NbRe-based superconducting thin films recently received relevant interest in the field of low-temperature electronics. However, for these materials the electrical conduction mechanisms, in particular ...in the normal state, still need to be investigated in more detail. Here, NbRe and NbReN films of different thicknesses have been deposited on two different substrates, namely monocrystalline Si and Formula: see text buffered Si. The films were characterized by DC electrical transport measurements. Moreover, a connection with the charge carriers fluctuation processes has been made by analyzing the electrical noise generated in the normal state region. Despite the films morphology seems not to be affected by the substrate used, a lower noise level has been found for the ones grown on Formula: see text, in particular for NbReN. From this study it emerges that both NbRe and NbReN ultrathin films are of very good quality, as far as the low-temperature electrical noise and conduction are concerned, with noise levels competitive with NbN. These results may further support the proposal of using these materials in a nanowire form in the field of superconducting electronics.
Since the 80 s when it was first proposed, Quantum Key Distribution (QKD) elicited great interest in the field of cryptography as a unique procedure for key generation that could in principle ...guarantee unconditionally secure communication “by the laws of Physics”. In the last fifteen years commercial solutions have started appearing on the market, showing that practical implementations of the protocol were not only possible but also competitive in terms of security and achievable secret-key rate. In this work we describe a simulation of the historical QKD protocol E91 on the
IBM Quantum
platform, making use of the qubit formalism to represent the quantum states received by two communicating nodes. Having implemented also the post-processing steps for the error correction and the privacy amplification, this model can represent a simple stand-alone tool to study the performance not only of one-to-one communication but of more complex systems that rely on QKD for security, one above all QKD networks.
Abstract
Superconducting microstrip single photon detectors (SMSPDs) received great interest since they are expected to combine the excellent performance of superconducting nanostrip single photon ...detectors with the possibility to cover large active areas using low-cost fabrication techniques. In this work, we fabricated SMSPDs based on NbRe to investigate the role of vortices in the dark counts events in this innovative material and in devices with micrometer size. We realized devices with different layouts, namely single microstrips and pairs of parallel microstrips. The energy barriers related to the motion of single vortices or vortex–antivortex pairs, responsible of detection events, have been determined and compared with the ones of similar devices based on different materials, such as MoSi, WSi and NbN. The analysis confirms the high potential of NbRe for the realization of superconducting single photon detectors with large areas.
Using the IBM Quantum Experience platform, we simulate the dissipative dynamics in the BB84 quantum key distribution protocol. We employ the Jaynes–Cummings model to simulate the attenuation in an ...optical fiber during the information transmission process and calculate the quantum bit error rate (QBER). The results of QBER as a function of the distance give a satisfactory agreement with experimental data when the system is in a Markovian regime.
Odd-frequency triplet Cooper pairs are believed to be the carriers of long-range superconducting correlations in ferromagnets. Such triplet pairs are generated by an inhomogeneous magnetism at the ...interface between a superconductor (S) and a ferromagnet (F). So far, reproducible long-range effects were reported only in complex layered structures designed to provide the magnetic inhomogeneity. Here we show that spin triplet pair formation can be found in simple unstructured Nb/permalloy ( Py = Ni 0.8 Fe 0.2 )/Nb trilayers and Nb/Py bilayers, but only when the thickness of the ferromagnetic layer ranges between 140 and 250 nm. The effect is related to the emergence of an intrinsically inhomogeneous magnetic state, which is a precursor of the well-known stripe regime in Py that in our samples sets in at thickness larger than 300 nm.
Selectivity in tumor targeting is one of the major issues in cancer treatment. Therefore, surface functionalization of drug delivery systems with active moieties, able to selectively target tumors, ...has become a worldwide-recognized strategy. The CD44 receptor is largely used as a biomarker, being overexpressed in several tumors, and consequently as a target thanks to the identification of the CD44 binding peptide. Here we implemented the CD44 binding peptide logic onto an oil core-polymer multilayer shell, taking into account and optimizing all relevant features of drug delivery systems, such as small size (down to 100 nm), narrow size distribution, drug loading capability, antifouling and biodegradability. Besides promoting active targeting, the oil core-based system enables the delivery of natural and synthetic therapeutic compounds. Biological tests, using curcumin as a bioactive compound and fluorescent tag, demonstrated that CD44 binding peptide-functionalized nanocapsules selectively accumulate and internalize in cancer cells, compared to the control, thanks to ligand-receptor binding.
CD44 binding peptide was implemented onto an oil core-polymer multilayer shell of 100 nm size and completely biodegradable. Biological tests, demonstrated that the proposed nanocarrier selectively accumulates and internalizes in cancer cells.
Photocurrent amplification by gate effect in a three terminal carbon nanotube /n-Si photodetector.
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•Three terminal Carbon Nanotube/n-Si photodetectors.•Time response to nanosecond ...laser pulse.•Collecting photocharges by interdigitated electrodes.•Voltage doping in carbon nanotube/n-Si photodetectors.
We investigated the response of carbon nanotube/Si photodetectors to nanosecond light pulse using two electrode configurations for photovoltaic and photoconductive operations. When operating in photovoltaic mode, the devices show a linear dependence of the photocurrent as a function of the light pulse energy with rise time of 20 ns. In photoconductive mode, an increase of the maximum photocurrent as high as 30 times and a gain in the number of photogenerated charges up to 200% is recorded with a correspondent decrease in the time response below 10 ns. Current voltage characteristics measured as a function of the temperature indicate that the fast response of these devices can be ascribed to the formation of Schottky junctions at carbon nanotube/Si interface. These results make our devices comparable to most commercial photodetectors and pave the way for their use as avalanche photomultipliers.
Two-dimensional materials, such as graphene, topological insulators, and two-dimensional electron gases, represent a technological playground to develop coherent electronics. In these systems, ...quantum interference effects, and in particular weak localization, are likely to occur. These coherence effects are usually characterized by well-defined features in dc electrical transport, such as a resistivity increase and negative magnetoresistance below a crossover temperature. Recently, it has been shown that in magnetic and superconducting compounds, undergoing a weak-localization transition, a specific low-frequency 1/f noise occurs. An interpretation in terms of nonequilibrium universal conductance fluctuations has been given. The universality of this unusual electric noise mechanism has been here verified by detailed voltage-spectral density investigations on ultrathin copper films. The reported experimental results validate the proposed theoretical framework, and also provide an alternative methodology to detect weak-localization effects by using electric noise spectroscopy.
Abstract
The surprisingly low current density required for inducing the insulator to metal transition has made Ca
2
RuO
4
an attractive candidate material for developing Mott-based electronics ...devices. The mechanism driving the resistive switching, however, remains a controversial topic in the field of strongly correlated electron systems. Here we probe an uncovered region of phase space by studying high-purity Ca
2
RuO
4
single crystals, using the sample size as principal tuning parameter. Upon reducing the crystal size, we find a four orders of magnitude increase in the current density required for driving Ca
2
RuO
4
out of the insulating state into a non-equilibrium phase which is the precursor to the fully metallic phase. By integrating a microscopic platinum thermometer and performing thermal simulations, we gain insight into the local temperature during simultaneous application of current and establish that the size dependence is not a result of Joule heating. The findings suggest an inhomogeneous current distribution in the nominally homogeneous crystal. Our study calls for a reexamination of the interplay between sample size, charge current, and temperature in driving Ca
2
RuO
4
towards the Mott insulator to metal transition.
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