Spontaneous Decay Research Articles

Spectroscopy on the electron-electric-dipole-moment–sensitive states of ThF+

An excellent candidate molecule for the measurement of the electron's electric dipole moment (eEDM) is thorium monofluoride (ThF$^+$) because the eEDM-sensitive state, $^3\Delta_1$, is the electronic ground state, and thus is immune to decoherence from spontaneous decay. We perform spectroscopy on $X\,^3\Delta_1$ to extract three spectroscopic constants crucial to the eEDM experiment: the hyperfine coupling constant, the molecular frame electric dipole moment, and the magnetic $g$-factor. To understand the impact of thermal blackbody radiation on the vibrational ground state, we study the lifetime of the first excited vibrational manifold of $X\,^3\Delta_1$. We perform ab initio calculations, compare them to our results, and discuss prospects for using ThF$^+$ in a new eEDM experiment at JILA.

Volatile and Nonvolatile Memristive Devices for Neuromorphic Computing

AbstractIon migration as well as electron transfer and coupling in resistive switching materials endow memristors with a physically tunable conductance to resemble synapses, neurons, and their networks. Four different types of volatile memristors and another four types of nonvolatile memristors are systemically surveyed in terms of the switching mechanisms and electrical properties that are the basis of different computing applications. The volatile memristor features spontaneous conductance decay after the cease of electrical/optical stimulations, which are closely related to the surface atom diffusion, metal–insulator–transition (including charge–density–wave), thermal spontaneous emission, and charge polarization. Such unique dynamic state evolution at the edge of chaos has enabled them to emulate certain synaptic and neural dynamics, leading to various applications ranging from spiking neural networks to combinatorial optimizations. Nonvolatile resistive switching behavior originated from the electron spins, ferroelectric polarization, crystalline‐amorphous transitions or interplay between ions and electrons enables the memristor array to implement the vector–matrix multiplication, which is the key convolutional operation in artificial neural networks. The progress, challenges, and opportunities for both volatile and nonvolatile memristor in the level of materials, integration technology, algorithm, and system are highlighted in this review.

Trigger linkage mechanism: Two or multiple steps initiate the spontaneous decay of energetic materials

The trigger linkage mechanism is usually employed to describe the spontaneous decay of energetic materials (EMs) when they are sufficiently stimulated. Based on this mechanism, large numbers of correlations between sensitivity and the strength of the weakest bond have been established. As an important aspect of the trigger linkage mechanism, it is necessary to clarify whether the trigger linkage mechanism proceeds along the one-step-reaction mechanism (OSRM) or the two-or-multiple-step-reaction mechanism (TMSRM). Based on a series of molecular dynamics simulations of the thermal decay of gaseous and solid EMs, this study confirms that the cleavage of the weakest bond alone is insufficient to initiate the spontaneous decay of EMs even though it usually takes place as the first step. The spontaneous decomposition occurs always later than the first cleavage of the trigger linkage and requires additional energy besides the bond dissociation energy, indicating that the trigger linkage mechanism proceeds along the TMSRM rather than the OSRM. This partly accounts for the roughness of many OSRM-based theories and methods for assessing the chemical stability of EMs, which are expected to be much improved since not only the first cleavage of the weakest bond but also a further step should be sufficiently considered as a true rate-determining step with increasingly strengthened computation capacity.

Production of massive bosons from the decay of a massless particle beam

Taking a two interacting scalar toy model with interaction term $g\ensuremath{\phi}{\ensuremath{\chi}}^{2}$, we study the production of $\ensuremath{\chi}$ particles coming from the decay of an asymptotic and highly occupied beam of $\ensuremath{\phi}$ particles. We perform a nonperturbative analysis coming from parametric resonant instabilities and investigate the possibility that massive $\ensuremath{\chi}$ particles are produced from decays of massless $\ensuremath{\phi}$ particles from the beam. Although this process is not present in a perturbative analysis, our nonperturbative approach allows it to happen under certain conditions. For a momentum $p$ of the beam particles and a mass ${m}_{\ensuremath{\chi}}$ of the produced ones, we find that the decay is allowed if the energy density of the beam exceeds the instability threshold ${p}^{2}{m}_{\ensuremath{\chi}}^{4}/(2{g}^{2})$. We also provide an analytical expression for the spontaneous decay rate at the earliest time.

