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The growing interest in quantum technologies, from fundamental physics experiments to quantum computing, demands for extremely performing electronics only adding the minimum amount of noise admitted by quantum mechanics to the input signal (i.e. quantum-limited electronics). Superconducting microwave amplifiers, due to their dissipationless nature, exhibit outstanding performances in terms of noise (quantum limited), and gain. However, bandwidth and saturation power still show space for substantial improvement. Within the DARTWARS* collaboration, we are developing state-of-the-art microwave superconducting amplifiers based on Josephson junction arrays and on distributed kinetic inductance transmission lines. Here we report the realization of a setup for the characterization of the performances of Josephson Traveling-Wave Parametric Amplifiers (JTWPA) at a temperature of 300 mK. Although in the final experimental setup these amplifiers will operate at a base temperature of about 20 mK, their characterization at 300 mK allows to evidence the main aspects of their performances, but the ultimate noise level. This represents a quick and relatively inexpensive way to test these superconductive devices that can be of help to improve their design and fabrication. IEEE

The recent developments in quantum technologies, as well as advanced detection experiments, have raised the need to detect extremely weak signals in the microwave frequency spectrum. To this aim, the Josephson travelling wave parametric amplifier, a device capable of reaching the quantum noise limit while providing a wide bandwidth, has been proposed as a suitable cryogenic front-end amplifier. This work deals with the numerical study of a Josephson travelling wave parametric amplifier, without approximations regarding the nonlinearity of the key elements. In particular, we focus on the investigation of the system of coupled nonlinear differential equations representing all the cells of the Josephson travelling wave parametric amplifier, with proper input and output signals at the boundaries. The investigation of the output signals generated by the parametric amplification process explores the phase-space and the Fourier spectral analysis of the output voltage, as a function of the parameters describing the pump and signal tones that excite the device. Beside the expected behavior, i.e., the signal amplification, we show that, depending on the system operation, unwanted effects (such as pump tone harmonics, incommensurate frequency generation, and noise rise), which are not accounted for in simple linearized approaches, can be generated in the whole nonlinear system. IEEE

The Italian institute for nuclear physics (INFN) has financed the SIMP project (2019-2021) in order to strengthen its skills and technologies in the field of meV detectors with the ultimate aim of developing a single microwave photon detector. This goal will be pursued by improving the sensitivity and the dark count rate of two types of photodetectors: current biased Josephson Junction (JJ) for the frequency range 10-50 GHz and Transition Edge Sensor (TES) for the frequency range 30-100 GHz. Preliminary results on materials and devices characterization are presented., Comment: 7 pages, 4 figures

Transition-Edge Sensors (TESs) are versatile superconducting microcalorimeters used as single photon detectors in a large range of electromagnetic wavelength, from X-rays to near-infrared. Among the many materials investigated in literature, Ti/Au is one of the most widely used bilayer to fabricate TES thanks to simple deposition process, long term stability material and protection against oxidation of Ti film by Au over layer. Moreover, the critical temperature of Ti/Au can be tuned by trimming the thickness of Ti and Au films. For low energy photon detection, the Ti/Au superconducting layer performs simultaneously as absorber and thermometer. This implies that a TES thickness reduction helps to significantly reduce the thermal capacitance, which has a direct impact on the detector energy resolution. In this paper we present a study of the superconducting properties of Ti/Au films, grown in UHV by thermal evaporation as a function of Ti thickness. The chemical state of Ti and Ti/Au were analyzed by X-ray photoelectron spectroscopy, to evaluate the protective effect of Au film. The film morphology, structure and optical properties were investigated by ellipsometry. The critical temperature showed a marked trend on film thickness and was strongly affected by Au cover layer. Ti film of only 12 nm thick covered with 10 nm Au film showed a remarkable critical temperature of about 300 mK.

