arXiv subjects

R. Taranko

Publications and source records attributed to R. Taranko.

12 recordsLinked to original sources

arXiv2026

Transient triplet blockade in Andreev junction

We study the time-dependent triplet configuration, appearing under nonequilibrium conditions in a nanoscopic junction with two quantum dots coupled in series between superconductor and normal metallic lead. We show that in the situation, when both quantum dots are singly occupied by identical spin electrons, the on-dot electron pairing is suppressed what substantially affects the subgap charge transport. We investigate processes in which such configuration can be temporarily encountered, either due to the initial conditions or by imposing the external magnetic field. Our analytical and numerical calculations provide estimations for the temporal scales, characterizing evolution of the triplet configuration which could be manifested in the time-resolved tunneling measurements. Such nonequilibrium features of the triplet configuration might be relevant to operations on superconducting qubits, in their conventional and/or topological realizations.

cond-mat.mes-hall↗

arXiv2023

Transient effects in quantum dots contacted via topological superconductor

We investigate gradual development of the quasiparticle states in two quantum dots attached to opposite sides of the topological superconducting nanowire, hosting the boundary modes. Specifically, we explore the non-equilibrium cross-correlations transmitted between these quantum dots via the zero-energy Majorana modes. From the analytical and numerical results we reveal nonlocal features in the transient behavior of electron pairing, which subsequently cease while the hybrid structure evolves towards its asymptotic steady limit configuration. We estimate duration of these temporary nonlocal phenomena and inspect their possible manifestation in the quench-driven processes. Such dynamical effects might play an important role in braiding protocols of the topological and/or conventional superconducting quantum bits using nanoscopic hybrid structures.

cond-mat.mes-hall↗

arXiv2021

Subgap dynamics of double quantum dot coupled between superconducting and normal leads

Dynamical processes induced by the external time-dependent fields can provide valuable insight into the characteristic energy scales of a given physical system. We investigate them here in a nanoscopic heterostructure, consisting of the double quantum dot coupled in series to the superconducting and the metallic reservoirs, analyzing its response to (i)~abrupt bias voltage applied across the junction, (ii) sudden change of the energy levels, and imposed by (iii)~their periodic driving. We explore subgap properties of this setup which are strictly related to the in-gap quasiparticles and discuss their signatures manifested in the time-dependent charge currents. The characteristic multi-mode oscillations, their beating patters and photon-assisted harmonics reveal a rich spectrum of dynamical features that might be important for designing the superconducting qubits.

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arXiv2021

Transient effects in double quantum dot sandwiched laterally between superconducting and metallic leads

We study the transient phenomena appearing in a subgap region of the double quantum dot coupled in series between the superconducting and normal metallic leads, focusing on the development of the superconducting proximity effect. For the uncorrelated nanostructure we derive explicit expressions of the time-dependent occupancies in both quantum dots, charge currents, and electron pairing induced on individual dots and between them. We show that the initial configurations substantially affect the dynamical processes, in which the in-gap bound states emerge upon coupling the double quantum dot to superconducting reservoir. In particular, the superconducting proximity effect would be temporarily blocked whenever the quantum dots are initially singly occupied. Such {\it triplet}/{\it Andreev blockade} has been recently reported experimentally for double quantum dots embedded in the Josephson [D. Bouman et al., Phys. Rev. B 102, 220505 (2020)] and Andreev [P. Zhang et al., arXiv:2102.03283 (2021)] junctions. We also address the role of correlation effects within the lowest-order decoupling scheme and by the time-dependent numerical renormalization group calculations. Competition of the repulsive Coulomb interactions with the superconducting proximity effect leads to renormalization of the in-gap quasiparticles, speeding up the quantum oscillations and narrowing a region of transient phenomena, whereas the dynamical Andreev blockade is well pronounced in the weak inter-dot coupling limit. We propose feasible methods for detecting the characteristic time-scales that could be observable by the Andreev spectroscopy.

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arXiv2020

Dynamical leakage of Majorana mode into side-attached quantum dot

We study a hybrid structure, comprising the single-level quantum dot attached to the topological superconducting nanowire, inspecting dynamical transfer of the Majorana quasiparticle onto normal region. Motivated by the recent experimental realization of such heterostructure and its investigation under the stationary conditions [L. Schneider et al., https://doi.org/10.1038/s41467-020-18540-3, Nature Communications 11, 4707 (2020)] where the quantum dot energy level can be tuned by gate potential we examine how much time is needed for the Majorana mode to leak into the normal region. We estimate, that for typical hybrid structures this dynamical process would take about 20 nanoseconds. We propose a feasible empirical protocol for its detection by means of the time-resolved Andreev tunneling spectroscopy.

