Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session K51: Quantum Error Mitigation Algorithms
3:00 PM–6:00 PM,
Tuesday, March 5, 2024
Room: 200IJ
Sponsoring
Unit:
DQI
Chair: Namit Anand, NASA Ames Research Center and KBR
Abstract: K51.00006 : Quantum computer simulation of near-surface oxygen vacancies in α-Al2O3 (0001)*
4:24 PM–4:36 PM
Presenter:
Vijaya Begum-Hudde
(University of Illinois at Urbana-Champaign)
Authors:
Vijaya Begum-Hudde
(University of Illinois at Urbana-Champaign)
Yi-Ting Lee
(University of Illinois at Urbana-Champai)
Barbara Jones
(IBM)
Andre Schleife
(University of Illinois at Urbana-Champaign)
Employing first-principles calculations we describe the electronic properties of pristine α-Al2O3 (0001) surface and of near-surface O vacancies. Using a hybrid exchange-correlation functional (HSE06), we first obtain the relaxed pristine (0001) surface with Al termination. These geometries are consistent with X-ray diffraction results. Upon introducing an O vacancy, a highly non-dispersive in-gap electronic defect state appears that was absent for the pristine surface. Its band-decomposed charge density and that of the second unoccupied state reveal a strong charge localization near the O vacancy and the adjacent surface Al atom.
Next, we study these vacancy states with quantum defect embedding theory (QDET) calculations to unravel their ground and excited-state properties. We define an active space consisting of strongly localized states near the defect and treat the remainder as environment. An effective Hamiltonian is solved for the active space which includes the effective screening from the environment within the random phase approximation to obtain the eigenvalues with full configurational interaction (FCI).
Furthermore, we solve the effective Hamiltonian on a quantum computer by employing a model consisting of an active space of one occupied and one unoccupied band from the QDET calculation. On a four-qubit circuit with a Unitary coupled-cluster (UCC-3) ansatz, we calculate the ground-state energy for the active space with Variational quantum eigensolver (VQE). On a noiseless simulator, we achieve excellent agreement with the reference FCI values. Upon running the calculations on a quantum computer, we obtain an error of 0.28±0.04 eV owing to the noise in the hardware. To mitigate noise, we employed Zero-Noise extrapolation with global folding and successfully reduced the error to 0.09±0.04 eV.
*We wish to acknowledge funding by the IBM-Illinois Discovery Accelerator Institute.
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