Photon Decay Research Articles

Ultrafast pump-probe spectroscopy studies of CeO2 thin film deposited on Ni-W substrate by RF magnetron sputtering

This study presents the first investigation of rapid dynamical processes that occur in pure CeO2 thin film, using ultra fast pump-probe spectroscopy at room temperature. For this purpose we have used a single (200) oriented CeO2 film deposited on biaxially textured Ni-W substrate by RF magnetron sputtering technique. The ultrafast transient spectra show initial sharp rise transition followed by an exponential photon decay. This rise time is about 10 ps irrespective of the probe wavelengths range 500–800 nm. The initial decay constant (τ) at 500 nm probe wavelength is found to be 171 ps, while at 800 nm probe wavelength it is 107.5 ps. The ultrafast absorption spectra show two absorption peaks at 745 and 800 nm, and are attributed to the electronic transitions from 2F7/2–2F5/2 and 1S0–1F3 respectively. The relatively high intensity absorption peak at 745 nm indicates dominant f–f electronic transition. Further, the absorption peak at 745 nm splits into two distinct peaks with respect to delay time, and is attributed to the charge transfer in between Ce4+ and Ce3+ ions. These results indicate that CeO2 itself is a potential candidate and can be used for optical applications.

Acceleration of Radiative Decay of Photon Counts With Increasing Numbers of Measurement Units: A Potential Large Scale Negative Zeno Effect That Matches With Lorentz Contraction and Photon Acceleration Durations

         The reverse Zeno effect whereby an unstable quantum state associated with radiative decay is accelerated by frequent measurements was demonstrated experimentally for numbers of “spontaneous” photons in a 3 m3 hyperdark chamber during the 60 s following a burst of applied photons. Numbers of photon counts were measured from one digital photomultiplier unit when either 1 (the reference) or 2, 3, or 4 units were measuring simultaneously. There was a median decrease of 50 photons per s with the addition of each additional simultaneous measurement by another unit. The energy was ~ 10-17 J per s and is equivalent to a wavelength of 10 nm. This quantity is equivalent to the energy of one neuron in the human brain displaying its upper limit (~1 kHz). The results suggest that this increment of energy may be a standard quantity that reflects the numbers of measurements by similar photoelectric currents to the decay of a single photon burst. The approximately 30 to 40 s required for the decay of photons per unit to inflect towards asymptote is consistent with the solution for the Lorentz contraction for the shift in electron mass-energy (10-17 J) with a wavelength of ~10 nm. The 30 to 40 s value is a solution for several applications to novel calculations involving fundamental parameters within the structure of space-time.

Fast generation of N-atom Greenberger–Horne–Zeilinger state in separate coupled cavities via transitionless quantum driving

By jointly using quantum Zeno dynamics and the approach of transitionless quantum driving (TQD) proposed by Berry to construct shortcuts to adiabatic passage, we propose an efficient scheme to fast generate multiatom Greenberger---Horne---Zeilinger (GHZ) state in separate cavities connected by optical fibers only by one-step manipulation. We first detail the generation of the three-atom GHZ state via TQD; then, we compare the proposed TQD scheme with the traditional ones with adiabatic passage. At last, the influence of various decoherence factors, such as spontaneous emission, cavity decay and fiber photon leakage, is discussed by numerical simulations. All of the results show that the present TQD scheme is fast and insensitive to atomic spontaneous emission and fiber photon leakage. Furthermore, the scheme can be directly generalized to realize N-atom GHZ state generation by the same principle in theory.

A VUV detection system for the direct photonic identification of the first excited isomeric state of 229Th

With an expected energy of 7.6(5) eV, $^{229}$Th possesses the lowest excited nuclear state in the landscape of all presently known nuclei. The energy corresponds to a wavelength of about 160 nm and would conceptually allow for an optical laser excitation of a nuclear transition. We report on a VUV optical detection system that was designed for the direct detection of the isomeric ground-state transition of $^{229}$Th. $^{229(m)}$Th ions originating from a $^{233}$U $\alpha$-recoil source are collected on a micro electrode that is placed in the focus of an annular parabolic mirror. The latter is used to parallelize the UV fluorescence that may emerge from the isomeric ground-state transition of $^{229}$Th. The parallelized light is then focused by a second annular parabolic mirror onto a CsI-coated position-sensitive MCP detector behind the mirror exit. To achieve a high signal-to-background ratio, a small spot size on the MCP detector needs to be achieved. Besides extensive ray-tracing simulations of the optical setup, we present a procedure for its alignment, as well as test measurements using a D$_2$ lamp, where a focal-spot size of $\approx$100 $\mu$m has been achieved. Assuming a purely photonic decay, a signal-to-background ratio of $\approx$7000:1 could be achieved.

