Cavity quantum electrodynamics using a near-resonance two-level system: emergence of the Glauber state

TL;DR

This paper demonstrates strong coupling between a two-level system and a microwave cavity in a silicon nitride dielectric, observing vacuum Rabi splitting and the emergence of the Glauber state, advancing cavity QED research beyond superconducting qubits.

Contribution

It reports the first measurement of an individual TLS in a silicon nitride dielectric within a cavity QED system, showing strong coupling and the transition to a coherent state.

Findings

Achieved vacuum Rabi splitting indicating strong coupling.

Observed a TLS coherence time of 3.2 microseconds.

Documented the transition from Rabi split states to the Glauber state with increased drive power.

Abstract

Random tunneling two-level systems (TLSs) in dielectrics have been of interest recently because they adversely affect the performance of superconducting qubits. The coupling of TLSs to qubits has allowed individual TLS characterization, which has previously been limited to TLSs within (thin) Josephson tunneling barriers made from aluminum oxide. Here we report on the measurement of an individual TLS within the capacitor of a lumped-element LC microwave resonator, which forms a cavity quantum electrodynamics (CQED) system and allows for individual TLS characterization in a different structure and material than demonstrated with qubits. Due to the reduced volume of the dielectric (80 $\mu$m$^{3}$), even with a moderate dielectric thickness (250 nm), we achieve the strong coupling regime as evidenced by the vacuum Rabi splitting observed in the cavity spectrum. A TLS with a coherence time of 3.2 $\mu$s was observed in a film of silicon nitride as analyzed with a Jaynes-Cummings spectral model, which is larger than seen from superconducting qubits. As the drive power is increased, we observe an unusual but explicable set of continuous and discrete crossovers from the vacuum Rabi split transitions to the Glauber (coherent) state.