Séminaires
(en anglais) The role of quantum measurement in stochastic thermodynamics
, C2N, Site marcoussis,Séminaires
I will present a new formalism to investigate stochastic thermodynamics in the quantum regime, where stochasticity and irreversibility primarily come from quantum measurement. In the absence of any bath, a purely quantum component to heat exchange, that corresponds to energy fluctuations caused by measurement back- action. Energetic and entropic signatures of measurement induced irreversibility are then investigated for canonical experiments of quantum optics, and the energetic cost of counter-acting decoherence is characterized on a simple state-stabilizing protocol. I will finally open on a new kind of genuinely quantum engines, where work is solely extracted from quantum measurement.
(en anglais) Thermodynamics of Quantum measurements
, C2N, bat D1, site de Marcoussis,Séminaires
Thermodynamics of Quantum measurements
(en anglais) On demand angle control in van der Waals heterostructures
, C2N, bat D1, site de Marcoussis,Séminaires
Van der Waals (vdW) heterostructures are formed by intercalation of layered, few atoms thick crystalline materials with different electronic, mechanical and optical properties (e.g. semiconductors, insulators). Beyond the individual study of such two-dimensional materials in the ultra-clean limit, this allows us to mix the properties of several materials, yielding new and as of yet inaccessible physics. While these heterostructures have become the gold standard for probing the electronic and optical properties of graphene and other exotic materials, the control over a crucial degree of freedom has been lacking so far: the relative angle between layers, or layers alignment. This angle changes the heterostructures' properties in dramatic ways. A wellknown example is graphene on boron nitride, where the relative angle between the two materials generates a periodic (Moiré) potential in graphene, strongly modifying its band structure. The absence of precise control over this angle has left these new properties out of reach so far. Here we developed an approach consisting in realizing heterostructures where the crystallographic alignment between layers can be manipulated in situ using an atomic force microscope to rotate one layer, while its mechanical and electronic properties are measured. We present results of in situ manipulation of a Moiré potential as well as tuning of the transmission between graphene layers by changing the relative orientation of the graphene crystals, Figure 1 a and b. In the later we found a 60° periodicity corresponding to crystal symmetry with additional sharp decreases around 22° and 39° (Fig. 1-c), which are among the commensurate angles of twisted bilayer graphene [1].
(en anglais) Planar optics with optical metasurfaces
, C2N, bat D1, site de Marcoussis,Séminaires
Abrupt modifications of the fields across an interface can be engineered by depositing an array of sub-wavelength resonators specifically tailored to address local amplitude, phase and polarization changes [1]. Physically, ultrathin nanostructure arrays (δ≪λ), also called ‘‘optical metasurfaces’’, control light by engineering artificial boundary conditions of Maxwell’s equations. Metasurfaces have been implemented to obtain various sorts of optical functionalities, ranging from the basic control of the transmission and reflection of light[1], to the control of the radiation patterns for comprehensive wavefront engineering and holography[2]. After transmission or reflection, however, the amount of propagation phase shift required to achieve any optical function depends on the wavelength, therefore, a specific phase profile imposed at interface will shape the light in a desired manner only for a single wavelength. This basic dispersion effect, which already affects bandwidth of conventional devices, is also limiting the operation of metasurfaces to a narrow bandwidth. We will discuss how to manage dispersion effect directly at interface to create multiwavelength achromatic metasurfaces for broadband control of light[3]. This approach is applied to fabricate dispersion-free beam deflectors and achromatic flat lenses in the near-infrared[6]. To conclude, we will talk about our recent results on free form optics and free-standing dielectric metasurfaces.
(en anglais) Potential use of Hydride Vapour Phase Epitaxy for discrete and integrated photonic devices
, C2N, bat D2 Site marcoussis,Séminaires
Hydride vapour phase epitaxy is a near equilibrium technique is unique in its potential use for fabricating certain specific photonic devices. I will demonstrate its usefulness with specific examples such as buried heterostructure quantum cascade lasers (BH-QCL) including BH photonic crystal QCL in the MIR range, monolithically integrated InP based devices on InP and on silicon and InP/Si heterojunction for high efficiency solar cells. Some recent results on these devices/structures obtained in our laboratory will be presented. We are also starting to look at the orientation-patterned GaP layers for second harmonic generation.
(en anglais) Ab initio calculations of the lattice thermal conductivity and the discovery of new thermoelectric..
, C2N-SITE orsay Salle P. Grivet (R-d-c pièce 44),Séminaires
Within the last few years it has been possible to compute the lattice thermal conductivity of bulk materials using ab initio methods. The interactions between the phonons are obtained from density functional theory and this information is incorporated into the Boltzmann to obtain the thermal conductivity. The good accuracy obtained from those calculations allows trying to use them to find new materials. We present several strategies that we used performing such a search. The first method we used is datamining. We screened the entire MPD library to find materials with ultra low thermal conductivity using a Bayesian algorithm based on kriging with gaussian regression processes. We were able to evidence new crystalline structures, some of them with a thermal conductivity lower than wood! Among these compounds some have good electronic properties that could make them exceptional thermoelectric materials. The second method we used is based on polymorphism. Starting from the experimentally known crystalline phase of the thermoelectric Zn-Sb compound, we reconstructed the energy surface using the Minima Hopping Method and discovered that the ground state is not the experimentally known phase. Computing the physical properties we realized that this new ground state has even better thermoelectric properties than the known ZnSb phase.
(en anglais) Growth of III-V semiconductors on Si
, C2N, bat D1, site de Marcoussis,Séminaires
Growth of III-V semiconductors on Si
Contrôle temporel des ondes : cristaux & miroirs temporels
None, Salle des séminaires Richard Planel, bâtiment D1, NoneSéminaires
(en anglais) Wave manipulation through temporal transformation
, C2N, bat D1, site de Marcoussis,Séminaires
Wave manipulation through temporal transformation
Photonique sur silicium : Réalité industrielle et challenges à venir
None, C2N, bat D1, site de Marcoussis, NoneSéminaires