Abstract-Out-of-Equilibrium Collective Oscillation as Phonon Condensation in a Model Protein

Ilaria Nardecchia, Jeremie Torres, Mathias Lechelon, Valeria Giliberti, Michele Ortolani, Philippe Nouvel, Matteo Gori, Yoann Meriguet, Irene Donato, Jordane Preto, Luca Varani, James Sturgis, Marco Pettini

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.031061

We describe the activation of out-of-equilibrium collective oscillations of a macromolecule as a classical phonon condensation phenomenon. If a macromolecule is modeled as an open system—that is, it is subjected to an external energy supply and is in contact with a thermal bath to dissipate the excess energy—the internal nonlinear couplings among the normal modes make the system undergo a nonequilibrium phase transition when the energy input rate exceeds a threshold value. This transition takes place between a state where the energy is incoherently distributed among the normal modes and a state where the input energy is channeled into the lowest-frequency mode entailing a coherent oscillation of the entire molecule. The model put forward in the present work is derived as the classical counterpart of a quantum model proposed a long time ago by Fröhlich in an attempt to explain the huge speed of enzymatic reactions. We show that such a phenomenon is actually possible. Two different and complementary THz near-field spectroscopic techniques—a plasmonic rectenna and a microwire near-field probe—have been used in two different labs to eliminate artifacts. By considering an aqueous solution of a model protein, the bovine serum albumin, we find that this protein displays a remarkable absorption feature around 0.314 THz, when driven in a stationary out-of-thermal equilibrium state by means of optical pumping. The experimental outcomes are in very good qualitative agreement with the theory developed in the first part of the paper and in excellent quantitative agreement with the theoretical result, allowing us to identify the observed spectral feature with a collective oscillation of the entire molecule.

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Abstract-Out-of-equilibrium collective oscillation as phonon condensation in a model protein

Ilaria Nardecchia, Jeremie Torres, Mathias Lechelon, Valeria Giliberti, Michele Ortolani, Philippe Nouvel, Matteo Gori, Yoann Meriguet, Irene Donato, Jordane Preto, Luca Varani, James Sturgis, and Marco Pettini

https://journals.aps.org/prx/accepted/2b071K1dY6a1e20d62871a345233bd6dc5eefd37f

In the first part of the present paper (theoretical), the activation of out-of-equilibrium collective oscillations of a macromolecule is described as a classical phonon condensation phenomenon. If a macromolecule is modeled as an open system, that is, it is subjected to an external energy supply and is in contact with a thermal bath to dissipate the excess energy, the internal nonlinear couplings among the normal modes make the system undergo a non-equilibrium phase transition when the energy input rate exceeds a threshold value. This transition takes place between a state where the energy is incoherently distributed among the normal modes, to a state where the input energy is channeled into the lowest frequency mode entailing a coherent oscillation of the entire molecule. The model put forward in the present work is derived as the classical counterpart of a quantum model proposed long time ago by H. Fr\"ohlich in the attempt to explain the huge speed of enzymatic reactions. In the second part of the present paper (experimental), we show that such a phenomenon is actually possible. Two different and complementary THz near-field spectroscopic techniques, a plasmonic rectenna, and a micro-wire near-field probe, have been used in two different labs to get rid of artefacts. By considering a aqueous solution of a model protein, the BSA (Bovine Serum Albumin), we found that this protein displays a remarkable absorption feature around 0.314 THz, when driven in a stationary out-of-thermal equilibrium state by means of optical pumping. The experimental outcomes are in very good qualitative agreement with the theory developed in the first part, and in excellent quantitative agreement with a theoretical result allowing to identify the observed spectral feature with a collective oscillation of the entire molecule.

Abstract-Confocal Imaging at 0.3 THz With Depth Resolution of a Painted Wood Artwork for the Identification of Buried Thin Metal Foils

Chiara Ciano, Mariano Flammini, Valeria Giliberti, Paolo Calvani, Eugenio DelRe,  Fabio Talarico, Mauro Torre,  Mauro Missori, Michele Ortolani

https://ieeexplore.ieee.org/document/8362985/

A compact confocal terahertz microscope working at 0.30 THz based on all-solid-state components is used to locate buried thin metal foils in a painted wood artwork. Metal foils are used for decoration, and their precise localization under the pictorial layer is relevant information for conservation scientists and restorers, which can neither be obtained by X-ray radiography nor by spectroscopic imaging in the infrared, as we directly show here. The confocal microscopy principle based on the spatial pinhole concept is here implemented by positioning the first focus of an ellipsoidal reflector at the phase center of horn antennas coupled to Schottky diode detector and emitter mounted in rectangular waveguide blocks, together with an optical beamsplitter. The second focus of the reflector is mechanically scanned inside the sample in three dimensions. The predictions of diffraction theory for a confocal microscope at an imaging wavelength of 1.00 mm with numerical aperture of 0.53 are verified experimentally (1.2 and 2.8 mm for the lateral and the axial resolution, respectively). These values of resolution allow a precise determination of the position of buried metal foils in an ancient piece of art hence making restoration interventions possible.

Abstract-Downconversion of terahertz radiation due to intrinsic hydrodynamic nonlinearity of a two-dimensional electron plasma

Valeria Giliberti, Alessandra Di Gaspare, Ennio Giovine, Michele Ortolani, Lucia Sorba, Giorgio Biasiol, Vyacheslav V. Popov, Denis V. Fateev, and Florestano Evangelisti

Phys. Rev. B 91, 165313 – Published 30 April 2015

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.165313

We have measured the electric signal downconverted from a terahertz frequency by an unbiased high mobility two-dimensional electron-gas (2DEG) device. The 2DEG was confined in an asymmetric plasmonic microcavity, and the radiation frequency was continuously tuned in the 0.2–0.4 THz range. The presence of resonant peaks at three frequencies corresponding to three plasma oscillation modes of the ungated 2DEG clearly points to the intrinsic nature of the hydrodynamic nonlinearity responsible for the downconversion as opposed to previously proposed plasmonic cavity configurations where the 2DEG oscillates under the metal gate that also acts as the source of the nonlinearity.

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Abstract-Superconductivity Induced Transparency in Terahertz Metamaterials

Odeta Limaj , Flavio Giorgianni , Alessandra Di Gaspare , Valeria Giliberti , Gianluca De Marzi ,Pascale Roy , Michele Ortolani , Xiaoxing Xi , Daniel Cunnane , and Stefano Lupi

http://pubs.acs.org/doi/abs/10.1021/ph500104k?journalCode=apchd5

Plasmonic analogue of Electromagnetically Induced Transparency is activated and tuned in the terahertz (THz) range in asymmetric metamaterials fabricated out of high critical temperature (Tc) superconductor thin films. The asymmetric design provides a near-field coupling between a superradiant and a subradiant plasmonic mode, which has been widely tuned through superconductivity and monitored by Fourier Transform Infrared spectroscopy. The sharp transparency window which appears in the extinction spectrum exhibits a relative modulation up to 50% activated by temperature change. The interplay between ohmic and radiative damping, which can be independently tuned and controlled, allows for engineering the electromagnetically induced transparency of the metamaterial far beyond the current state-of-the-art, which relies on standard metals or low-Tc superconductors.