CMQED group

Vortex-based Digital Superconducting Diode

2025-10-22T15:22:58Z

Last several decades the importance of creating effective superconducting electronics arises again for two main reasons. The first one is the energy consumption of modern computers based on semiconductors because of its large resistance, a dissipated heat in large-scale circuits becomes a significant problem.
This resistance also limits the possible operation speed. Superconductors have zero resistance and can work in THz range, that is two order of magnitude faster than current semiconductor processors. The second reason is the progress in quantum computing [1]. Qubits are very sensitive and can work only at very low temperature, and the question of having some preliminary operating circuit, that can de-couple
qubits from room-temperature computers, while making some classical computation efficiently, arises naturally.
Recent improvements in cryogenic and nanofabrication allow us not only show concepts of superconducting electronics but open a path to a real competition against semiconducting one. One of a basic element of any circuits is the diode — the element, that can provide signal flow only in one direction [2, 3]. It is used in rectifiers, AC–DC converters, and antennas for detecting electromagnetic signals. One of possible realizations of the superconducting diode is based on the operation of Abrikosov vortices — magnetic flux quantum [4]. The main advantages of this type is a relative fabrication simplicity. But there are still a lot of optimization in terms of design and operating protocols. Coupling vortices with external periodic drive can lead to effect of their synchronous motion [5].
Using that effect, it is possible to make a digital version of the superconducting diode : vortices move synchronously “1” or asynchronously “0”. In the Fig.1 these two states and transition from one to another are presented. Realization of this basic device with high-efficiency leads to more complex superconducting integrated circuits.

In this internship we propose to study properties of a vortex-based superconducting diode and optimizing its parameters for the best efficiency. It consists of three main parts : fabrication of different diode designs, transport measurements at cryogenic temperatures and numerical modelling based on time-dependent Ginzburg-Landau formalism for an optimal performance. The intern will acquire skills in nanofabrication, cryogenics, low-noise measurements and numerical modelling, as well as knowledge
in the field of superconductivity and condensed matter physics in general.

Prerequisite : A strong background in superconductivity and a taste for simulations and Python coding are recommended. If you are interested : please contact cheryl.feuilletpalma@espci.fr and sergei.kozlov@espci.fr.

Reference :
[1] F. Arute, K. Arya, R. Babbush, D. Bacon, J. C. Bardin, R. Barends, R. Biswas, S. Boixo, F. G. S. L. Brandao, D. A. Buell, B. Burkett, Y. Chen, Z. Chen,
B. Chiaro, R. Collins, W. Courtney, A. Dunsworth, E. Farhi, B. Foxen, A. Fowler, C. Gidney, M. Giustina, R. Graff, K. Guerin, S. Habegger, M. P.
Harrigan, M. J. Hartmann, A. Ho, M. Hoffmann, T. Huang, T. S. Humble, S. V. Isakov, E. Jeffrey, Z. Jiang, D. Kafri, K. Kechedzhi, J. Kelly, P. V.
Klimov, S. Knysh, A. Korotkov, F. Kostritsa, D. Landhuis, M. Lindmark, E. Lucero, D. Lyakh, S. Mandra, J. R. McClean, M. McEwen, A. Megrant, `
X. Mi, K. Michielsen, M. Mohseni, J. Mutus, O. Naaman, M. Neeley, C. Neill, M. Y. Niu, E. Ostby, A. Petukhov, J. C. Platt, C. Quintana, E. G. Rieffel,
P. Roushan, N. C. Rubin, D. Sank, K. J. Satzinger, V. Smelyanskiy, K. J. Sung, M. D. Trevithick, A. Vainsencher, B. Villalonga, T. White, Z. J. Yao,
P. Yeh, A. Zalcman, H. Neven, and J. M. Martinis, “Quantum supremacy using a programmable superconducting processor,” Nature, vol. 574,
pp. 505–510, Oct. 2019.
[2] P. J. W. Moll and V. B. Geshkenbein, “Evolution of superconducting diodes,” Nature Physics, vol. 19, pp. 1379–1380, Oct. 2023.
[3] M. Nadeem, M. S. Fuhrer, and X. Wang, “The superconducting diode effect,” Nature Reviews Physics, vol. 5, pp. 558–577, Sept. 2023.
[4] D. Margineda, A. Crippa, E. Strambini, Y. Fukaya, M. T. Mercaldo, M. Cuoco, and F. Giazotto, “Sign reversal diode effect in superconducting
Dayem nanobridges,” Communications Physics, vol. 6, p. 343, Nov. 2023.
[5] S. Kozlov, J. Lesueur, D. Roditchev, and C. Feuillet-Palma, “Dynamic metastable vortex states in interacting vortex lines,” Communications Physics,
vol. 7, pp. 1–8, June 2024.

