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Opportunity at Air Force Research Laboratory (AFRL)

Positron Annihilation Spectroscopy and Modeling for Materials Science

Location

Air Force Institute of Technology

RO# Location
13.50.00.B5871 AFIT, Wright-Patterson AFB, OH 454337542

Advisers

name email phone
Burggraf, Larry W. larry.burggraf@afit.edu 9372553636 x4507

Description

Experimental methods of chemical physics are applied to excitonics, quantum computing and positron spectrometry.  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]

2. We 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.  

Keywords:
Chemical Physics; Excitonics; Quantum Entanglement; Positron Spectroscopy; Positron, Positronium (PS); Annihilation; Additive Manufacture; Quality Control (QC); Entanglement; Qubit; Solid State; 2D Materials; Compton Polarimetry; Single-Shot PALS; Doppler Broadening

Eligibility

Citizenship:  Open to U.S. citizens
Level:  Open to Postdoctoral and Senior applicants

Stipend

Base Stipend Travel Allotment Supplementation
$76,542.00 $4,000.00

$3,000 Supplement for Doctorates in Engineering & Computer Science

Experience Supplement:
Postdoctoral and Senior Associates will receive an appropriately higher stipend based on the number of years of experience past their PhD.

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