Trilateration-based reconstruction of ortho-positronium decays into three photons with the J-PET detector

This work reports on a new reconstruction algorithm allowing us to reconstruct the decays of ortho-positronium atoms into three photons using the places and times of photons recorded in the detector. The method is based on trilateration and allows for a simultaneous reconstruction of both location and time of the decay. Results of resolution tests of the new reconstruction in the J-PET detector based on Monte Carlo simulations are presented, which yield a spatial resolution at the level of 2cm (FWHM) for X and Y and at the level of 1cm (FWHM) for Z available with the present resolution of J-PET after application of a kinematic fit. Prospects of employment of this method for studying angular correlations of photons in decays of polarized ortho-positronia for the needs of tests of CP and CPT discrete symmetries are also discussed. The new reconstruction method allows for discrimination of background from random three-photon coincidences as well as for application of a novel method for determination of the linear polarization of ortho-positronium atoms, which is also introduced in this work.

On-the-fly Estimation Strategy for Uncertainty Propagation in Two-Step Monte Carlo Calculation for Residual Radiation Analysis

In analyzing residual radiation, researchers generally use a two-step Monte Carlo (MC) simulation. The first step (MC1) simulates neutron transport, and the second step (MC2) transports the decay photons emitted from the activated materials. In this process, the stochastic uncertainty estimated by the MC2 appears only as a final result, but it is underestimated because the stochastic error generated in MC1 cannot be directly included in MC2. Hence, estimating the true stochastic uncertainty requires quantifying the propagation degree of the stochastic error in MC1. The brute force technique is a straightforward method to estimate the true uncertainty. However, it is a costly method to obtain reliable results. Another method, called the adjoint-based method, can reduce the computational time needed to evaluate the true uncertainty; however, there are limitations. To address those limitations, we propose a new strategy to estimate uncertainty propagation without any additional calculations in two-step MC simulations. To verify the proposed method, we applied it to activation benchmark problems and compared the results with those of previous methods. The results show that the proposed method increases the applicability and user-friendliness preserving accuracy in quantifying uncertainty propagation. We expect that the proposed strategy will contribute to efficient and accurate two-step MC calculations.

Modulation response of nanolasers: what rate equation approaches miss

Rate equation approaches are a standard method to describe and examine the modulation dynamics of various semiconductor lasers, including nanolasers with high spontaneous emission rates. Using the more complex Bloch equation model we investigate the impact of the internal timescales on the stability and the modulation response. We demonstrate the limitation of rate equation approaches for systems where photon decay rate and polarization decay have similar orders of magnitude.

Theoretical studies on the radiative electron capture and subsequent radiative decay in the collision of Xe53+ ions with neutral Xe

The radiative electron capture (REC) and subsequent radiative decay of initial hydrogen-like Xe52+ ions are studied in the collision of Xe53+ with Xe atom at a projectile energy of 197 MeV/u within the framework of the multiconfiguration Dirac-Fock method and the density matrix theory. We calculate the differential and total cross sections as well as the REC photon energies for REC to the 1snp1/2, 3/2 Jf=1 (n=2-5) levels of finally helium-like Xe53+ ions. Moreover, the transition energies and rates of the subsequent 1snp3/2 Jf=1 1s2 Jd = 0 decay as well as the angular distribution and linear polarization of the associated characteristic photons are also calculated. It is found that the REC photons are remarkably anisotropic. Through the analysis of the REC angular distribution characteristics, we find that the different configurations of the REC angular distribution are similar in quality, and they all have a peak at the 90. That is to say, the REC process can more easily occur in the direction perpendicular to the incident direction of the projectile ions. In addition, while the characteristic photons from the subsequent 1snp3/2 Jf=11s2 Jd= 0 radiative decay of Xe52+ ions exhibit an anisotropic angular distribution and strong linear polarization, their counterparts from the 1snp1/2 Jf = 1 1s2 Jd = 0 decay are almost isotropic and linearly unpolarized. The angular distribution and linear polarization of the radiation photon decay from the (1s np1/2,3/2 Jf = 0) states to the ground state（1s2 Jd = 0）both reach a maximum value at the 90, their characteristics are similar to those of the REC photons, that is to say, the deexcited process can more easily occur in the direction perpendicular to the incident direction of the projectile ions, and in this direction the decay photons have much larger polarization degree.

