arXiv subjects

M. V. Fistul

Publications and source records attributed to M. V. Fistul.

At least 37 records · Page 2Linked to original sources

arXiv2016

Quantum synchronization in disordered superconducting metamaterials

I report a theoretical study of collective coherent quantum-mechanical oscillations in disordered superconducting quantum metamaterials (SQMs), i.e artificially fabricated arrays of interacting qubits (two-levels system). An unavoidable disorder in qubits parameters results in a substantial spread of qubits frequencies, and in the absence of electromagnetic interaction between qubits these individual quantum-mechanical oscillations of single qubits manifest themselves by a large number of small resonant drops in the frequency dependent transmission of electromagnetic waves propagating through disordered SQM, $D(ω)$. We show that even a weak electromagnetic interaction between adjacent qubits can overcome the disorder and establish completely or partially \emph{synchronized} quantum-mechanical dynamic state in the disordered SQM. In such a state a large amount of qubits displays the collective quantum mechanical oscillations, and this collective behavior manifests itself by a few giant resonant drops in the $D(ω)$ dependence. The size of a system $r_0$ showing the collective (synchronized) quantum-mechanical behavior is determined in the one-dimensional SQMs as $r_0 \simeq a [K/δΔ]^2$, where $K$, $δΔ$, $a$ are the energy of nearest-neighbor interaction, the spread of qubits energy splitting, and the distance between qubits, accordingly. We show that this phenomenon has an origin in the Anderson localization of spinon-type excitations arising in the SQM. Our analysis is also in a good accord with recent experiments on the electrodynamics of the disordered 1D SQMs.

quant-ph↗

arXiv2016

Double resonance response of a superconducting quantum metamaterial: manifestation of non-classical states of photons

We report a theoretical study of ac response of superconducting quantum metamaterials (SQMs), i.e. an array of qubits (two-levels system) embedded in the low-dissipative resonator. By making use of a particular example of SQM, namely the array of charge qubits capacitively coupled to the resonator, we obtain a second-order phase transition between an incoherent (the high-temperature phase) and coherent (the low-temperatures phase) states of photons. This phase transition in many aspects resembles the paramagnetic-ferromagnetic phase transition. The critical temperature of the phase transition, $T^\star$, is determined by the energy splitting of two-level systems $δ$, number of qubits in the array $N$, and the strength of the interaction $η$ between qubits and photons in the cavity. We obtain that the photon states manifest themselves by resonant drops in the frequency dependent transmission $D(ω)$ of electromagnetic waves propagating through a transmission line weakly coupled to the SQM. At high temperatures the $D(ω)$ displays a single resonant drop, and at low temperatures a peculiar \emph{double resonance response} has to be observed. The physical origin of such a resonant splitting is the quantum oscillations between two coherent states of photons of different polarizations.

cond-mat.supr-con↗

arXiv2015

Bound states induced giant oscillations of the conductance in the quantum Hall regime

We theoretically studied the quasiparticle transport in a 2D electron gas biased in the quantum Hall regime and in the presence of a lateral potential barrier. The lateral junction hosts the specific magnetic field dependent quasiparticle states highly localized in the transverse direction. The quantum tunnelling across the barrier provides a complex bands structure of a one-dimensional energy spectrum of these bound states, $ε_n(p_y)$, where $p_y$ is the electron momentum in the longitudinal direction $y$. Such a spectrum manifests itself by a large number of peaks and drops in the dependence of the magnetic edge states transmission coefficient $D(E)$ on the electron energy $E$. E.g., the high value of $D$ occurs as soon as the electron energy $E$ reaches gaps in the spectrum. These peaks and drops of $D(E)$ result in giant oscillations of the transverse conductance $G_x$ with the magnetic field and/or the transport voltage. Our theoretical analysis based on the coherent macroscopic quantum superposition of the bound states and the magnetic edge states propagating along the system boundaries, is in a good accord with the experimental observations found in Ref. W. Kang et al., Letters to Nature, 403, 59 (2000).

cond-mat.mes-hall↗

arXiv2014

Electrodynamics of a planar Archimedean spiral resonator

We present a theoretical and experimental study of electrodynamics of a planar spiral superconducting resonator of a finite length. The resonator is made in the form of a monofilar Archimedean spiral. By making use of a general model of inhomogeneous alternating current flowing along the resonator and specific boundary conditions on the surface of the strip, we obtain analytically the frequencies $f_n$ of resonances which can be excited in such system. We also calculate corresponding inhomogeneous RF current distributions $ψ_n (r)$, where $r$ is the coordinate across a spiral. We show that the resonant frequencies and current distributions are well described by simple relationships $f_n=f_1 n$, and $ψ_n(r)\simeq \sin[πn (r/R_e)^2]$, where $n=1,2...$, and $R_e$ is the external radius of the spiral. Our analysis of electrodynamic properties of spiral resonators' is in good accord with direct numerical simulations and measurements made using specifically designed magnetic probe and laser scanning microscope.

