Tunneling Spectroscopy of Two-level Systems Inside Josephson Junction

TL;DR

This paper proposes a method to detect and characterize two-level systems inside Josephson junctions through Rabi oscillations induced by Josephson oscillations, aiding in understanding decoherence in qubits.

Contribution

It introduces a tunneling spectroscopy technique using noise measurements to analyze two-level systems within Josephson junctions, linking their dynamics to decoherence.

Findings

Rabi oscillations can be driven by Josephson oscillations near resonance.

Current and voltage oscillations reveal two-level system properties.

Method enables characterization of two-level systems affecting qubit coherence.

Abstract

We consider a two-level (TL) system with energy level separation Omega_0 inside a Josephson junction. The junction is shunted by a resistor R and is current I (or voltage V = RI) biased. If the TL system modulates the Josephson energy and/or is optically active, it is Rabi driven by the Josephson oscillations in the running phase regime near the resonance 2eV = Omega_0. The Rabi oscillations, in turn, translate into oscillations of current and voltage which can be detected in noise measurements. This effect provides an option to fully characterize the TL systems and to find the TL's contribution to the decoherence when the junction is used as a qubit.