Several research efforts are ongoing in the AFIT Positron Annihilation Spectroscopy (PAS) Laboratories.   Proposals in the following areas are particularly interesting. 

1. The use of bulk and surface PAS experimental techniques are investigated for their effectiveness as non-destructive, Quality Control (QC) methods for Laser Additive Manufacture (AM). The ability to provide depth specific and bulk atomistic-level information on defects, microstructure and oxygen content of AM alloys offers unique capabilities not matched by currently used or investigated QC methods.  These studies will employ modern Positron Annihilation Lifetime Spectroscopy, Doppler Broadening Annihilation Spectroscopy, Single-Shot PALS (SSPALS) and Slow Positron Beamline.  [“Single-shot positron annihilation lifetime spectroscopy using a liquid scintillator”, J. R. Machacek, S. McTaggart, and L.W. Burggraf, AIP Advances 11, 055223, May 2021, https://doi.org/10.1063/5.0048366 and “Laser Powder Bed Fusion of Molybdenum and Mo-0.1 SiC Studied by Positron Annihilation Lifetime Spectroscopy and Electron Backscatter Diffraction Methods”, Nathan E Ellsworth, Joshua R Machacek, Ryan A Kemnitz, Cayla C Eckley, Brianna M Sexton, Joel A Gearhart, Larry W Burggraf, Materials 16 (4), 1636 (2023) https://www.mdpi.com/1996-1944/16/4/1636.

2. We propose to conduct measurements of o-Ps in 2D solid-state systems using our positron spectroscopy techniques, particularly Single-Shot PALS and Compton Polarimetry of Annihilation Radiation, to investigate the entanglement of 2 gamma and 3 gamma annihilation in comparison to o-Ps annihilation in 3D.  We will interpret these experimental results employing theory of 2D positronium annihilation that we propose to develop in order to model the momentum and spin space deviations of 2D qubits from 3D qubits. The modeling point of departure for virtual o-Ps will be to expand NEO-positron codes to incorporate spin correlation to model solid-state qubits.  ["Semiconductor color-center structure and excitation spectra: Equation-of-motion coupled-cluster description of vacancy and transition-metal defect photoluminescence" J. J. Lutz, X. F. Duan, and L. W. Burggraf, Physical Review B,  97, 115108 (2018); "Calculation of the Positron Annihilation Rate in PsH with the Positronic Extension of the Explicitly Correlated Nuclear−Electronic Orbital Method" M. V. Pak, A. Chakraborty , and S. Hammes-Schiffer J. Phys. Chem. A 2009, 113, 16, 4004–4008]. Three photon annihilation in 3D o-Ps produces 3 entangled particles in a plane whose entanglement exists in one of three states: Q(SEP), Q(W), Q(GHZ).  Theory has shown that in 3D these states have a unique angular intensity distribution which can be detected by angle-resolved positron annihilation spectroscopy (PAS).  Annihilation of virtual o-Ps in a 2D system for which spin-orbit coupling is not perturbative gives a 3-particle annihilation distribution having no directional preference in stark contrast to the 3D entangled annihilation particles.  So the idealized experiment to recognize SO(2) 2D anyon behavior of o-Ps by distinguishing between o-Ps spin states in 3D and 2D is much more tractable than any other experimental technique.  

key words

Positron, Positronium (PS), Annihilation, Additive Manufacture, Quality Control (QC), Entanglement, Qubit, Solid State, 2D Materials, Compton Polarimetry, Single-Shot PALS, Doppler Broadening

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral and Senior applicants