Collective, Coherent, and Ultrastrong Coupling of 2D Electrons with Terahertz Cavity Photons

Understand

Nonperturbative coupling of light with condensed matter in an optical cavity is expected to reveal a host of coherent many-body phenomena and states.

• In addition, strong coherent light-matter interaction in a solid-state environment is of great interest to emerging quantum-based technologies.
• However, creating a system that combines a long electronic coherence time, a large dipole moment, and a high cavity quality ($Q$) factor has been a challenging goal.
• Here, we report collective ultrastrong light-matter coupling in an ultrahigh-mobility two-dimensional electron gas in a high-$Q$ terahertz photonic-crystal cavity in a quantizing magnetic field, demonstrating a cooperativity of $\sim$360.