Radiation due to Josephson oscillations in layered superconductors

We derive the power of direct radiation into free space induced by Josephson oscillations in intrinsic Josephson junctions of layered superconductors. We consider the superradiation regime for a crystal cut in the form of a thin slice parallel to the c axis. We find that the radiation correction to the current-voltage characteristic in this regime depends only on crystal shape. We show that at a large number of junctions oscillations are synchronized providing high radiation power and efficiency in the terahertz frequency range. We discuss the crystal parameters and bias current optimal for radiation power and crystal cooling.     

Rabi-type oscillations in a classical Josephson junction

We study analytically and numerically the phase-modulation properties of a classical Josephson tunnel junction biased in the zero-voltage state and phase locked to an external ac field. We show that the phase-locked state is being modulated in the transients, or in response to perturbations, and the modulation frequency is calculated as a function of relevant system parameters, such as microwave field amplitude. Our analysis demonstrates that the modulation of a phase-locked state in an entirely classical Josephson junction produces oscillations analogous to quantum mechanical Rabi oscillations, expected to be observed under the same conditions.     

Driving of a single vortex in a long Josephson junction

The driving of a single vortex by a bias current in a long Josephson junction with a finite width has been studied with the two-dimensional Josephson equation. The applicable range of the equivalent one-dimensional equation is shown.     

Nondemolition measurements of a single quantum spin using Josephson oscillations

We consider a single localized spin-1/2 between the singlet superconducting leads of a Josephson junction (e.g., a superconducting STM). For the spin subject to a dc magnetic field B parallel z, we study the spin dynamics and the possibility to measure the spin state via transport through the junction embedded in a dissipative circuit. Turning on the tunneling or a voltage bias induces oscillations of the Josephson current, with an amplitude sensitive to the initial value of the z component of the spin, S(z)=+/-1/2. At low temperatures, when effects of quasiparticles are negligible, this procedure realizes a quantum nondemolition measurement of S(z).     

Radiation linewidth of a long Josephson junction in the flux-flow regime

Theoretical model for the radiation linewidth in a multi-fluxon state of a long Josephson junction is presented. Starting from the perturbed sine-Gordon model with the temperature dependent noise term, we use a collective coordinate approach in order to calculate the finite radiation linewidth due to the internal degrees of freedom in the moving fluxon chain. At low fluxon density, the radiation linewidth is expected to be substantially larger than that of a lumped Josephson oscillator. With increasing the fluxon density, a crossover to a much smaller linewidth approaching the lumped oscillator limit is predicted.     

Realization of a single Josephson junction for Bose–Einstein condensates

We report on the realization of a double-well potential for Rubidium-87 Bose-Einstein condensates. The experimental setup allows for the investigation of two different dynamical phenomena known for this system – Josephson oscillations and self-trapping. We give a detailed discussion of the experimental setup and the methods used for calibrating the relevant parameters. We compare our experimental findings with the predictions of an extended two-mode model and find quantitative agreement. PACS 74.50.+r; 03.75.Lm; 05.45.-a     

Electromagnetically induced transparency from a single atom in free space

In this Letter, we report an absorption spectroscopy experiment and the observation of electromagnetically induced transparency from a single trapped atom. We focus a weak and narrow band Gaussian light beam onto an optically cooled 138Ba+ ion using a high numerical aperture lens. Extinction of this beam is observed with measured values of up to 1.35%. We demonstrate electromagnetically induced transparency of the ion by tuning a strong control beam over a two-photon resonance in a three-level Λ-type system. The probe beam extinction is inhibited by more than 75% due to population trapping.     

Direct observation of tunneling and nonlinear self-trapping in a single bosonic Josephson junction

We report on the first realization of a single bosonic Josephson junction, implemented by two weakly linked Bose-Einstein condensates in a double-well potential. In order to fully investigate the nonlinear tunneling dynamics we measure the density distribution in situ and deduce the evolution of the relative phase between the two condensates from interference fringes. Our results verify the predicted nonlinear generalization of tunneling oscillations in superconducting and superfluid Josephson junctions. Additionally, we confirm a novel nonlinear effect known as macroscopic quantum self-trapping, which leads to the inhibition of large amplitude tunneling oscillations.     

