arXiv subjects

Andrey Tayduganov

Publications and source records attributed to Andrey Tayduganov.

At least 19 recordsLinked to original sources

arXiv2025

Routing algorithm within the multiple non-overlapping paths approach for quantum key distribution networks

We develop a novel key routing algorithm for quantum key distribution (QKD) networks that utilizes a distribution of keys between remote, i.e., not directly connected by a QKD link, nodes through multiple non-overlapping paths. This approach enchases the security of QKD network by minimizing potential vulnerabilities associated with individual trusted nodes. The algorithm ensures a balanced allocation of the workload across the QKD network links, while aiming for the target key generation rate between directly connected and remote nodes. We present the results of testing the algorithm on two QKD network models consisting of 6 and 10 nodes. The testing demonstrates the ability of the algorithm to distribute secure keys among the nodes of the network in an all-to-all manner, ensuring that the information-theoretic security of the keys between remote nodes is maintained even when one of the trusted nodes is compromised. These results highlight the potential of the algorithm to improve the performance of QKD networks.

quant-ph↗

arXiv2024

Preparing a commercial quantum key distribution system for certification against implementation loopholes

A commercial quantum key distribution (QKD) system needs to be formally certified to enable its wide deployment. The certification should include the system's robustness against known implementation loopholes and attacks that exploit them. Here we ready a fiber-optic QKD system for this procedure. The system has a prepare-and-measure scheme with decoy-state BB84 protocol, polarisation encoding, qubit source rate of 312.5 MHz, and is manufactured by QRate. We detail its hardware and post-processing. We analyse the hardware for known implementation loopholes, search for possible new loopholes, and discuss countermeasures. We then amend the system design to address the highest-risk loopholes identified. We also work out technical requirements on the certification lab and outline its possible structure.

quant-ph↗

arXiv2023

Security of the decoy-state BB84 protocol with imperfect state preparation

The quantum key distribution (QKD) allows two remote users to share a common information-theoretic secure secret key. In order to guarantee the security of a practical QKD implementation, the physical system has to be fully characterized and all deviations from the ideal protocol due to various imperfections of realistic devices have to be taken into account in the security proof. In this work, we study the security of the efficient decoy-state BB84 QKD protocol in the presence of source flaws, caused by imperfect intensity and polarization modulation. We investigate the non-Poissonian photon-number statistics due to coherent-state intensity fluctuations and the basis-dependence of the source due to non-ideal polarization state preparation. The analysis is supported by experimental characterization of intensity and phase distributions.

quant-ph↗

arXiv2023

Asymmetric adaptive LDPC-based information reconciliation for industrial quantum key distribution

We develop a new approach for asymmetric LDPC-based information reconciliation in order to adapt to the current channel state and achieve better performance and scalability in practical resource-constrained QKD systems. The new scheme combines the advantages of LDPC codes, a priori error rate estimation, rate-adaptive and blind information reconciliation techniques. We compare the performance of several asymmetric and symmetric error correction schemes using real industrial QKD setup. The proposed asymmetric algorithm achieves significantly higher throughput, providing a secret key rate very close to the symmetric one in a wide range of error rates. Thus, our approach turns out to be particularly efficient for applications with high key rates, limited classical channel capacity and asymmetric computational resource allocation.

quant-ph↗

arXiv2021

Optimizing the deployment of quantum key distribution switch-based networks

Quantum key distribution (QKD) networks provide an infrastructure for establishing information-theoretic secure keys between legitimate parties via quantum and authentic classical channels. The deployment of QKD networks in real-world conditions faces several challenges, which are related in particular to the high costs of QKD devices and the condition to provide reasonable secret key rates. In this work, we present a QKD network architecture that provides a significant reduction in the cost of deploying QKD networks by using optical switches and reducing the number of QKD receiver devices, which use single-photon detectors. We describe the corresponding modification of the QKD network protocol. We also provide estimations for a network link of a total of 670 km length consisting of 8 nodes, and demonstrate that the switch-based architecture allows achieving significant resource savings of up to 28%, while the throughput is reduced by 8% only.

quant-ph↗

arXiv2021

Go-and-return phase encoded SR QKD and its security consideration

In this work, we study the security of coherent-state quantum key distribution with a strong reference pulse. The consideration is based on a powerful soft filtering attack and uses realistic parameters of the equipment. Our model allows us to relate the secure key generation rate and distance with the energy of signal and reference pulses. We propose a two-pass quantum key distribution phase encoding optical scheme with a strong reference pulse. This simple for realization scheme is experimentally tested showing stable operation. Here we describe the tuning technique and solution for the problem of weak signal pulse shadowing by a bright reference pulse with the relative intensity difference of more than 60\,dB between them.

quant-ph↗

arXiv2021

Investigating the coherent state detection probability of InGaAs/InP SPAD-based single-photon detectors