In this work, the interface composition of the superconducting Ti/PdAu bilayer is tuned by an annealing process in N2 from 100 to 500 &deg, C to control the superconducting transition temperature (Tc). This Ti-PdAu composition layer is characterized with a high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) to show the infiltration process. The surface topography, electrical, and cryogenic properties are also shown. The inter-infiltration of Ti and PdAu induced by the thermal treatments generates an intermixed layer at the interface of the bilayer film. Due to the enforced proximity effect by the annealing process, the Tc of Ti (55 nm)/PdAu (60 nm) bilayer thin films is tuned from an initial value of 243 to 111 mK which is a temperature that is suitable for the application as the function unit of a superconducting transition edge sensor.

The room temperature dual-mode self-calibrating detector combines low-loss photodiodes with electrical substitution radiometry for determination of optical power. By using thermal detection as a built-in reference in the detector, the internal losses of the photodiode can be determined directly, without the need of an external reference. Computer simulations were used to develop a thermal design that minimises the electro-optical non-equivalence in electrical substitution. Based on this thermal design, we produced detector modules that we mounted in a trap structure for minimised reflection loss. The thermal simulations predicted a change in response of around 280 parts per million per millimeter when changing the position of the beam along the centre line of the photodiode, and we were able to reproduce this change experimentally. We report on dual-mode internal loss estimation measurements with radiation of 488 nm at power levels of 500 μW, 875 μW and 1250 μW, using two different methods of electrical substitution. In addition, we present three different calculation algorithms for determining the optical power in thermal mode, all three showing consistent results. We present room temperature optical power measurements at an uncertainty level approaching that of the cryogenic radiometer with 400 ppm (k = 2), where the type A standard uncertainty in the thermal measurement only contributed with 26 ppm at 1250 μW in a 6 hour long measurement sequence.

Josephson junctions, in appropriate configurations, can be excellent candidates for detection of single photons in the microwave frequency band. Such possibility has been recently addressed in the framework of galactic axion detection. Here are reported recent developments in the modelling and simulation of dynamic behaviour of a Josephson junction single microwave photon detector. For a Josephson junction to be enough sensitive, small critical currents and operating temperatures of the order of ten of mK are necessary. Thermal and quantum tunnelling out of the zero-voltage state can also mask the detection process. Axion detection would require dark count rates in the order of 0.001 Hz. It is, therefore, is of paramount importance to identify proper device fabrication parameters and junction operation point., Comment: 7 pages, 9 figures

Transition edge sensors (TESs) with high energy resolution (ΔE) at telecommunication wavelengths have been realized in the last years for application to experiments of quantum optics and quantum information. In these fields, lasers with repetition rate of the order of 50 MHz are usually applied and hence TES with recovery times lower than 20 ns would be desirable. To this aim, Ti TESs with area ranging between 1 μm × 1 μm and 2 μm × 2 μm are fabricated and characterized, to study the effects of the different sizes of active areas and critical temperatures on the energy resolutions and on the response times. Titanium TESs have been fabricated by thermal evaporation and Electron Beam Lithography technique on Si/SiN substrates, and they have been electrically and optically characterized. The experimental data have been analyzed and correlated to the detector geometrical parameters. The superconducting transitions of TESs with areas down to 1 μm × 1 μm result to be affected by lateral proximity effects of Nb wirings. Ti TESs with critical temperature of 470 mK show response time of about 150 ns and energy resolution of 0.16 eV.

The increasing demand for light emitting diodes (LEDs) is driven by a number of application categories, including display backlighting, communications, signage, and general illumination. Nowadays, they have also become attractive candidates as new photometric standards. In recent years, LEDs have started to be applied as wavelength-selective photo-detectors as well. Nevertheless, manufacturers’ datasheets are limited about LEDs used as sources in terms of degradation with operating time (aging) or shifting of the emission spectrum as a function of the forward current. On the contrary, as far as detection is concerned, information about spectral responsivity of LEDs is missing. We investigated, mainly from a radiometric point of view, more than 50 commercial LEDs of a wide variety of wavelength bands, ranging from ultraviolet (UV) to near infrared (NIR). Originally, the final aim was to find which LEDs could better work together as detector-emitter pairs for the creation of self-calibrating ground-viewing LED radiometers; however, the findings that we are sharing here following, have a general validity that could be exploited in several sensing applications.

