arXiv subjects

Andrew G. Semenov

Publications and source records attributed to Andrew G. Semenov.

At least 19 recordsLinked to original sources

arXiv2026

Mass quench in interacting finite-size quantum field system

In this work, we theoretically investigate the non-equilibrium evolution of the correlation functions of a quantum scalar field following a mass quantum quench in a finite-size system. The self-consistent equation for the Keldysh (statistical) correlation function is solved numerically in the one-loop approximation. A specific spatio-temporal effect is observed: at a point in time approximately equal to half the system size, the effective mass experiences a strong disturbance. It is shown that this effect is driven by the interference of counter-propagating wave fronts of fluctuations that propagate within the light cone and is induced by periodic boundary conditions.

hep-th↗

arXiv2026

Measuring correlations using local and nonlocal quenches

We present a theoretical proposal for measuring correlation functions in a quantum field system based on the use of quantum quenches. Using the examples of massive and massless scalar field theories, we show that a short-term perturbation of the system leads to a dependence of the further evolution of the average field on the initial state's correlation functions. Considering two types of perturbations, namely local and nonlocal quenches, we show which correlation functions can be measured in each of these cases. The proposed procedure can be applied to study non-Gaussian correlations.

hep-th↗

arXiv2025

Fluxon cotunneling in coupled Josephson junctions: Perturbation theory

We investigate the effects of fluxon cotunneling and quantum Coulomb drag in a system of two small Josephson junctions coupled by means of mutual capacitance $C_m$. Depending on the value of $C_m$ we identify three different regimes of strong, intermediate and weak coupling. Focusing our attention on the last two regimes we develop a perturbation theory in the interaction and explicitly derive fluxon cotunneling amplitudes at sufficiently small mutual capacitance values. We demonstrate that the Coulomb drag effect survives at any non-zero $C_m$ and evaluate the non-local voltage response that is in general determined by a trade off between two different cotunneling processes. Our predictions can be straightforwardly generalized to bilinear Josephson chains and directly verified in future experiments.

cond-mat.supr-con↗

arXiv2024

Quantum Coulomb drag mediated by cotunneling of fluxons and Cooper pairs

We predict two novel quantum drag effects which can occur in macroscopically quantum coherent Josephson circuits. We demonstrate that biasing one resistively shunted Josephson junction by an external current one can induce a non-zero voltage drop across another such junction capacitively coupled to the first one. This quantum Coulomb drag is caused by cotunneling of magnetic flux quanta across both junctions which remain in the "superconducting" regime. Likewise, Cooper pair cotunneling across a pair of connected in series Josephson junctions in the "insulating" regime is responsible for another -- dual -- quantum Coulomb drag effect.

cond-mat.supr-con↗

arXiv2023

Ising Game on Graphs

Static and dynamic equilibria in noisy binary choice (Ising) games on complete and random graphs in the annealed approximation are analysed. Two versions, an Ising game with interaction term defined in accordance with the Ising model in statistical physics and a reduced Ising game with a customary definition of interaction term in game theory on graphs, are considered. A detailed analysis of hysteresis phenomenon shaping the pattern of static equilibria based on consideration of elasticity with respect to external influence is conducted. Fokker-Planck equations describing dynamic versions of the games under consideration are written and their asymptotic stationary solutions derived. It is shown that domains of parameters corresponding to the maxima of these probability distributions are identical with the corresponding hysteresis ranges for static equilibria. Same result holds for domains defining local stability of solutions of the evolution equations for the moments. In all the cases considered it is shown that the results for the reduced Ising game coincide with those obtained for the Ising game on complete graphs. It is shown that for s special case of logistic noise the results obtained for static equilibria for the Ising game reproduce those in the Ising model on graphs in statistical physics.

physics.soc-ph↗

arXiv2023

Comment on the paper SciPost Phys. Core 6, 019 (2023) by João F. Melo (arXiv:2112.09119)

In the paper by João F. Melo "The propagator matrix reloaded" (SciPost Phys. Core 6, 019 (2023), arXiv:2112.09119) the author provides a derivation of a formalism which includes interactions in the initial conditions for non-equilibrium quantum field theory. The main statement of this paper is that one cannot ignore interactions in the initial conditions, so quantum field theories at finite temperature are not free in the infinite past. In this comment we revise in details calculations from the section 5 of the paper and demonstrate explicitly that the main statement of this paper should be reconsidered.

