| Abstract: |
How would our world look like if the fine structure constant $\alpha$
were of order unity? While in our small $\alpha$ world an atom excited
to the first excited state has negligible probability of decaying to
the ground state while emitting more than a single photon, such
processes are important in a large $\alpha$ world, making photon
frequency conversion effective in the single-photon regime. We show
how such behavior can be realized in a superconducting circuit QED
system, where a transmon, which serves as an artificial atom, is
galvanically coupled to a high-impedance Josephson junction array,
which acts as a waveguide for microwave photons with a high effective
$\alpha$. Instantons (phase slips) that occur in the transmon interact
with the microwave photons, and lead to inelastic scattering
probabilities which approach unity and greatly exceed the effect of
the quartic anharmoncity of the Josephson potential [1]. The
instanton-photon cross section is calculated using a novel formalism
which allows to directly observe the dynamical properties of the
instantons, and should be useful in other quantum field theoretical
contexts. The calculated inelastic decay rates compare well with
recent measurements from the Manucharyan group at Maryland [2].
[1] Photon-instanton collider implemented by a superconducting
circuit, A. Burshtein, R. Kuzmin, V. E. Manucharyan and M. Goldstein,
Phys. Rev. Lett. 126 137701 (2021)
[2] Photon decay in circuit quantum
electrodynamics, R. Kuzmin, N.
Grabon, N. Mehta, A. Burshtein, M. Goldstein, M. Houzet, L. I. Glazman
and V. E. Manucharyan, arxiv:2010.02099 (2020) |