Over the past decade, autonomous stabilization of bosonic qubits has emerged as a promising approach for hardware-efficient protection of quantum information. However, applying these techniques to more complex encodings than the Schrödinger cat code requires exquisite control of high-order wave mixing processes. The challenge is to enable specific multiphotonic dissipation channels while avoiding unintended non-linear interactions. In this work, we leverage a genuine six-wave mixing process enabled by a near Kerr-free Josephson element to enforce dissipation of quartets of excitations in a high-impedance superconducting resonator. Owing to residual non-linearities stemming from stray inductances in our circuit, this dissipation channel is only effective when the resonator holds a specific number of photons. Applying it to the fourth excited state of the resonator, we show an order of magnitude enhancement of the state decay rate while only marginally impacting the relaxation and coherence of lower energy states. Given that stray inductances could be strongly reduced through simple modifications in circuit design and that our methods can be adapted to activate even higher-order dissipation channels, these results pave the way toward the dynamical stabilization of four-component Schrödinger cat qubits and even more complex bosonic qubits.

PtSe2 is a van der Waals material transitioning from an indirect band gap semiconductor to a semimetal with increasing thickness. Its absorption threshold has been conjectured to originate from interband indirect transitions. By quantitative comparison between broadband (0.8-3.0 eV) optical absorption of high-quality exfoliated crystals and DFT ab initio simulations, we prove instead that the optical absorption arises only from direct transitions. This understanding allows us to shed light on the semiconductor-to-semimetal transition in an emblematic strongly thickness-dependent 2D material, and to explore the effect of stacking and excitons on the optical absorption.

The quantum anomalous Hall (QAH) effect, with its single chiral, topologically protected edge state, offers a platform for flying Majorana states as well as nonreciprocal microwave devices. While recent research showed the nonreciprocity of edge plasmons in Cr-doped (BixSb1-x)2Te3, the understanding of their dissipation remains incomplete. Our study explores edge plasmon dissipation in V-doped (BixSb1-x)2Te3 films, analyzing microwave transmission across various conditions. We identify interactions with charge puddles as a primary source, providing insights critical for developing improved QAH-based technologies.

High-frequency transport in the edge states of the quantum spin Hall (QSH) effect has to date rarely been explored, though it could cast light on the scattering mechanisms taking place therein. We here report on the measurement of the plasmon velocity in topological HgTe quantum wells both in the QSH and quantum Hall (QH) regimes, using harmonic GHz excitations and phase-resolved detection. We observe low plasmon velocities corresponding to large transverse widths, which we ascribe to the prominent influence of charge puddles forming in the vicinity of edge channels. Together with other recent works, it suggests that puddles play an essential role in the edge state physics and probably constitute a main hurdle on the way to clean and robust edge transport.

High-frequency transport in the edge states of the quantum spin Hall (QSH) effect has to date rarely been explored, though it could cast light on the scattering mechanisms taking place therein. We here report on the measurement of the plasmon velocity in topological HgTe quantum wells both in the QSH and quantum Hall (QH) regimes, using harmonic GHz excitations and phase-resolved detection. We observe low plasmon velocities corresponding to large transverse widths, which we ascribe to the prominent influence of charge puddles forming in the vicinity of edge channels. Together with other recent works, it suggests that puddles play an essential role in the edge state physics and probably constitute a main hurdle on the way to clean and robust edge transport.

Arrays of field-effect transistors are fabricated from chemical vapor deposition grown graphene (GFETs) and label-free detection of DNA hybridization performed down to femtomolar concentrations. A process is developed for large-area graphene sheets, which includes a thin Al2 O3 layer, protecting the graphene from contamination during photolithographic patterning and a SiOx capping for biocompatibility. It enables fabrication of high-quality transistor arrays, exhibiting stable close-to-zero Dirac point voltages under ambient conditions. Passivation of the as-fabricated chip with a layer composed of two different oxides avoids direct electrochemical contact between the DNA solutions and the graphene layer during hybridization detection. DNA probe molecules are electrostatically immobilized via poly-l-lysine coating of the chip surface. Adsorption of this positively charged polymer induces a positive shift of the Dirac point and subsequent immobilization of negatively charged DNA probes induces a negative shift. Spatially resolved hybridization of DNA sequences is performed on the GFET arrays. End-point as well as real-time in situ measurements of hybridization are achieved. A detection limit of 10 fm is observed for hybridization of 20-nucleotide DNA targets. Typical voltage signals are around 100 mV and spurious drifts below 1 mV per hour.

