26 research outputs found
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
m to 10 m allowed decreasing the dark current in the linear mode by
about 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