cond-mat.supr-con↗

arXiv2014

Resonant enhancement of MQT in Josephson junctions: the influence of coherent two-level systems

We report a theoretical study of the macroscopic quantum tunneling (MQT) in small Josephson junctions containing randomly distributed two-level systems. We focus on the magnetic field dependent crossover temperature $T_{cr}$ between the thermal fluctuation and quantum regimes of switching from the superconducting (the zero-voltage) state to a resistive one. In the absence of two-levels systems the crossover temperature shows a smooth decrease with an applied magnetic field characterized by an external flux $Φ$. Beyond that we predict a narrow peak in the dependence of $T_{cr}(Φ)$ occurring in the intermediate range of $Φ$. The effect becomes more pronounced as the junction size increases. We explain this effect quantitatively by a strong resonant suppression of a potential barrier for the Josephson phase escape that is due to the coherent quantum Rabi oscillations in two-level systems present in the junction.

cond-mat.supr-con↗

arXiv2014

Radiation-induced quantum Fano-type resonances in the transport of $N$-$P$-$N$ graphene based junctions

We present a theoretical study of quantum resonances in the ballistic transport of graphene based $N$-$P$-$N$ junction subject to an externally applied electromagnetic field (EF). By making use of the Floquet analysis and the quasi-classical approach we analyze the dynamics of electrons in the presence of time and coordinate dependent potential $U(z,t)$. In the absence of EF the resonant tunneling results in a set of sharp resonances in the dependence of dc conductance $σ$ on the gate voltage $V_g$. In irradiated $N$-$P$-$N$ junctions we obtain the Fano-type resonances in the dependence of $σ(V_g)$. This \emph{coherent quantum-mechanical phenomenon} is due to the interplay of two effects: the resonant tunneling through quasi-bound states and the quantum-interference effect in the region between the "resonant points", where the resonant absorption (emission) of photons occurs, and junction interfaces.

cond-mat.mes-hall↗

arXiv2013

Electrodynamics of a ring-shaped spiral resonator

We present analytical, numerical and experimental investigations of electromagnetic resonant modes of a compact monofilar Archimedean spiral resonator shaped in a ring, with no central part. Planar spiral resonators are interesting as components of metamaterials for their compact deep-subwavelength size. Such resonators couple primarily to the magnetic field component of the incident electromagnetic wave, offering properties suitable for magnetic meta-atoms. Surprisingly, the relative frequencies of the resonant modes follow the sequence of the odd numbers, despite the nearly identical boundary conditions for electromagnetic fields at the extremities of the resonator. In order to explain the observed spectrum of resonant modes, we show that the current distribution inside the spiral satisfies a particular Carleman type singular integral equation. By solving this equation, we obtain a set of resonant frequencies. The analytically calculated resonance frequencies and the current distributions are in good agreement with experimental data and the results of numerical simulations. By using low-temperature laser scanning microscopy of a superconducting spiral resonator, we compare the experimentally visualized ac current distributions over the spiral with the calculated ones. Theory and experiment agree well with each other. Our analytical model allows for calculation of a detailed three-dimensional magnetic field structure of the resonators.

cond-mat.supr-con↗

arXiv2013

Collective quantum coherent oscillations in a globally coupled array of qubits

We report a theoretical study of coherent collective quantum dynamic effects in an array of N qubits (two-level systems) incorporated into a low-dissipation resonant cavity. Individual qubits are characterized by energy level differences $Δ_i$ and we take into account a spread of parameters $Δ_i$. Non-interacting qubits display coherent quantum beatings with N different frequencies, i.e. $ω_i=Δ_i/\hbar$ . Virtual emission and absorption of cavity photons provides a long-range interaction between qubits. In the presence of such interaction we analyze quantum correlation functions of individual qubits $C_i(t)$ to obtain two collective quantum-mechanical coherent oscillations, characterized by frequencies $ω_1=\barΔ/\hbar$ and $ω_2=\tildeω_R$, where $\tildeω_R$ is the resonant frequency of the cavity renormalized by interaction. The amplitude of these oscillations can be strongly enhanced in the resonant case when $ω_1 \simeq ω_2$.

cond-mat.mes-hall↗

arXiv2013

Generation of non-classical photon states in superconducting quantum metamaterials

