Cavity-QED of a quantum metamaterial with tunable disorder

TL;DR

This study experimentally investigates a superconducting quantum metamaterial with 25 tunable qubits, demonstrating collective mode behavior, disorder effects, and the transition towards thermodynamic limit through microwave response measurements.

Contribution

It introduces a controllable quantum metamaterial with tunable disorder and characterizes its collective modes and fluctuations, advancing understanding of many-body quantum systems.

Findings

Energy gap scales as N^{1/2} with qubit number.

Disorder causes decay of mesoscopic fluctuations.

Bright states persist despite disorder when coupling dominates.

Abstract

We explore experimentally a quantum metamaterial based on a superconducting chip with 25 frequency-tunable transmon qubits coupled to a common coplanar resonator. The collective bright and dark modes are probed via the microwave response, i.e., by measuring the transmission amplitude of an external microwave signal. All qubits have individual control and readout lines. Their frequency tunability allows to change the number N of resonantly coupled qubits and also to introduce a disorder in their excitation frequencies with preassigned distributions. While increasing N, we demonstrate the expected $N^{1/2}$ scaling law for the energy gap (Rabi splitting) between bright modes around the cavity frequency. By introducing a controllable disorder and averaging the transmission amplitude over a large number of realizations, we demonstrate a decay of mesoscopic fluctuations which mimics an approach towards the thermodynamic limit. The collective bright states survive in the presence of disorder when the strength of individual qubit coupling to the cavity dominates over the disorder strength.