Circuit approach to photonic heat transport

We discuss the heat transfer by photons between two metals coupled by a linear element with a reactive impedance. Using a simple circuit approach, we calculate the spectral power transmitted from one resistor to the other and find that it is determined by the photon transmission coefficient, which depends on the impedances of the metals and the coupling element. We study the total photonic power flow for different coupling impedances, both in the linear regime, where the temperature difference between the metals is small, and in the non-linear regime of large temperature differences.Comment: 6 pages, 6 figure

Competition between electronic cooling and Andreev dissipation in a superconducting micro-cooler

We discuss very low temperature experiments on superconducting micro-coolers made of a double Normal metal - Insulator - Superconductor junction. We investigate with a high resolution the differential conductance of the micro-cooler as well as of additional probe junctions. There is an explicit crossover between the single quasi-particle current and the phase-coherent Andreev current. We establish a thermal model by considering the thermal contribution due to the Andreev current. The related increase of the electron temperature is discussed, including the influence of several parameters like the phase-coherence length or the tunnel junction transparency

Optimal Control of Superconducting N-level quantum systems

We consider a current-biased dc SQUID in the presence of an applied time-dependent bias current or magnetic flux. The phase dynamics of such a Josephson device is equivalent to that of a quantum particle trapped in a $1-$D anharmonic potential, subject to external time-dependent control fields, {\it i.e.} a driven multilevel quantum system. The problem of finding the required time-dependent control field that will steer the system from a given initial state to a desired final state at a specified final time is formulated in the framework of optimal control theory. Using the spectral filter technique, we show that the selected optimal field which induces a coherent population transfer between quantum states is represented by a carrier signal having a constant frequency but which is time-varied both in amplitude and phase. The sensitivity of the optimal solution to parameter perturbations is also addressed

Conductance Fluctuations in a Metallic Wire Interrupted by a Tunnel Junction

The conductance fluctuations of a metallic wire which is interrupted by a small tunnel junction has been explored experimentally. In this system, the bias voltage V, which drops almost completely inside the tunnel barrier, is used to probe the energy dependence of conductance fluctuations due to disorder in the wire. We find that the variance of the fluctuations is directly proportional to V. The experimental data are consistently described by a theoretical model with two phenomenological parameters: the phase breaking time at low temperatures and the diffusion coefficient.Comment: 9 pages RevTeX and 4 PS figures (accepted for publication in Physical Review Letters

Single Cooper pair tunneling induced by non-classical microwaves

A mesoscopic Josephson junction interacting with a mode of non-classical microwaves with frequency $\omega$ is considered. Squeezing of the electromagnetic field drastically affects the dynamics of Cooper tunneling. In particular, Bloch steps can be observed even when the microwaves are in the squeezed vacuum state with {\em zero} average amplitude of the field $\langle E(t) \rangle = 0$. The interval between these steps is double in size in comparison to the conventional Bloch steps.Comment: 8 pages, 2 figures are available upon request to: [email protected]

Quantum dynamics of a driven three-level Josephson-atom maser

Recently, a lasing effect has been observed in a superconducting nano-circuit where a Cooper pair box, acting as an artificial three-level atom, was coupled to a resonator. Motivated by this experiment, we analyze the quantum dynamics of a three-level atom coupled to a quantum-mechanical resonator in the presence of a driving on the cavity within the framework of the Lindblad master equation. As a result, we have access to the dynamics of the atomic level populations and the photon number in the cavity as well as to the output spectrum. The results of our quantum approach agree with the experimental findings. The presence of a fluctuator in the circuit is also analyzed. Finally, we compare our results with those obtained within a semiclassical approximation.Comment: 6 pages, 6 figure

Diffusive conductors as Andreev interferometers

We present a novel mechanism of phase-dependent electric transport in diffusive normal metal-superconductor structures. We provide a detailed theoretical and numerical analysis of recent unexplained experiments essentially explaining them.Comment: Self extracting file, 7 pages latex and 4 postscript figures. The paper is also available at http://www.tn.tudelft.nl/tn/thspap.html In this revision we resolved some printing problems concerning figures 2 and

Andreev Current-Induced Dissipation in a Hybrid Superconducting Tunnel Junction

We have studied hybrid superconducting micro-coolers made of a double Superconductor-Insulator-Normal metal tunnel junction. Under subgap conditions, the Andreev current is found to dominate the single-particle tunnel current. We show that the Andreev current introduces additional dissipation in the normal metal equivalent to Joule heating. By analyzing quantitatively the heat balance in the system, we provide a full description of the evolution of the electronic temperature with the voltage. The dissipation induced by the Andreev current is found to dominate the quasiparticle tunneling-based cooling over a large bias range

Magnetotunneling as a Probe of Luttinger-Liquid Behavior

A novel method for detecting Luttinger-liquid behavior is proposed. The idea is to measure the tunneling conductance between a quantum wire and a parallel two-dimensional electron system as a function of both the potential difference between them, $V$, and an in-plane magnetic field, $B$. We show that the two-parameter dependence on $B$ and $V$ allows for a determination of the characteristic dependence on wave vector $q$ and frequency $\omega$ of the {\it spectral function}, $A_{\rm LL}(q,\omega)$, of the quantum wire. In particular, the separation of spin and charge in the Luttinger liquid should manifest itself as singularities in the $I$-$V$-characteristic. The experimental feasibility of the proposal is discussed.Comment: Accepted for publication in Phys. Rev. Let