hep-ph↗

arXiv2022

Superconducting quantum fluctuations in one dimension

We review some recent developments in the field of quasi-one-dimensional superconductivity. We demonstrate that low temperature properties of superconducting nanowires are essentially determined by quantum fluctuations. Smooth (Gaussian) fluctuations of the superconducting phase (also associated with plasma modes propagating along the wire) may significantly affect the electron density of states in such nanowires and induce persistent current noise in superconducting nanorings. Further interesting phenomena such as, e.g., non-vanishing resistance and shot noise of the voltage in current-biased superconducting nanowires, are caused by non-Gaussian fluctuations of the order parameter -- quantum phase slips (QPS). Such phenomena may be interpreted in terms of tunneling of fluxons playing the role of effective quantum "particles" dual to Cooper pairs and obeying complicated full counting statistics which reduces to Poissonian one in the low frequency limit. We also demonstrate that QPS effects may be particularly pronounced in thinnest wires and rings where quantum phase slips remain unbound and determine a non-perturbative length scale $L_c$ beyond which the supercurrent gets suppressed by quantum fluctuations. Accordingly, for $T \to 0$ such nanowires should become insulating at scales exceeding $L_c$, whereas at shorter length scales they may still exhibit superconducting properties. We argue that certain non-trivial features associated with quantum fluctuations of the order parameter may be sensitive to specific circuit topology and may be observed in structures like, e.g., a system of capacitively coupled superconducting nanowires.

cond-mat.supr-con↗

arXiv2021

Superconducting insulators and localization of Cooper pairs

Rapid miniaturization of electronic devices and circuits demands profound understanding of fluctuation phenomena at the nanoscale. Superconducting nanowires -- serving as important building blocks for such devices -- may seriously suffer from fluctuations which tend to destroy long-range order and suppress superconductivity. In particular, quantum phase slips (QPS) proliferating at low temperatures may turn a quasi-one-dimensional superconductor into a resistor or an insulator. Here, we introduce a physical concept of QPS-controlled localization of Cooper pairs that may occur even in uniform nanowires without any dielectric barriers being a fundamental manifestation of the flux-charge duality in superconductors. We demonstrate -- both experimentally and theoretically -- that deep in the "insulating" state such nanowires actually exhibit non-trivial superposition of superconductivity and weak Coulomb blockade of Cooper pairs generated by quantum tunneling of magnetic fluxons across the wire.

cond-mat.mes-hall↗

arXiv2020

Superconductor-insulator transition in capacitively coupled superconducting nanowires

We investigate superconductor-insulator quantum phase transitions in ultrathin capacitively coupled superconducting nanowires with proliferating quantum phase slips. We derive a set of coupled Berezinskii-Kosterlitz-Thouless-like renormalization group equations demonstrating that interaction between quantum phase slips in one of the wires gets modified due to the effect of plasma modes propagating in another wire. As a result, the superconductor-insulator phase transition in each of the wires is controlled not only by its own parameters but also by those of the neighboring wire as well as by mutual capacitance. We argue that superconducting nanowires with properly chosen parameters may turn insulating once they are brought sufficiently close to each other.

cond-mat.mes-hall↗

arXiv2020

Topology controlled phase coherence and quantum fluctuations in superconducting nanowires

Superconducting properties of metallic nano-wires may strongly depend on specific experimental conditions. Here we consider a setup where superconducting phase fluctuations are restricted at one point inside the wire and equilibrium supercurrent flows along the wire segment of an arbitrary length $L$. Low temperature physics of this structure is essentially determined, on one hand, by smooth phase fluctuations and, on the other hand, by quantum phase slips. The zero temperature phase diagram is controlled by the wire cross section and consists of a truly superconducting phase and two different phases where superconductivity can be observed only at shorter length scales. One of the latter phases exhibits more robust short-scale superconductivity whereas another one demonstrates a power-law decay of the supercurrent with increasing $L$ already at relatively short scales.

cond-mat.supr-con↗

arXiv2019

Quantal Response Equilibria in Binary Choice Games on Graphs

Static and dynamic equilibria in noisy binary choice games on graphs are considered. Equations defining static quantal response equilibria (QRE) for binary choice games on graphs with arbitrary topology and noise distribution are written. It is shown that in the special cases of complete graph and arbitrary noise distribution, and circular and star topology and logistic noise distribution the resulting equations can be cast in the form coinciding with that derived in the earlier literature. Explicit equations QRE for non-directed graphs in the annealed approximation are derived. It is shown that the resulting effect on the phase transition is the same as found in the literature on phase transition in the Ising model on graphs in the same approximation.Evolutionary noisy binary choice game having the earlier described QRE as its stationary equilibria in the mean field approximation is constructed using the formalism of master equation.

