Atomic Decay Research Articles

Cosmic antihelium-3 nuclei sensitivity of the GAPS experiment

The General Antiparticle Spectrometer (GAPS) is an Antarctic balloon experiment designed for low-energy (0.1–0.3 GeV/n) cosmic antinuclei as signatures of dark matter annihilation or decay. GAPS is optimized to detect low-energy antideuterons, as well as to provide unprecedented sensitivity to low-energy antiprotons and antihelium nuclei. The novel GAPS antiparticle detection technique, based on the formation, decay, and annihilation of exotic atoms, provides greater identification power for these low-energy antinuclei than previous magnetic spectrometer experiments. This work reports the sensitivity of GAPS to detect antihelium-3 nuclei, based on full instrument simulation, event reconstruction, and realistic atmospheric influence simulations. The report of antihelium nuclei candidate events by AMS-02 has generated considerable interest in antihelium nuclei as probes of dark matter and other beyond the Standard Model theories. GAPS is in a unique position to detect or set upper limits on the cosmic antihelium nuclei flux in an energy range that is essentially free of astrophysical background. In three 35-day long-duration balloon flights, GAPS will be sensitive to an antihelium flux on the level of 1.3−1.2+4.5·10−6 m-2sr-1s-1(GeV/n)-1 (95% confidence level) in the energy range of 0.11–0.3 GeV/n, opening a new window on rare cosmic physics.

Enhanced optomechanically induced transparency via atomic ensemble in optomechanical system.

We investigate the optomechanically induced transparency phenomena assisted through cavity optomechanical system. The system consists of an optical cavity system filled with the two-level atomic ensemble and driven by a weak probe laser as well as a strong coupling fields. Under different driving conditions, the system can exhibit the phenomena of optomechanical induced transparency dip. Specifically, the width of the transparency window increases with an increase in the coupling constant, while decreasing with an increase in atomic decay rate. Furthermore, the induced transparency phenomena are strongly affected by the number of atoms, coupling, and the decay rate. It is found that the larger the number of atoms, the wider the window of induced transparency, and therefore enhance the depth of transparency window. These results may have spectacular applications for slowing and on-chip storage of light pulses by the use of a micro-fabricated optomechanical array.

Resilient quantum gates on periodically driven Rydberg atoms

Fault-tolerant implementation of quantum gates is one of preconditions for realizing quantum computation. The platform of Rydberg atoms is one of the most promising candidates for achieving quantum computation. We propose to implement a controlled-$Z$ gate on Rydberg atoms where an amplitude-modulated field is employed to induce Rydberg antiblockade. Gate robustness against the fluctuations in the Rydberg-Rydberg interaction can be largely enhanced by adjusting amplitude-modulated field. Furthermore, we introduce a Landau-Zener-St\"uckelberg transition on the target atom so as to improve the gate resilience to the deviation in the gate time and the drift in the pulse amplitude. With feasible experimental parameters, one can achieve the gate with low fidelity errors caused by atomic decay, interatomic dipole-dipole force, and Doppler effects. Finally, we generalize the gate scheme into multiqubit cases, where resilient multiqubit phase gates can be obtained in one step with an unchanged gate time as the number of qubits increases.

Local Structure and Anti-Structural Defects of Tin in Amorphous and Crystalline Ge2Sb2Te5 Films

The absorption Mossbauer spectroscopy on 119Sn impurity centers shows that germanium atoms in the structure of amorphous and polycrystalline Ge2Sb2Te5 films have different local symmetries (tetrahedral in the amorphous phase and octahedral in the crystalline). By emission Mossbauer spectroscopy on 119mSn impurity centers formed after the radioactive decay of 119Sb or 119mTe parent atoms, tin antisite defects at antimony and tellurium sites of crystalline Ge2Sb2Te5 films are identified.

