We show that self sustained mechanical vibrations in a model magnetic shuttle device can be drive... more We show that self sustained mechanical vibrations in a model magnetic shuttle device can be driven by both the charge and the spin accumulated on the movable central island of the device. Different scenarios for how spin-and charge-induced shuttle instabilities may develop are discussed and shown to depend on whether there is a Coulomb blockade of tunneling or not. The crucial role of electronic spin flips in a magnetically driven shuttle is established and shown to cause giant magnetoresistance and dynamic magnetostriction effects. V
Fano resonances are proposed to perform a measurement of a spin state (whether it is up or down) ... more Fano resonances are proposed to perform a measurement of a spin state (whether it is up or down) of a single electron in a quantum dot via a spin-polarized current in an adjacent quantum wire. Rashba-like spin-orbit interaction in a quantum dot prohibits spin-flip events (Kondo-like phenomenon). That ensures the measurement to be non-demolishing.
An implementation of a quantum computer based on space states in double quantum dots is discussed... more An implementation of a quantum computer based on space states in double quantum dots is discussed. There is no charge transfer in qubits during calculation, therefore, uncontrollable entanglement between them due to long-range Coulomb interaction is suppressed. Other plausible sources of decoherence caused by interaction with phonons and gates could be substantially suppressed in the structure too. We also demonstrate how all necessary quantum logic operations, initialization, writing, and read-out could be carried out in the computer.
We consider dc-electronic transport through a nanowire suspended between two normal-metal leads i... more We consider dc-electronic transport through a nanowire suspended between two normal-metal leads in the presence of an external magnetic field. We show the very mechanism through which such a system, whose stationary current-voltage characteristic is essentially characterized by positive differential conductance, becomes unstable with respect to an onset of self-excited oscillations in electrical transport and mechanical vibrations. The self-excitation mechanism is based on the correlation between the occupancy of the quantized spin-split electronic energy levels inside the nanowire and the velocity of the nanowire with the crucial influence of strong enough retardation effects in magnetomotive coupling coming from mechanical vibrations.
We demonstrate that a supercurrent can pump energy from a battery that provides a voltage bias in... more 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.
We demonstrate that a supercurrent can pump energy from a battery that provides a voltage bias in... more 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.
The key physical processes in polymeric filters used for the blood purification include transport... more The key physical processes in polymeric filters used for the blood purification include transport across the capillary wall and the interaction of blood cells with the polymer membrane surface. Theoretical modeling of membrane transport is an important tool which provides researchers with a quantification of the complex phenomena involved in dialysis. In the paper, we present a dense review of the most successful theoretical approaches to the description of transport across the polymeric membrane wall as well as the cell–polymer surface interaction, and refer to the corresponding experimental methods while studying these phenomena in dialyzing filters.
A coherent hybrid of states with different number of Cooper pairs can be built in a superconducto... more A coherent hybrid of states with different number of Cooper pairs can be built in a superconductor grain as a result of periodically repeated discrete encounters with bulk superconductor leads. As a direct manifestation of such states a non-dissipative current depending on the phase difference between the leads can be measured.
We have studied a one-dimensional channel with a wider, straight region irradiated by an external... more We have studied a one-dimensional channel with a wider, straight region irradiated by an external electromagnetic field. In this system the interplay between interference effects and resonance phenomena manifests itself and provides a new behavior of conduction. We show that the transport properties of the system can be affected by changing frequency and the amplitude of the external field. We also show that for certain combinations of these parameters electron transport through the system is complitely blocked.
We consider the supercurrent flow through gated mesoscopic semiconductor hetrostructures in which... more We consider the supercurrent flow through gated mesoscopic semiconductor hetrostructures in which a twodimensional normal constriction is confined between superconducting electrodes. We show that for these structures the Josephson current, carried by quantized electron modes, can be strongly affected by an electromagnetic field. Photonassisted Landau-Zener transitions between Andreev bound states in the constriction manifest themselves in one of two ways: (i) If the phase difference between the superconducting elements is fixed a series of reversals in the direction of supercurrent flow occurs (Somersault effect). (ii) If instead the junction is current biased a series of voltage spikes is seen. Both manifestations are a direct consequence of the discrete energy spectrum of the mesoscopic junction. We discuss necessary conditions for the described phenomena to be experimentally observable.