In this work we investigate the probabilities of detecting single- and multi-photon coherent states on InGaAs/InP sine-gated and free-run single-photon avalanche diodes. As a result, we conclude that multi-photon state detection cannot be regarded as independent events of absorption of individual single-photon states. However, if a greater number of states are one- and two-photon, then an Independent model is permissible. We conclude that physical processes must occur in the diode structure, determining the correlation when several photons are absorbed simultaneously. We present two models that we can use to describe photon interactions in a structure. The Dependent model is based on an increase/decrease in the probability of detecting an n-th photon upon an unfortunate detection of an (n-1)-th photon in an n-photon state and is well physically grounded; The Empirical model offers a simple and accurate empirical relationship.

quant-ph↗

arXiv2021

The New Physics Reach of Null Tests with $D \to π\ell \ell$ and $D_s \to K \ell \ell $ Decays

$|Δc|=|Δu|=1$ processes are unique probes of flavor physics in the up-sector within and beyond the Standard Model (SM). SM tests with rare semileptonic charm meson decays are based on an approximate CP--symmetry, a superior GIM--mechanism, angular distributions, lepton-universality and lepton flavor conservation. We analyze the complete set of null test observables in $D \to π\ell \ell^{(\prime)}$ and $D_s \to K \ell \ell^{(\prime)}$ decays, $\ell^{(\prime)}=e, μ$, and find large room for new physics safely above the SM contribution. We identify signatures of supersymmetry, leptoquarks and anomaly-free $U(1)^\prime$-models with generation-dependent charges, for which we provide explicit examples. $Z^\prime$-effects in $c \to u \ell \ell^{(\prime)}$ transitions can be sizable if both left-handed and right-handed couplings to quarks are present.

hep-ph↗

arXiv2019

Lepton Flavor Universality tests through angular observables of $\overline{B}\to D^{(\ast)}\ell\overlineν$ decay modes

We discuss the possibility of using the observables deduced from the angular distribution of the $B\to D^{(\ast)} \ell\barν$ decays to test the effects of lepton flavor universality violation (LFUV). We show that the measurement of even a subset of these observables could be very helpful in distinguishing the Lorentz structure of the New Physics contributions to these decays. To do so we use the low energy effective theory in which besides the Standard Model contribution we add all possible Lorentz structures with the couplings (Wilson coefficients) that are determined by matching theory with the measured ratios $R{(D^{(\ast)})}^\mathrm{exp}$. We argue that even in the situation in which the measured $R{(D^{(\ast)})}^\mathrm{exp}$ becomes fully compatible with the Standard Model, one can still have significant New Physics contributions the size of which could be probed by measuring the observables discussed in this paper and comparing them with their Standard Model predictions.

hep-ph↗

arXiv2018

Testing the standard model with $D_{(s)} \to K_1 (\to Kππ) γ$ decays

The photon polarization in $D_{(s)} \to K_1 (\to Kππ) γ$ decays can be extracted from an up-down asymmetry in the $K ππ$ system, along the lines of the method known to $B \to K_1 (\to Kππ) γ$ decays. Charm physics is advantageous as partner decays exist: $D^+ \to K_1^+ (\to Kππ) γ$, which is standard model-like, and $D_s \to K_1^+ (\to Kππ) γ$, which is sensitive to physics beyond the standard model in $|Δc| =|Δu|=1$ transitions. The standard model predicts their photon polarizations to be equal up to U-spin breaking corrections, while new physics in the dipole operators can split them apart at order one level. We estimate the proportionality factor in the asymmetry multiplying the polarization parameter from axial vectors $K_1(1270)$ and $K_1(1400)$ to be sizable, up to the few ${\cal{O}}(10)\%$ range. The actual value of the hadronic factor matters for the experimental sensitivity, but is not needed as an input to perform the null test.

hep-ph↗

arXiv2018

Testing leptoquark models in $\bar B \to D^{(*)} τ\barν$

We study potential New Physics effects in the $\bar B \to D^{(*)} τ\barν$ decays. As a particular example of New Physics models we consider the class of leptoquark models and put the constraints on the leptoquark couplings using the recently measured ratios $R(D^{(*)})=BR(\bar B \to D^{(*)} τ\barν)/BR(\bar B \to D^{(*)} μ\barν)$. For consistency, some of the constraints are compared with the ones coming from the current experimental bound on $BR(B \to X_s ν\barν)$. In order to discriminate various New Physics scenarios, we examine the correlations between different observables that can be measured in future.

hep-ph↗

arXiv2018

Determining the photon polarization of the b --> s gamma using the B --> K1(1270) gamma --> (K pi pi) gamma decay

Recently the radiative B decay to the strange axial-vector mesons, B --> K1(1270) gamma, has been observed with rather large branching ratio. This process is particularly interesting as the subsequent K1 decay into its three body final state allows us to determine the polarization of the photon, which is mostly left- (right-)handed for Bbar (B) in the SM while various new physics models predict additional right- (left-)handed components. A new method is proposed to determine the polarization, exploiting the full Dalitz plot distribution, which seems to reduce significantly the statistical errors. This polarization measurement requires however a detailed knowledge of the K1--> K pi pi strong interaction decays, namely, the various partial wave amplitudes into the several possible quasi two-body channels, as well as their relative phases. The pattern of partial waves is especially complex for the K1(1270). We attempt to obtain the information through the combination of an experimental input and a theoretical one, provided by the 3P0 quark-pair-creation model.