Subradiance of Cold and Dilute Atomic Ensembles Excited by Resonant Pulsed Radiation

The fluorescence dynamics of optically dense but dilute atomic ensembles cooled to sub-Doppler temperatures and excited by resonant pulsed radiation is studied. Apart from total radiation intensity, the temporal variations of the spectral composition of fluorescence and its polarization, as well as the variation of the spatial distribution of excitation in the atomic ensemble, are analyzed. Based on this analysis, it is shown that the role of radiation trapping becomes smaller with time, and subradiance quantum states formed as a result of the resonant dipole–dipole interatomic interaction become the main factor determining the slow atomic excitation decay. The dependence of the subradiance form on the ensemble size is analyzed.

TALIF measurements of hydrogen and deuterium surface loss probabilities on quartz in low pressure high density plasmas

This article deals with surface loss on quartz of atomic hydrogen (H) and its isotope deuterium (D) in a low-pressure (10 Pa) pulsed inductively coupled plasma. The atomic temporal decay in the post discharge is measured by two-photon absorption laser-induced fluorescence (TALIF). From the loss rate, the atomic surface loss probability is determined. In pure hydrogen or pure deuterium gas, no isotopic effect on surface kinetics has been observed and the surface loss probabilities of H and D were found to be almost identical and equal to ∼1.8%. However, despite the lack of difference in surface loss probability, a net isotopic effect on surface loss rate due to the mass difference between the isotopes is measured. Hydrogen atoms diffuse faster and have higher flux to the plasma chamber walls than deuterium atoms. Hydrogen atoms are therefore lost at higher rate than deuterium atoms. Based on the observed isotopic difference and on the comparison between H and D TALIF signals, the isotopic effects on H and D atom production are discussed.

Kinetics of spontaneous decay in cold atomic systems

We discuss the spontaneous decay in a system of cold identical two-level atoms when, due to the strong dipole–dipole interaction, the collision-induced spontaneous decay plays a leading role in the process. We show that the time profile of the spontaneous transition is essentially non-exponential. Also, we argue that at a low initial temperature of the atomic system the spontaneous decay is accompanied by strong heating caused by the inelastic atom–atom collisions. We show that the spontaneous emission spectrum is asymmetric. In addition, the width of the emission spectrum is a function of time. When atoms decay, the emission spectrum becomes broader. The spectrum’s asymmetry and the atomic system’s heating have the same physical origin: coming from the peculiarities of the atoms’ distribution function.

Evidence of ultrafast dissociation in the CHCl3 molecule

In the present work, we use tunable synchrotron radiation to investigate experimentally and theoretically the dissociation of a chlorinated methane, the CHCl3 molecule, by exciting a chlorine 2p core electron into the LUMO and LUMO + 1 orbitals. The Auger electron energy distribution measured at the Cl 2p3/2 → 10a1 resonance shows narrow lines which energies correspond to the Cl* → Cl+ atomic decay, a clear evidence that the Auger decay takes place after consummation of the dissociation, when the moieties were already far away from each other. Our experimental data are endorsed theoretically by a series of high-level ab initio quantum mechanical calculations. The excited states are calculated to be strongly repulsive in the Franck–Condon region (−dE/dy ∼ 0.15 a.u.) along the C–Cl bond direction.

Plasma environment effects on K lines of astrophysical interest

Aims.Within the framework of compact-object accretion disks, we calculate plasma environment effects on the atomic structure and decay parameters used in the modeling of K lines in lowly charged iron ions, namely Fe II–Fe VIII.Methods.For this study, we used the fully relativistic multiconfiguration Dirac–Fock method approximating the plasma electron–nucleus and electron-electron screenings with a time-averaged Debye-Hückel potential.Results.We report modified ionization potentials, K-threshold energies, wavelengths, radiative emission rates, and Auger widths for plasmas characterized by electron temperatures and densities in the ranges 105 − 107K and 1018 − 1022cm−3. In addition, we propose two universal fitting formulae to predict the IP and K-threshold lowerings in any elemental ion.Conclusions.We conclude that the high-resolution X-ray spectrometers onboard the future XRISM and ATHENA space missions will be able to detect the lowering of the K edges of these Fe ions due to the extreme plasma conditions occurring in the accretion disks around compact objects.

