEC with N = 104 atoms, we may do an arbitrary unitary rotation with an infidelity of about 10-7 that takes approximately 100 ns.

Facial Rejuvenation: 40th Anniversary Review.

For decades, devices and peels have been used for facial rejuvenation and the treatment of skin damage. In recent years, new laser systems have been developed, including fractionated ablative and non-ablative lasers which, while not as effective as the traditional laser resurfacing, can provide nice results with reduced side effects. While fractionated hybrid systems, picosecond lasers, and daylight photodynamic therapy have all been rolled out for clinicians to assess their efficacy, future technology, including TRASER (total reflection amplification of spontaneous emission of radiation) technology, should be just around the corner. These technologies offer new potential applications, efficacy, and recovery periods. Semin Cutan Med Surg 35(supp6):S122-S124.

Controlling spin relaxation with a cavity.

Spontaneous emission of radiation is one of the fundamental mechanisms by which an excited quantum system returns to equilibrium. For spins, however, spontaneous emission is generally negligible compared to other non-radiative relaxation processes because of the weak coupling between the magnetic dipole and the electromagnetic field. In 1946, Purcell realized that the rate of spontaneous emission can be greatly enhanced by placing the quantum system in a resonant cavity. This effect has since been used extensively to control the lifetime of atoms and semiconducting heterostructures coupled to microwave or optical cavities, and is essential for the realization of high-efficiency single-photon sources. Here we report the application of this idea to spins in solids. By coupling donor spins in silicon to a superconducting microwave cavity with a high quality factor and a small mode volume, we reach the regime in which spontaneous emission constitutes the dominant mechanism of spin relaxation. The relaxation rate is increased by three orders of magnitude as the spins are tuned to the cavity resonance, demonstrating that energy relaxation can be controlled on demand. Our results provide a general way to initialize spin systems into their ground state and therefore have applications in magnetic resonance and quantum information processing. They also demonstrate that the coupling between the magnetic dipole of a spin and the electromagnetic field can be enhanced up to the point at which quantum fluctuations have a marked effect on the spin dynamics; as such, they represent an important step towards the coherent magnetic coupling of individual spins to microwave photons.

Spontaneous emission and spectral properties of radiation by relativistic electrons in a gyro-klystron and optical-klystron undulator.

In this paper spontaneous emission of radiation by relativistic electrons in a gyro-klystron is studied. The scheme consists of two solenoid sections separated by a dispersive section. In the dispersive section the electrons are made non-resonant with the radiation. The dispersive section transforms a small change of the velocity into changes of the phases of the electrons. This leads to enhanced radiation due to klystron-type modulation as compared with a conventional gyrotron-type device driven by cyclotron maser interaction. It is shown that the klystron-modulated spectrum depends on the dispersive field strength, finite perpendicular velocity component and length of the solenoids but is independent of the axial magnetic field strength. A simple scheme to design a gyro-klystron is discussed.

Spontaneous emission of radiation by relativistic electrons in a gyro-klystron

Abstract In this paper, we study spontaneous emission of radiation by relativistic electrons in a gyro-klystron. The scheme consists of two solenoid sections separated by a dispersive section. In the dispersive section the electrons are made non resonant with the radiation. The dispersive section transforms a small change of the velocity into changes of the phases of the electrons.This leads to enhanced radiation as compared to a conventional gyrotron type device driven by cyclotron maser interaction. It is shown that the klystron modulated spectrum depends on the dispersive field strength, finite perpendicular velocity component and length of the solenoids but do not depend on the axial magnetic field strength. The analysis is further extended to include the combined effects of the undulator aided gyrotron klystron radiation.

Physical, structural and spectroscopic investigations of Sm3+ doped ZnO mixed alkali borate glass

Glass of 20ZnO-15 Li2O-15 Na2O-49.9 B2O3 doped with 0.1mol% of Sm3+ (ZLNB) was prepared by the melt quenching technique. Physical properties were studied and analysed. The XRD studies confirm the amorphous nature of sample. The FT-IR spectral investigation discloses the BO3, BO4 groups, H and OH bonds. Optical absorption and emission spectra were recorded and characterized. Judd–Ofelt theory was applied to f↔f transitions to evaluate Judd–Ofelt intensity parameters (Ωλ). The oscillator strengths and bonding parameters were determined from absorption spectra. The trend observed was Ω4>Ω6>Ω2. High value of Ω4 reveals higher rigidity and covalency around the Sm3+ ion. Low value of Ω2 implies ionic nature of ligands and site symmetry around Sm3+ ion. luminescence data and Judd–Ofelt parameters Ωλ (λ=2, 4, and 6) were used to evaluate various radiative probabilities like spontaneous radiative emission probabilities (AR), radiative lifetime (τR) and branching ratios (βR) stimulated emission cross section (σe) and CIE colour coordinates were measured, CCT temperature evaluated and the values were used to ascertain potential laser transitions at the optimum mixed alkali effect observed for the glass sample prepared. The preparedness of the material as the efficient laser active material is examined.