Coherent and incoherent laser pump on a five-level atom in a strongly coupled cavity-QED system

We propose a cavity quantum electrodynamic system consisting of a five-level atom coupled to a single mode of the cavity electromagnetic field. The study is focused on the regime of strong coupling between the cavity and atom. Pump laser fields and cavity fields connect the split energy levels of the atom. Instead of the well-known two-level Dicke model obtained by adiabatic elimination of the high-energy levels, we consider the pump lasers' detunings to the atomic transitions to be very small such that we can examine the influence of the higher-energy states. We have studied the effect of an external coherent drive and incoherent pumping on these higher-energy levels and observed the enhancement of intracavity photon numbers due to quantum coherence effects. The amplification of intracavity photons is achieved even without a population inversion. However, the effect of the coherent and incoherent drive is negligible for very large detunings when the higher-energy states are adiabatically eliminated. At zero and small detunings, the system reaches the steady state at an earlier instant of time for higher incoherent pumping. We find an almost agreeable steady-state behavior of the system's exact full quantum dynamics model and its semiclassical approximation. Our model tries to accurately simulate the open system by considering the cavity decay, spontaneous decay, and dephasing of the system.

A Rydberg hydrogen beam for studies of stimulated deexcitation

We present a Rydberg hydrogen beamline developed to commission techniques of stimulated deexcitation for application in antihydrogen experiments at CERN’s Antiproton Decelerator. The stimulation of spontaneous decay is a key technology to enhance the number of ground-state anti-atoms available in a beam toward precision spectroscopy and gravity measurements.

Zeeman-Sisyphus Deceleration of Molecular Beams

We present a robust, continuous molecular decelerator that employs high magnetic fields and few optical pumping steps. CaOH molecules are slowed, accumulating at low velocities in a range sufficient for loading both magnetic and magneto-optical traps. During the slowing, the molecules scatter only seven photons, removing around 8K of energy. Because large energies can be removed with only a few spontaneous radiative decays, this method can in principle be applied to nearly any paramagnetic atomic or molecular species, opening a general path to trapping of complex molecules.

In-Memory Realization of Eligibility Traces Based on Conductance Drift of Phase Change Memory for Energy-Efficient Reinforcement Learning.

Reinforcement learning (RL) has shown outstanding performance in handling complex tasks in recent years. Eligibility trace (ET), a fundamental and important mechanism in reinforcement learning, records critical states with attenuation and guides the update of policy, which plays a crucial role in accelerating the convergence of RL training. However, ET implementation on conventional digital computing hardware is energy hungry and restricted by the memory wall due to massive calculation of exponential decay functions. Here, in-memory realization of ET for energy-efficient reinforcement learning with outstanding performance in discrete- and continuous-state RL tasks is demonstrated. For the first time, the inherent conductance drift of phase change memory is exploited as physical decay function to realize in-memory eligibility trace, demonstrating excellent performance during RL training in various tasks. The spontaneous in-memory decay computing and storage of policy in the same phase change memory give rise to significantly enhanced energy efficiency compared with traditional graphics processing unit platforms. This work therefore provides a holistic energy and hardware efficient method for both training and inference of reinforcement learning.

Short-Chain Fatty Acids Promote Immunotherapy by Modulating Immune Regulatory Property in B Cells.