We report a theoretical study of diverse non-classical photon states that can be realized in superconducting quantum metamaterials. As a particular example of superconducting quantum metamaterials an array of SQUIDs incorporated in a low-dissipative transmission line (resonant cavity) will be studied. This system will be modeled as a set of two-levels systems (qubits) strongly interacting with resonant cavity photons. We predict and analyze {a second(first)-order phase transition} between an incoherent (the high-temperature phase) and coherent (the low-temperatures phase) states of photons. In equilibrium state the partition function $Z$ of the electromagnetic field (EF) in the cavity is determined by the effective action $S_{eff}\{P(τ)\}$ that, in turn, depends on imaginary-time dependent momentum of photon field $P(τ)$. We show that the order parameter of this phase transition is the $P_{0}(τ)$ minimizing the effective action of a whole system. In the incoherent state the order parameter $P_{0}(τ)=0$ but at low temperatures we obtain various coherent states characterized by non-zero values of $P_{0}(τ)$. This phase transition in many aspects resembles the Peierls metal-insulator and the metal-superconductor phase transitions. The critical temperature of such phase transition $T^\star$ is determined by the energy splitting of two-level systems $Δ$, a number of SQUIDs in the array $N$, and the strength of the interaction $η$ between SQUIDs and photons in cavity.

cond-mat.mes-hall↗

arXiv2010

Radiation-induced quantum interference in low-dimensional $n$-$p$ junctions

We predict and analyze {\it radiation-induced quantum interference effect} in low-dimensional $n$-$p$ junctions. This phenomenon manifests itself by large oscillations of the photocurrent as a function of the gate voltage or the frequency of the radiation. The oscillations result from the quantum interference between two electron paths accompanied by resonant absorption of photons. They resemble Ramsey quantum beating and Stueckelberg oscillations well-known in atomic physics. The effect can be observed in one- and two-dimensional $n$-$p$ junctions based on nanowires, carbon nanotubes, monolayer or bilayer graphene nanoribbons.

cond-mat.mes-hall↗

arXiv2010

Fiske Steps and Abrikosov Vortices in Josephson Tunnel Junctions

We present a theoretical and experimental study of the Fiske resonances in the current-voltage characteristics of "small" Josephson junctions with randomly distributed misaligned Abrikosov vortices. We obtained that in the presence of Abrikosov vortices the resonant interaction of electromagnetic waves, excited inside a junction, with the ac Josephson current manifests itself by Fiske steps in a current-voltage characteristics even in the absence of external magnetic field. We found that the voltage positions of the Fiske steps are determined by a junction size, but the Fiske step magnitudes depend both on the density of trapped Abrikosov vortices and on their misalignment parameter. We measured the magnetic field dependence of both the amplitude of the first Fiske step and the Josephson critical current of low-dissipative small $Nb$ based Josephson tunnel junctions with artificially introduced Abrikosov vortices. A strong decay of the Josephson critical current and a weak non-monotonic decrease of the first Fiske step amplitude on the Abrikosov vortex density were observed. The experimentally observed dependencies are well described by the developed theory.

cond-mat.supr-con↗

arXiv2008

Effect of radiation on transport in graphene

We study transport properties of graphene-based p-n junctions irradiated by an electromagnetic field (EF). The resonant interaction of propagating quasiparticles with an external monochromatic radiation opens dynamical gaps in their spectrum, resulting in a strong modification of current-voltage characteristics of the junctions. The values of the gaps are proportional to the amplitude of EF. We find that the transmission of the quasiparticles in the junctions is determined by the tunneling through the gaps, and can be fully suppressed when applying a sufficiently large radiation power. However, EF can not only suppress the current but also generate it. We demonstrate that if the height of the potential barrier exceeds a half of the photon energy, the directed current (photocurrent) flows through the junction without any dc bias voltage applied. Such a photocurrent arises as a result of inelastic quasiparticle tunneling assisted by one- or two-photon absorption. We calculate current-voltage characteristics of diverse graphene based junctions and estimate their parameters necessary for the experimental observation of the photocurrent and transmission suppression.

cond-mat.mes-hall↗

arXiv2008

Macroscopic Coulomb blockade in large Josephson junction arrays

We investigate theoretically transport properties of one- and two-dimensional regular Josephson junction arrays (JJAs) in an insulating state. We derive the low-temperature current-voltage characteristics for the current mediated by the Cooper pair transfer across the system. In the case where the screening length associated with the capacitance of the islands to the ground is much larger than the island's size, we find that transport is governed by the macroscopic Coulomb blockade effect with the gap well exceeding a single island charging energy. In the limit when the screening length is much larger than the linear size of the array, the gap establishes the dependence on the array size, namely, the Coulomb gap grows linearly with the system size in 1D and grows as logarithm of the system size in the two-dimensional array. We find two transport regimes: At moderate temperatures, above the BKT-like charge binding-unbinding transition the low bias transport is thermally activated, the activation energy being equal to the Coulomb blockade energy. At low temperatures, below the binding-unbinding transition, a JJA falls into a superinsulating state with the resistance exhibiting a double-exponential temperature dependence.

