Tobias Classen

Tobias Classen

Biography

Tobias Classen is a fourth-year Physics major at Wesleyan University. His interest in
the intersection of math and material science was sparked during his time as a TIG welding
instructor, and his passion for teaching has remained constant. At Wesleyan, he serves as a
teaching assistant for quantum mechanics and hopes to one day teach as a professor. He is
also committed to ensuring that his research benefits society, not war. At his home institution,
Tobias researches halide segregation in perovskite solar cells, exploring polaron models to
explain local inhomogeneities. During his REU at UPenn, he investigated preliminary steps
for biodegradable supercapacitors for sensors used to combat agricultural overwatering. Now,
at MIT, he simulates cosmic neutron radiation on superconducting quantum devices to combat
correlated error. He plans to continue this journey through a PhD in condensed matter physics.

Bogoliubov Quasiparticle Distribution in Superconducting Circuits from
Neutron Impacts
Tobias Classen1, Mingyu Li2, Doug Pinckney2, Joseph Formaggio2
1Department of Physics, Wesleyan University
2Department of Physics, Massachusetts Institute of Technology

Quantum devices are limited in their applicability due to radiation-induced correlated errors.
These errors arise from quasiparticles (QPs) forcing qubit relaxation. QPs are born when
Cooper pairs, made from electron-phonon attraction, split during radiation impacts. Current
techniques such as gap engineering, the tuning of the difference in superconducting gap
across the device, present a partial solution. Gap-engineered quantum circuits successfully
prevent errors from QPs from radiation depositing < 1 MeV, but errors from > 1 MeV remain.
Additionally, prior work has ignored QP diffusion within the devices. Our models aim to
provide a more rigorous exploration of how these QPs move and change energies. We aim
to determine the QPs’ distribution by simulating a 241-AmBe neutron source’s effect on
our superconducting circuit. Using Geant4, a Monte Carlo particle simulator developed at
CERN, along with G4CMP, a condensed matter physics library for Geant4, we simulated
the QPs formed from neutron impacts and compared them to experimental results. Our
research simulated QP diffusion to better understand density as a function of time, along with
energy distribution from radiation impacts. Understanding the distribution opens avenues
for engineering the superconducting circuits to mitigate this source of error, aiding quantum
devices’ reliability.