23 research outputs found
Resonant coupling of a SQUID to a mechanical resonator
No full textWe analyze the properties of a mechanical resonator embedded into a quantum SQUID and analyze under which conditions it is possible to realize a resonant coupling between the SQUID and the resonator. We find, within the present technology, how it is possible to tune the system into the regime where the plasma frequency of the SQUID matches the resonator frequency and maximizes the corresponding coupling. In these conditions the doubly degenerate quantum level of the system is split by the coupling between the SQUID and the resonator.QN/Quantum NanoscienceApplied Science
Dynamics of a SQUID ratchet coupled to a nanomechanical resonator
No full textWe investigate the dynamics of a superconducting rectifying circuit, namely, a three-junction superconducting quantum interference device (SQUID), where one arm of the superconducting loop consists of a nanomechanical resonator. We find that the dc characteristic curve of the system displays features that are directly related to the frequency and amplitude of the mechanical oscillations; these effects can be further enhanced by biasing the SQUID with an ac current. We discuss potential future developments of this idea in the field of ultrasensitive position detection, and assess their feasibility in current setup
Detecting phonon blockade with photons
No full textMeasuring the quantum dynamics of a mechanical system, when few phonons are involved, remains a challenge. We show that a superconducting microwave resonator linearly coupled to the mechanical mode constitutes a very powerful probe for this scope. This new coupling can be much stronger than the usual radiation pressure interaction by adjusting a gate voltage. We focus on the detection of phonon blockade, showing that it can be observed by measuring the statistics of the light in the cavity. The underlying reason is the formation of an entangled state between the two resonators. Our scheme realizes a phonotonic Josephson junction, giving rise to coherent oscillations between phonons and photons as well as a self-trapping regime for a coupling smaller than a critical value. The transition from the self-trapping to the oscillating regime is also induced dynamically by dissipation.QN/Quantum NanoscienceApplied Science
dc Josephson Effect in Metallic Single-Walled Carbon Nanotubes
No full textThe dc Josephson effect is investigated in a single-walled metallic carbon nanotube connected to two superconducting leads. In particular, by using the Luttinger liquid theory, we analyze the effects of the electron-electron interaction on the supercurrent. We find that in the long junction limit the strong electronic correlations of the nanotube, together with its peculiar band structure, induce oscillations in the critical current as a function of the junction length and/or the nanotube electron filling. These oscillations represent a signature of the Luttinger liquid physics of the nanotube, for they are absent if the interaction is vanishing. We show that this effect can be exploited to reverse the sign of the supercurrent, realizing a tunable π-junctio
Electron tunneling into a quantum wire in the Fabry-Perot regime
No full textWe study a gated quantum wire contacted to source and drain electrodes in the Fabry-Pérot regime. The wire is also coupled to a third terminal (tip), and we allow for an asymmetry of the tip tunneling amplitudes of right-moving and left-moving electrons. We analyze configurations where the tip acts as an electron injector or as a voltage probe and show that the transport properties of this three-terminal setup exhibit very rich physical behavior. For a noninteracting wire we find that a tip in the voltage-probe configuration affects the source-drain transport in different ways, namely, by suppressing the conductance, by modulating the Fabry-Pérot oscillations, and by reducing their visibility. The combined effect of electron-electron interaction and finite length of the wire, accounted for by the inhomogeneous Luttinger liquid model, leads to significantly modified predictions as compared to models based on infinite wires. We show that when the tip injects electrons asymmetrically the charge fractionalization induced by interaction cannot be inferred from the asymmetry of the currents flowing in source and drain. Nevertheless interaction effects are visible as oscillations in the nonlinear tip-source and tip-drain conductances. Important differences with respect to a two-terminal setup emerge, suggesting new strategies for the experimental investigation of Luttinger liquid behavio
Floquet theory of Cooper pair pumping
No full textWe derive a general formula for the charge pumped in a superconducting nanocircuit. Our expression generalizes previous results in several ways; it is applicable in both the adiabatic and in the nonadiabatic regimes and it takes into account also the effect of an external environment. More specifically, by applying Floquet theory to Cooper pair pumping, we show that under a cyclic evolution the total charge transferred through the circuit is proportional to the derivative of the associated Floquet quasi-energy with respect to the superconducting phase difference. In the presence of an external environment the expression for the transferred charge acquires a transparent form in the Floquet representation. It is given by the weighted sum of the charge transferred in each Floquet state, the weights being the diagonal components of the stationary density matrix of the system expressed in the Floquet basis. To test the power of this formulation we apply it to the study of pumping in a Cooper pair sluice. We reproduce the known results in the adiabatic regime and we show new data in the nonadiabatic case
DC Josephson Effect through Metallic Carbon Nanotubes
No full textIn this work we wish to study from a theoretical point of view the transport
properties of metallic carbon nanotubes coupled to superconducting leads. In
particular we wish to study the Josephson effect that consists of a supercurrent
flowing among two superconductors through an insulating barrier (M. Tinkham ,
Introduction to Superconductivity , 1996) due to coherent propagation of
Cooper pairs. The current that can flow has a sine dependence on the phase
difference of the two superconductors and the maximum current (or critical current)
is found to decay exponentially with the separation of the superconducting
systems. If the coupling among the two superconductors is realized with a onedimensional
conductor (the contacts with the superconductors are treated as
tunnel barriers) the critical current is found to decay as a power law of the
separation at zero temperature (R. Fazio et Al. , Physical Review B 53 , 6653
(1996)), making this kind of couplings of potential technological interest.
Since electron–electron interactions play a prominent role in this effect, it is
interesting to study what happens when using carbon nanotubes as linking conductors;
this implementation has been studied experimentally in a recent work
(P. Jarillo-Herrero et Al , Nature 439 , 953 (2006))
LTER Northern Adriatic Sea (Italy) marine data from 1965 to 2015
No full textThe present database contains observations for 21 parameters of abiotic, phyto and zooplankton data collected in the Northern Adriatic Sea region (Italy). It relies on a Comma Separated Values file and it is composed by 108687 records. Due to its long temporal coverage, it is classifiable as Long Term Ecological data. Due to the long temporal coverage, the great part of parameters changed collection and analysis method in time. These variations are reported in the database. A long term database can be useful for multiple purposes. This database has been released under a research project focused on Open Science principles application to marine ecology
LTER Northern Adriatic Sea (Italy) marine data from 1965 to 2015
No full textThe present database contains observations for 21 parameters of abiotic, phyto and zooplankton data collected in the Northern Adriatic Sea region (Italy). It relies on a Comma Separated Values file and it is composed by 108687 records. Due to its long temporal coverage, it is classifiable as Long Term Ecological data. Due to the long temporal coverage, the great part of parameters changed collection and analysis method in time. These variations are reported in the database. A long term database can be useful for multiple purposes. This database has been released under a research project focused on Open Science principles application to marine ecology