Dynamical Coulomb blockade with NbN metamaterial resonators

2025-10-22T15:15:38Z

The ability to confine light at very small volumes is of paramount importance for enhancing light-matter interactions, both for devices and fundamental studies [1]. The Terahertz and sub-THz spectral domains are particularly prominent for building metallic resonators with ultra-sub-wavelength mode volumes. Indeed, the corresponding wavelengths are large (= 1mm – 100µm), one can leverage from nanofabrication techniques with nanometer resolution, and metals feature low losses, and even superconducting materials such as NbN are available [2]. The resonant architectures of choice are either double-metal cavities [3] or metamaterial resonators that can be engineered into 3D geometries [4], that are well mastered by our group.
In the present project, we will exploit such resonators made of NbN in order to realize and study an elementary system for both electronic transport and light-matter interaction : a semiconductor tunnel junction coupled with an ultra-subwavelength metamaterial resonator. This structure can operate in the Dynamical Coulomb Blockade, where the tunneling of electrons is coupled to the electromagnetic fluctuations of the resonator, providing thus a probe for the its quantum state. This concept was pioneered by M. Devoret, 2025 Nobel prize winner [5], and can even be used to study light-matter coupling systems in the extreme interaction regime known as Ultra-strong coupling [6].
Figure : Metamaterial resonators combined with semiconductor tunnel junctions realized in the CMQED team.
As an intern, the candidate will model, fabricate and characterize electromagnetic resonators in the 100 GHz range made from NbN layers. The internship will then be pursued as a PhD project funded by the ANR project HyQD100 where the resonators will be integrated with semiconductor tunnel junctions for the study of the regime of Dynamical Coulomb blockade, (Figure), for various applications both in the THz and sub-THz ranges. In particular, these junctions will be used for non-demolition quantum measurements of the 100 Qbits that will be produced in HyQD100. These studies open exciting possibilities for new types of devices which benefit from both concepts of semiconductor optoelectronics and superconducting quantum circuits.
The PhD candidate will receive a full training on nanofabrication techniques in the Paris Center cleanroom, and will acquire strong experience in the domains of quantum technologies and condensed matter physics, as well as advanced electromagnetism.

References :
[1] M. Fox, “Quantum Optics : An Introduction” (Oxford Master Series in Physics, 2006)
[2] H.T. Cheng et al., “Tuning the Resonance in High-Temperature Superconducting Terahertz Metamaterials”, Phys. Rev. Lett. 105, 247402 (2026)
[3] C. Feuillet-Palma et al., “Extremely sub-wavelength THz metal-dielectric wire microcavities”, Optics Express Vol. 20, Issue 27, pp. 29121-29130 (2012).
[4] M. Jeannin, et al. “Ultrastrong light–matter coupling in deeply subwavelength THz LC resonators “, ACS Photonics 6 (5), 1207-1215 (2019).
[5] M. H. Devoret, et al., “Effect of the electromagnetic environment on the Coulomb blockade in ultrasmall tunnel junctions”, Phys. Rev. Lett. 64, 1824 (1990).
[6] U. Iqbal, C. Mora, Y. Todorov,” Dynamical Coulomb blockade : An all-electrical probe of the ultrastrong light-matter coupling regime”, Physical Review Research 6 (3), 033097 (2024).

Quantum devices in the ultra-strong light-matter coupling regime

2025-10-22T15:07:48Z

The absorption and emission of light in an optoelectronic device are often considered as perturbative phenomena, which are treated in a single-particle picture. When the light-matter coupling energy, ћW_R, exceeds the dissipation rates of the system then the light-matter interaction is no longer a perturbative process, but instead energy is periodically exchanged with the microcavity at a frequency W_R, The system enters the strong coupling regime, where the cavity mode is split into two light-matter coupled (polariton) states separated by energy 2ћW_R. The last decade has seen the emergence of yet stronger interaction regime, where the coupling constant WR becomes comparable to the frequency of the matter excitation, W_m. This regime with W_R/W_m 1 is known as “ultra-strong” light-matter coupling and sets new frontiers for cavity quantum electrodynamics [1]. This regime can be realized with quantum heterostructures that interact with far infrared photons (TeraHertz, = 30µm-300µm and Mid-Infrared,lambda= 3µm-30µm domains) [2]. A very interesting topic is the possibility of observing the signatures of ultra-strong coupling in the electronic transport of devices such as infrared detectors [3] and tunnel junctions [4]. Such devices could enable the readout of the quantum properties of light in
the MIR and THz frequencies, thus opening a new field of application for quantum technologies.

As an intern, the candidate will characterize optoelectronic devices that have been already fabricated in clean room. She/he will thus acquire advanced training in infrared spectroscopy and electrical measurements of quantum devices, including in cryogenic conditions.

