If you break a magnet in two, you don't get a north half and a south half - you get two new magnets, each with two poles.
"Monopoles" were famously predicted to exist by physicist Paul Dirac in 1931 - but they have remained elusive.
Now scientists have engineered a synthetic monopole in a quantum system for the first time, allowing its mysterious properties to be explored.
They describe their breakthrough in Nature journal.
"Detecting a natural magnetic monopole would be a revolutionary event comparable to the discovery of the electron," wrote the team from Aalto University, Finland, and Amherst College, US, in their paper.
"[Our work] provides conclusive and long-awaited experimental evidence of the existence of Dirac monopoles.
"It provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment."
The discovery of magnetic monopoles has been long-awaited as they can help to explain various physical phenomena ( via bbc.co.uk ).