Helium is recognized as a model system for the study of phase transitions. Of particular interest is the superfluid phase in two dimensions. We report measurements on superfluid helium films adsorbed on the surface of a suspended carbon nanotube. We measure the mechanical vibrations of the nanotube to probe the adsorbed helium film. We demonstrate the formation of helium layers up to five atoms thickness. Upon increasing the vapor pressure, we observe layer-by-layer growth with discontinuities in both the number of adsorbed atoms and the speed of the third sound in the adsorbed film. These hitherto unobserved discontinuities point to a series of first-order layering transitions. Our results show that helium multilayers adsorbed on a nanotube are of unprecedented quality compared to previous works. They pave the way to new studies of quantized superfluid vortex dynamics on cylindrical surfaces, of the Berezinskii-Kosterlitz-Thouless phase transition in this new geometry, and perhaps also to supersolidity in crystalline single layers as predicted in quantum Monte Carlo calculations.

Helium-4 atoms are bosons, with the capability to turn superfluid at very low temperature. Remarkably, this property is conserved even when the thickness of the Helium film is reduced down to few atoms thick only. The study of 2D helium films has led to several breakthrough in condensed matter physics including the study of third sound and topological phase transitions, the latter being rewarded by the 2016 Nobel Prize. In most experimental studies helium was adsorbed on large scale substrates, such as mm2 scale grafoil plates or Mylar. Recent advances in the field of optomechanics and nanomechanics now opens up the possibility to study fluids and superfluids of smaller dimensions. In this talk, we present our recent experiments on helium films probed through the mechanical vibrations of a carbon nanotube. We observed a strong discontinuity in the adsorption of He on the nanotube surface, that we attributed to a layering transition. In addition, the low-temperature dependence of the mechanical mode of the nanotube exhibit a mode softening. Thanks to the tunability of the nanotube resonator, we confirmed the spring nature of this effect and drawn a link with the propagation of third sound in He 2D films.

This paper presents a new method based on Non Destructive Readout (NDRO) to improve multi-exposure High Dynamic Range (HDR) Imaging. A sequence of Low-Dynamic Range (LDR) images can then be acquired during a single exposure. The concept enables the latency between LDR images to be removed as well as the intrinsic ghost artifacts observed using state-of-art HDR systems based on multi-exposures. The method has been applied to improve the performances of HDR sensor based on logarithmic pixels. Using the NDRO method, a Short Wave InfraRed (SWIR) camera has been designed to produce HDR IR videos. A real-time HDR video stream generation is achieved based on GPU implantation.

J. Chaste, 2 E. Pallecchi, 2 P. Morfin, 2 G. Fève, 2 T. Kontos, 2 J.-M. Berroir, 2 P. Hakonen, and B. Plaçais 2, ∗ Ecole Normale Supérieure, Laboratoire Pierre Aigrain, 24 rue Lhomond, 75005 Paris, France CNRS UMR8551, Laboratoire associé aux universités Pierre et Marie Curie et Denis Diderot, France Helsinki University of Technology, Low Temperature Laboratory, Puumiehenkuja 2 B, Espoo, P.O. Box 5100, FI-02015 TKK, FINLAND (Dated: September 30, 2009)

The Kondo effect is a very active subject in condensed matter physics and a paradigm for strongly correlated electronic system s. It arises as a resonant antiferromagnetic coupling between the spin of an impurity with the spin of the conduction electrons in the host matrix. In nanoscale conductors like carbon nanotube devices, the spin impurity is formed in a strong Coulomb blockade region where charge is quenched. Such artificial impurities offer new perspectives for the study of the Kondo effect, in particular in out-of-equilibrium situations. We report here on {\it current noise} measurements in a carbon nanotube quantum dot tuned to the Kondo regime. A strong enhancement of the current noise is observed within the Kondo resonance compared to simple non-interacting theories. While the measured conductances come close to the unitary limit $2 e^2/h$, the noise is not suppressed as in a coherent conduc tor but remains sizeable. This effect can not be accounted for, either by a resonant level model, or by a simple SU(2) Kondo mode l. This emphasizes the importance of the doubly degenerate orbital degree of freedom (in addition to the spin degeneracy) in the dot related to clockwise and counterclockwise motion around the nanotube. Moreover, the addition of this orbital pseudo-spin with the true spin could lead to Kondo screening with an enhanced SU(4) symmetry. In fact, using an interacting slave-boson mean field (SBMFT) approach with SU(4) symmetry to describe the Kondo effect, we can account~\cite{delattre:09} for both conductance and noise measurements with a rather good agreement. Noisy Kondo impurities Nature Physics 5 (2009) 208-212

At LPA, we study, among other things, the physical properties of Semiconductor Nanostructures. Many of these properties are in the optical domain. Until 2002 we only used monochromator systems with Avalanche Photodiodes (APD) and a spectrometer. The Performance of this kind of detector system is no longer efficient and so we began the development of CCD camera. As soon as the first system was installed, we were able to observe physical effects in these Nanostructures, as predicted by theory.