This activity will be followed by a PhD project, where the aim is to explore non-linear quantum devices operating in the ultra-strong light-matter coupling regime. We will study devices where semiconductor quantum wells are integrated into optical resonators featuring deep sub-wavelength electromagnetic confinement [5] (Figure). This activity will be guided by recent theoretical work from our group which studies non-linear optical conversion in the ultra-strong coupling regime [6]. For this project, the Ph.D. student will actively participate in the conception and fabrication of the nano-devices, starting from 3D numerical modeling, through clean-room processing and optical characterization of the structures. She/he will acquire not only strong scientific expertise in solid state devices and quantum optics, but also in nanofabrication techniques. The PhD project will be funded by an ANR project which is experimental collaboration with IEMN Lille.
References
[1] C. Ciuti, G. Bastard, and I. Carusotto, Phys. Rev. B 72, 115303 (2005).
[2] Y. Todorov, et al., Phys. Rev. Lett. 105, 196402 (2010).
[3] F. Pisani et al., Nature Comm. 14, 3914 (2023).
[4] U. Iqbal, C. Mora, Y. Todorov, Phys. Rev. Research 6, 033097 (2024).
[5] M. Jeannin et al. ACS Photonics 6, (5) 1207-1215 (2019).
[6] T. Krieguer, Y. Todorov, Phys. Rev. B 111, 165304 (2025).

Building Integrated SNSPDs to Develop an hBN Quantum Photonic Platform Including Single-Photon Emitters.

2025-10-22T14:07:37Z

The rapid progress of quantum technologies has revealed two key challenges. First, we need to precisely control quantum systems without disturbing their sensitive states — meaning keeping their quantum coherence.
Second, we must find efficient ways to convert quantum information into classical signals, so that the results of quantum operations can be measured and used at large scale. In quantum photonics, information is carried by individual photons. This approach depends on two main building blocks : single-photon sources, which generate one photon at a time, and single-photon detectors, which can detect them individually. These components are essential for many areas of quantum information science, such as quantum computing and quantum simulation.
So far, the most advanced systems use either external single-photon emitters that are distributed across several channels (demultiplexed), or on-chip processes that create photons in a probabilistic way, along with external detectors. However, these methods are still limited in efficiency, which makes it very hard to scale up to experiments involving many photons.
This technological bottleneck mainly comes from the fact that we still lack reliable fabrication methods to integrate high-performance photon sources and detectors directly onto photonic chips.

This proposal focuses on the experimental realization of integrated superconducting nanowire single-photon detectors [1, 2, 3, 4](SNSPDs) in hexagonal boron nitride (hBN) photonic circuits. The project aims to achieve a fully integrated quantum photonic platform where single photons are generated, routed, and detected on the same chip with high efficiency.

The intern will develop NbN-based superconducting nanowire single-photon detectors (SNSPDs) integrated into hBN waveguides. This internship is expected to lead to a PhD project funded by the ANR BONI&CLIDE in collaboration with GEMac group and LPENS [5, 6, 7, 8].

Through three main research axes during this PhD project such as fabrication and optimization of SNSPDs, experimental characterization of detector performance, and integration into quantum photonic demonstrators, we will develop an hBN-based platform for on-chip quantum experiments.
The PhD candidate will receive a full training on nanofabrication techniques in the Paris Center cleanroom, and will acquire strong experience in the domains of quantum technologies and condensed matter physics, superconductivity as well as advanced electromagnetism.

Prerequisite : A strong background in quantum physics and/or solid state physics. A taste for nanofabrication and transport measurements under cryogenic environnement.
Contact cheryl.feuilletpalma@espci.fr and sergei.kozlov@espci.fr.

References :
[1] Iman Esmaeil Zadeh et al. Superconducting nanowire single-photon detectors : A perspective on evolution, state-of-the-art, future developments,
and applications. Applied Physics Letters, 118:190502, 05 2021.
[2] Cheryl Feuillet-Palma. Transport et interaction mati`ere–rayonnement
dans des mat´eriaux corr´el´es. Comptes Rendus. Physique, 26:129–180,
2025.
[3] Paul Amari et al. Scalable Nanofabrication of High-Quality YBCO
Nanowires for Single-Photon Detectors. Physical Review Applied,
20(4):044025, October 2023.
[4] Sergei Kozlov et al. Dynamic metastable vortex states in interacting vortex lines. Communications Physics, 7(1):1–8, June 2024.
[5] Clarisse Fournieret al. Position-controlled spes with reproducible wavelength in hbn. Nature Communications, 12(1):3779, 2021. [Open Access].
[6] Domitille G´erard et al. Quantum efficiency and vertical position of
quantum emitters in hbn determined by purcell effect in hybrid metaldielectric planar photonic structures. ACS Photonics, 11:5188, 2024.
[Open Access].
[7] Clarisse Fournier et al. Investigating the fast spectral diffusion of a quantum emitter in hbn using resonant excitation and photon correlations.
Physical Review B, 107:195304, 2023. [Open Access].
[8] Domitille G´erard et al. Crossover from inhomogeneous to homogeneous
response of a resonantly driven hbn quantum emitter. Physical Review B,
111:085304, 2025.