Fifty years ago, Hanbury Brown and Twiss (HBT) discovered photon bunching in light emitted by a chaotic source1, highlighting the importance of two-photon correlations2 and stimulating the development of modern quantum optics3. The quantum interpretation of bunching relies on the constructive interference between amplitudes involving two indistinguishable photons, and its additive character is intimately linked to the Bose nature of photons. Advances in atom cooling and detection have led to the observation and full characterization of the atomic analogue of the HBT effect with bosonic atoms4,5,6. By contrast, fermions should reveal an antibunching effect (a tendency to avoid each other). Antibunching of fermions is associated with destructive two-particle interference, and is related to the Pauli principle forbidding more than one identical fermion to occupy the same quantum state. Here we report an experimental comparison of the fermionic and bosonic HBT effects in the same apparatus, using two different isotopes of helium: 3He (a fermion) and 4He (a boson). Ordinary attractive or repulsive interactions between atoms are negligible; therefore, the contrasting bunching and antibunching behaviour that we observe can be fully attributed to the different quantum statistics of each atomic species. Our results show how atom–atom correlation measurements can be used to reveal details in the spatial density7,8 or momentum correlations9 in an atomic ensemble. They also enable the direct observation of phase effects linked to the quantum statistics of a many-body system, which may facilitate the study of more exotic situations10.
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This work was supported by the access programme of Laserlab Europe. The LCVU group in Amsterdam is supported by the ‘Cold Atoms’ programme of the Dutch Foundation for Fundamental Research on Matter (FOM) and by the Space Research Organization Netherlands (SRON). The Atom Optics group of LCFIO is a member of the IFRAF institute and of the Fédération LUMAT of the CNRS, and is supported by the French ANR and by the SCALA programme of the European Union.
Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.
This file contains Supplementary Figures 1-2 with legends and Supplementary Table 1 with Supplementary Data and commentary concerning the correlation length measurements. The Supplementary Figure 1 shows two examples of unnormalized histograms. The Supplementary Figure 2 and the Supplementary Table 1 show the detailed results our fits to a theoretical model. (PDF 530 kb)
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Jeltes, T., McNamara, J., Hogervorst, W. et al. Comparison of the Hanbury Brown–Twiss effect for bosons and fermions. Nature 445, 402–405 (2007). https://doi.org/10.1038/nature05513
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