Manipulating quantum Hall phases with cavity vacuum fields

The possibility of manipulating solid-state systems to achieve exotic quantum phases has thrived in the past decade due to recent successes in tailoring electronic interactions with intense electromagnetic fields, high pressure, or moiré patterning. Here we demonstrate a complementary approach, namely the control of quantum materials using the vacuum fields of engineered cavities, to achieve highly nonperturbative effects while maintaining the system at equilibrium.

In this work, we leverage the quantum Hall states of the two-dimensional electron liquid (2DEL) as a paradigmatic system where correlated electronic phases arise due to the interplay between Coulomb and light-matter interactions, being the kinetic energy irrelevant due to its quenching by the magnetic field. We unveil an enhancement by about 50% of the many-body gap of fractional quantum Hall states in the spin-resolved first Landau level, via a new platform which allows to continuously tune in situ the coupling between the 2DEL and a resonator hovering above it. At the same time, we observe a suppression of the single-particle gap due to the renormalization of the exchange interaction, reducing the g-factor from 6.5 to 4.4. More recently, through a suitable resonator design, we have been able to steer the stripe-ordered phase arising in the half-integer filling factor Hall states, inducing a resistivity reduction by a factor of 50.

These findings offer a promising way to actively control and stabilize quantum states in two-dimensional materials.