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SUMMARY:Theoretical magneto-optical spectroscopy for solid state defect qu
 antum bits - Adam Gali (Wigner Research Centre for Physics &amp\; Budapest
  University of Technology and Economics)
DTSTART:20230608T130000Z
DTEND:20230608T140000Z
UID:TALK194917@talks.cam.ac.uk
CONTACT:Bo Peng
DESCRIPTION:We live in the era of second quantum revolution in which solid
  state defect quantum bits play a significant role. An exemplary solid sta
 te defect quantum bit is the nitrogen-vacancy center in diamond which can 
 be effectively initialized and readout at room temperature. We show how th
 eoretical magneto-optical spectroscopy on nitrogen-vacancy center explaine
 d its optical spinpolarization loop which is the key mechanism in the init
 ialization and readout. To this end\, methods to calculate highly correlat
 ed electronic states and levels embedded in the itinerant solid state elec
 tron system with thousands of electrons has been developed [1] which is of
 ten called “quantum embedding” method or can be viewed as a multiscale
  method where the itinerant electron system is treated by density function
 al theory whereas the Coulomb-interaction between the strongly interacting
  orbitals in the system is directly calculated\, i.e.\, so called configur
 ational interaction theory. We have recently started to use density matrix
  renormalization group wavefunction methods too based on density functiona
 l theory ground state calculations which produce promising results for def
 ect spins in hexagonal boron nitride [2\,3]. We show that understanding th
 e optical spinpolarization loop requires the exploitation of dynamical eff
 ects due to the enhanced electron-phonon interaction. In this regard\, we 
 show the power of Jahn-Teller theorem when combined with density functiona
 l theory calculations of few thousands of electrons system [4\,5]. In part
 icular\, we show the extension of Herzberg-Teller theorem from the optical
  transition to intersystem crossing [6] which is the key of quantum bit op
 eration of nitrogen-vacancy center and related quantum systems. We briefly
  touch the importance of ab initio spin-related coupling tensors in the de
 scription of defect qubits\, such as hyperfine tensors\, in understanding 
 the qubit’s spin dephasing\, spin coherence and spin relaxation times.\n
 \n[1] Michel Bockstedte\, Felix Stütz\, Thomas Garrat\, Viktor Ivády\, a
 nd Adam Gali\, npj Quantum Materials 3\, 31 (2018)\n\n[2] Viktor Ivády\, 
 Gergely Barcza\, Gergô Thiering\, Song Li\, Hanen Hamdi\, Jyh-Pin Chou\, 
 Örs Legeza\, and Adam Gali\, npj Computational Materials 6\, 41 (2020)\n\
 n[3] Gergely Barcza\, Viktor Ivády\, Tibor Szilvási\, Márton Vörös\, 
 Libor Veis\, Ádám Gali\, and Örs Legeza\, Journal of Chemical Theory an
 d Computation 17\, 1143 (2021)\n\n[4] Gergő Thiering and Adam Gali\, Phys
 ical Review B 98\, 085207 (2018)\n\n[5] Adam Gali\, Nanophotonics 8\, 1907
  (2019)\n\n[6] Gary Wolfowicz\, F. Joseph Heremans\, Christopher P. Anders
 on\, Shun Kanai\, Hosung Seo\, Adam Gali\, Giulia Galli & David D. Awschal
 om\, Nature Reviews Materials 6\, 906 (2021)
LOCATION:TCM Seminar Room
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