Journal of Computational and Theoretical Nanoscience, 2007
The coupling between mechanical deformations and electronic charge transport in nanostructures an... more The coupling between mechanical deformations and electronic charge transport in nanostructures and in composite materials with nanoscale components gives rise to a new class of phenomenananoelectromechanical transport -and opens up a new route in nanotechnology. The interplay between the electronic and mechanical degrees of freedom is especially important in nanocomposites consisting of materials with very different elastic properties. Mechanical degrees of freedom take on a primary role in the charge transfer process in many single-electron devices, where transport is controlled by quantum-mechanical tunnelling and Coulomb interactions, but where tunnel barriers can be modified as a result of mechanical motion. A typical system of this kind is a single-electron transistor (SET) with deformable tunnel barriers, a so called Nano-Electro-Mechanical SET (NEM-SET). The new kind of electron transport in this and other types of nanodevices is referred to as "shuttle transport" of electrons, which implies that electrons is transferred between metallic leads via a movable small-sized cluster. The present review is devoted to the fundamental aspects of shuttle transport and to a description of major developments in the theoretical and experimental research in the field. Prospective applications of this exciting phenomenon that remarkably combines traditional mechanics of materials with the most advanced effects of quantum physics, will also be touched upon.
We consider "shuttling" of spin-polarized electrons between two magnetic electrodes (half-metals)... more 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.
The effects of a coupling between the quantized mechanical vibrations of a quantum dot and cohere... more The effects of a coupling between the quantized mechanical vibrations of a quantum dot and coherent tunneling of electrons through a single level in the dot are studied. The equation of motion for the reduced density operator describing the vibrational degree of freedom is obtained. It is shown that that the expectation value of the displacement is an oscillating function of time with an exponentially increasing amplitude, which is the signature of a quantum shuttle instability.
Effects of irradiation on the electronic conductance in nanowires, for field-free conditions and ... more Effects of irradiation on the electronic conductance in nanowires, for field-free conditions and under the influence of applied longitudinal magnetic fields, were investigated. The nanowires were modeled within the free-electron framework with a parabolic ͑transverse͒ confining potential. Our results for the dependence of the photoconductance of irradiated nanowires on the photon energy and/or the strength of the applied magnetic field show that such measurements may be used as a magneto-optic spectroscopy for determination of ͑i͒ the electron Fermi energy, ͑ii͒ the electron effective mass, and ͑iii͒ the number of quantized modes in the nanowire. Such measurements may also be used to assess to what degree the electron transport through the nanowire is adiabatic. Furthermore, our results suggest a method for controlling and tuning electronic transport in nanowires via external electromagnetic fields. ͓S0163-1829͑98͒07348-2͔
Room-temperature Coulomb blockade of charge transport through composite nanostructures containing... more Room-temperature Coulomb blockade of charge transport through composite nanostructures containing organic interlinks has recently been observed. A pronounced charging effect in combination with the softness of the molecular links implies that charge transfer gives rise to a significant deformation of these structures. For a simple model system containing one nanoscale metallic cluster connected by molecular links to two bulk metallic electrodes we show that self-excitation of periodic cluster oscillations in conjunction with sequential processes of cluster charging and decharging appears for a sufficiently large bias voltage. This new 'electron shuttle' mechanism of discrete charge transfer gives rise to a current through the nanostructure, which is proportional to the cluster vibration frequency.
