In this work, we reveal a property of the Schwinger model associated with the fractal structure of its ground state. We provide the results of recurrent calculating ground-state wave functions based on the self-similarity property using the analytical approach and automized software package for image processing of fractals. Also, we demonstrate the results on ground state energies obtained with the recurrent procedure are close to those predicted by the matrix product states approach.

The linear dissipation of an arbitrary single-mode optical system is considered in terms of Wigner function. An analytical expression is obtained for the Wigner function of this system.

The linear dissipation of an optical mixed-state qubit on the following basis vectors is considered: (A) |0> and |1>, (B) |0> and |n>, (C) |1> and |2>.

The evolution of nonclassicality of these states during linear dissipation is analytically and numerically investigated.

The crucial task for polarization-encoding fiber QKD is to compensate polarization drift occurring in an optical fiber. To solve this problem, the receiver usually uses a polarization controller. For proper operation, this device must be efficiently managed. In this work, a real-time compensation protocol is proposed to solve this problem. The protocol was implemented and tested on a QRate commercial QKD fiber system. Low and stable QBER has been obtained during 12 hours of continuous operation.

Collective modes fluctuations represent a challenging obstacle in the description of most quantum many-body systems, including those, which are used as physical realizations of quantum computing systems. In this work we propose to use the Fluctuating local field approach to treat the spin fluctuations in the strong correlative regime, namely in the vicinity of the atomic limit. We show that the developed procedure significantly improves the results in comparison with the mean field theory.

The paper presents a new scheme for calibrating single-photon detectors without using a standard.

The interaction of quantum system with environment makes the system change its coherent dynamics, so it is extremely important to estimate this deviation in correct and simple way. We consider measure of decoherence based on trace norm appropriate for such an evaluation. For typical decohernce processes we establish the property of additivity for short times: the sum of the individual qubit error measures provides an estimate of the error for a multiqubit system.

We propose a model of coplanar superconducting resonators with kinetic inductance bridge at the end and its experimental realisation. Such resonators show an interesting nonlinear behaviour and can be useful for many practical applications.

Our work provides a method to reconstruct a state of quantum light in a continuous basis. For these purposes, feedforward neural network approximates wavefunction in the position basis. We reconstructed pure and mixed states based on experimental and artificial homodyne measurements with high fidelity. The main advantage of the method is the ability to describe states containing a large number of photons.

А tunable coupling scheme for implementing parametric two-qubit iSWAP-like gates on fixed-frequency fluxonium qubits, biased at a half flux quantum.

We consider a two-component ultracold dipolar Fermi gas in the two-dimensional geometry. We have calculated superfluid transition BCS temperature and the temperature of the BKT transition from weak to strong inter-particle interaction. In addition, we have discussed the interplay between interaction and disorder. Apart from fundamental interest, this research has practical applications. With the help of ultracold quantum gases one can build quantum simulators.

We propose a tunable scheme for implementing two-qubit CZ gate on inductively coupled fluxoniums. We simulate the system dynamics during the flux pulses and determine optimal pulse shape parameters for performing high fidelity CZ gate. The fidelity of this gate equals 0.9999.

In this work, we investigate how the presence of the third energy level affects the Rabi oscillations between ground and excited states of a two-level system in near-resonant external fields and the fidelity of quantum operations by numerically solving the master equation of Vee system confuguration.

A system of addressing to individual qubits was realized. The qubits was a pair of single rubidium-87 atoms trapped in the dipole traps. The logic levels was the sublevels of hyperfine splitting of the 5s1/2 ground state, transition was induced by the microwave radiation. Individual addressing was carried out using additional laser radiation, which caused detuning of the microwave transition of one of the atoms, thereby bringing it out of resonance with the microwave radiation.

This work is devoted to the study of the interference of spin waves excited in a bismuth-substituted yttrium iron garnet (YIG) by sequences of femtosecond laser pulses. We reveal the possibility to create magnon logical gates by manipulating the spatial arrangement of the local spin-wave sources.

Photon counting is one of the simplest way for measuring properties of coherent state of light. But realistic measurement effects (for example, dead-time) leads to deviation between probability distribution of the photon number and observed photon counting statistics. We analyse distributed dead time corrections of statistics and its applicability for weak coherent states of light.

In this work, we want to present QCreator: a toolbox for the automated design of systems of superconducting qubits. After the creation of a multi-qubit chip design, QCreator simultaneously maps it into a transmission line model (a set of known lumped elements, e.g. capacitors and inductors). Then, using mathematical methods for the model of lumped elements we can calculate the main parameters of the system and its Hamiltonian.

Trapped ions have recently become one of the most promising platforms for quantum computing realisation due to the highest coherence time of qubits and fidelity of operations. One of the approaches for scaling this system consists of Surface Electrode Trap based architecture. This work presents a tool for simulation of the classical motion of several ions in a planar trap using the molecular dynamics method.  

We present a monitoring system for quantum processors compoments that allows estimating their parameters based on the set of executed quantum circuits and its corresponding outputs.
Since our method uses only already accessible data from implemented circuits without the need to run additional algorithms, it can complement already existing approaches.

We show, that the use of the qutrit's upper level makes it possible to implement an N-qubit Toffoli gate using 2N-3 two-qutrit gates with an arbitrary qutrits' connection topology in superconducting and trapped-ion-based platforms.

We propose a new perspective on the dynamics of the topological local markers in inhomogeneous Chern insulators. This approach allows us to introduce the currents of the marker explicitly. Our definition satisfies the lattice continuity equation and has a clear physical interpretation in terms of density currents. Using this method, we demonstrated numerically the position control of a topologically nontrivial subsystem inside a finite sample. 

We present a chip that is potentially suitable for creating a 4-qubit superconducting quantum processor.

In the present work, we examine the sympathetic cooling behaviour of trapped ion chains comprised of ⁴⁰Ca+ and ⁴³Ca+. Using method of molecular dynamics we simulate strings of seven ions and analyze the influence of ancilla ion configuration in terms of normal modes.

We have applied the fluctuating local field approach for the Ising model with arbitrary couplings. The method provides a framework to treat competing fluctuations on equal footing and has the same numerical complexity as the mean-field method. We have found that such an approach successfully works for small- and mid-sized clusters for regular and random interactions between spins.

In this work, we build a precise data-driven model of open quantum dynamics using experimentally observed data. Our method allows capturing the most important characteristics of open quantum systems such as the effective dimension of the environment, the spectrum of the joint system-environment dynamics. It also provides a framework for the prediction of quantum dynamics and denoising of measured quantum trajectories.

One of the problems that arise when working with trapped atomic ions in order to perform quantum logic or precision spectroscopy is excessive beams of evaporated atoms. This can lead to the build up of material on trap electrodes and nearby surfaces which can cause the generation of stray electric fields and also degrade the quality of the vacuum. 

Here we present an alternative technique of producing neutral atoms that can be used for the future loading into Penning trap. 

Quantum key distribution (QKD) protocols contain post-processing procedure, which is mainly divided into error correction and privacy amplification. We improve the exiting error correction method to adapt them to QKD applications in which expensive components and computing power are concentrated on Bobs' side, while Alices' side is required to be as mobile as possible (star-like networks). In the work, we compete with the symmetric blind method and manage to achieve higher secret key rate.