Mode-Locking in Quantum-Hall-Effect Point Contacts

We study the effect of an ac drive on the current-voltage (I-V) characteristics of a tunnel junction between two fractional Quantum Hall fluids at filling $\nu ^{-1}$ an odd integer. Within the chiral Luttinger liquid model of edge states, the point contact dynamics is described by a driven damped quantum mechanical pendulum. In a semi-classical limit which ignores electron tunnelling, this model exhibits mode-locking, which corresponds to current plateaus in the I-V curve at integer multiples of $I= e\omega /2\pi$, with $\omega$ the ac drive angular frequency. By analyzing the full quantum model at non-zero $\nu$ using perturbative and exact methods, we study the effect of quantum fluctuation on the mode-locked plateaus. For $\nu=1$ quantum fluctuations smear completely the plateaus, leaving no trace of the ac drive. For $\nu \ge 1/2$ smeared plateaus remain in the I-V curve, but are not centered at the currents $I=n e \omega /2\pi$. For $\nu < 1/2$ rounded plateaus centered around the quantized current values are found. The possibility of using mode locking in FQHE point contacts as a current-to-frequency standard is discussed.Comment: 12 pages, 8 figures, minor change

Magnetocardiographic mapping of the P-R interval phenomena in an unshielded hospital laboratory

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Magnetocardiographic study of the P-R segment in normals

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Analisi computerizzata di segnali magnetocardiografici ad alta risoluzione: una nuova metodica per lo studio elettrofisiologico non invasivo nell'uomo

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High Frequency Properties of Josephson Junctions

In this chapter we will discuss the high frequency properties of Josephson junctions. In the first part we review the effect of a large ac perturbation on the current voltage characteristic (IVC) of a Josephson junction. Here we follow closely the original treatment by Barone and Paterno [1]. For large ac perturbations the externally applied microwave frequency (and integer multiples of it) lock to the Josephson oscillation causing distinct current steps at fixed voltage values in the IVC. In the second part we give a short overview on the response of an underdamped\ua0Josephson junction to small microwave perturbations. In this case, when the applied microwave frequency is in resonance with the electromagnetic plasma frequency\ua0higher levels of this plasma mode get excited. This mechanism, also called resonant activation, leads for instance to a premature switching from the zero voltage state to the finite voltage state of a current biased Josephson junction. This procedure can be exploited to detect the quantized nature, i.e. the quantized energy levels, of the plasma modes. In fact the lowest two quantized energy levels\ua0of the plasma resonance mode are the key ingredient of superconducting qubits, such as the phase qubit\ua0and the transmon qubit