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that
We theoretically analyse the dynamics of a suspended graphene membrane which is in tunnel contact... more We theoretically analyse the dynamics of a suspended graphene membrane which is in tunnel contact with grounded metallic electrodes and subjected to ac-electrostatic potential induced by a gate electrode. It is shown that for such system the retardation effects in the electronic subsystem generate an effective pumping for the relatively slow mechanical vibrations if the driving frequency exceeds the inverse charge relaxation time. Under this condition there is a critical value of the driving voltage amplitude above which the pumping overcomes the intrinsic damping of the mechanical resonator leading to a mechanical instability. This nonresonant instability is saturated by nonlinear damping and the system exhibits self-sustained oscillations of relatively large amplitude. Rapid progress in carbon nanostructures manufacturing stimulated new experimental and theoretical efforts in studying their unique optical, electrical, and mechanical properties. 1,2 In particular, the very high stiffness and low density of graphene make it an ideal
Transportation of Cooper-pairs by a movable single Cooper-pair-box placed between two remote supe... more Transportation of Cooper-pairs by a movable single Cooper-pair-box placed between two remote superconductors is shown to establish coherent coupling between them. This coupling is due to entanglement of the movable box with the leads and is manifested in the supression of quantum fluctuations of the relative phase of the order parameters of the leads. It can be probed by attaching a high resistance Josephson junction between the leads and measuring the current through this junction. The current is suppressed with increasing temperature.
We have calculated the photoconductance of a quantum point contact subject to a high-frequency el... more We have calculated the photoconductance of a quantum point contact subject to a high-frequency electromagnetic field. We find very pronounced steplike oscillations of the photoconductance as a function of gate voltage. The absorption of the electromagnetic field, which is polarized in the transverse direction, is due to transitions between different modes of the quantum point contact. A transition between a propagating and a nonpropagating mode results effectively in a backscattering process, and gives a negative or positive contribution to the current, depending on the gate voltage. When the number of propagating modes through the point contact exceeds a cutoff value, the photoconductance disappears. The cutoff value depends on the frequency of the electromagnetic field. We also find that the oscillation amplitude increases with the number of propagating modes. As a result of the electron-photon interaction, the total quantized conductance acquires an additional step structure.
We show that self sustained mechanical vibrations in a model magnetic shuttle device can be drive... more We show that self sustained mechanical vibrations in a model magnetic shuttle device can be driven by both the charge and the spin accumulated on the movable central island of the device. Different scenarios for how spin-and charge-induced shuttle instabilities may develop are discussed and shown to depend on whether there is a Coulomb blockade of tunneling or not. The crucial role of electronic spin flips in a magnetically driven shuttle is established and shown to cause giant magnetoresistance and dynamic magnetostriction effects. V
Fano resonances are proposed to perform a measurement of a spin state (whether it is up or down) ... more Fano resonances are proposed to perform a measurement of a spin state (whether it is up or down) of a single electron in a quantum dot via a spin-polarized current in an adjacent quantum wire. Rashba-like spin-orbit interaction in a quantum dot prohibits spin-flip events (Kondo-like phenomenon). That ensures the measurement to be non-demolishing.
An implementation of a quantum computer based on space states in double quantum dots is discussed... more An implementation of a quantum computer based on space states in double quantum dots is discussed. There is no charge transfer in qubits during calculation, therefore, uncontrollable entanglement between them due to long-range Coulomb interaction is suppressed. Other plausible sources of decoherence caused by interaction with phonons and gates could be substantially suppressed in the structure too. We also demonstrate how all necessary quantum logic operations, initialization, writing, and read-out could be carried out in the computer.
We consider dc-electronic transport through a nanowire suspended between two normal-metal leads i... more We consider dc-electronic transport through a nanowire suspended between two normal-metal leads in the presence of an external magnetic field. We show the very mechanism through which such a system, whose stationary current-voltage characteristic is essentially characterized by positive differential conductance, becomes unstable with respect to an onset of self-excited oscillations in electrical transport and mechanical vibrations. The self-excitation mechanism is based on the correlation between the occupancy of the quantized spin-split electronic energy levels inside the nanowire and the velocity of the nanowire with the crucial influence of strong enough retardation effects in magnetomotive coupling coming from mechanical vibrations.