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arXiv2020

Quench dynamics of correlated quantum dot proximitized to superconducting lead

Quantum system abruptly driven from its stationary phase can reveal nontrivial dynamics upon approaching a new final state. We investigate here such dynamics for a correlated quantum dot sandwiched between the metallic and superconducting leads, considering two types of quenches feasible experimentally. In particular, we examine an interplay between the proximity induced electron pairing with correlations caused by the on-dot Coulomb repulsion. We discuss the time-dependent charge occupancy, complex order parameter, transient currents, and analyze evolution of the subgap quasiparticles which could be empirically observed in the tunneling conductance.

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arXiv2018

Time-dependent Andreev bound states of a quantum dot coupled to two superconducting leads

Sub-gap transport properties of a quantum dot (QD) coupled to two superconducting and one metallic leads are studied theoretically, solving the time-dependent equation of motion by the Laplace transform technique. We focus on time-dependent response of the system induced by a sudden switching on the QD-leads couplings, studying the influence of initial conditions on the transient currents and the differential conductance. We derive analytical expressions for measurable quantities and find that they oscillate in time with the frequency governed by the QD-superconducting lead coupling and acquire damping, due to relaxation driven by the normal lead. Period of these oscillations increases with the superconducting phase difference $ϕ$. In particular, for $ϕ=π$ the QD occupancy and the normal current evolve monotonically (without any oscillations) to their stationary values. In such case the induced electron pairing vanishes and the superconducting current is completely blocked. We also analyze time-dependent development of the Andreev bound states. We show, that the measurable conductance peaks do not appear immediately after sudden switching of the QD coupling to external leads but it takes some finite time-interval for the system needs create these Andreev states. Such time-delay is mainly controlled by the QD-normal lead coupling.

cond-mat.mes-hall↗

arXiv2018

How long does it take to form the Andreev quasiparticles ?

We study transient effects in a setup, where the quantum dot (QD) is abruptly sandwiched between the metallic and superconducting leads. Focusing on the proximity-induced electron pairing, manifested by the in-gap bound states, we determine characteristic time-scale needed for these quasiparticles to develop. In particular, we derive analytic expressions for (i) charge occupancy of the QD, (ii) amplitude of the induced electron pairing, and (iii) the transient currents under equilibrium and nonequilibrium conditions. We also investigate the correlation effects within the Hartree-Fock-Bogolubov approximation, revealing a competition between the Coulomb interactions and electron pairing.

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arXiv2005

Photon-assisted electron transport through a three-terminal quantum dot system with nonresonant tunneling channels

We have studied the electron transport through a quantum dot coupled to three leads in the presence of external microwave fields supplied to different parts of the considered mesoscopic system. Additionally, we introduced a possible nonresonant tunneling channels between leads. The quantum dot charge and currents were determined in terms of the appropriate evolution operator matrix elements and under the wide band limit the analytical formulas for time-averaged currents and differential conductance were obtained. We have also examined the response of the considered system on the rectangular-pulse modulation imposed on different quantum dot-leads barriers as well as the time-dependence of currents flowing in response to suddenly removed (or included) connection of a quantum dot with one of the leads.

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arXiv2004

Time-dependent electron transport through the multi-terminal quantum dot

We consider the time-dependent electron transport through a quantum dot connected to multiple leads in the presence of the additional over-dot (bridge) tunnelling channels by using the evolution operator technique. Each terminal and quantum dot are disturbed by an external oscillating field resulting in a time-dependence of the corresponding energy levels. The final analytical expressions for the currents flowing in the system are given assuming the wide-band limit approximation. We investigate also the transient-current characteristics in the case of the rectangular-pulse modulations imposed on the dot-lead barriers. The time-averaged current and its derivative with respect to the gate voltage have been calculated for a wide range of parameters.

cond-mat.mes-hall↗

arXiv2004

Aspects of electron transport through a quantum dot

The work of the Lublin group on the non-equillibrium transport through the quantum dot coupled to external leads (normal or superconducting) and subject to external time dependent fields has been reviewed.

cond-mat.mes-hall↗

arXiv2003

Influence of microwave fields on the electron transport through a quantum dot in the presence of a direct tunneling between leads

We consider the time-dependent electron transport through a quantum dot coupled to two leads in the presence of the additional over-dot (bridge) tunneling channel. By using the evolution operator method together with the wide-band limit approximation we derived the analytical formulaes for the quantum dot charge and current flowing in the system. The influence of the external microwave field on the time-average quantum dot charge, the current and the derivatives of the average current with respect to the gate and source-drain voltages has been investigated for a wide range of parameters.

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