arXiv subjects

S. I. Kulinich

Publications and source records attributed to S. I. Kulinich.

At least 19 recordsLinked to original sources

arXiv2023

Andreev probing of Cooper-pair flying qubit

We propose a nanomechanical device which can actuate and probe a flying qubit that can be used to facilitate quantum information transfer over a long distance. The flying qubit is formed by a movable Cooper pair box (CPB) consisting of a superconducting dot and a bulk superconductor which are entangled by removing the Coulomb blockade of Cooper pair tunneling electrostatically. We suggest that flying qubit states formed on movable CPB can be observed in electron transport to a normal electrode via Andreev reflections. The charge transfer due to periodic mechanical motion of CPB leads to nonzero current at zero voltage and its coherence can be identified through oscillatory dependence of the current on a gate voltage.

cond-mat.mes-hall↗

arXiv2023

Transduction of quantum information from charge qubit to nanomechanical cat-state

We suggest a nanoelectromechanical setup and corresponding time protocol of its manipulation by which we transduce quantum information from charge qubit to nanomechanical cat state. The setup is based on the AC Josephson effect between bulk superconductors and mechanically vibrating mesoscopic superconducting island in the regime of the Cooper pair box. Starting with a pure state with quantum information initially encoded into superposition of the Cooper pair box states, applying a specially tailored time protocol upon bias voltage and gate electrodes, we obtain a new pure state with information finally encoded into superposition of nanomechanical coherent states constituting the cat state. This performance is achieved using quantum entanglement between electrical and mechanical states. Nanomechanical cat states serve as a storage of quantum information, motivated by significantly longer decoherence time with respect to the charge qubit states, from which the information can be transdued back to the charge qubit applying the reverse time protocol.

cond-mat.mes-hall↗

arXiv2022

Cooling of nanomechanical vibrations by Andreev injection

A nanoelectromechanical weak link composed of a carbon nanotube suspended between two normal electrodes in a gap between two superconducting leads is considered. The nanotube is treated as a movable single-level quantum dot in which the position-dependent superconducting order parameter is induced due to the Cooper pair tunneling. We show that electron tunneling processes significantly affect the state of the mechanical subsystem. We found that at a given direction of the applied voltage between the electrodes, the stationary state of the mechanical subsystem has a Boltzmann form with an effective temperature depended on the parameters of the device. As this takes place, the effective temperature can reach significantly small values (cooling effect). We also demonstrate that nanotube fluctuations strongly affect the dc current through the system. The latter can be used to probe the predicted effects in an experiment.

cond-mat.mes-hall↗

arXiv2021

Nanomechanics driven by the superconducting proximity effect

We consider a nanoelectromechanical weak link composed of a carbon nanotube suspended above a trench in a normal metal electrode and positioned in a gap between two superconducting leads. The nanotube is treated as a movable single-level quantum dot in which the position-dependent superconducting order parameter is induced as a result of Cooper pair tunneling. We show that in such a system, self-sustained bending vibrations can emerge if a bias voltage is applied. The occurrence of this effect crucially depends on the direction of the bias voltage and the relative position of the quantum dot level. We also demonstrate that the nanotube vibrations strongly affect the dc current through the system, a characteristic that can be used for the direct experimental observation of the predicted phenomenon.

cond-mat.mes-hall↗

arXiv2021

Entanglement between charge qubit states and coherent states of nanomechanical resonator generated by AC Josephson effect

We considered a nanoelectromechanical system consisting of a movable Cooper-pair box qubit which is subject to an electrostatic field, and coupled to the two bulk superconductors via tunneling processes. We suggest that qubit dynamics is related to the one of a quantum oscillator and demonstrate that a bias voltage applied between superconductors generates states represented by the entanglement of qubit states and coherent states of the oscillator if certain resonant conditions are fulfilled. It is shown that a structure of this entanglement may be controlled by the bias voltage in a way that gives rise to the entanglement incorporating so-called cat-states - the superposition of coherent states. We characterize the formation and development of such states analyzing the entropy of entanglement and corresponding Wigner function. The experimentally feasible detection of the effect by measuring the average current is also considered.

cond-mat.mes-hall↗

arXiv2021

Polaronic effects induced by non-equilibrium vibrons in a single-molecule transistor