cond-mat.supr-con↗

arXiv2007

Photon-assisted spin transport in a two-dimensional electron gas

We study spin-dependent transport in a two-dimensional electron gas subject to an external step-like potential $V(x)$ and irradiated by an electromagnetic field (EF). In the absence of EF the electronic spectrum splits into spin sub-bands originating from the "Rashba" spin-orbit coupling. We show that the resonant interaction of propagating electrons with the component EF parallel to the barrier induces a \textit{% non-equilibrium dynamic gap} $(2Δ_{R})$ between the spin sub-bands. Existence of this gap results in coherent spin-flip processes that lead to a spin-polarized current and a large magnetoresistance, i.e the spin valve effect. These effects may be used for controlling spin transport in semiconducting nanostructures, e.g. spin transistors, spin-blockade devices etc., by variation of the intensity S and frequency $ω$ of the external radiation.

cond-mat.mes-hall↗

arXiv2007

Collective transport in the insulating state of Josephson junction arrays

We investigate collective Cooper-pair transport of one- and two-dimensional Josephson junction arrays in the insulating state. We derive an analytical expression for the current-voltage characteristic revealing thermally activated conductivity at small voltages and threshold voltage depinning. The activation energy and the related depinning voltage represent a dynamic Coulomb barrier for collective charge transfer over the whole system and scale with the system size. We show that both quantities are non-monotonic functions of magnetic field. We propose that formation of the dynamic Coulomb barrier as well as the size scaling of the activation energy and the depinning threshold voltage, are consequences of the mutual phase synchronization. We apply the results for interpretation of experimental data in disordered films near the superconductor-insulator transition.

cond-mat.supr-con↗

arXiv2007

Electromagnetic field induced suppression of transport through $n$-$p$ junctions in graphene

We study quasi-particle transmission through an $n $-$p$ junction in a graphene irradiated by an electromagnetic field (EF). In the absence of EF the electronic spectrum of undoped graphene is gapless, and one may expect the perfect transmission of quasi-particles flowing perpendicular to the junction. We demonstrate that the resonant interaction of propagating quasi-particles with the component of EF parallel to the junction induces a \textit{non-equilibrium dynamic gap} $(2Δ_R)$ between electron and hole bands in the quasi-particle spectrum of graphene. In this case the strongly suppressed quasi-particle transmission is only possible due to interband tunnelling. The effect may be used for controlling transport properties of diverse structures in graphene, like, e.g., $n$-$p$-$n$ transistors, single electron transistors, quantum dots, etc., by variation of the intensity $S$ and frequency $ω$ of the external radiation.

cond-mat.mes-hall↗

arXiv2006

Quantum cavity modes in spatially extended Josephson systems

We report a theoretical study of the macroscopic quantum dynamics in spatially extended Josephson systems. We focus on a Josephson tunnel junction of finite length placed in an externally applied magnetic field. In such a system, electromagnetic waves in the junction are excited in the form of cavity modes manifested by Fiske resonances, which are easily observed experimentally. We show that in the quantum regime various characteristics of the junction as its critical current $I_c$, width of the critical current distribution $σ$, escape rate $Γ$ from the superconducting state to a resistive one, and the time-dependent probability $P(t)$ of the escape are influenced by the number of photons excited in the junction cavity. Therefore, these characteristics can be used as a tool to measure the quantum states of photons in the junction, e.g. quantum fluctuations, coherent and squeezed states, entangled Fock states, etc.

cond-mat.supr-con↗

arXiv2006

Macroscopic quantum tunneling in globally coupled series arrays of Josephson junctions

We present a quantitative analysis of an escape rate for switching from the superconducting state to a resistive one in series arrays of globally coupled Josephson junctions. A global coupling is provided by an external shunting impedance. Such an impedance can strongly suppress both the crossover temperature from the thermal fluctuation to quantum regimes, and the macroscopic quantum tunneling (MQT) in short Josephson junction series arrays. However, in large series arrays we obtain an enhancement of the crossover temperature, and a giant increase of the MQT escape rate. The effect is explained by excitation of a {\it spatial-temporal charge instanton} distributed over a whole structure. The model gives a possible explanation of recently published experimental results on an enhancement of the MQT in single crystals of high-$T_c$ superconductors.

cond-mat.supr-con↗