cs.GT↗

arXiv2019

Quantum fluctuations and phase coherence in superconducting nanowires

Quantum behavior of superconducting nanowires may essentially depend on the employed experimental setup. Here we investigate a setup that enables passing equilibrium supercurrent across an arbitrary segment of the wire without restricting fluctuations of its superconducting phase. The low temperature physics of the system is determined by a combined effect of collective sound-like plasma excitations and quantum phase slips. At $T=0$ the wire exhibits two quantum phase transitions, both being controlled by the dimensionless wire impedance $g$. While thicker wires with $g>16$ stay superconducting, in thinnest wires with $g<2$ the supercurrent is totally destroyed by quantum fluctuations. The intermediate phase with $2<g<16$ is characterized by two different correlation lengths demonstrating superconducting-like behavior at shorter scales combined with vanishing superconducting response in the long scale limit.

cond-mat.mes-hall↗

arXiv2019

Quantum phase slips and voltage fluctuations in superconducting nanowires

We argue that quantum phase slips (QPS) may generate non-equilibrium voltage fluctuations in superconducting nanowires. In the low frequency limit we evaluate all cumulants of the voltage operator which obey Poisson statistics and show a power law dependence on the external bias. We specifically address quantum shot noise which power spectrum $S_Ω$ may depend non-monotonously on temperature. In the long wire limit $S_Ω$ decreases with increasing frequency $Ω$ and vanishes beyond a threshold value of $Ω$ at $T \to 0$. Our predictions can be directly tested in future experiments with superconducting nanowires.

cond-mat.mes-hall↗

arXiv2019

Full counting statistics of quantum phase slips

We work out a microscopic theory describing complete statistics of voltage fluctuations generated by quantum phase slips (QPS) in superconducting nanowires. We evaluate the cumulant generating function and demonstrate that shot noise of the voltage as well as the third and all higher voltage cumulants differ from zero only due to the presence of QPS. In the zero-frequency limit voltage fluctuations in superconducting nanowires are described by Poisson statistics just as in a number of other tunneling-like problems. However, at non-zero frequencies quantum voltage fluctuations in superconducting nanowires become much more complicated and are not anymore accounted for by Poisson statistics. In the case of short superconducting nanowires we explicitly evaluate all finite-frequency voltage cumulants and establish a non-trivial relation between these cumulants and the current-voltage characteristics of our system.

cond-mat.mes-hall↗

arXiv2017

Shot noise in ultrathin superconducting wires

Quantum phase slips (QPS) may produce non-equilibrium voltage fluctuations in current-biased superconducting nanowires. Making use of the Keldysh technique and employing the phase-charge duality arguments we investigate such fluctuations within the four-point measurement scheme and demonstrate that shot noise of the voltage detected in such nanowires may essentially depend on the particular measurement setup. In long wires the shot noise power decreases with increasing frequency $Ω$ and vanishes beyond a threshold value of $Ω$ at $T \to 0$

cond-mat.supr-con↗

arXiv2017

Quantum phase fluctuations and density of states in superconducting nanowires

We argue that quantum fluctuations of the phase of the order parameter may strongly affect the electron density of states (DOS) in ultrathin superconducting wires. We demonstrate that the effect of such fluctuations is equivalent to that of a quantum dissipative environment formed by sound-like plasma modes propagating along the wire. We derive a non-perturbative expression for the local electron DOS in superconducting nanowires which fully accounts for quantum phase fluctuations. At any non-zero temperature these fluctuations smear out the square-root singularity in DOS near the superconducting gap and generate quasiparticle states at subgap energies. Furthermore, at sufficiently large values of the wire impedance this singularity is suppressed down to $T=0$ in which case DOS tends to zero at subgap energies and exhibits the power-law behavior above the gap. Our predictions can be directly tested in tunneling experiments with superconducting nanowires.

cond-mat.mes-hall↗

arXiv2016

Quantum Phase Slip Noise

Quantum phase slips (QPS) generate voltage fluctuations in superconducting nanowires. Employing Keldysh technique and making use of the phase-charge duality arguments we develop a theory of QPS-induced voltage noise in such nanowires. We demonstrate that quantum tunneling of the magnetic flux quanta across the wire yields quantum shot noise which obeys Poisson statistics and is characterized by a power law dependence of its spectrum $S_Ω$ on the external bias. In long wires $S_Ω$ decreases with increasing frequency $Ω$ and vanishes beyond a threshold value of $Ω$ at $T \to 0$. Quantum coherent nature of QPS noise yields non-monotonous dependence of $S_Ω$ on $T$ at small $Ω$.

cond-mat.mes-hall↗

arXiv2014

Supercurrent dephasing by electron-electron interactions

We demonstrate that in sufficiently long diffusive superconducting-normal-superconducting ($SNS$) junctions dc Josephson current is exponentially suppressed by electron-electron interactions down to zero temperature. This suppression is caused by the effect of {\it Cooper pair dephasing} which occurs in the normal metal and defines a new fundamental length scale $L_φ$ in the problem. Provided the temperature length exceeds $L_φ$ this dephasing length can be conveniently extracted from equilibrium measurements of the Josephson current.

cond-mat.mes-hall↗