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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 theory1,2,3,4 has been complemented by experiments using matter waves coupled to external photons5,6,7 or molecules8, and by investigations using coherent photon states9, trapped ions10 and electron interferometers11,12. 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.

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Figure 1: Set-up for the observation of thermal decoherence in a Talbot–Lau molecule interferometer.
Figure 2: Molecule interferograms for C70 at 190 m s-1 for increasing laser heating powers, P.
Figure 3: Spectral photon emission rate Rλ of C70 molecules, as used for the calculation of thermal decoherence.
Figure 4: Decoherence curves.

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We thank S. Uttenthaler for his support in an early stage of the experiment. We acknowledge support by the Austrian START programme, the Austrian FWF, the European TMR and Marie Curie programmes, and the DFG Emmy-Noether programme.Authors' contributions L.H. performed most of the experiments as a part of her Ph.D. thesis. K.H. developed the decoherence theory, and made the quantitative comparison between experiment and theory.

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Correspondence to Markus Arndt.

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Hackermüller, L., Hornberger, K., Brezger, B. et al. Decoherence of matter waves by thermal emission of radiation. Nature 427, 711–714 (2004).

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