CMQED group

Hybridization of Terahertz Phonons and Magnons in Disparate and Spatially-Separated Material Specimens

2025-10-22T08:35:31Z

The interaction between condensed matter excitations and electromagnetic cavity fields serves as a rich playground for fundamental research and lies at the core of photonic and quantum technologies. Herein, the intriguing concept of composite states formed by distinct quasiparticles strongly coupled to the same optical cavity modes is experimentally and theoretically demonstrated. Specifically, magnons excited in a slab of an antiferromagnetic crystal and phonons excited in a distinct specimen of an insulating material are explored. The crystal slabs form an optical cavity with Fabry–Pérot oscillations in the terahertz range. Hybridized phonon–magnon polariton modes and their tunability by adjusting the distance between the slabs, showing that hybridization persists even at separations of up to several millimeters is demonstrated. The experimental results are interpreted using both classical and quantum electrodynamical models. The quantum description allows us to quantify the degree of hybridization linked to a topological behavior of the electric field phasor, in agreement with the classical electrodynamics expectations. The presented results are obtained at room temperature and cavities of millimeter size, paving the way for the engineering of realistic, frequency-tunable THz devices through the hybridization of electric (phononics) and magnetic (spintronics) elementary excitations of matter.

Patch antenna enhanced charge-sensitive infrared phototransistors

2025-10-20T18:31:19Z

Charge-sensitive infrared phototransistors (CSIP) constitute an outstanding technology for mid-infrared detection with sensitivities demonstrated at the single photon level. Here, we report on the performances of CSIP detectors operating at a wavelength λ = 8.9 μm that are integrated into double-metal patch antenna resonators. In order to build such devices, we have developed a fabrication protocol that allows accommodating the phototransistor architecture with the double-metal geometry providing very strong electromagnetic field confinement. We observe minimal photon fluxes in the order of 7000 photons/s.μm^2 that are 10^3 smaller with respect to previous realizations of devices with similar absorbing regions in a mesa geometry. This work opens additional perspectives for building ultra-small area devices, as required for single photon counters, while keeping high quantum absorption efficiencies.

3D Meta-Atoms for High Confinement of Mid-IR Radiation

2025-10-20T18:27:18Z

This is our work on 3D meta-atoms for Mid-Infrared waves !

The ability to confine photons into structures with highly sub-wavelength volumes is extremely interesting for many applications such as sensing, nonlinear optics, and strong light-matter interactions. However, their realization is increasingly difficult as the wavelength becomes shorter, due to fabrication challenges and increased metal losses. In this work, the first experimental characterization of 3D circuit-like resonators operating in the mid-infrared is presented. Through a combination of simulations, reflectivity measurements, and scanning near-field optical microscopy, an analytical model capable of predicting the electromagnetic response of these structures based on their geometrical parameters is developed. The studied design offers a high degree of flexibility, enabling precise control over the resonant frequency of the various modes supported by the resonator, as well as independent control over radiative and non-radiative losses. Combined with the extreme field confinement demonstrated, these meta-atoms are highly promising for applications
in detectors, emitters, nonlinear processes, and strong light-matter coupling.

Image produced by Francesco Pisani @ 2024

Quantum theory for nonlinear optical effects in the ultrastrong light-matter coupling regime

2025-10-20T18:05:04Z

A theoretical work where we describe non-linear effects that occur in microcavity-coupled quantum well systems that operate in the ultra-strong light-matter coupling regime.