ANITA-2000 activation code package - updating of the decay data libraries and validation on the experimental data of the 14 MeV Frascati Neutron Generator

ANITA-2000 is a code package for the activation characterization of materials exposed to neutron irradiation released by ENEA to OECD-NEADB and ORNL-RSICC. The main component of the package is the activation code ANITA-4M that computes the radioactive inventory of a material exposed to neutron irradiation. The code requires the decay data library (file fl1) containing the quantities describing the decay properties of the unstable nuclides and the library (file fl2) containing the gamma ray spectra emitted by the radioactive nuclei. The fl1 and fl2 files of the ANITA-2000 code package, originally based on the evaluated nuclear data library FENDL/D-2.0, were recently updated on the basis of the JEFF-3.1.1 Radioactive Decay Data Library. This paper presents the results of the validation of the new fl1 decay data library through the comparison of the ANITA-4M calculated values with the measured electron and photon decay heats and activities of fusion material samples irradiated at the 14 MeV Frascati Neutron Generator (FNG) of the NEA-Frascati Research Centre. Twelve material samples were considered, namely: Mo, Cu, Hf, Mg, Ni, Cd, Sn, Re, Ti, W, Ag and Al. The ratios between calculated and experimental values (C/E) are shown and discussed in this paper.

Nanofriction in Cavity Quantum Electrodynamics.

The dynamics of cold trapped ions in a high-finesse resonator results from the interplay between the long-range Coulomb repulsion and the cavity-induced interactions. The latter are due to multiple scatterings of laser photons inside the cavity and become relevant when the laser pump is sufficiently strong to overcome photon decay. We study the stationary states of ions coupled with a mode of a standing-wave cavity as a function of the cavity and laser parameters, when the typical length scales of the two self-organizing processes, Coulomb crystallization and photon-mediated interactions, are incommensurate. The dynamics are frustrated and in specific limiting cases can be cast in terms of the Frenkel-Kontorova model, which reproduces features of friction in one dimension. We numerically recover the sliding and pinned phases. For strong cavity nonlinearities, they are in general separated by bistable regions where superlubric and stick-slip dynamics coexist. The cavity, moreover, acts as a thermal reservoir and can cool the chain vibrations to temperatures controlled by the cavity parameters and by the ions' phase. These features are imprinted in the radiation emitted by the cavity, which is readily measurable in state-of-the-art setups of cavity quantum electrodynamics.

Effective single photon decay mode of positronium via electroweak interactions

We consider the decay of positronium to a neutrino-antineutrino accompanied by a single photon. Since the neutrino pair go undetected, this appears as a single photon decay of positronium. These decay channel are mediated through the exchange of the massive W and Z vector bosons of the electroweak interaction. After summing over the various neutrino channels, the standard model calculation yields the rate for such a single photon decay process of = 2 × 10−12 s−1.

Stabilizing a Bell state by engineering collective photon decay

We propose a dissipation-engineering method for generation and stabilization of a Bell state for two superconducting qubits in coupled circuit quantum electrodynamics architecture. In the scheme, the large dispersive qubit---resonator interaction and resonant photon hopping between resonators jointly induce asymmetric energy gaps in the dressed state subspaces for the qubits and the collective resonator photon modes. The target steady state is reached and protected by applying each qubit with two microwave drives, that perturbatively induce the specific dressed state transition, while simultaneously by employing the decay of the collective photon modes. Numerical simulation verifies that high-fidelity and long-lived two-qubit Bell state can be obtained (based on the recently available experimental parameters) and is robust against the potential fluctuation of the system parameters.

