OIST Centre for Quantum Technologies (OCQT) Seminar

The OIST Center for Quantum Technologies (OCQT) is pleased to invite you to the next installment of the OCQT Seminar Series. This time, we are excited to host Dr. Nikita Astrakhantsev, a Senior Quantum Research Scientist at Google Quantum AI, who will deliver a talk entitled:

“Using interference in Pauli space to measure beyond-classical local out-of-time-order correlator”

Date and time

Monday, September 22, 2025 – 13:30 - 15:00

Location

Seminar Room E48 in Lab 4 (L4E48)

Abstract

Quantum observables in the form of few-point correlators are the key to characterizing the dynamics of quantum many-body systems. In dynamics with fast entanglement generation, quantum observables generally become insensitive to the details of the underlying dynamics at long times due to the effects of scrambling. In experimental systems, repeated time-reversal protocols have been successfully implemented to restore sensitivities of quantum observables. Using a 103-qubit superconducting quantum processor, we characterize ergodic dynamics using the second-order out-of-time-order correlators, OTOC(2). In contrast to dynamics without time reversal, OTOC(2) are observed to remain sensitive to the underlying dynamics at long time scales. Furthermore, by inserting Pauli operators during quantum evolution and randomizing the phases of Pauli strings in the Heisenberg picture, we observe substantial changes in OTOC(2) values. This indicates that OTOC(2) is dominated by constructive interference between Pauli strings that form large loops in
configuration space. The observed interference mechanism endows OTOC(2) with a high degree of classical simulation complexity, which culminates in a set of large-scale OTOC(2) measurements exceeding the simulation capacity of known classical algorithms. Further supported by an example of Hamiltonian learning through OTOC(2), our results  indicate a viable path to practical quantum advantage.

Biography

• 2011–2017: Moscow Institute of Physics and Technology — Bachelor’s and Master’s degrees; researched Lattice QCD
• 2019–2023: University of Zurich (Ph.D.) with Prof. Titus Neupert — theory of frustrated magnets
• 2023–present: Research Scientist at Google Quantum AI — working on designing beyond-classical applications