The dysfunction of regulatory B cells (Breg) may result in immune inflammation such as allergic rhinitis (AR); the underlying mechanism is not fully understood yet. Short-chain fatty acids, such as propionic acid (PA), have immune regulatory functions. This study is aimed at testing a hypothesis that modulates PA production alleviating airway allergy through maintaining Breg functions. B cells were isolated from the blood obtained from AR patients and healthy control (HC) subjects. The stabilization of IL-10 mRNA in B cells was tested with RT-qPCR. An AR mouse model was developed to test the role of PA in stabilizing the IL-10 expression in B cells. We found that the serum PA levels were negatively correlated with the serum Th2 cytokine levels in AR patients. Serum PA levels were positively associated with peripheral CD5+ B cell frequency in AR patients; the CD5+ B cells were also IL-10+. The spontaneous IL-10 mRNA decay was observed in B cells, which was prevented by the presence of PA through activating GPR43. PA counteracted the effects of Tristetraprolin (TTP) on inducing IL-10 mRNA decay in B cells through the AKT/T-bet/granzyme B pathway. Administration of Yupinfeng San, a Chinese traditional medical formula, or indole-3-PA, induced PA production by intestinal bacteria to stabilize the IL-10 expression in B cells, which promoted the allergen specific immunotherapy, and efficiently alleviated experimental AR. In summary, the data show that CD5+ B cells produce IL-10. The serum lower PA levels are associated with the lower frequency of CD5+ B cells in AR patients. Administration with Yupinfeng San or indole-3-PA can improve Breg functions and alleviate experimental AR.

Anapole due to a tangentially polarized dipole near a subwavelength sphere: Inhibition and enhancement of spontaneous emission

There exist oscillating current distributions that cannot generate radiation; these configurations are known as anapoles. Our goal is to theoretically demonstrate that an oscillating electric dipole, located in the vicinity of a subwavelength sphere and polarized tangentially, can yield an anapole. This paper complements our recent study [J. R. Zurita-S\'anchez, Phys. Rev. Research 1, 033064 (2019)], devoted to an anapole arising from an electric dipole with radial polarization. Our methodology relies on the multipolar expansion of the excitation and scattered electromagnetic fields with respect to the center of the spherical particle. We found that an anapole arises when the effective electric and magnetic dipoles, induced by the dipolar source, vanish. The aforementioned anapole condition considers that the lowest multipolar order contribution is responsible for the radiative response of the emitter. However, high-order multipoles yield an unavoidable residual radiated power which is much smaller still than the radiated power of the dipole in the absence of the scatterer. Particularly, for a nonabsorbing sphere, the geometrical and dielectromagnetic parameters that lead to an anapole state are determined. As a practical scenario, we exploit the anapole excitation for controlling the spontaneous emission decay rate of an excited atom (or a molecule). In comparison to the decay rate of an excited atom without the scatterer, the radiative decay in the presence of the particle can be inhibited by a factor of about three orders of magnitude; this factor is quite large for an open system like ours. Furthermore, we show that by varying the orientation of the atomic transition dipole moment from a tangential direction, where the anapole condition is satisfied, to a radial direction, the atom can change from a state in which the spontaneous emission rate is inhibited to one in which this rate is enhanced. Hence, the anapole setup enables the versatile control of the radiative properties of an atom, and it provides the possibility for implementing applications related to the sensing and localization of atoms.

Quantum algorithms for open lattice field theory

Certain aspects of some unitary quantum systems are well-described by evolution via a non-Hermitian effective Hamiltonian, as in the Wigner-Weisskopf theory for spontaneous decay. Conversely, any non-Hermitian Hamiltonian evolution can be accommodated in a corresponding unitary system + environment model via a generalization of Wigner-Weisskopf theory. This demonstrates the physical relevance of novel features such as exceptional points in quantum dynamics, and opens up avenues for studying many body systems in the complex plane of coupling constants. In the case of lattice field theory, sparsity lends these channels the promise of efficient simulation on standardized quantum hardware. We thus consider quantum operations that correspond to Suzuki-Lee-Trotter approximation of lattice field theories undergoing non-Hermitian time evolution, with potential applicability to studies of spin or gauge models at finite chemical potential, with topological terms, to quantum phase transitions - a range of models with sign problems. We develop non-Hermitian quantum circuits and explore their promise on a benchmark, the quantum one-dimensional Ising model with complex longitudinal magnetic field, showing that observables can probe the Lee-Yang edge singularity. The development of attractors past critical points in the space of complex couplings indicates a potential for study on near-term noisy hardware.