Transition-edge sensors (TESs) are single photon detectors attractive for applications in quantum optics and quantum information experiments owing to their photon number resolving capability. Nowadays, high-energy resolution TESs for telecommunication are based on either W or Au/Ti films, demonstrating slow recovery time constants. We report our progress on the development of an Al/Ti TES. Since bulk aluminum has a critical temperature (Tc) of ca. 1.2 K and a sufficiently low specific heat (less than 10(-4) J/cm³K²), it can be employed to produce the sensitive material for optical TESs. Furthermore, exploiting its high Tc, Al-based TESs can be trimmed in a wider temperature range with respect to Ti or W. A first Al/Ti TES with a Tc ≈ 142 mK, investigated from a thermal and optical point of view, has shown a response time constant of about 2 μs and single photon discrimination with 0.34 eV energy resolution at telecom wavelength, demonstrating that Al/Ti films are suitable to produce TESs for visible and NIR photon counting.

Optical sources that deterministically produce single photons with a high suppression of multi-photon emission and a negligible background component are promising candidates for standard sources for quantum metrology, quantum communication and foundations of quantum mechanics. In this paper, the photon number distribution of non-classical light emitted by nitrogen vacancy (NV) centres in nano-diamonds is studied by three different experimental techniques. The photon number resolving transition edge sensor (TES) detector and the On/Off detection method are applied to determine the diagonal elements of the optical density matrix. From the data measured by the two methods the second order correlation function at time delay zero is calculated and compared with the g2(0)-values obtained by Hanbury Brown?Twiss (HBT) interferometric measurements. Among the g2(0)-values evaluated with the three techniques, we found good agreement in the results for a single photon emitter with a g2(0)-value close to zero and a multi-photon source with a g2(0)-value of approximately 0.5.

Single photon detectors are fundamental devices in several scientific fields, like in optical science and technology. We introduce the state of the art of Transition Edge Sensors, developed and characterized at INRIM, to detect photons from optical to near-infrared wavelength range (406–1570 nm). Both the capability to resolve up to 29 incident photons in a single pulse and to discriminate up to 2 photons with an energy resolution of 0.18 eV have been reached.

Transition-edge sensors (TESs) are promising micro-calorimeters for applications in the field of quantum information, quantum computation and metrology due to their photon-number resolving capability. Quantum efficiency (QE) is fundamental in single-photon detection and it should be as high as possible. For this reason the coupling between the light source and the sensor plays a crucial role.

Single photon detectors are fundamental tools for quantum metrology, e.g. to calibrate both detectors and sources, as for quantum information. One of the most promising detectors able to resolve single photons is the transition-edge sensor (TES). We report our last results obtained with Ti/Au TES deposited on SiN substrate. Photon counting measurements, obtained by using pulsed sources, in the NIR-visible wavelength range, show the ability to resolve up to fourteen photons with an energy resolution of 0.44 eV at 690 nm (1.80 eV) and 0.38 eV at 1310 nm (0.95 eV), with a good linearity. A preliminary measurement obtained by using a parametric down conversion (PDC) heralded single photon source, at 812 nm (1.53 eV), is also reported.

In previous papers (Mazzetti et al. in Phys. Rev. B 77:064516, 2008; Ponta et al. in Phys. Rev. B 79:134513, 2009) the mechanism of resistive transition of MgB 2 films has been investigated by the analysis of the non-stationary noise produced during the transition process. The developed model suggested that when the transition occurs very near to T C at low bias current, a mixed state, consisting of normal and superconductive domains, takes place. A different model based on fluxoids dynamics, generated by the current and/or by an external field, is appropriate when the transition occurs at strong bias currents and temperatures much lower than T C . The purpose of this paper is a further investigation of the transition process at low bias currents by analyzing the 1/f power spectra of the noise, taken in stationary conditions at different values of the specimen resistance. These spectra, when renormalized to represent the relative fluctuation of the specimen resistance, are practically coincident, a fact in agreement with the developed model.