We present a microscopic quantum theory for the nonlinear optical phenomena in semiconductor quantum well heterostructures operating in the regime of ultrastrong light-matter coupling regime. This work extends the Power-Zienau-Wooley (PZW) formulation of quantum electrodynamics to account for nonlinear interactions based on a fully fermionic approach, without resorting to any bosonization approximation. It provides a unified description of the microcavity and the local field enhancement effects on the nonlinear optical response, thus encompassing the phenomena known as epsilon near zero (ENZ) effect. In particular, our theory describes the impact of the light-matter coupled states on the high-frequency generation process, relevant for recent experimental investigations with polaritonic metasurfaces. We unveil the limitations of traditional single-particle approaches and propose novel design principles to optimize nonlinear conversion efficiencies in dense, microcavity-coupled electronic systems. The theoretical framework developed here provides an efficient tool for the development of advanced quantum optical applications in the midinfrared and terahertz spectral domains. Furthermore, it establishes a foundation for exploring the quantum properties of the ultrastrong light-matter regime through frequency-converted polariton states.

Dynamic metastable vortex states in interacting vortex lines

Alexis — 2024-08-30T08:21:42Z

Synchronisation is a phenomenon which can be found in incredibly enormous fields of studies : from a two coupled clocks to a ruby nuclear magnetic resonance laser with a delayed feedback, from atrial pacemaker cells to periodically stimulated fireflies. Historically, Christiaan Huygens first observed that two coupled or forced pendulum clocks can be synchronised. Then it turns out that this effect is very general for systems consist of coupled oscillators, no matter what nature of these oscillators or coupling is.

In our paper, we consider a synchronisation in a superconductivity domain. The usual example of synchronisation in superconductivity is the Josephson junction, which, forced by external microwave, shows typical synchronisation features. For example, the Shapiro steps, regions where while direct current changes, voltage remains the same corresponding to the second Josephson relation. In the non-linear community, they are better known as Arnold's tongues.). Here we consider another superconducting phenomenon — the Abrikosov vortex, that can also be synchronised and show that it lead not just the same Shapiro steps, to underline that it is an effect of synchronisation, but even to so-called fractional ones.

The first object of our study is a superconducting nanowire with linear defect, which we study numerically by means of Time-Dependent Ginzburg-Landau (TDGL) framework. We do not restrict ourselves to a particular nature of this defect : it can be as natural grain-boundaries in High-Temperature superconductors, or artificially made defects with Force Ion Beam or sputtered ferromagnetic material on top of the nanowire. Applying direct current with alternate microwave component with constant frequency and measuring voltage at some extent of the defect. When current reaches the critical one, Abrikosov vortex and its antivortex enters into the defect under the Lorenz force from the current, and then attracts each other and finally annihilate in the centre. Then the process repeats. When the vortex moves, it dissipates energy and we can calculate instantaneous voltage. Averaging this voltage in time, we can restore current-voltage characteristic (CVC) that usually are measured in experiment. In our simulation, we observed that not only the Shapiro steps are appeared when microwave current component increases, but a so-called fractional Shapiro Steps. These fractional steps are the sign of strongly anharmonic instantaneous voltage that leads to, that is also known as high-order Arnold's tongues.

In this first model, we discuss one simple vortex-antivortex oscillator, that can mimic Josephson junction with non-sinusoidal current-phase relationship, showing Shapiro steps and fractional Shapiro Steps. But there is still a significant difference. In our next step, we add another parallel linear defect at the distance that vortices in different lines can slightly interact. Now we have two coupled vortex-antivortex oscillators with applying direct current to create vortices and periodic drive of microwave alternate current with fixed frequency as in the first model. Increasing microwave current at first glance, we reproduce the results of the first model. But, starting from some value of microwave current, we observe some abrupt jumps and falls on a CVC. Having a closer look at what happens with vortices motion, we will see that they have different patterns of motion : when vortices enter simultaneously in each line and when they enter sequentially. The first situation appears to have a higher voltage, it is metastable and possible only with sufficient microwave current component because vortices in the neighbouring lines repel each other. This state is responsible for abrupt jumps on the current-voltage characteristic to high Shapiro steps. Then, when the direct current component increases to restore a CVC, a microwave current component is not sufficient and voltage drops as the system transits to a second sequential patter. But both patterns can be synchronous states.

To know more, this link will direct you to the paper.