Semi-empirical determination of radiative parameters for metastable Sc II levels

We present a semi-empirical parametrization method for calculation of spontaneous radiative decay rates of forbidden transitions on an example of analysis of experimental data for Sc II. The values of transition probabilities and radiative lifetimes of metastable levels are in perfect agreement with experimental ones. The obtained results are compared with other calculated data available. The predicted values of radiative parameters for all Sc II metastable levels are presented.

Spontaneous decay of artificial atoms in a three-qubit system

We study the evolution of qubits amplitudes in a one-dimensional chain consisting of three equidistantly spaced noninteracting qubits embedded in an open waveguide. The study is performed in the frame of single-excitation subspace, where the only qubit in the chain is initially excited. We show that the dynamics of qubits amplitudes crucially depend on the value of $kd$, where $k$ is the wave vector, $d$ is a distance between neighbor qubits. If $kd$ is equal to an integer multiple of $\pi$, then the qubits are excited to a stationary level. In this case, it is the dark states which prevent qubits from decaying to zero even though they do not contribute to the output spectrum of photon emission. For other values of $kd$ the excitations of qubits exhibit the damping oscillations which represent the vacuum Rabi oscillations in a three-qubit system. In this case, the output spectrum of photon radiation is determined by a subradiant state which has the lowest decay rate. We also investigated the case with the frequency of a central qubit being different from that of the edge qubits. In this case, the qibits decay rates can be controlled by the frequency detuning between the central and the edge qubits.

IR-photon quenching of delayed electron detachment from hot pentacene anions

The authors report a detailed study of the spontaneous decay and the laser-induced delayed detachment associated with radiative cooling processes of hot anions of pentacene, a prototypical member of the polycyclic aromatic hydrocarbon (PAH) family of molecules. As an important constituent of interstellar clouds, this molecule is of particular interest to the fields of astrophysics and astrochemistry.

Spontaneous decay-induced quantum dynamics in Rydberg-blockaded Λ-type atoms

Strongly Rydberg-blockaded two-level atoms form a Rydberg superatom which is excited only to a collective symmetrical Dicke state. However, emerging often in the alkali-earth atoms, spontaneous decay from the Rydberg state to an additional pooling state renders the ensemble no longer a closed superatom. Herein we present a computationally efficient model to characterize the interaction between a fully Rydberg-blockaded ensemble of N Λ-type three-level atoms and a strong probe light field in a coherent state. The model enables us to achieve a decomposition of the coupled dynamics in the strong field limit, which significantly reduces the complexity of computing the N-body system evolution and paves the way for practical analysis in experiments. A quasi-steady-state power spectrum with multiple sidebands is found in the scattered field. The relative heights of the sidebands show a time-dependence determined by the atomic relaxation, which illuminates potential applications of using the system in information transfer of quantum networks. With negligible dissipative flipping to the unsymmetrical states, the atomic relaxation time, indicating a linearly increasing pooling state fraction, is derived analytically as a function of the number of atoms.

Shaping the Microstructure of High-Aluminum Cast Iron in Terms of the Phenomenon of Spontaneous Decomposition Generated by the Presence of Aluminum Carbide.

A suitable aluminum additive in cast iron makes it resistant to heat in a variety of environments and increases the abrasion resistance of the cast iron. It should be noted that high-aluminum cast iron has the potential to become an important eco-material. The basic elements from which it is made—iron, aluminum and a small amount of carbon—are inexpensive components. This material can be made from contaminated aluminum scrap, which is increasingly found in metallurgical scrap. The idea is to produce iron castings with the highest possible proportion of aluminum. Such castings are heat-resistant and have good abrasive properties. The only problem to be solved is to prevent the activation of the phenomenon of spontaneous decomposition. This phenomenon is related to the Al4C3 hygroscopic aluminum carbide present in the structure of cast iron. Previous attempts to determine the causes of spontaneous disintegration by various researchers do not describe them comprehensively. In this article, the mechanism of the spontaneous disintegration of high-aluminum cast iron castings is defined. The main factor is the large relative geometric dimensions of Al4C3 carbide. In addition, methods for counteracting the phenomenon of spontaneous decay are developed, which is the main goal of the research. It is found that a reduction in the size of the Al4C3 carbide or its removal lead to the disappearance of the self-disintegration effect of high-aluminum cast iron. For this purpose, an increased cooling rate of the casting is used, as well as the addition of elements (Ti, B and Bi) to cast iron, supported in some cases by heat treatment. The tests are conducted on the cast iron with the addition of 34–36% mass aluminum. The molten metal is superheated to 1540 °C and then the cast iron samples are cast at 1420 °C. A molding sand with bentonite is used to produce casting molds.

