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Measurement of non-monotonic Casimir forces between silicon nanostructures


Casimir forces are of fundamental interest because they originate from quantum fluctuations of the electromagnetic field1. Apart from controlling this force via the optical properties of materials2,3,4,5,6,7,8,9,10,11, a number of novel geometries have been proposed to generate repulsive and/or non-monotonic Casimir forces between bodies separated by vacuum gaps12,13,14. Experimental realization of these geometries, however, is hindered by the difficulties in alignment when the bodies are brought into close proximity. Here, using an on-chip platform with integrated force sensors and actuators15, we circumvent the alignment problem and measure the Casimir force between two surfaces with nanoscale protrusions. We demonstrate that the force depends non-monotonically on the displacement. At some displacements, the Casimir force leads to an effective stiffening of the nanomechanical spring. Our findings pave the way for exploiting the Casimir force in nanomechanical systems using structures of complex and non-conventional shapes.

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Figure 1: Geometry of interacting surfaces designed to generate non-monotonic Casimir forces.
Figure 2: Detection and actuation scheme.
Figure 3: Calibration by electrostatic force.
Figure 4: Measured force gradient per unit cell after compensating for residual voltage.


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H.B.C., L.T. and M.W. are supported by HKUST 16300414 from the Research Grants Council of Hong Kong SAR. C.Y.N. and C.T.C. are supported by AoE/P-02/12 from the Research Grants Council of Hong Kong SAR. M.N. and A.W.R. are supported by the National Science Foundation (grant no. DMR-1454836).

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L.T. and M.W. fabricated the devices and conducted the measurements. C.Y.N., M.N., A.W.R. and C.T.C. performed the theoretical calculations. H.B.C. conceived and supervised the experiment. All authors discussed the results and contributed to the writing.

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Correspondence to H. B. Chan.

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The authors declare no competing financial interests.

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Tang, L., Wang, M., Ng, C. et al. Measurement of non-monotonic Casimir forces between silicon nanostructures. Nature Photon 11, 97–101 (2017).

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