Photon-number discriminating detectors are fundamental to new quantum photon-based standards. We report results on superconducting transition-edge sensors based on Ti/Au and Ti/Pd bilayers allowing pulses containing up to five photons to be discriminated.

An original model for the interpretation of the noise produced during the resistive transition of disordered granular superconductive films, induced by a slow temperature change, has been recently developed and tested on MgB2 films. Both the amplitude and frequency behavior of the noise power spectrum, simulated on the basis of this model, are in very good agreement with the experimental data, practically without the introduction of adjustable parameters. The model is based on the onset of correlated transitions of large sets of grains, forming resistive layers through the film cross-section area during the transition process. The strong non-linear behavior and correlation of the grains produces abrupt resistance variations, giving rise to the large noise, of the 1/f3 type, observed in experiments. Presently this model is tested under more general conditions, producing the resistive transition under an external magnetic field. The results show that the field reduces the grain critical current density but does not change the mechanism of the transition process. An alternative transition model, based on fluxoids depinning and motion, which would produce a much lower, 1/f type transition noise, can thus be excluded by the present analysis.

The quantum efficiency of superconducting light detectors with film thicknesses ≥ 100 nm is mainly limited by the reflection losses at the superconducting film surface, which are usually higher than 50%. In this work we show that it is possible to reduce the reflection of Ti/Au and Ir/Au films to under 1% at telecommunication wavelengths, by means of properly designed antireflection coatings. The effect of optical cavity structures is also considered in the case of highly transmitting Ti and Ir films with thickness lower than 50 and 70 nm respectively in order to enhance absorption.

High efficiency and negligible dark-count rates of transition-edge sensor (TES) microcalorimeters as single photon detector at telecommunications and optical visible wavelengths make them powerful tools for quantum information and quantum computation. In this work we report details on the fabrication of Au/Ti for photon counting and analyse the effects on the critical temperature and the transition steepness of the structuring process and wiring material. Au/Ti films deposited by electron-beam at substrate temperature lower than 435 K show sharp transition and reproducible Tc. Moreover, we observe that TES with Al wiring are more stable and have better characteristics of TES with Nb wiring. Using 20 micron×20 micron Ti/Au TES single photon detection has been obtained in the UV-visible range.

The calibration of a quantum channel, i.e. the determination of the transmission losses affecting it, is definitely one of the principal objectives in both the quantum communication and quantum metrology frameworks. Another task of the utmost relevance is the identification, e.g. by extracting its photon number distribution, of the noise potentially present in the channel. Here we present a protocol, based on the response of a photon-number-resolving detector at different quantum efficiencies, able to accomplish both of these tasks at once, providing with a single measurement an estimate of the transmission losses as well as the photon statistics of the noise present in the exploited quantum channel. We show and discuss the experimental results obtained in the practical implementation of such protocol, with different kinds and levels of noise., 6 pages, 4 figures

In this work, we present the experimental results obtained in the fabrication and characterization of a superconducting MgB 2 bolometer. The device was made from an MgB2 meander-like structure suspended on a 500 nm thick SiN membrane. The MgB 2 meander line was 50 μm wide and 7.6 mm long and it was defined by optical lithography and dry etching. The SiN membrane had an area of 1. 3m m× 1.3 mm and it was obtained by a silicon micromachining technique. The electrical and thermal properties of the device were measured at low temperature in a closed-cycle cryocooler. The resulting Tc of the meander was unchanged with respect to the unprocessed film and the transport properties, measured in voltage-biased mode, indicated av alue forJc of the order of 10 5 Ac m −2 at 27 K. The logarithmic sensitivity of the bolometer turned out to be higher than 150. The study of the thermal properties of the bolometer on the membrane showed a thermal conductance of the order 10 −5 WK −1 at a working temperature of 32 K. The bolometer, irradiated by a chopped laser beam, showed a cut-off frequency of 94 Hz. The maximum experimental responsivity was estimated to be 2.3 × 10 3 VW −1 .

