Superconductor-Metal Transition in an Ultrasmall Josephson Junction Biased by a Noisy Voltage Source

We propose to use the phenomenon of resonant tunneling for the detection of noise. The main idea of this method relies on the effect of homogeneous broadening of the resonant tunneling peak induced by the emission and absorption of collective charge excitations in the measurement circuit. In thermal equilibrium, the signalto-noise ratio of the detector as a function of the detector bandwidth ͑the detector function͒ is given by the universal hyperbolic tangent, which is the statement of the fluctuation-dissipation theorem. The universality breaks down if nonequilibrium processes take place in the measurement circuit. We propose a theory of this phenomenon and make predictions for the detector function in the case when nonequilibrium noise is created by a mesoscopic conductor. We investigate measurement circuit effects and prove the universality of the classical noise detection. Finally, we evaluate the contribution of the third cumulant of current and make suggestions of how it can be measured.

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Direct access to quantum fluctuations through cross-correlation measurements

Chernii

Sukhorukov

2012

Phys. Rev. B

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Detection of the quantum fluctuations by conventional methods meets certain obstacles, since it requires high-frequency measurements. Moreover, quantum fluctuations are normally dominated by classical noise and are usually further obstructed by various accompanying effects such as a detector backaction. In the present work, we demonstrate that these difficulties can be bypassed by performing the cross-correlation measurements. We propose to use a pair of two-level detectors, weakly coupled to a collective mode of an electric circuit. Fluctuations of the current source accumulated in the collective mode induce stochastic transitions in the detectors. These transitions are then read off by quantum-point contact (QPC) electrometers and translated into two telegraph processes in the QPC currents. Since both detectors interact with the same collective mode, this leads to a certain fraction of the correlated transitions. These correlated transitions are fingerprinted in the cross correlations of the telegraph processes, which can be detected at zero frequency, i.e., with long-time measurements. Concerning the dependance of the cross correlator on the detectors' energy splittings ε 1 and ε 2 , the most interesting region is at the degeneracy points ε 1 = ±ε 2 , where it exhibits a sharp nonlocal resonance, that stems from higher-order processes. We find that at certain conditions, the main contribution to this resonance comes from the quantum noise. Namely, while the resonance line shape is weakly broadened by the classical noise, the height of the peak is directly proportional to the square of the quantum component of the noise spectral function.

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Superconductor-Metal Transition in an Ultrasmall Josephson Junction Biased by a Noisy Voltage Source

Cited by 3 publications

References 24 publications

Modeling and Characterization of Bloch Oscillating Junction Transistors

Modeling and Characterization of Bloch Oscillating Junction Transistors

Theory of quantum noise detectors based on resonant tunneling

Direct access to quantum fluctuations through cross-correlation measurements

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