Generation and control of attosecond laser pulse

Time-resolved measurement enables us to reveal the dynamical evolution of the system. The ultrashort laser and pump-probe method provide a powerful tool for achieving the time resolved measurement. With the development of laser technology, e.g., Q -switching, mode-locking, chirped pulse amplification and the application of the Ti:Sapphire crystal, the pulse width of laser is getting shorter and shorter, and the pulse energy is getting higher and higher. It has brought tremendous changes to the field of optics and photonics. For example, in the 1980s, femtosecond (1 fs =10–15 s) lasers have been used to study the evolution of molecular intermediate states during chemical reactions, which revealed the dynamics of chemical reactions at the molecular level. Nevertheless, the electron inside atoms and molecules moves even faster on a timescale of “attosecond” (1 as =10–18 s). At the dawn of the 21st century, attosecond pulses were produced from the high harmonics generated in the interaction between intense femtosecond laser and novel atoms. In 2001, an isolated attosecond pulse with a duration of 650 as was produced in the experiment via a 7 fs few-cycle driving laser. In the same year, an attosecond pulse train with a duration of 250 as for single pulse was produced by a multicycle driving laser. These results marked that the pulse width of the laser broke through the femtosecond timescale, and opened the door to attosecond science. In the next decades, lots of ultrafast processes inside atoms and molecules, e.g., tunneling ionization, Auger decay of atoms and electron localization and internal charge transfer of molecules, have been invested by pump-probe measurement combining the attosecond pulses and few-cycle near infrared laser pulses. In addition, the applications of attosecond pulses have been gradually extended from gas to solid materials. By using the attosecond pulse, it is possible to manipulate the electron motion in the attosecond time scale, which corresponds to an extremely high frequency rate of petahertz. Such manipulation is considered to be the basis for developing the photoelectric information processing at petahertz. Attosecond science has become one of the most important achievements in the field of ultrafast optics in the past two decades. The crucial issue is the generation and control of attosecond laser pulses. Many schemes have been demonstrated to produce the isolated attosecond pulses. The most popular scheme is few-cycle driving laser, which requires carrier-envelope phase stabilized ultrashort laser pulse. On the other hand, since the generation efficiency of the attosecond pulse depends on the driving laser ellipticity, a polarization gating scheme has also been developed, which was later generalized to double optical gating. Another scheme is the two-color field scheme, which synthesizes the laser pulses with different wavelengths. The advantage of this method is that multi-cycle driving laser pulse can be used to produce isolated attosecond pulse. Recently, this method has been extended to the three-color cases. In addition, ionization gating and lighthouse schemes are also demonstrated in experiment. With these methods, the pulse duration of the attosecond pulse decreases gradually. At present, the shortest pulse width has reached 43 as and high power isolated attosecond pulse with a peak power of 2.6 GW has been produced. But how to improve the attosecond pulse energy and generation of circularly polarized attosecond pulses are still the hot topics currently.

Decay of a bound muon into a bound electron

When a muon bound in an atom decays, there is a small probability that the daughter electron remains bound. That probability is evaluated. Surprisingly, a significant part of the rate is contributed by the negative energy component of the wave function, neglected in a previous study. A simple integral representation of the rate is presented. In the limit of close muon and electron masses, an analytic formula is derived.

Stellar 78,80,84,86Kr(n,γ) Reactions Studied by Activation at SARAF-LiLiT, Atom Trap Trace Analysis and Decay Counting

We report on (n,γ) neutron capture experiments performed with the Liquid-Lithium Target (LiLiT) and the mA-proton beam at 1.92 MeV (2-3 kW) from the Soreq Applied Research Accelerator Facility (SARAF). The setup yields high-intensity 30-keV quasi-Maxwellian neutrons (3-5 × 1010 n/s) closely reproducing the conditions of s-process stellar nucleosynthesis. The 78,80,8486Kr(n,γ) reactions at the border between weak- and strong- s-process were studied. A Ti sphere filled with 107.7 mg of natural Kr gas was placed in an irradiation chamber downstream of LiLiT with a gold foil used as a neutron fluence monitor during the activation. The activities of the short-lived Kr isotopes (7985m87Kr) were measured by γ decay counting with a HPGe detector. The long-lived Kr isotopes (81,85gKr) were measured by atom counting via Atom Trap Trace Analysis (ATTA) at Argonne and Low-Level Counting (LLC) at Bern.

