Matériaux et Phénomènes Quantiques

MPQ

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Université Paris Diderot

UFR de rattachement >

UFR Physique

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UMR

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CNRS

Présentation

The laboratory « Matériaux et Phénomènes Quantiques » (Quantum Materials and Phenomena) is a joint research unit (UMR) of University Paris Diderot and CNRS. It involves about 120 people in total with a permanent staff of 51.

The laboratory specializes in the study of frontier quantum materials and in the development of novel quantum devices. These activities rely on a large spectrum of theoretical and experimental expertise in material physics, transport and optics, and technological platforms of clean-room fabrication, spectroscopy and high-resolution electronic microscopy.

The activities of the laboratory span:

novel materials at the nanoscale: nanocrystals, functionalized nanotubes, multiferroics, 2D materials, etc.
novel phases of matter: quantum fluids of light, ultrastrong coupling in cavity, unconventional superconductivity, strongly correlated systems, topological phases, etc.
nano-optical systems: optomechanics, nonlinear nanophotonics, nanoplasmonics, etc.
quantum engineering and quantum information: quantum optoelectronic devices, quantum photonic circuits, trapped ions, hybrid organic/inorganic devices, surface and interface engineering.

Current projects of the laboratory include the development of novel probes for the investigation of quantum materials, such as time-resolved Raman spectroscopy, optomechanical atomic force microscopy, and scanning tunneling microscopy under optical excitation. Reciprocally, frontier materials are being tested as building blocks to realize novel functionalities in optomechanical sensors, nonlinear and quantum photonics devices, or in cavity embedded transport experiments.

[hal-01944732] Demonstration of an Effective Ultrastrong Coupling between Two Oscillators

Date: 4 Dec 2018 - 18:55

Desc: When the coupling rate between two quantum systems becomes as large as their characteristic frequencies, it induces dramatic effects on their dynamics and even on the nature of their ground state. The case of a qubit coupled to a harmonic oscillator in this ultrastrong coupling regime has been investigated theoretically and experimentally. Here, we explore the case of two harmonic oscillators in the ultrastrong coupling regime. Probing the properties of their ground state remains out of reach in natural implementations. Therefore, we have realized an analog quantum simulation of this coupled system by dual frequency pumping a nonlinear superconducting circuit. The pump amplitudes directly tune the effective coupling rate. We observe spectroscopic signature of a mode hybridization that is characteristic of the ultrastrong coupling. We experimentally demonstrate a key property of the ground state of this simulated ultrastrong coupling between modes by observing simultaneous single- and two-mode squeezing of the radiated field below vacuum fluctuations.

[hal-02464078] On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

Date: 2 Feb 2020 - 21:58

Desc: Precious metal-free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells are gaining momentum, with Fe-N-C catalysts comprising atomic FeN x sites the most promising candidate. Research and development is shifting from activity targets to improved stability of Fe-N-C catalysts in fuel cells. Their durability has hitherto been extensively studied using accelerated stress tests (AST) performed at room temperature and in inert-gas saturated acidic pH electrolyte. Here, we reveal stronger degradation of the Fe-N-C structure and four times higher ORR activity loss when performing load cycling AST in O2-vs. Ar-saturated pH 1 electrolyte. Raman spectroscopy results point towards strong carbon corrosion after AST in O2 , even when cycling at low potentials of 0.3-0.7 V vs. the reversible hydrogen electrode, while no corrosion occurred after any load cycling AST in Ar. The load cycling AST in O2 leads to the loss of a significant fraction of FeN x sites, as shown by energy dispersive X-ray spectroscopy analyses, and to the formation of Fe oxides. The results support that the unexpected carbon corrosion occurring at such low potential in the presence of O2 is due to reactive oxygen species produced between H 2 O 2 and Fe sites via Fenton reactions.

[hal-01914019] Porous Hollow PtNi/C Nanoparticles and Their Many Facets

Date: 6 Nov 2018 - 16:22

Desc: Hollow nanoparticles made of a noble metal and a non-noble metal can be synthesized by a combination of galvanic replacement and the nanoscale Kirkendall effect. In these nanostructures, a metallic shell composed of individual nanocrystallites interconnected via grain boundaries surrounds a central cavity that is accessible to molecules through nanometre-sized pores. Moreover, because atomic vacancies enter the metal lattice during their formation, the surface of hollow metal nanoparticles is jagged both at the atomic and the nanometre scale. That gives them specific electrocatalytic properties, which are illustrated with reactions of increasing complexity (COads monolayer electrooxidation, oxygen reduction reaction, methanol and ethanol electrooxidation) and rationalized with Density Functional Theory calculations.

[hal-01914007] Effect of Atomic Vacancies on the Structure and the Electrocatalytic Activity of Pt-rich/C Nanoparticles: A Combined Experimental and Density Functional Theory Study

Date: 6 Nov 2018 - 16:21

Desc: We present a joint experimental and density functional theory (DFT) study on the effect of atomic vacancies on the restructuring of platinum-transition metal alloy nanocatalysts and the associated changes in electrocatalytic activity. Atomic vacancies were introduced into slabs composed of pure Pt monolayers, and the structures were relaxed using the Vienna ab initio simulation package code. Effects of i) the concentration and ii) the spatial distribution of atomic vacancies in the slabs on surface and bulk restructuring were investigated. Highly disordered nanostructures featuring large variations of the in-plane and out-of-plane nearest-neighbour distances around the mean were observed upon relaxation. These findings were confirmed experimentally by using hollow PtNi/C nanoparticles synthesized by a combination of galvanic replacement and the nanoscale Kirkendall effect (a vacancy-mediated interdiffusion mechanism). The experimental results also show that hollow PtNi/C nanoparticles feature a combination of oxophilic and oxophobic catalytic sites on their surface and are thus highly active both for electrochemical oxidation and reduction reactions.