Current-voltage characteristics of a single-electron transistor with a vibrating quantum dot were calculated assuming vibrons to be in a coherent (non-equilibrium) state. For a large amplitude of quantum dot oscillations we predict strong suppression of conductance and the lifting of polaronic blockade by bias voltage in the form of steps in $I-V$ curves. The height of the steps differs from the prediction of the Franck-Condon theory (valid for equilibrated vibrons) and the current saturates at lower voltages then for the case, when vibrons are in equilibrium state.

cond-mat.mes-hall↗

arXiv2021

Interplay of Vibration and Coulomb Effects in Transport of Spin-Polarized Electrons in a Single-Molecule Transistor

Tunnel transport of interacting spin-polarized electrons through a single-level vibrating quantum dot in external magnetic field is studied. By using density matrix method, the current-voltage characteristics and the dependence of conductance on temperature of a single-electron transistor were calculated. We found that a lifting of Coulomb blockade in external magnetic field happens in stages. The Franck-Condon steps associated with inelastic electron tunneling in our case are doubled due to contribution of two Zeeman-split levels in electron transport. The doubling of steps can be also observed in the presence of Coulomb interaction. For strong electron-vibron interaction the temperature dependence of conductance is shown to be non-monotonic and anomalous growth of conductance maximum weakly depends both on the Coulomb strength and the external magnetic field.

cond-mat.mes-hall↗

arXiv2018

Mechanically Induced Thermal Breakdown in Magnetic Shuttle Structures

A theory of a thermally induced single-electron "shuttling" instability in a magnetic nanomechanical device subject to an external magnetic field is presented in the Coulomb blockade regime of electron transport. The model magnetic shuttle device considered comprises a movable metallic grain suspended between two magnetic leads, which are kept at different temperatures and assumed to be fully spin polarized with antiparallel magnetizations. For a given temperature difference shuttling is found to occur for a region of external magnetic fields between a lower and an upper critical field strength, which separate the shuttling regime from normal small-amplitude "vibronic" regimes. We find that (i) the upper critical magnetic field saturates to a constant value in the high temperature limit and that the shuttle instability domain expands with a decrease of the temperature, (ii) the lower critical magnetic field depends not only on the temperature independent phenomenological friction coefficient used in the model but also on intrinsic friction (which vanishes in the high temperature limit) caused by magnetic exchange forces and electron tunneling between the quantum dot and the leads. The feasibility of using thermally driven magnetic shuttle systems to harvest thermal breakdown phenomena is discussed.

cond-mat.mes-hall↗

arXiv2016

Spin-mediated photomechanical coupling of a nanoelectromechanical shuttle

We show that nano-mechanical vibrations in a magnetic shuttle device can be strongly affected by external microwave irradiation through photo-assisted electronic spin-flip transitions. Mechanical consequences of these spin-flips are due to a spin-dependent magnetic force, which may lead to a nano-mechanical instability in the device. We derive a criterion for the instability to actually occur and analyze different regimes of possible nano-mechanical oscillations. Possible experimental realizations of the spin-mediated photo-mechanical instability and detection of the device back action are discussed.

cond-mat.mes-hall↗

arXiv2015

Shuttling of Spin Polarized Electrons in Molecular Transistors

Shuttling of electrons in single-molecule transistors with magnetic leads in the presence of an external magnetic field is considered theoretically. For a current of partially spin-polarized electrons a shuttle instability is predicted to occur for a finite interval of external magnetic field strengths. The lower critical magnetic field is determined by the degree of spin polarization and it vanishes as the spin polarization approaches 100%. The feasibility of detecting magnetic shuttling in a $C_{60}$-based molecular transistor with magnetic (Ni) electrodes is discussed [A.~N.~Pasupathy et al., Science 306, 86 (2004)].

cond-mat.mes-hall↗

arXiv2014

Electronic spin working mechanically

A single-electron tunneling (SET) device with a nanoscale central island that can move with respect to the bulk source- and drain electrodes allows for a nanoelectromechanical (NEM) coupling between the electrical current through the device and mechanical vibrations of the island. Although an electromechanical "shuttle" instability and the associated phenomenon of single-electron shuttling were predicted more than 15 years ago, both theoretical and experimental studies of NEM-SET structures are still carried out. New functionalities based on quantum coherence, Coulomb correlations and coherent electron-spin dynamics are of particular current interest. In this article we present a short review of recent activities in this area.

cond-mat.mes-hall↗

arXiv2012

Magnetopolaronic effects in electron transport through a single-level vibrating quantum dot

