On First Order Formalism in String Theory

We consider the first order formalism in string theory, providing a new off-shell description of the nontrivial backgrounds around an "infinite metric". The OPE of the vertex operators, corresponding to the background fields in some "twistor representation", and conditions of conformal invariance results in the quadratic equation for the background fields, which appears to be equivalent to the Einstein equations with a Kalb-Ramond B-field and a dilaton. Using a new representation for the Einstein equations with B-field and dilaton we find a new class of solutions including the plane waves for metric (graviton) and the B-field. We discuss the properties of these background equations and main features of the BRST operator in this approach.Comment: LaTeX2e, 18 pages, Phys. Lett. B, in press, corrected typo

The avalanche delay effect in sine-gated single-photon detector based on InGaAs/InP SPADs

A sine-gated single-photon detector (SPD) intended for use in a quantum key distribution (QKD) system is considered in this paper. An "avalanche delay" effect in the sine-gated SPD is revealed. This effect consists in the appearance of an avalanche triggered at the next gate after the photon arrival gate. It has been determined experimentally that the nature of this effect is not related to the known effects of afterpulsing or charge persistence. This effect negatively affects the overall error rate in the QKD system. The influence of the main detector control parameters, such as temperature, gate amplitude and comparator's threshold voltage, on the avalanche delay effect was experimentally established

Investigation of the Effects of the Multiplication Area Shape on the Operational Parameters of InGaAs/InAlAs SPADs

A 2D model of an InGaAs/InAlAs single photon avalanche photodiode has been developed. The influence of the active area structure in the multiplication region on the diode's operating parameters has been studied. It was found that changing the diameter of the structure's active region leads to a change in the dark current in the linear part of the current-voltage curve and a change in the breakdown voltage. Reducing the diameter of the active region from 25 $\mu$m to 10 $\mu$m allowed decreasing the dark current in the linear mode by about $10$ dB. It has been shown that the quality of the SPAD device can be assessed by knowing the avalanche breakdown voltage and the overall current-voltage curve plot if we consider structures with the same multiplication region thickness and different remaining layers. The higher the breakdown voltage, the better the structure's quality due to smaller local increases in the field strength. Following this statement, we conclude that for further use in single-photon detectors, it is reasonable to pick specific SPADs from a batch on the sole basis of their current-voltage curves

BRST, Generalized Maurer-Cartan Equations and CFT

The paper is devoted to the study of BRST charge in perturbed two dimensional conformal field theory. The main goal is to write the operator equation expressing the conservation law of BRST charge in perturbed theory in terms of purely algebraic operations on the corresponding operator algebra, which are defined via the OPE. The corresponding equations are constructed and their symmetries are studied up to the second order in formal coupling constant. It appears that the obtained equations can be interpreted as generalized Maurer-Cartan ones. We study two concrete examples in detail: the bosonic nonlinear sigma model and perturbed first order theory. In particular, we show that the Einstein equations, which are the conformal invariance conditions for both these perturbed theories, expanded up to the second order, can be rewritten in such generalized Maurer-Cartan form.Comment: LaTeX2e, elsart.cls, 36 pages, typos corrected, references and acknowledgements adde

Automated verification of countermeasure against detector-control attack in quantum key distribution

Attacks that control single-photon detectors in quantum key distribution using tailored bright illumination are capable of eavesdropping the secret key. Here we report an automated testbench that checks the detector's vulnerabilities against these attacks. We illustrate its performance by testing a free-running detector that includes a rudimentary countermeasure measuring an average photocurrent. While our testbench automatically finds the detector to be controllable in a continuous-blinding regime, the countermeasure registers photocurrent significantly exceeding that in a quantum regime, thus revealing the attack. We then perform manually a pulsed blinding attack, which controls the detector intermittently. This attack is missed by the countermeasure in a wide range of blinding pulse durations and powers, still allowing to eavesdrop the key. We make recommendations for improvement of both the testbench and countermeasure.Comment: 11 pages, 11 figures. Revised after referee reports from EPJ Quantum Techno

Quantum Mass and Central Charge of Supersymmetric Monopoles - Anomalies, current renormalization, and surface terms

We calculate the one-loop quantum corrections to the mass and central charge of N=2 and N=4 supersymmetric monopoles in 3+1 dimensions. The corrections to the N=2 central charge are finite and due to an anomaly in the conformal central charge current, but they cancel for the N=4 monopole. For the quantum corrections to the mass we start with the integral over the expectation value of the Hamiltonian density, which we show to consist of a bulk contribution which is given by the familiar sum over zero-point energies, as well as surface terms which contribute nontrivially in the monopole sector. The bulk contribution is evaluated through index theorems and found to be nonvanishing only in the N=2 case. The contributions from the surface terms in the Hamiltonian are cancelled by infinite composite operator counterterms in the N=4 case, forming a multiplet of improvement terms. These counterterms are also needed for the renormalization of the central charge. However, in the N=2 case they cancel, and both the improved and the unimproved current multiplet are finite.Comment: 1+40 pages, JHEP style. v2: small corrections and additions, references adde

Dead time duration and active reset influence on the afterpulse probability of InGaAs/InP SPAD based SPDs

We perform the detailed study of the afterpulse probability's dependence in the InGaAs/InP sine-gated SPAD on the dead time and the used approach for its implementation. We have found that the comparator's simple latching can significantly reduce afterpulses' probability, even without using a dead time pulse that lowers the diode bias voltage. We have found that with a low probability of afterpulse ( 10 mus), it is sufficient to use a circuit with latching of the comparator, which will significantly simplify the development of an SPD device for applications in which such parameters are acceptable. We also proposed a precise method for measuring and the afterpulse and presented a model describing the recurrent nature of this effect. We have shown that it should not use a simple model to describe the afterpulse probability due to rough underlying physical processes. A second-order model is preferable

Perturbed Beta-Gamma Systems and Complex Geometry

We consider the equations, arising as the conformal invariance conditions of the perturbed curved beta-gamma system. These equations have the physical meaning of Einstein equations with a B-field and a dilaton on a hermitian manifold, where the B-field 2-form is imaginary and proportional to the canonical form associated with hermitian metric. We show that they decompose into linear and bilinear equations and lead to the vanishing of the first Chern class of the manifold where the system is defined. We discuss the relation of these equations to the generalized Maurer-Cartan structures related to BRST operator. Finally we describe the relations of the generalized Maurer-Cartan bilinear operation and the Courant/Dorfman brackets.Comment: LaTeX2e, 27 page

Mechanical and biocompatible properties of the poly(lactide-co-glycolide) matrices produced by antisolvent 3D printing

Three-dimensional scaffolds were made from a solution of poly(lactide-co-glycolide) mixed with tetraglycol using antisolvent 3D printing. The elastic properties and the structure of the obtained matrices were studied. MTT-test and staining with PKH-26, Calcein-AM, DAPI with subsequent fluorescence microscopy were used to study biological properties. The three-dimensional scaffolds had good mechanical properties. Young’s modulus value was 18±2 MPa, tensile strength was 0.43±0.05 MPa. The relative survival rate of cells after the first day was 99.58±2.28%, on the 14th day – 98.14±2.22%. The structure of the scaffold promoted cell adhesion and spreading on its surface. The poly(lactide-co-glycolide) matrices produced by antisolvent printing have high porosity, biocompatibility and good mechanical properties. It is allowed to use them in the future as a basis for personalized constructions for the replacement of extensive bone defects