CMQED group

Anne Le Floc'h

2026-10-15T08:02:23Z

Anne Le Floc'h is a PhD student focusing on memory effects induced by vortex dynamics in ultra-thin disordered Nb and NbN films for possible applications in superconducting electronics as memristor or self-learning artificial synapse for neuromorphic computations.

Lunding Guo

2026-10-14T15:37:56Z

Lunding is currently pursuing her PhD at ESPCI Paris, focusing on the design, fabrication, and characterization of superconducting nanowire single-photon detectors (SNSPDs) and their integration with hexagonal boron nitride (hBN). Her research aims to develop an integrated quantum photonic platform combining single-photon emission and detection on a chip.

Lunding received her Bachelor's degree in China and subsequently obtained her Master's degree in Quantum Engineering from École Normale Supérieure (ENS), Paris. Her previous research experience includes working on photodetectors based on two-dimensional transition metal dichalcogenides (TMDs) and quantum-dot-based whispering-gallery-mode microlasers.

She is currently pursuing her PhD at ESPCI Paris, focusing on the design, fabrication, and characterization of superconducting nanowire single-photon detectors (SNSPDs) and their integration with hexagonal boron nitride (hBN). Her research aims to develop an integrated quantum photonic platform combining single-photon emission and detection on a chip.

Ninghshun Chen

Alexis — 2026-10-02T13:22:47Z

Ning obtained his bachelor's degrees at the University of Virginia and worked as a software developer in the private industry. He then pursued a master's degree at the École Normale Supérieure in Paris. His internship work on the theory and simulation of Markovianity in light-matter excitation laid the foundation for his current research.This includes uncovering the impacts of static Coulomb interactions on nonlinear effects in highly-doped cavity-coupled asymmetric quantum well heterostructures.The results of these studies supplement his search for a full description of the ultrastrong light-matter coupled system's quantum properties. This requires going beyond the semiclassical factorization scheme by taking into consideration the microscopic quantum fluctuations in the optoelectronic devices.

Local sub-THz photons for coherent light-matter interaction

Alexis — 2026-09-28T18:40:34Z

Condensed matter systems are the center of many gamechanging technologies : superconductivity for example has allowed quantum-limited amplifiers for more sensitive detection schemes, and spin excitations, called magnons, hold the promise for energyefficient computation with the emerging field of spintronics. By developing the first on-chip microwave-to-THz frequency converter combined with state-of-the-art topological metamaterials for guiding the signal, this project will provide access to typical coherence times of magnons in nano-resonators made of YIG thin films, and access the dressed magnonic state resulting from light-matter interaction. Ultimately, this platform will allow for the exploration of novel physics such as quantum magnonic [1].

Figure 1 : a) Lumped resonator for the coupling between light and a magnonic excitation
in a YIG thin film. b) Schematic of a THz local sensing platform. On-chip frequency conversion allows for a short distance
over which the THz signal will propagate. A lumped resonator coupled to the system under study is probed using a coherent excitation.

In a thin film geometry the number of spin is very low (N ∼ 10⁵) and the magnons energy is in the meV range, which corresponds to sub-THz frequencies. To provide a local probe on mesoscopic scales (typically 1 μm), the PhD student will simulate, fabricate and characterize lumped superconducting THz resonators (see fig. 1a), that will increase the coupling between the so called 'circuit' photons and the magnons. In parallel, the student will develop an integrated THz detection platform using the non-linearity induced by a thin superconducting film to realize four-wave parametric frequency conversion [2]. Finally, to convey the signal from the converter to the resonator, a topological metamaterial will be designed. These metamaterials have already been used to strongly attenuate the losses due to radiation [3].

The goal of this PhD is to bring together a frequency converter based on NbN superconducting thin films, and topological waveguides in Silicon to guide THz signals towards a high quality resonator for the detection of magnons in thin films (see fig. 1 b). The applications of such a platform for THz physics goes from fundamental condensed matter physics to state-of-the-art quantum information.