This work addresses the problem of designing superconducting photodetector readout circuits. A preliminary investigation of a selection of commercially available components to implement a radio-frequency, broadband, low-noise preamplifier operated in a cryogenic environment is presented. Wide band, high gain, low noise and stability under input mismatching load conditions have been the leading criteria taken into account to choose the devices. A set of monolithic microwave integrated circuits (MMIC) based on different technologies (GaAs, InP, HEMT, HBT) has been considered. The prototypes have been characterized at room temperature and low temperature by means of a cryocooler; their main parameters, gain and noise figure, have been measured.

We have developed a multi-band ground viewing radiometer based on light-emitting diodes (LEDs) to create a self-calibrating sensing system for land-based measurements. The system is intended for in-situ data collection needed for vicarious calibration, using the reflectance-based method, for earth observing satellites. An autonomous prototype radiometer, which is part of a sensor web of 5 radiometers which could be geographically distributed over hundreds of meters, has been realized. Temporally continuous in-situ measurement of the land reflectance in 4 spectral bands, from 350 nm to 900 nm, are acquired. The system has the ability to regularly re-calibrate autonomously and in the field, communicating results to a remote home base.

In the present paper, fabrication and structural, optical and electrical characterization of ZnO thin films grown by electron gun technique are reported and the performances of a prototype of UV photodetector based on them are illustrated. ZnO thin films, fabricated on sapphire by e-beam evaporation followed by a two-step ex situ treatment (annealing and oxidation), are polycrystalline, with a smooth surface and show very good visible transparency and an energy gap of 3.2eV. Preliminary results on fabrication and characterization of an UV detector are reported. The Al interdigitated contacts show a Schottky behavior, which is strongly desired in view of applications since it has many advantages in the aspects of high quantum efficiency, response time, low dark current, high UV/visible contrast and possible zero-bias operation.

In this paper we present measurements concerning the current noise produced during the resistive transition in a MgB2 polycrystalline thin film. The power spectrum of the current noise, observed when the temperature is slowly changed across its critical value, presents a large electrical noise of the 1/fn type (n 3) over a quite wide range of frequencies. This noise may be considered as generated by the abrupt creation of resistive strips across the specimen constituted by grains which have undergone the resistive transition. A computer model that takes into account fluctations of the grain critical currents and of the number of grain per strips, has been developed to simulate the resistive transition and to evaluate the noise power spectrum. When the temperature is incresed and reaches its critical value, resistive strips are formed according to a percolative process, giving rise to resistance steps which are at the origin of the noise. The theoretical results obtained by this model are in good agreement, concerning both the shape and intensity of the noise power spectrum, with the experimental data directly measured on the specimen.

In this contribution, we present the results on the preparation and the characterization of MgB2 thick films supported on metal/Al2O3 and metal/BN substrates via electrophoretic deposition technique (EPD) under the electric field of 120–180 V/cm. We followed two different routes: deposition of MgB2 powder, both pure and SiC doped and deposition of boron powder. EPD was followed by a high T/high p treatment in a furnace in saturated Mg atmosphere for sinterization or annealing. The structural and morphological properties of MgB2 thick films were monitored by X-ray diffraction and scanning electron microscopy: the diffraction patterns were characteristic of the hexagonal MgB2 phase and the surfaces resulted homogeneous with grain dimensions up to 1 µm. The good superconducting properties, together with the great adherence to the substrate, possibly make these films important in view of shielding and power applications. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The preparation of highly pure MgB 2 powder is here presented. The two steps preparation method, together with an ad hoc projected reactor, permits us to obtain the desired stoichiometric phase without MgO impurities and other degradation compounds, which depress the superconductive properties. The formation of a liquid phase during the first step of the preparation leads to small grain size particles. New techniques of film preparation (Electrophoretic deposition) have also been approached. By this method thick films suitable for practical applications have been obtained in a very simple and reproducible way at room temperature. Electrophoretic deposition has been carried out with success on low cost substrates. The deposited thick films looks to be very homogeneous, with the same crystal structure of the starting materials and without impurities and can be easily syntherised.