hep-ph↗

arXiv2016

Angular distributions of $\bar B \to D^{(\ast)}\ell\bar ν_\ell$ decays and search of New Physics

We derive the expressions for the full angular distributions of $\bar B\to D\ell\bar ν_\ell$ and $\bar B\to D^{\ast }\ell\bar ν_\ell$ decays and discuss the spectra on each angle separately. The coefficient functions, depending on helicity amplitudes, can then be combined in an ensemble of observables which can then be used to check for the presence of New Physics. We examine the sensitivity of each of these observables on the presence of non-Standard Model interaction terms at low energies. The expressions presented here are general and can be used for studying any other semileptonic pseudoscalar to pseudoscalar/vector meson decay. We also examine the problem of pollution of the $\bar B\to D^{\ast}(\to Dπ)_S\ell\bar ν_\ell$ decay sample by the $\bar B\to D_0^{\ast}(\to Dπ)\ell\bar ν_\ell$ events, and point out that a measurement of two particular quantities could clarify whether or not the $(Dπ)_{S-\rm wave}$ in the vicinity of $D^\ast$-peak is (approximately) described by the Breit-Wigner formula.

hep-ph↗

arXiv2014

Probing New Physics with $q^2$ distributions in $\bar{B} \to D^{(*)} τ\barν$

Recent experimental results for the ratios of the branching fractions of the decays $\bar{B} \to D^{(*)} τ\barν$ and $\bar{B} \to D^{(*)} μ\barν$ came as a surprise and lead to a discussion of possibility of testing New Physics beyond the Standard Model through these modes. We show that these decay channels can provide us with good constraints on New Physics and several New Physics cases are favored by the present experimental data. In order to discriminate various New Physics scenarios, we examine the $q^2$ distributions and estimate the sensitivity of this potential measurement at the SuperKEKB/Belle II experiment.

hep-ph↗

arXiv2013

Testing the Standard Model in $B \to D τ\bar ν$ decay with minimal theory input

Recent experimental results for the ratio of the branching fractions of $\bar B \to D^{(*)}τν_τ$ and $B\to D^{(*)} μν_μ$ decays came as a surprise and lead to a discussion of possibility to constraining new physics through these modes. Here we focus on $Br(B \to D τ\barν_τ)/Br(B \to D μ\barν_μ)$ and argue that the result is consistent with the Standard Model within $2\,σ$ and that the test of compatibility of this ratio with the Standard Model can be done experimentally with a minimal theory input. We also show that these two decay channels can provide us with quite good constraints of the new physics couplings.

hep-ph↗

arXiv2012

Impact of $B\to K^\ast_0 \ell^+\ell^-$ on the New Physics search in $B\to K^\ast \ell^+\ell^-$ decay

We discuss the uncertainty related to the amount of unwanted $B\to K_0^\ast (Kπ)\ell^+\ell^-$ events in the sample of $B\to K^\ast (Kπ)\ell^+\ell^-$. Those events can increase the measured differential decay rate by up to 10% in the low $q^2$ region, and can be a source of non-negligible uncertainty in the full angular distribution of the $B\to K^\ast (Kπ)\ell^+\ell^-$ decay. Although the transverse asymmetries should be unaffected by the presence of the $S$-wave $Kπ$ pairs, coming from the scalar $K_0^\ast$ meson, we show that in practice their normalization might be sensitive to those events and could entail a sizable uncertainty in transverse asymmetries around $q^2=2 GeV^2$. For other $q^2$'s that error is under about 10%.

hep-ph↗

arXiv2012

$\bar B\to Dτ\bar ν_τ$ vs. $\bar B\to Dμ\bar ν_μ$

Recent experimental results for the ratio of the branching fractions of $\bar B\to D^{(*)}τ\bar ν_τ$ and $\bar B\to D^{(*)}μ\bar ν_μ$ decays came as a surprise and lead to a discussion of possibility to constraining New Physics through these modes. Here we focus on ${\cal B}(\bar B\to Dτ\bar ν_τ)/{\cal B}(\bar B\to Dμ\bar ν_μ)$ and argue that the result is consistent with the Standard Model within $2σ$, and that the test of compatibility of this ratio with the Standard Model can be done experimentally with a minimal theory input. We also show that these two decay channels can provide us with quite good constraints of the New Physics couplings.

hep-ph↗

arXiv2012

Future prospects for the determination of the Wilson coefficient $C_{7γ}^\prime$

We discuss the possibilities of assessing a non-zero $C_{7γ}^\prime$ from the direct and the indirect measurements of the photon polarization in the exclusive $b \to sγ^{(*)}$ decays. We focus on three methods and explore the following three decay modes: $B \to K^*(\to K_Sπ^0)γ$, $B \to K_1(\to Kππ)γ$, and $B \to K^*(\to Kπ)\ell^+\ell^-$. By studying different New Physics scenarios we show that the future measurement of conveniently defined observables in these decays could provide us with the full determination of $C_{7γ}$ and $C_{7γ}^\prime$.

hep-ph↗