On the radiation from inhomogeneous Josephson junction

The electromagnetic radiation produced by the single moving Josephson vortex in the inhomogeneous junction has been theoretically considered. The radiation is shown to appear at the definite threshold vortex velocity. The expressions for the energy flux and the radiation frequency have been found.     

Suppression of interference by quantum fluctuations in a Josephson interferometer with a single small junction

The geometric inductance of a single-junction interferometer at which quantum fluctuations suppress interference and the Coulomb blockade of Cooper pairs is observed is found.     

On bifurcations and transition to chaos in a Josephson junction

Chaos in the dc and rf current driven Josephson junction is investigated by measurements on a phase-locked loop. The method allows a direct display of the Poincaré map and the bifurcation diagram, as the parameter space is searched. In some regions of the parameter space the Feigenbaum period-doubling route to chaos is observed upon a change of any parameter.     

Quantum coherence in a superfluid Josephson junction

We report a new kind of experiment in which we take an array of nanoscale apertures that form a superfluid (4)He Josephson junction and apply quantum phase gradients directly along the array. We observe collective coherent behaviors from aperture elements, leading to quantum interference. Connections to superconducting and Bose-Einstein condensate Josephson junctions as well as phase coherence among the superfluid aperture array are discussed.     

Emission of radiation from a long Josephson junction in a thin film

Space-time nonlocal electrodynamic equations are derived for nonlinear vortex states of a Josephson junction in a film of thickness much smaller than the London penetration depth. The spectrum and damping of generalized Swihart waves propagating in such a junction are analyzed. The radiation damping constant associated with the possible emission of electromagnetic radiation is determined in the range of Swihart wave phase velocities exceeding the speed of light. The emission of radiation from nonlinear states having dimensions greater than the distance traversed by light in vacuum during the characteristic time of variation of the phase difference is investigated. It is shown that the flux density of radiation emitted by such states is localized in a plane orthogonal to the axis of the tunnel junction and depends weakly on the angle of observation in this plane. Zh. éksp. Teor. Fiz. 115, 1426–1449 (April 1999)     

Fluctuation power spectrum of a Josephson junction

The fluctuation power spectrum of the Josephson junction has been evaluated in the limit of large energy barriers [(U _n ^max−U _n ^min)γ]≫1 and small currents [x≪x _e]. The result is valid for finite capacitance of the junction. The effect of the fluctuating Josephson current on the voltageV(t) across the junction has also been taken into account.     

Josephson effect in a Coulomb-blockaded SINIS junction

The problem of a Josephson current through a Coulomb-blocked nanoscale superconductor-normal-superconductor structure with tunnel contacts is reconsidered. Two different contributions to the phase-biased supercurrent I(?) are identified, which are dominant in the limits of weak and strong Coulomb interaction. Full expression for the free energy valid at arbitrary Coulomb strength is found. The current derived from this free energy interpolates between known results for weak and strong Coulomb interaction as the phase bias changes from 0 to π. In the broad range of Coulomb strength, the current-phase relation is substantially nonsinusoidal and qualitatively different from the case of semiballistic SNS junctions. The Coulomb interaction leads to the appearance of a local minimum in the current at some intermediate value of the phase difference applied to the junction.     

Novel spin dynamics in a Josephson junction

We address the dynamics of a single spin embedded in the tunneling barrier between two superconductors. As a consequence of pair correlations in the superconducting state, the spin displays a rich and unusual dynamics. To properly describe the time evolution of the spin we find the generalized Wess-Zumino-Witten-Novikov term in the effective action for the spin on the Keldysh contour. The superconducting correlations lead to an effective spin action which is nonlocal in time leading to unconventional precessions. Our predictions might be directly tested for macroscopic spin clusters.