Constraining the axion\u2013photon coupling using radio data of the Bullet cluster

Axion is one of the most popular candidates of the cosmological dark matter. Recent studies considering the misalignment production of axions suggest some benchmark axion mass ranges near m_a sim 20 μeV. For such axion mass, the spontaneous decay of axions can give photons in radio band frequency nu sim 1{-}3 GHz, which can be detected by radio telescopes. In this article, we show that using radio data of galaxy clusters would be excellent to constrain axion dark matter. Specifically, by using radio data of the Bullet cluster (1E 0657-55.8), we find that the upper limit of the axion–photon coupling constant can be constrained to g_{a gamma gamma } sim 10^{-12}{-}10^{-11} GeV^{-1} for m_a sim 20 μeV, which is tighter than the limit obtained by the CERN Axion Solar Telescope (CAST).

Semiclassical control theory of coherent anti-Stokes Raman scattering maximizing vibrational coherence for remote detection

A semiclassical theory that describes the generation of a coherent anti-Stokes Raman scattering (CARS) signal is presented that maximizes vibrational coherence in a mode predetermined by the pump, the Stokes, and the probe chirped pulse trains and takes into account the field propagation effects in a cloud of molecules. The buildup of the anti-Stokes signal, which may be used as a molecular signature in the backward CARS signal, is demonstrated numerically. The theory is based on the solution of the coupled Maxwell's and Liouville--von Neumann equations and focuses on the quantum effects induced in the target molecules by the control pulse trains. A deep convolutional neural network technique is implemented to evaluate time-dependent phase characteristics of the control fields. The effect of decoherence induced by spontaneous decay and collisional dephasing is examined.

Quantification of Surface Reactive Oxygen Species at Co-Modified BiVO4 with Surface Interrogation Mode of Scanning Electrochemical Microscopy

Our recent study suggests that cobalt modification can greatly improve the photoelectrochemical (PEC) water oxidation activities of n-BiVO4 (ACS Appl. Energy Mater., 1(5), 2283 (2018)). This enhancement is attributed to (1) the formation of a top layer of Co3O4 at BiVO4 surface as a cocatalyst and (2) the enrichment in electronic conductivity of BiVO4 upon Co doping. Here, surface interrogation mode of scanning electrochemical microscopy (SI-SECM) technique equipped with an ultramicroelectrode (UME) tip was employed to in-situ interrogate and quantify the surface adsorbed reactive oxygen species at Co-BiVO4 generated during PEC water oxidation. Experimental conditions of PEC water oxidation including applied potential and illumination time were found to play an important role in determining the surface coverage of the oxygen species. Their spontaneous decay under the open circuit condition was also characterized by increasing the time delay before interrogating the Co-BiVO4 surface.

Spontaneous decay of artificial atoms in a multi-qubit system

We consider a one-dimensional chain of N equidistantly spaced noninteracting qubits embedded in an open waveguide. In the frame of single-excitation subspace, we systematically study the evolution of qubits' amplitudes if the only qubit in the chain was initially excited. We show that the temporal dynamics of qubits' amplitudes crucially depend on the value of kd, where k is the wave vector, d is a distance between neighbor qubits. If kd is equal to an integer multiple of π, then the qubits are excited to a stationary level which scales as N−1. We show that in this case, it is the dark states which prevent qubits from decaying to zero even though they do not contribute to the output spectrum of photon emission. For other values of kd the excitations of qubits have the form of damping oscillations, which represent the vacuum Rabi oscillations in a multi-qubit system. In this case, the output spectrum of photon radiation is defined by a subradiant state with the smallest width.