Quantum superposition of molecules beyond 25 kDa

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Matter-wave interference experiments provide a direct confirmation of the quantum superposition principle, a hallmark of quantum theory, and thereby constrain possible modifications to quantum mechanics1. By increasing the mass of the interfering particles and the macroscopicity of the superposition2, more stringent bounds can be placed on modified quantum theories such as objective collapse models3. Here, we report interference of a molecular library of functionalized oligoporphyrins4 with masses beyond 25,000 Da and consisting of up to 2,000 atoms, by far the heaviest objects shown to exhibit matter-wave interference to date. We demonstrate quantum superposition of these massive particles by measuring interference fringes in a new 2-m-long Talbot–Lau interferometer that permits access to a wide range of particle masses with a large variety of internal states. The molecules in our study have de Broglie wavelengths down to 53 fm, five orders of magnitude smaller than the diameter of the molecules themselves. Our results show excellent agreement with quantum theory and cannot be explained classically. The interference fringes reach more than 90% of the expected visibility and the resulting macroscopicity value of 14.1 represents an order of magnitude increase over previous experiments2.

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Fig. 1: Experimental schematic and molecule details.
Fig. 2: Interference data.
Fig. 3: Macroscopicity and CSL bounds.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on request.


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We thank L. Mairhofer and M. Debiossac for early contributions to the experiment, A. Shayeghi for computational and experimental support, and B. Stickler and K. Hornberger for discussions and support on macroscopicity and near-field interference theory. This project has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program (grant no. 320694) and the Austrian Science Fund (FWF) within programme W1210-N25 (COQUS) and P-30176 (COLMI). Financial support by the Swiss National Science Foundation (grant number 200020-178808) is acknowledged. M.M. acknowledges support by the 111 project (90002-18011002). We acknowledge support from the Vienna Doctoral School.

Author information

M.A. conceived the experiment. Y.Y.F., S.G. and P.G. designed and constructed the experiment. P.Z. and M.M. synthesized the molecules used in the experiment. Y.Y.F, S.G., S.P. and P.G. carried out the experiments described here. Y.Y.F., F.K. and S.G. analysed the data, and Y.Y.F., S.G. and M.A. prepared the manuscript.

Correspondence to Markus Arndt.

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Fein, Y.Y., Geyer, P., Zwick, P. et al. Quantum superposition of molecules beyond 25 kDa. Nat. Phys. 15, 1242–1245 (2019) doi:10.1038/s41567-019-0663-9

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