Comment on "Electrostatics-induced breakdown of the integer quantum Hall effect in cavity QED''
We comment on the preprint arXiv:2511.04744 by Andolina et al.
cond-mat.mes-hall↗
arXiv subjects
G. Scalari
Publications and source records attributed to G. Scalari.
Cavity-Driven Attractive Interactions in Quantum Materials
Many-body phenomena in quantum materials emerge from the interplay among a broad continuum of electronic states, and controlling these interactions is critical for engineering novel phases. One promising approach exploits fluctuations of the vacuum electromagnetic field confined within optical cavities to tailor electronic properties. Here, we demonstrate that cavity photons can mediate attractive interactions in a tunable van der Waals material and reorganize a continuum of electron-hole transitions into an exciton-like state. We introduce a broadband, sub-wavelength time-domain microscope that integrates exfoliated, dual-gated two-dimensional quantum materials into a terahertz cavity. This approach enables the first-ever measurement of the field-tunable bandgap of bilayer graphene at terahertz frequencies while revealing ultrastrong coupling with a vacuum Rabi frequency exceeding $\Omega_{Rabi}/\omega\approx 40\%$ of the bare photon energy. Crucially, we identify a novel cavity-induced resonance emerging from the interband continuum that resembles Coulomb-bound excitons and remains stable across a broad temperature range. By uniting longstanding theoretical predictions with advanced experimental techniques, our findings open new avenues for designing and probing unique light-matter states and realizing hybrid correlated phases in quantum materials.
cond-mat.mtrl-sci↗
THz optical beat-note detection with a fast Hot Electron Bolometer operating up to 31 GHz
We study the performance of an hot-electron bolometer (HEB) operating at THz frequencies based on superconducting niobium nitride films. We report on the voltage response of the detector over a large optical bandwidth carried out with different THz sources. We show that the impulse response of the fully packaged HEB at 7.5 K has a 3 dB cut-off around 2 GHz. Remarkably, detection capability is still observed above 30 GHz in an heterodyne beating experiment using a THz quantum cascade laser frequency comb. Additionally, the HEB sensitivity has been evaluated and an optical noise equivalent power NEP of 0.8 pW/sqrt(Hz) has been measured at 1 MHz.
physics.optics↗
Controlling and Phase-Locking a THz Quantum Cascade Laser Frequency Comb by Small Optical Frequency Tuning
Full phase control of THz emitting quantum cascade laser (QCL) combs has recently been demonstrated, opening new perspectives for even the most demanding applications. In this framework, simplifying the set-ups for control of these devices will help to accelerate their spreading in many fields. We report a new way to control the emission frequencies of a THz QCL comb by small optical frequency tuning (SOFT), using a very simple experimental setup, exploiting the incoherent emission of an ordinary white light emitting diode. The slightly perturbative regime accessible in these condition allows tweaking the complex refractive index of the semiconductor without destabilizing the broadband laser gain. The SOFT actuator is characterized and compared to another actuator, the QCL driving current. The suitability of this additional degree of freedom for frequency and phase stabilization of a THz QCL comb is shown and perspectives are discussed.
physics.app-ph↗
Gain dynamics in a heterogeneous terahertz quantum cascade laser
The gain recovery time of a heterogeneous active region terahertz quantum cascade laser is studied by terahertz-pump,i terahertz-probe spectroscopy. The investigated active region, which is based on a bound-to-continuum optical transition with an optical phonon assisted extraction, exhibits a gain recovery time in the range of 34$\,$-$\,$50$\,$ps dependent on the operation condition of the laser. The recovery time gets shorter for stronger pumping of the laser while the recovery dynamics slows down with increasing operation temperature. These results indicate the important role of the intracavity light intensity for the fast gain recovery.
physics.optics↗
Room temperature operation of n-type Ge/SiGe terahertz quantum cascade lasers predicted by non-equilibrium Green's functions
n-type Ge/SiGe terahertz quantum cascade laser are investigated using non-equilibrium Green's functions calculations. We compare the temperature dependence of the terahertz gain properties with an equivalent GaAs/AlGaAs QCL design. In the Ge/SiGe case, the gain is found to be much more robust to temperature increase, enabling operation up to room temperature. The better temperature robustness with respect to III-V is attributed to the much weaker interaction with optical phonons. The effect of lower interface quality is investigated and can be partly overcome by engineering smoother quantum confinement via multiple barrier heights.
cond-mat.mes-hall↗
Two-well quantum cascade laser optimization by non-equilibrium Green's function modelling
We present a two-quantum well THz intersubband laser operating up to 192 K. The structure has been optimized with a non-equilibrium Green's function model. The result of this optimization was confirmed experimentally by growing, processing and measuring a number of proposed designs. At high temperature (T>200 K), the simulations indicate that lasing fails due to a combination of electron-electron scattering, thermal backfilling, and, most importantly, re-absorption coming from broadened states.
physics.app-ph↗
Superconducting complementary metasurfaces for THz ultrastrong light-matter coupling
A superconducting metasurface operating in the THz range and based on the complementary metamaterial approach is discussed. Experimental measurements as a function of temperature and magnetic field display a modulation of the metasurface with a change in transmission amplitude and frequency of the resonant features. Such a metasurface is successively used as a resonator for a cavity quantum electrodynamic experiment displaying ultrastrong coupling to the cyclotron transition of a 2DEG. A finite element modeling is developed and its results are in good agreement with the experimental data. In this system a normalized coupling ratio of $\fracΩ{ω_c}=0.27$ is measured and a clear modulation of the polaritonic states as a function of the temperature is observed.
cond-mat.mes-hall↗