We demonstrate that a supercurrent can pump energy from a battery that provides a voltage bias in... more 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.
We demonstrate that a supercurrent can pump energy from a battery that provides a voltage bias in... more 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.
The key physical processes in polymeric filters used for the blood purification include transport... more The key physical processes in polymeric filters used for the blood purification include transport across the capillary wall and the interaction of blood cells with the polymer membrane surface. Theoretical modeling of membrane transport is an important tool which provides researchers with a quantification of the complex phenomena involved in dialysis. In the paper, we present a dense review of the most successful theoretical approaches to the description of transport across the polymeric membrane wall as well as the cell–polymer surface interaction, and refer to the corresponding experimental methods while studying these phenomena in dialyzing filters.
A coherent hybrid of states with different number of Cooper pairs can be built in a superconducto... more A coherent hybrid of states with different number of Cooper pairs can be built in a superconductor grain as a result of periodically repeated discrete encounters with bulk superconductor leads. As a direct manifestation of such states a non-dissipative current depending on the phase difference between the leads can be measured.
We have studied a one-dimensional channel with a wider, straight region irradiated by an external... more We have studied a one-dimensional channel with a wider, straight region irradiated by an external electromagnetic field. In this system the interplay between interference effects and resonance phenomena manifests itself and provides a new behavior of conduction. We show that the transport properties of the system can be affected by changing frequency and the amplitude of the external field. We also show that for certain combinations of these parameters electron transport through the system is complitely blocked.
We consider the supercurrent flow through gated mesoscopic semiconductor hetrostructures in which... more We consider the supercurrent flow through gated mesoscopic semiconductor hetrostructures in which a twodimensional normal constriction is confined between superconducting electrodes. We show that for these structures the Josephson current, carried by quantized electron modes, can be strongly affected by an electromagnetic field. Photonassisted Landau-Zener transitions between Andreev bound states in the constriction manifest themselves in one of two ways: (i) If the phase difference between the superconducting elements is fixed a series of reversals in the direction of supercurrent flow occurs (Somersault effect). (ii) If instead the junction is current biased a series of voltage spikes is seen. Both manifestations are a direct consequence of the discrete energy spectrum of the mesoscopic junction. We discuss necessary conditions for the described phenomena to be experimentally observable.
Journal of Computational and Theoretical Nanoscience, 2007
The coupling between mechanical deformations and electronic charge transport in nanostructures an... more The coupling between mechanical deformations and electronic charge transport in nanostructures and in composite materials with nanoscale components gives rise to a new class of phenomenananoelectromechanical transport -and opens up a new route in nanotechnology. The interplay between the electronic and mechanical degrees of freedom is especially important in nanocomposites consisting of materials with very different elastic properties. Mechanical degrees of freedom take on a primary role in the charge transfer process in many single-electron devices, where transport is controlled by quantum-mechanical tunnelling and Coulomb interactions, but where tunnel barriers can be modified as a result of mechanical motion. A typical system of this kind is a single-electron transistor (SET) with deformable tunnel barriers, a so called Nano-Electro-Mechanical SET (NEM-SET). The new kind of electron transport in this and other types of nanodevices is referred to as "shuttle transport" of electrons, which implies that electrons is transferred between metallic leads via a movable small-sized cluster. The present review is devoted to the fundamental aspects of shuttle transport and to a description of major developments in the theoretical and experimental research in the field. Prospective applications of this exciting phenomenon that remarkably combines traditional mechanics of materials with the most advanced effects of quantum physics, will also be touched upon.
We consider "shuttling" of spin-polarized electrons between two magnetic electrodes (half-metals)... more 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.
The effects of a coupling between the quantized mechanical vibrations of a quantum dot and cohere... more The effects of a coupling between the quantized mechanical vibrations of a quantum dot and coherent tunneling of electrons through a single level in the dot are studied. The equation of motion for the reduced density operator describing the vibrational degree of freedom is obtained. It is shown that that the expectation value of the displacement is an oscillating function of time with an exponentially increasing amplitude, which is the signature of a quantum shuttle instability.