Prerequisite : A strong background in quantum mechanics, condensed matter physics and a taste for simulations and Python coding are recommended.

[1] Y. Tabuchi, S. Ishino, A. Noguchi, T. Ishikawa, R. Yamazaki, K. Usami, and Y. Nakamura, “Quantum magnonics : The magnon meets the superconducting qubit,” Sci. Direct, vol. 17, pp. 729–739, 2016.
[2] M. Pechal and A. H. Safavi-Naeini, “Millimeter-wave interconnects for microwave-frequency quantum machines,” PRA, vol. 96, 2017.
[3] Y. Yang, Y. Yamagami, X. Yu, P. Pitchappa, J. Webber, B. Zhang, M. Fujita, T. Nagatsuma, and R. Singh, “Terahertz topological photonics for on-chip communication,” Nature Photonics, vol. 14, pp. 446–451, 2020.

Contact : alexis.jouan@espci.fr

Bio-inspired superconducting sensors for sub-THz technologies

Alexis — 2026-09-28T18:17:09Z

The human cochlea is an extraordinarily sensitive sensor that decomposes sound into spatially separated frequencies across three decades with a dynamic range exceeding 120 dB. At its core, the human ear is based on a collection of sub-wavelength non-linear resonators. In the sub-THz frequency range, the losses become too high to realize efficient detectors, but superconductors exhibit minimal ohmic dissipation and a kinetic inductance that varies quadratically with current [1, 2]. For example, Fig. 1 a shows the dependance in temperature of a CPW resonator frequency due to this kinetic inductance.

The goal of this PhD project is to use this intrinsic nonlinearity to mimic the non-linear amplification occurring in the cochlea, providing tunability and enhanced spectral selectivity. At first, the candidate will characterize the response of a few subwavelength superconducting resonators at 100 GHz. The measurement of the self-Kerr non-linearity will give access to the quadratic dependance on the current I inside the superconducting resonator (see Fig. 1 b). This will give the opportunity to study non-reciprocal behavior in non-linear systems which may have crucial applications in the field of quantum technologies.

Figure 1 : a, NbN resonator measured bolow its critical temperature b, Nonreciprocal transmission within a planar superconducting metamaterial based on the nonlinear inductance of NbN. c, Rainbow trap geometry

The PhD student will then create a rainbow trap experiment in the sub-THz as depicted on Fig. 1 c. This structure introduces a radically new approach to sub-THz spectroscopy, inspired by the acoustic behavior of the human cochlea. Unlike conventional TDS systems relying on bulky optics and timegating, it aims for a single-shot, fully integrated superconducting on-chip spectrometer that directly maps frequencies in space. Its originality stems from three main elements : bio-inspired active graded designs, superconducting metamaterials with minimal dissipation and intrinsic kinetic-inductance nonlinearities, and operation in the underexplored sub-THz regime, promising for molecular and quantum sensing. By exploiting the synergy between biological efficiency with quantum-graded materials, we aim to establish a new class of compact, high-performance spectroscopic sensors.

[1] B. Ho Eom, P. K. Day, H. G. LeDuc, and J. Zmuidzinas, “A wideband, low-noise superconducting amplifier with high dynamic range,” Nature Physics, vol. 8, no. 8, pp. 623–627, 2012.
[2] J. Luomahaara, V. Vesterinen, L. Gr¨onberg, and J. Hassel, “Kinetic inductance magnetometer,” Nature Communications, vol. 5, no. 1, p. 4872, 2014.

Contact : alexis.jouan@espci.fr and fabrice.lemoult@espci.fr

Redza Zainudin

Alexis — 2026-04-30T09:04:18Z

Building a 100GHz qubit for quantum sensing applications

Redza studied at National University of Malaysia and did his master at the university of Tokyo. He discovered superconducting circuits during his internship in the Nakamura Group where he worked on the photon generation and absorption using a Fluxonium qubit. His PhD is part of the ANR project HyQD100. The goal is to develop a tunable mm-wave qubit which will be integrated with semi-conducting structures in order to detect and control condensed matter excitations.

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.