Structure and vibrational properties of sodium silicate glass surfaces.

Using molecular dynamics simulations, we investigate how the structural and vibrational properties of the surfaces of sodo-silicate glasses depend on the sodium content as well as the nature of the surface. Two types of glass surfaces are considered: A melt-formed surface (MS) in which a liquid with a free surface has been cooled down into the glass phase and a fracture surface (FS) obtained by tensile loading of a glass sample. We find that the MS is more abundant in Na and non-bridging oxygen atoms than the FS and the bulk glass, whereas the FS has higher concentration of structural defects such as two-membered rings and under-coordinated Si than the MS. We associate these structural differences to the production histories of the glasses and the mobility of the Na ions. It is also found that for Na-poor systems, the fluctuations in composition and local atomic charge density decay with a power-law as a function of distance from the surface, while Na-rich systems show an exponential decay with a typical decay length of ≈2.3 Å. The vibrational density of states shows that the presence of the surfaces leads to a decrease in the characteristic frequencies in the system. The two-membered rings give rise to a pronounce band at ≈880 cm-1, which is in good agreement with experimental observations.

Direct inner-shell photoionization of Xe atoms embedded in helium nanodroplets

We present the first measurements of photoelectron spectra of atomic clusters embedded in superfluid helium (He) nanodroplets. Owing to the large absorption cross section of xenon (Xe) around 100 eV photon energy (4d inner-shell ionization), direct dopant photoionization exceeds charge transfer ionization via the ionized He droplets. Despite the predominant creation of Xe2+ and Xe3+ by subsequent Auger decay of free Xe atoms, for Xe embedded in He droplets only singly charged , k = 1, 2, 3 fragments are observed. Broad Xe+ ion kinetic-energy distributions indicate Coulomb explosion of the ions due to electron transfer to the primary Auger ions from surrounding neutral atoms. The electron spectra correlated with Xe ions emitted from the He nanodroplets contain a low-energy feature and nearly unshifted Xe photolines. These results pave the way to extreme ultraviolet and x-ray photoelectron spectroscopy of clusters and molecular complexes embedded in He nanodroplets.

Heralded atomic nonadiabatic holonomic quantum computation with Rydberg blockade

We propose a protocol to realize atomic nonadiabatic holonomic quantum computation (NHQC) with two computational atoms and an auxiliary atom. Dynamics of the system is analyzed in the regime of Rydberg blockade, and robust laser pulses are designed via reverse engineering, so that quantum gates can be easily realized with high fidelities. In addition, we also study the evolution suffering from dissipation with a master equation. The result indicates that decays of atoms can be heralded by measuring the state of the auxiliary atom, and nearly perfect unitary evolution can be obtained if the auxiliary atom remains in its Rydberg state. Therefore, the protocol may be helpful to realize NHQC in dissipative environment.

Tripartite Entanglement Dynamics in the System Consisting of Three Damping Jaynes-Cummings Models

In this paper we consider the situation that three identical two-level atoms resonantly interact with three distant single-mode optical cavities via a one-photon hopping separately, and there exist the phenomena of atom-decay and cavity-decay. Under Jaynes-Cummings model the time evolution of the system is given. The tripartite negativity is used to quantify the degree of tripartite entanglement. The tripartite entanglement dynamics among atoms and among cavities are studied. The influences of the atom-decay and the cavity-decay on tripartite entanglement are discussed. The results obtained using the numerical method show that the tripartite entanglement among atoms and that among cavities all display damping oscillation behavior. On the other hand, as the atomic decay rate increases, their decays are accelerated, and so do they with the increase of cavity decay rate.