Effects of irradiation on the electronic conductance in nanowires, for field-free conditions and ... more Effects of irradiation on the electronic conductance in nanowires, for field-free conditions and under the influence of applied longitudinal magnetic fields, were investigated. The nanowires were modeled within the free-electron framework with a parabolic ͑transverse͒ confining potential. Our results for the dependence of the photoconductance of irradiated nanowires on the photon energy and/or the strength of the applied magnetic field show that such measurements may be used as a magneto-optic spectroscopy for determination of ͑i͒ the electron Fermi energy, ͑ii͒ the electron effective mass, and ͑iii͒ the number of quantized modes in the nanowire. Such measurements may also be used to assess to what degree the electron transport through the nanowire is adiabatic. Furthermore, our results suggest a method for controlling and tuning electronic transport in nanowires via external electromagnetic fields. ͓S0163-1829͑98͒07348-2͔
Room-temperature Coulomb blockade of charge transport through composite nanostructures containing... more Room-temperature Coulomb blockade of charge transport through composite nanostructures containing organic interlinks has recently been observed. A pronounced charging effect in combination with the softness of the molecular links implies that charge transfer gives rise to a significant deformation of these structures. For a simple model system containing one nanoscale metallic cluster connected by molecular links to two bulk metallic electrodes we show that self-excitation of periodic cluster oscillations in conjunction with sequential processes of cluster charging and decharging appears for a sufficiently large bias voltage. This new 'electron shuttle' mechanism of discrete charge transfer gives rise to a current through the nanostructure, which is proportional to the cluster vibration frequency.
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that
We theoretically analyse the dynamics of a suspended graphene membrane which is in tunnel contact... more We theoretically analyse the dynamics of a suspended graphene membrane which is in tunnel contact with grounded metallic electrodes and subjected to ac-electrostatic potential induced by a gate electrode. It is shown that for such system the retardation effects in the electronic subsystem generate an effective pumping for the relatively slow mechanical vibrations if the driving frequency exceeds the inverse charge relaxation time. Under this condition there is a critical value of the driving voltage amplitude above which the pumping overcomes the intrinsic damping of the mechanical resonator leading to a mechanical instability. This nonresonant instability is saturated by nonlinear damping and the system exhibits self-sustained oscillations of relatively large amplitude. Rapid progress in carbon nanostructures manufacturing stimulated new experimental and theoretical efforts in studying their unique optical, electrical, and mechanical properties. 1,2 In particular, the very high stiffness and low density of graphene make it an ideal
Transportation of Cooper-pairs by a movable single Cooper-pair-box placed between two remote supe... more Transportation of Cooper-pairs by a movable single Cooper-pair-box placed between two remote superconductors is shown to establish coherent coupling between them. This coupling is due to entanglement of the movable box with the leads and is manifested in the supression of quantum fluctuations of the relative phase of the order parameters of the leads. It can be probed by attaching a high resistance Josephson junction between the leads and measuring the current through this junction. The current is suppressed with increasing temperature.
We have calculated the photoconductance of a quantum point contact subject to a high-frequency el... more We have calculated the photoconductance of a quantum point contact subject to a high-frequency electromagnetic field. We find very pronounced steplike oscillations of the photoconductance as a function of gate voltage. The absorption of the electromagnetic field, which is polarized in the transverse direction, is due to transitions between different modes of the quantum point contact. A transition between a propagating and a nonpropagating mode results effectively in a backscattering process, and gives a negative or positive contribution to the current, depending on the gate voltage. When the number of propagating modes through the point contact exceeds a cutoff value, the photoconductance disappears. The cutoff value depends on the frequency of the electromagnetic field. We also find that the oscillation amplitude increases with the number of propagating modes. As a result of the electron-photon interaction, the total quantized conductance acquires an additional step structure.
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Papers by Leonid Gorelik