Magnetic monopoles—particles that behave as isolated north or south magnetic poles—have been the subject of speculation since the first detailed observations of magnetism several hundred years ago1. Numerous theoretical investigations and hitherto unsuccessful experimental searches2 have followed Dirac’s 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field3. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge3,4. Although analogues of magnetic monopoles have been found in exotic spin ices5,6 and other systems7,8,9, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10, 11, 12, 13). Here we demonstrate the controlled creation14 of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose–Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.
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We acknowledge funding by the National Science Foundation (grants PHY–0855475 and PHY–1205822), by the Academy of Finland through its Centres of Excellence Program (grant no. 251748) and grants (nos 135794, 272806 and 141015), and the Finnish Doctoral Programme in Computational Sciences. CSC – IT Center for Science Ltd is acknowledged for computational resources (project no. ay2090). We thank G. Volovik, M. Krusius, R. H. Romer, M. Nakahara and J. R. Friedman for their comments on the manuscript. We also thank H. Valja for his artistic input. M.W.R. and D.S.H. acknowledge discussions with R. P. Anderson and K. Jagannathan, and experimental assistance from N. B. Bern.
Extended data figures
This file contains Supplementary Text and Supplementary Figure 1 providing additional information regarding the underlying theory of the system.
About this article
Scientific Reports (2017)