IAP Seminar (Emergent Harmonics in Josephson Tunnel Junctions Due to Series Inductance)
일시 : 2026-02-24 10:30 ~ 12:00
연사 : Junghyun Kim (MIT)
담당 : Prof. Eunjong Kim
장소 : 56-521
Emergent Harmonics in Josephson Tunnel Junctions Due to Series Inductance
Junghyun Kim (MIT)
Over the last decade, Josephson junctions have become central to quantum technologies ranging from quantum information processing to sensing. In particular, the tunnel junction -- one of their most common variants, comprising a superconductor-insulator-superconductor (SIS) layer structure -- has become a key element in today's superconducting quantum circuits. The operability of these circuits presumes a 2pi-periodic sinusoidal Josephson potential of the tunnel junction. However, higher-order corrections to this potential, often referred to as “harmonics,” cause deviations from the expected circuit behavior.
In this talk, we first discuss the two potential sources of these harmonics: the intrinsic current-phase relationship of the Josephson junction arising from Andreev processes and the inductance of the metallic traces connecting the junction to other circuit elements. Next, we present a method to measure the energy-phase relationship of a standard tunnel junction circuit using a circuit-QED-based technique and to extract corrections beyond the standard sinusoidal relationship. Finally, we discuss how to distinguish the origin of the observed harmonics using nearly symmetric superconducting quantum interference devices (SQUIDs) based on the proposed method.
We show that spectroscopic measurements of level transitions in multiple devices reveal features that cannot be explained by a standard cosine potential, but are accurately reproduced when accounting for a second-harmonic contribution to the model. The observed scaling of the second harmonic with Josephson-junction size indicates that it is due almost entirely to the trace inductance.