Tests of discrete symmetries in positronium decays with the J-PET detector

The newly constructed Jagiellonian Positron Emission Tomograph (J-PET) is the first tomograph built from plastic scintillators. As a detector optimized for the registration of photons from the electron-positron annihilations, it also capable to tests discrete symmetries in decays of positronium atoms via the determination of the expectation values of the discrete-symmetries-odd operators, which may be constructed from the spin of ortho-positronium atom and the momenta and polarization vectors of photons originating from its annihilation.

Non-equilibrium Kinetics of Dissociation of Molecular Hydrogen in Microwave Discharge in Liquid Hydrocarbons

A semi-empirical level-based model is developed that describes the detailed kinetics of the formation and decay of hydrogen atoms during relaxation of the vibrational energy of hydrogen molecules in the gas phase of a microwave discharge in liquid hydrocarbons in the range of the translational temperature from 600 to 3000 K at atmospheric pressure. It is shown that, depending on the conditions in the gas phase, the monomolecular decomposition of hydrogen can consist of two stages—the early and late stages. At the early stage, the dissociation of a hydrogen molecule occurs with a non-equilibrium energy distribution over the internal degrees of freedom of the molecule. At the late stage, chemical equilibrium in the concentration of hydrogen atoms is established. The specific energy stored in the vibrational degree of freedom of the hydrogen molecule decreases as a result of the dissociation of molecules during the equilibrium between the translational-rotational and vibrational degrees of freedom of the molecule. As a result, the relaxation time of the vibrational energy increases and becomes equal to the time at which the equilibrium of hydrogen atoms concentration is established.

A subradiant optical mirror formed by a single structured atomic layer.

Versatile interfaces with strong and tunable light-matter interactions are essential for quantum science1 because they enable mapping of quantum properties between light and matter1. Recent studies2-10 have proposed a method of controlling light-matter interactions using the rich interplay of photon-mediated dipole-dipole interactions in structured subwavelength arrays of quantum emitters. However,a key aspect of this approach-the cooperative enhancement of the light-matter coupling strength and the directional mirror reflection of the incoming light using an array of quantum emitters-has not yet been experimentally demonstrated. Here we report the direct observation of the cooperative subradiant response of a two-dimensional square array of atoms in an optical lattice. We observe a spectral narrowing of the collective atomic response well below the quantum-limited decay of individual atoms into free space. Through spatially resolved spectroscopic measurements, we show that the array acts as an efficient mirror formed by a single monolayer of a few hundred atoms. By tuning the atom density in the array and changing the ordering of the particles, we are able to control the cooperative response of the array and elucidate the effect of the interplay of spatial order and dipolar interactions on the collective properties of the ensemble. Bloch oscillations of the atoms outside the array enable us to dynamically control the reflectivity of the atomic mirror. Our work demonstrates efficient optical metamaterial engineering based on structured ensembles of atoms4,8,9 and paves the way towards controlling many-body physics with light5,6,11 and light-matter interfaces at the single-quantum level7,10.

Microresonators enhancing long-distance dynamical entanglement generation in chiral quantum networks

Chiral quantum networks provide a promising route for realising quantum information processing and quantum communication. Here, we describe how two distant quantum nodes of chiral quantum network become dynamically entangled by a photon transfer through a common 1D chiral waveguide. We harness the directional asymmetry in chirally-coupled single-mode ring resonators to generate entangled state between two atoms. We report a concurrence of up to 0.969, a huge improvement over the 0.736 which was suggested and analyzed in great detail in Ref. [1]. This significant enhancement is achieved by introducing microtoroidal resonators which serve as efficient photonic interface between light and matter. Robustness of our protocol to experimental imperfections such as fluctuations in inter-nodal distance, imperfect chirality, various detunings and atomic spontaneous decay is demonstrated. Our proposal can be utilised for long-distance entanglement generation in quantum networks which is a key ingredient for many applications in quantum computing and quantum information processing.