Experimentally revealing anomalously large dipoles in a quantum-circuit dielectric

TL;DR

This study reveals the existence of two distinct ensembles of TLSs in amorphous silicon, including one with anomalously large electric dipole moments, which impacts understanding of decoherence in quantum devices.

Contribution

It experimentally uncovers a new class of TLSs with large dipoles and distinguishes their interaction regimes, advancing knowledge of amorphous solids in quantum technology.

Findings

Identification of two TLS ensembles with different phonon interactions

Discovery of TLSs with anomalously large electric dipole moments

Implications for quantum device decoherence and material understanding

Abstract

Quantum two-level systems (TLSs) intrinsic to glasses induce decoherence in many modern quantum devices, such as superconducting qubits. Although the low-temperature physics of these TLSs is usually well-explained by a phenomenological standard tunneling model of independent TLSs, the nature of these TLSs, as well as their behavior out of equilibrium and at high energies above 1 K, remain inconclusive. Here we measure the non-equilibrium dielectric loss of TLSs in amorphous silicon using a superconducting resonator, where energies of TLSs are varied in time using a swept electric field. Our results show the existence of two distinct ensembles of TLSs, interacting weakly and strongly with phonons, where the latter also possesses anomalously large electric dipole moment. These results may shed new light on the low temperature characteristics of amorphous solids, and hold implications to experiments and applications in quantum devices using time-varying electric fields.