In this work we demonstrate the benefits and the feasibility, of different antireflection coatings made with hydrogenated amorphous silicon–nitrogen alloys for the most used superconducting film materials. Such materials, having a refractive index tunable up to 4 in the visible range, allow to realise multilayers that reduce reflectance to few percent.

SiO x films with thickness ranging from 50 nm to several micrometres were evaporated on crystalline Si at difTerent O2 pressures. The stress of these films, evaluated by profilometer measurements, is tensile and increases with increasing O2 pressure. Atomie force microscopy data show a quite smooth surface of the SiO x films, with a rms roughness less than 1 nm for all film deposited at low O2 pressures. The growth in a reactive atmosphere increases the roughness to 1.5 nm and changes strongly the film morphology. Surface morphology also evolves on the thickness, following a dynamie growth model with negligible surface diffusion. The chemical composition and the inner structure were investigated by Raman spectroscopy.

Transition-edge sensor (TES) microcalorimeters are promising for application in the field of quantum information and quantum computation thanks to their outstanding single photon detection capabilities. Good energy resolution and photon number discrimination at visible and near-infrared wavelengths make them extensively used as single photon detectors. In this work we report details on the fabrication of Pd/Ti TESs deposited by e-beam evaporation on silicon nitride substrates. We use Pd as alternative to Au layer thanks to its stronger influence on the Ti layer, that allows to obtain the same temperature reduction with thinner layers. The transition temperatures Tc of the devices range from 83 to 110 mK with a transition width DeltaTc=0.5 mK. Thermal and electric characteristics of Pd/Ti TESs at different temperatures and its capability as single photon sensor are reported.

MgB2 meander lines with width ranging from 250 to 500 nm have been fabricated by electron beam lithography (EBL)-based technique. Magnesium diboride films grown by all-in-situ method have been used. A critical current density of 8 MA/cm2 was measured for meander with width down to 300 nm. For sake of comparison the measurements have been performed as well on 10 mum wide strip patterned on the same sample. The results show that the nanostructuring process doesn't affect the superconducting properties of the structure. The flexibility of the EBL approach makes it interesting in view of fabrication of MgB2 superconducting devices, such as photon detectors.

The optical properties of cholesteric and chiral smectic-$C$ liquid crystals having a pitch shorter than the light wavelength are studied, both theoretically and experimentally. A particular emphasis is placed on the optical activity. For smectics, the optical rotation is maximum for a tilt angle of $45\ifmmode^\circ\else\textdegree\fi{}$ and for light propagating orthogonally to the helix axis; for short-pitch cholesterics, the optical activity is, in any case, very small. The limits of validity of a recently proposed macroscopic model for such media are discussed, in the framework of a more general discussion on optical models for gyrotropic media. It is shown that the macroscopic models generally work well for the bulk properties. However, for chiral smectics with the smectic planes parallel or nearly parallel to the boundary planes, no homogeneous model is able to account for the gyrotropic properties, independently of how small the pitch is and for any sample thickness. Our experimental data are in agreement with these theoretical findings.