Transferring multipartite entanglement among different cavities

The transfer of quantum entanglement (or quantum coherence) is not only fundamental in quantum mechanics but also important in quantum information processing. We here propose a way to achieve the coherent transfer of $W$-class entangled states of qubits among different cavities. Because no photon is excited in each cavity, decoherence caused by the photon decay is suppressed during the transfer. In addition, only one coupler qubit and one operational step are needed and no classical pulses are used in this proposal, thus the engineering complexity is much reduced and the operation is greatly simplified. We further give a numerical analysis, showing that high-fidelity transfer of a three-qubit $W$ state is feasible within the present circuit QED technique. The proposal can be applied to a wide range of physical implementation with various qubits such as quantum dots, nitrogen-vacancy centers, atoms, and superconducting qubits.

Structural and electrical characteristics of GaN, n-GaN and A1xGa1−xN

GaN, n-GaN (n∼̴ 1 × 1018/cm3) and AlxGa1−xN (x = 0. 14, 0.26, 0.45) were epitaxially grown by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrate. The composition and thickness of AlxGa1-xN layers were found by employing ω-2θ scan with simulation fit. The dislocation densities of epilayers were determined from symmetric and asymmetric planes of ω-scan rocking curve. The (105) plane reciprocal space mapping was employed to measure the in-plane strain (εxx) of the AlxGa1−xN layers grown on GaN. The in-plane strain of GaN and n-GaN were calculated from 2θ scan. The second derivative of the capacitance of the AFM tip-sample system was determined using electrostatic force microscopy (EFM). Photon decay time was measured using time resolved photoluminescence and the results correlated with structural property of the epilayers. The Schottky behavior of Ni/Au contacts on grown layers were studied using current–voltage (I–V) measurements. The Schottky barrier height of each device was compared with the edge dislocation density of the layers.

Quantum interference effects in laser spectroscopy of muonic hydrogen, deuterium, and helium-3

Quantum interference between energetically close states is theoretically investigated, with the state structure being observed via laser spectroscopy. In this work, we focus on hyperfine states of selected hydrogenic muonic isotopes, and on how quantum interference affects the measured Lamb shift. The process of photon excitation and subsequent photon decay is implemented within the framework of nonrelativistic second-order perturbation theory. Due to its experimental interest, calculations are performed for muonic hydrogen, deuterium, and helium-3. We restrict our analysis to the case of photon scattering by incident linear polarized photons and the polarization of the scattered photons not being observed. We conclude that while quantum interference effects can be safely neglected in muonic hydrogen and helium-3, in the case of muonic deuterium there are resonances with close proximity, where quantum interference effects can induce shifts up to a few percent of the linewidth, assuming a pointlike detector. However, by taking into account the geometry of the setup used by the CREMA collaboration, this effect is reduced to less than 0.2% of the linewidth in all possible cases, which makes it irrelevant at the present level of accuracy.

Precision natural SUSY at CEPC, FCC-ee, and ILC

Testing the idea of naturalness is and will continue to be one of the most important goals of high energy physics experiments. It will play a central role in the physics program of future colliders. In this paper, we present projections of the reach of natural SUSY at future lepton colliders: CEPC, FCC-ee and ILC. We focus on the observables which give the strongest reach, the electroweak precision observables (for left-handed stops), and Higgs to gluon and photon decay rates (for both left- and right-handed stops). There is a “blind spot” when the stop mixing parameter X t is approximately equal to the average stop mass. We argue that in natural scenarios, bounds on the heavy Higgs bosons from tree-level mixing effects that modify the $$ hb\overline{b} $$ coupling together with bounds from b → sγ play a complementary role in probing the blind spot region. For specific natural SUSY scenarios such as folded SUSY in which the top partners do not carry Standard Model color charges, electroweak precision observables could be the most sensitive probe. In all the scenarios discussed in this paper, the combined set of precision measurements will probe down to a few percent in fine-tuning.

