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Register a new userCross correlations in disordered, four-terminal graphene-ribbon conductor: Hanbury-Brown and Twiss exchange as a sign of non-universality of noise
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We have investigated current-current correlations in a cross-shaped conductor made of graphene ribbons. We measured auto and cross correlations and compared them with the theoretical predictions for ideal diffusive conductors. Our data deviate from these predictions and agreement can be obtained only by adding contributions from occupation-number noise in the central region connecting the arms of the cross. Furthermore, we have determined Hanbury -- Brown and Twiss (HBT) exchange correlations in this system. Contrary to expectations for a cross-shaped diffusive system, we find finite HBT exchange effects due to the occupation-number noise at the crossing. The strength of these HBT exchange correlations is found to vary with gate voltage, and very a distinct HBT effect with large fluctuations is observed near the Dirac point.
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We investigate the current-current correlations in a four-terminal Al-AlOx-Al tunnel junction where shot noise dominates. We demonstrate that cross-correlations in the presence of two biasing sources of the Hanbury-Brown and Twiss type are much stronger (approximately twice) than an incoherent sum of correlations generated by single sources. The difference is due to voltage fluctuations of the central island that give rise to current-current correlations in the four contacts of the junction. Our measurements are in close agreement with results obtained using a simple theoretical model based on the theory of shot noise in multi-terminal conductors, generalized here to arbitrary contacts.
Quadratic detection in linear mesoscopic transport systems produces cross terms that can be viewed as interference signals reflecting statistical properties of charge carriers. In electronic systems these cross term interferences arise from exchange effects due to Pauli principle. Here we demonstrate fermionic Hanbury Brown and Twiss (HBT) exchange phenomena due to indistinguishability of charge carriers in a diffusive graphene system. These exchange effects are verified using current-current cross correlations in combination with regular shot noise (autocorrelation) experiments at microwave frequencies. Our results can be modeled using semiclassical analysis for a square-shaped metallic diffusive conductor, including contributions from contact transparency. The experimentally determined HBT exchange factor values lie between the calculated ones for coherent and hot electron transport.
We report measurements of Hanbury Brown and Twiss correlation of coherent light transmitted through disordered one-dimensional photonic lattices. Although such a lattice exhibits transverse Anderson localization when a single input site is excited, uniform excitation precludes its observation. By examining the Hanbury Brown--Twiss correlation for a uniformly excited disordered lattice, we observe intensity anticorrelations associated with photon antibunching--a signature of non-Gaussian statistics. Although the measured average intensity distribution is uniform, transverse Anderson localization nevertheless underlies the observed anticorrelation.
A fundamental property of a three-dimensional Bose-Einstein condensate (BEC) is long-range coherence, however, in systems of lower dimensionality, not only is the long range coherence destroyed, but additional states of matter are predicted to exist. One such state is a `transverse condensate, first predicted by van Druten and Ketterle [Phys. Rev. Lett. 79, 549 (1997)], in which the gas condenses in the transverse dimensions of a highly anisotropic trap while remaining thermal in the longitudinal dimension. Here we detect the transition from a three-dimensional thermal gas to a gas undergoing transverse condensation by probing Hanbury Brown--Twiss correlations.
We propose using the LIGO-Virgo detector network as a Hanbury Brown--Twiss (HBT) interferometer. Our focus is on the behavior of the gravitational waves at the detector rather than the source. We examine HBT interferometry for gravitational waves from binary inspirals which are currently detectable with the LIGO-Virgo network. Previous work on HBT interferometry for gravitational waves has concentrated on characterization of both classical and non-classical properties of signals from cosmological sources in the early Universe which are not detectable by the LIGO-Virgo network. Since the HBT effect can be described equally via classical intensities or via quantum graviton creation/annihilation operators, observation of this effect would not provide an unambiguous demonstration of the quantization of gravity. However, the observation of the HBT effect by LIGO-Virgo would provide a new tool in the detection and analysis of gravitational wave signals.
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