Detector-device-independent QKD: security analysis and fast implementation

One of the most pressing issues in quantum key distribution (QKD) is the problem of detector side- channel attacks. To overcome this problem, researchers proposed an elegant "time-reversal" QKD protocol called measurement-device-independent QKD (MDI-QKD), which is based on time-reversed entanglement swapping. However, MDI-QKD is more challenging to implement than standard point- to-point QKD. Recently, an intermediary QKD protocol called detector-device-independent QKD (DDI-QKD) has been proposed to overcome the drawbacks of MDI-QKD, with the hope that it would eventually lead to a more efficient detector side-channel-free QKD system. Here, we analyze the security of DDI-QKD and elucidate its security assumptions. We find that DDI-QKD is not equivalent to MDI-QKD, but its security can be demonstrated with reasonable assumptions. On the more practical side, we consider the feasibility of DDI-QKD and present a fast experimental demonstration (clocked at 625 MHz), capable of secret key exchange up to more than 90 km.Comment: 9 pages, 4 figure

Adversarial Smoothed Analysis

The purpose of this note is to extend the results on uniform smoothed analysis of condition numbers from \cite{BuCuLo:07} to the case where the perturbation follows a radially symmetric probability distribution. In particular, we will show that the bounds derived in \cite{BuCuLo:07} still hold in the case of distributions whose density has a singularity at the center of the perturbation, which we call {\em adversarial}.Comment: 8 page

Compressive gate set tomography

Flexible characterization techniques that identify and quantify experimental imperfections under realistic assumptions are crucial for the development of quantum computers. Gate set tomography is a characterization approach that simultaneously and self-consistently extracts a tomographic description of the implementation of an entire set of quantum gates, as well as the initial state and measurement, from experimental data. Obtaining such a detailed picture of the experimental implementation is associated with high requirements on the number of sequences and their design, making gate set tomography a challenging task even for only two qubits. In this work, we show that low-rank approximations of gate sets can be obtained from significantly fewer gate sequences and that it is sufficient to draw them randomly. Such tomographic information is needed for the crucial task of dealing with coherent noise. To this end, we formulate the data processing problem of gate set tomography as a rank-constrained tensor completion problem. We provide an algorithm to solve this problem while respecting the usual positivity and normalization constraints of quantum mechanics by using second-order geometrical optimization methods on the complex Stiefel manifold. Besides the reduction in sequences, we demonstrate numerically that the algorithm does not rely on structured gate sets or an elaborate circuit design to robustly perform gate set tomography and is therefore more broadly applicable than traditional approaches.Comment: 14+12 pages, several figures and diagram

Прибор для измерения параметров магнитопровода бетатрона

В данной выпускной квалификационной работе рассмотрен способ контроля параметров центральных вкладышей малогабаритного бетатрона. На основании теоретических данных и экспериментально полученных зависимостей был разработан прибор, позволяющий оценивать качество изготовления центральных вкладышей магнитопроводящей системы бетатрона. В основе принципа работы прибора лежит способ определение добротности колебательного контура по скорости затухания его электрических колебаний.The method of controlling the parameters of the central inserts block of a betatron was considered in this final qualifying work. The device, which can measure the quality of manufacturing of central inserts block of the magnetic system of the betatron, was developed on the basis of theoretical data and experimentally obtained dependences. The principle of operation of the device is based on the method for determining the quality factor of an oscillating circuit in terms of the rate of damping of its electric oscillations

Estimating the effects of regulation when treated and control firms compete: a new method with application to the EU ETS

This paper presents a method for estimating treatment effects of regulations when treated and control firms compete on the output market. We develop a GMM estimator that recovers reduced-form parameters consistent with a model of differentiated product markets with multi-plant firms, and use these estimates to evaluate counterfactual revenues and emissions. Our procedure recovers unbiased estimates of treatment effects in Monte Carlo experiments, while difference-in-differences estimators and other popular methods do not. In an application, we find that the European carbon market reduced emissions at regulated plants without undermining revenues of regulated firms, relative to an unregulated counterfactual