Andrei Pokatilov

Effect of Keysight 3458A Jitter on Precision of Phase Difference Measurement

A new method improving precision of the phase difference measurement performed by two Keysight 3458A multimeters is proposed. The method is based on external synchronization of the multimeters by a specially selected sampling interval reducing the effect of the finite resolution of an internal time base (jitter) on the performance of the multimeters. By using this method, precision of the phase difference estimation in the audio frequency band can significantly be improved as compared with the commonly used synchronization schemes.

European coordinated metrological effort for quantum cryptography

Quantum Key Distribution, a fundamental component of quantum secure communication that exploits quantum states and resources for communication protocols, can future-proof the security of digital communications, when if advanced quantum computing systems and mathematical advances render current algorithmic cryptography insecure. A QKD system relies on the integration of quantum physical devices, as quantum sources, quantum channels and quantum detectors, in order to generate a true random (unconditionally secure) cryptographic key between two remote parties connected through a quantum channel. The gap between QKD implemented with ideal and real devices can be exploited to attack real systems, unless appropriate countermeasures are implemented. Characterization of real devices and countermeasure is necessary to guarantee security. Free-space QKD systems can provide secure communication to remote parties of the globe, while QKD systems based on entanglement are intrinsically less vulnerable to attack. Metrology to characterize the optical components of these systems is required. Actually, the “Optical metrology for quantum-enhanced secure telecommunication” Project (MIQC2) is steering the metrological effort for Quantum Cryptography in the European region in order to accelerate the development and commercial uptake of Quantum Key Distribution (QKD) technologies. Aim of the project is the development of traceable measurement techniques, apparatus, and protocols that will underpin the characterisation and validation of the performance and quantum-safe security of such systems, essential steps towards standardization and certification of practical implementations of quantum-based technologies.

Method for obtaining linear spectral responsivity of InGaAs-photodetector in the NIR wavelength range

A simple linear interpolation of the spectral responsivity of a special type detector has been obtained in the range from 960 nm to 1550 nm. The detector consisted of three InGaAs-based photodiodes arranged in reflection trap detector mode. In such a detector, the photodiodes are mounted in a configuration where the non-absorbed reflected light from the first photodiode is directed to the subsequent photodiode having totally five reflections in the detector. As a result, the overall reflectance of the trap detector is smaller than that of a single photodiode improving responsivity performance significantly. The trap detector was calibrated in the wavelength range from 840 nm to 1700 nm. We found that in the near infrared (NIR) spectral range from 960 nm to 1550 nm the responsivity of our trap detector is almost linear function of on the wavelength: the deviation of measured responsivity values from fitted line was within ±0.8 %.

Eddy Current Model for Nondestructive Testing of Electrically Conducting Materials with Cylindrical Symmetry

Eddy current method is widely used in practice for quality testing of conducting materials (examples include determination of electrical conductivity, thickness of metal coatings, identification of flaws in a conducting medium). In the present paper a semi-analytical method for solution of direct eddy current problems for the case of a conducting medium of finite size is considered. The method is applied to several eddy current problems with cylindrical symmetry. The following problem is analyzed in detail. Consider a coil with alternating current located above a conducting medium in the form of a circular cylinder (such a model can be used for design of coin validators which are based on the estimation of electrical conductivity of a coin). We assume that the electromagnetic field is exactly zero at a sufficiently large distance from the coil (the distance can be chosen on the basis of the required accuracy of the solution). The solution is constructed using the method of separation of variables which includes two steps where numerical calculations are necessary: (a) computation of complex eigenvalues without good initial guess for the roots and (b) solution of a system of linear algebraic equations. Computations of the change in impedance of the coil for different frequencies with the semi-analytical method are in good agreement with experimental data and results of numerical simulation with finite element method. Solution of other problems with cylindrical symmetry is also discussed (a flaw in the form of a circular cylinder in a conducting half-space or a plate). Such models can be used for the analysis of quality of spot welding (in case of a volumetric flaw) and estimation of the effect of corrosion (for surface flaws).