Fluctuation-enhanced sensing

We present a short survey on fluctuation-enhanced gas sensing. We compare some of its main characteristics with those of classical sensing. We address the problem of linear response, information channel capacity, missed alarms and false alarms.Comment: Keynote Talk at SPIE's 4th international symposium on Fluctuations and Noise, Conference Noise and Fluctuations in Circuits, Devices and Materials, Florence, Italy, May 20-24, 200

Influence of molecular temperature on the coherence of fullerenes in a near-field interferometer

We study C70 fullerene matter waves in a Talbot-Lau interferometer as a function of their temperature. While the ideal fringe visibility is observed at moderate molecular temperatures, we find a gradual degradation of the interference contrast if the molecules are heated before entering the interferometer. A method is developed to assess the distribution of the micro-canonical temperatures of the molecules in free flight. This way the heating-dependent reduction of interference contrast can be compared with the predictions of quantum theory. We find that the observed loss of coherence agrees quantitatively with the expected decoherence rate due to the thermal radiation emitted by the hot molecules.Comment: 11 pages, 9 figure

Decoherence of matter waves by thermal emission of radiation

Emergent quantum technologies have led to increasing interest in decoherence - the processes that limit the appearance of quantum effects and turn them into classical phenomena. One important cause of decoherence is the interaction of a quantum system with its environment, which 'entangles' the two and distributes the quantum coherence over so many degrees of freedom as to render it unobservable. Decoherence theory has been complemented by experiments using matter waves coupled to external photons or molecules, and by investigations using coherent photon states, trapped ions and electron interferometers. Large molecules are particularly suitable for the investigation of the quantum-classical transition because they can store much energy in numerous internal degrees of freedom; the internal energy can be converted into thermal radiation and thus induce decoherence. Here we report matter wave interferometer experiments in which C70 molecules lose their quantum behaviour by thermal emission of radiation. We find good quantitative agreement between our experimental observations and microscopic decoherence theory. Decoherence by emission of thermal radiation is a general mechanism that should be relevant to all macroscopic bodies.Comment: 5 pages, 4 figure

Higher-order spectra in nanoparticle gas sensors. Fluctuation and Noise

It has previously been shown that resistance fluctuations in resistive sensors provide enhanced sensitivity and selectivity for gas detection. We report measurements and analysis of non-Gaussian components in nanoparticle Pdz(WO3)1-z film gas sensors, with z being 0.01 or 0.12, in different ambients. These components can be characterized by higher-order spectra. Contour plots are given of bispectra, and plots of integrated bispectra and trispectra. The phase of the integrated higher-order spectra is analyzed as well

Optimization of OCT signal-to-noise ratio, when excess photon noise increases due to mismatch of the balanced receiver

In optical coherence tomography (OCT), it is often assumed that the signal-to-noise ratio, at higher optical power regimes, is limited by beat noise. Nonetheless it was often noticed that the limiting value could not be experimentally achieved, despite minimizing the stray reflectance and increasing the optical source effective bandwidth. In this work we present a new model for the noise in a balanced OCT configuration, which accounts for the limited spectral response of fiber directional couplers, as well as imperfections in the photo-detectors. As a consequence, and due to different spectrum content between the two balanced-OCT outputs, excess photon noise is larger than previously considered. The model also allows for the determination of SNR optimized parameters for maximum performance of the balanced system, and can be applied to any coupler or broadband source. Results for optimized and non-optimized configurations, for different balanced detection configurations, implemented in an OCT system, are presented and discussed