Josephson tunnel junctions have recently proved to be fairly sensitive photodetectors over a broad range of wavelengths. This paper shows the results obtained with Nb/Al-AlOx/Nb Josephson junctions at 4.2 K irradiated via an optical fibre and laser light at λ = 633 nm and 690 nm. The responsivity of the devices is about 50 V/W and is linear over several decades. Moreover, stacks of two Josephson junctions are shown to have twice the responsivity of a single junction. A thermal model of the device is considered and the responsivity is calculated as a function of the temperature derivative of the energy gap, the thermal parameters of the junction, and the modulation frequency of the incident beam.

The optical properties of short pitch chiral smectic C liquid crystals change drastically around a given critical tilt angle, θc. At this angle, the material behaves as an optically isotropic liquid but with a strong optical activity for light propagating orthogonally to the helix axis. It is shown that the polarization properties of the reflected and transmitted beams undergo large changes even for small variations of the tilt angle around the critical one. Some possible applications of the investigated effect are briefly discussed.

In this work we report details on fabrication and characterization of MgB 2 films grown on silicon nitride by co-evaporation of B and Mg and post annealing in-situ. The optimised films show critical temperatures between 32 and 36 K with a residual resistivity ratio around 1.1–1.3. The critical current densities at 4.2 K, evaluated by transport method is close to 5×10 6 A/cm 2 . Optical and morphological characterizations show that films have smooth surfaces with a reflectance typical of MgB 2 with clean surface.

A new goniometer for in situ spectro-directional measurements of the reflection and transmission properties of individual leaves is presented. One diffuse and five directional illumination angles can be chosen. A multichannel spectrometer allows simultaneous detection of the scattered light at 80 viewing angles in the spectral range from 400 nm to 1000 nm., JRC.H.7-Climate Risk Management

We present some Quantum Tomography related results recently obtained in the Quantum Optics labs of the National Institute of Metrological Research (INRIM). Initially we describe the first experimental implementation of a new protocol for the reconstruction of a photon-number-resolving (PNR) detector’s POVM (Positive Operator-Valued Measure): such a protocol, exploiting the strong quantum correlations of an ancillary state, results more robust and efficient than its classical counterparts. The second part of the paper focuses on the quantum characterization of a transition-edge sensor (TES) based PNR detector, i.e. the experimental tomography of the POVM of a TES, with a method based on a quorum of coherent probes: we show the reconstruction of the POVM elements up to 11 detected photons and 100 incoming photons, demonstrating the linearity of such a device. Finally, we present a method for the experimental reconstruction of the modal structure of multimode optical fields exploiting a single measurement of higher-order photon number autocorrelation functions. We show our reconstructions of up to three different modes per optical state, demonstrating the excellent agreement with the theoretical predictions and the robustness of our method itself.

We theoretically analyze the orientation of a nematic liquid crystal close to an interface, by means of a semi-microscopic model. We find that long-range van der Waals interactions, depending on the molecules with respect to their relative position, give rise to subsurface deformations on a molecular scale. This result is compared with the predictions of recently proposed elastic theories.

In this paper we present some experimental results concerning the current noise produced during the resistive transition in MgB2 thin films. Preliminary investigations evidenced the presence of electrical noise whose power spectrum has a region of the 1/fn type with n ∼ 3. We suggest that the noise may originate from abrupt rearrangement of the current distribution inside the specimen during the percolative process of a diphasic system. Experimental measurements of the spectral components of the current noise taken during the resistive transition will be given and discussed.

Transition Edge Sensors (TESs) are characterized by the intrinsic figures of merit to resolve both the energy and the statistical distribution of the incident photons. These properties lead TES devices to become the best single photon detectors for quantum technology experiments. For a TES based on titanium and gold, has been reached, at telecommunication wavelength, an unprecedented intrinsic energy resolution (0.113 eV). The uncertainty analysis of both energy resolution and photon state assignment has been discussed. The thermal properties of the superconductive device have been studied by fitting the bias curves to evaluate the theoretical limit of the energy resolution.

An impedance spectroscopy experimental characterization of a new synthetized Palladium complex organo-metallic liquid crystal is reported. It has been found that although organo-metallic complexes ...