Positron Cooling and Annihilation in Noble Gases

Probing Positron Cooling in Noble Gases via Annihilation γ Spectra

“…The increase in magnitude of the spectra as k → 0 accords with the rise of the effective annihilation rate Z eff (k) (see Fig. 2 in [18]). This effect is due to the existence of positron-atom virtual levels [31], signified by large scattering lengths for Ar, Kr and Xe (see Table I in [21]).…”

“…Positron cooling in atomic gases has traditionally been probed by positron annihilation lifetime spectroscopy (PALS) (see [16,17] for reviews), which involves measurement of the spectrum of positron lifetimes. The dynamics of positron cooling in noble gases was recently elucidated in [18], where Monte-Carlo (MC) simulations based on accurate scattering and annihilation cross sections calculated using manybody theory (MBT) were used to determine the time-evolving positron momentum distribution and normalized annihilation rateZ eff (t). That work found that a strikingly small fraction of initial positrons survive to thermalization, affecting the measured positron annihilation rate, and explaining the discrepancy between trap-based and gas-cell measurements in Xe.…”

“…It provided an accurate description of the measured spectra for Ar, Kr and Xe and firmly established the relative contributions of various atomic orbitals to the spectra. Using the spectra calculated at all positron momenta, together with the time-evolving positron-momentum distributions calculated using MBT based MC simulations in [18], we calculate the γ spectra produced during positron cooling. We analyze the dynamics of the theS andW shape parameters, which characterize the low and high (two-γ) momentum parts of the spectra, during the process of positron thermalization.…”

Many-Body Theory for Positronium-Atom Interactions

“…Many-body theory (MBT) is a powerful and systematic method of accounting for virtual excitations of both objects and the electron-positron correlation effects. It provided an accurate description of low-energy electron-atom scattering [23][24][25][26][27][28] and positron interaction with atoms [19,20,[29][30][31][32][33], with scattering cross sections, annihilation rates, and γ spectra all found to be in excellent agreement with experiment.…”

Progress toward cryogen-free spin-photon interfaces based on nitrogen-vacancy centers and optomechanics

“…Approaches to overcome this problem include looking for alternative stationary qubits that have good optical and spin properties at room temperature [14,15], drastically speeding up the photon emission using ultra-small mode volume cavities [16], or a combination of both. We propose a promising strategy based on room-temperature quantum optomechanics, which has the additional advantage of allowing one to freely choose the photon wavelength.…”