Magneto-polaronic effects are considered in electron transport through a single-level vibrating quantum dot subjected to a transverse (to the current flow) magnetic field. It is shown that the effects are most pronounced in the regime of sequential electron tunneling, where a polaronic blockade of the current at low temperatures and an anomalous temperature dependence of the magnetoconductance are predicted. In contrast, for resonant tunneling of polarons the peak conductance is not affected by the magnetic field.

cond-mat.mes-hall↗

arXiv2011

Umklapp-Assisted Electron Transport Oscillations in Metal Superlattices

We consider a superlattice of parallel metal tunnel junctions with a spatially non-homogeneous probability for electrons to tunnel. In such structures tunneling can be accompanied by electron scattering that conserves energy but not momentum. In the special case of a tunneling probability that varies periodically with period $a$ in the longitudinal direction, i.e., perpendicular to the junctions, electron tunneling is accompanied by "umklapp" scattering, where the longitudinal momentum changes by a multiple of $h/a$. We predict that as a result a sequence of metal-insulator transitions can be induced by an external electric- or magnetic field as the field strength is increased.

cond-mat.mes-hall↗

arXiv2011

Hot electrons in magnetic point contacts as a photon source

We propose to use a point contact between a ferromagnetic and a normal metal in the presence of a magnetic field for creating a large inverted spin-population of hot electrons in the contact core. The key point of the proposal is that when these hot electrons relax by flipping their spin, microwave photons are emitted, with a frequency tunable by the applied magnetic field. While point contacts is an established technology their use as a photon source is a new and potentially very useful application. We show that this photon emission process can be detected by means of transport spectroscopy and demonstrate stimulated emission of radiation in the 10-100 GHz range for a model point contact system using a minority-spin ferromagnetic injector. These results can potentially lead to new types of lasers based on spin injection in metals.

cond-mat.mes-hall↗

arXiv2010

Superconductive pumping of nanomechanical vibrations

We demonstrate that a supercurrent can pump energy from a battery that provides a voltage bias into nanomechanical vibrations. Using a device containing a nanowire Josephson weak link as an example we show that a nonlinear coupling between the supercurrent and a static external magnetic field leads to a Lorentz force that excites bending vibrations of the wire at resonance conditions. We also demonstrate the possibility to achieve more than one regime of stationary nonlinear vibrations and how to detect them via the associated dc Josephson currents and we discuss possible applications of such a multistable nanoelectromechanical dynamics.

cond-mat.mes-hall↗

arXiv2006

Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts

We consider the electrical current through a magnetic point contact in the limit of a strong inelastic scattering of electrons. In this limit local Joule heating of the contact region plays a decisive role in determining the transport properties of the point contact. We show that if an applied constant bias voltage exceeds a critical value, the stationary state of the system is unstable, and that periodic, non-harmonic oscillations in time of both the electrical current through the contact and the local temperature in the contact region develop spontaneously. Our estimations show that the necessary experimental conditions for observing such oscillations with characteristic frequencies in the range $10^8 ÷10^9$ Hz can easily be met. We also show a possibility to manipulate upon the magnetization direction of a magnetic grain coupled through a point contact to a bulk ferromagnetic by exciting the above-mentioned thermal-electric oscillations.

cond-mat.mtrl-sci↗

arXiv2005

Coulomb Promotion of Spin-Dependent Tunnelling

We study transport of spin-polarized electrons through a magnetic single-electron transistor (SET) in the presence of an external magnetic field. Assuming the SET to have a nanometer size central island with a single electron level we find that the interplay on the island between coherent spin-flip dynamics and Coulomb interactions can make the Coulomb correlations promote rather than suppress the current through the device. We find the criteria for this new phenomenon -- Coulomb promotion of spin-dependent tunnelling -- to occur.

cond-mat.mes-hall↗

arXiv2004

Spin-Dependent Transport of Electrons in a Shuttle Structure

We consider "shuttling" of spin-polarized electrons between two magnetic electrodes (half-metals) by a movable dot with a single electronic level. If the magnetization of the electrodes is antiparallel we show that the transmittance of the system can be changed by orders of magnitude if an external magnetic field, perpendicular to the polarization of the electronic spins, is applied. A giant magnetotransmittance effect can be achieved for weak external fields of order $1÷10$ Oe.

cond-mat.mes-hall↗