Parton-model calculation of a nonstandard decay process in isotropic modified Maxwell theory

We have performed a calculation in the parton-model approximation of a nonstandard decay process in isotropic modified Maxwell theory coupled to standard Dirac theory, with a single Lorentz-violating parameter $\kappa$ in the photonic sector. Previous calculations of this process (vacuum Cherenkov radiation by a proton for the theory with $\kappa>0$) were performed for pointlike particles, and an upper bound on $\kappa$ at the $10^{-19}$ level was obtained from experimental data on ultra-high-energy cosmic rays. The parton-model results change the decay rate by about an order of magnitude but give the same upper bound on $\kappa$ because the threshold energy is unchanged. The previous point-particle calculation of photon decay into an electron-positron pair for the theory with $\kappa<0$ remains valid, and experimental results on cosmic gamma rays provide a lower bound on $\kappa$ at the $-10^{-15}$ level.

Lepton jets from radiating dark matter

The idea that dark matter forms part of a larger dark sector is very intriguing, given the high degree of complexity of the visible sector. In this paper, we discuss lepton jets as a promising signature of an extended dark sector. As a simple toy model, we consider an $\mathcal{O}(\text{GeV})$ DM fermion coupled to a new $U(1)'$ gauge boson (dark photon) with a mass of order GeV and kinetically mixed with the Standard Model photon. Dark matter production at the LHC in this model is typically accompanied by collinear radiation of dark photons whose decay products can form lepton jets. We analyze the dynamics of collinear dark photon emission both analytically and numerically. In particular, we derive the dark photon energy spectrum using recursive analytic expressions, using Monte Carlo simulations in Pythia, and using an inverse Mellin transform to obtain the spectrum from its moments. In the second part of the paper, we simulate the expected lepton jet signatures from radiating dark matter at the LHC, carefully taking into account the various dark photon decay modes and allowing for both prompt and displaced decays. Using these simulations, we recast two existing ATLAS lepton jet searches to significantly restrict the parameter space of extended dark sector models, and we compute the expected sensitivity of future LHC searches.

Quantitative Analysis of Pharmaceutical Bilayer Tablets Using Transmission Raman Spectroscopy

Transmission Raman Spectroscopy (TRS) has become an increasingly applied technology in the analysis of pharmaceutical tablets for quality control purposes and developing formulation and process understanding. One area that has received only cursory attention to date is that of bilayered tablets that represents an unusually challenging situation. This study aims to provide an understanding of the relationship of the active pharmaceutical ingredient (API) content and the transmission Raman spectral response in bilayered pharmaceutical tablets to facilitate development of quantitative models for the prediction of API content in multilayer tablets. The Raman intensity was considered as a function of the Raman photon generation and decay in a layer of interest (the API layer) and Raman photon decay from a second layer (the non-API layer). To separate and understand the various contributions, a variety of tablet configurations were studied and it was found that (1) with increasing the thickness of the non-API layer, the API Raman signal displayed an exponential decay as a function of the non-API layer thickness as well as the total tablet thickness; (2) when only changing API concentration, the Raman signal linearly responds to the API content; and (3) when increasing the weight/thickness of the API layer and keeping the non-API layer constant, the Raman signal reaches a maximum at a particular thickness and then decays as tablets become thicker. The complex spectral response was effectively modeled according to a modified Schrader, Kubelka-Munk model where both the Raman photon generation factor and photon losses were accounted for. Coupling the results of these studies together yields a comprehensive approach for modeling multi-component bilayer tablets. The addition of a beam enhancer on the bottom surface allowed for a selective over-enhancement of the bottom layer, which helps in the analysis of thin layers or coatings.

Ground-state excitation of heavy highly-charged ions

We have studied the excitation of H-like and He-like uranium (U91+ and U90+) in relativistic collisions with gaseous targets by observing the subsequent x-ray emission. The experiment was conducted at the ESR storage ring of the GSI accelerator facility in Darmstadt, Germany. The measurements were performed with a newly developed multi-phase target at different collision energies. This enabled us to explore the proton (nucleus) impact excitation as well as the electron impact excitation processes in the relativistic collisions. The large fine-structure splitting in uranium allowed us to unambiguously resolve excitation to different L-shell levels. Moreover, information about the population of different magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The experimental results are compared with calculations performed within the relativistic framework including excitation mechanisms due to both protons (nucleus) and electrons.