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. Researchers have hunted for them since Paul Dirac first theorised their quantum-mechanical characteristics in 1931. He demonstrated that if even a single monopole exists, then all electrical charge must come in discrete packets – which has indeed been demonstrated. To observe and test them in the lab, scientists engineered a quantum system – the magnetic field of a cloud of rubidium atoms in an unusual state of matter known as a Bose-Einstein condensate. Using direct imaging, they detected a distinct signature of the Dirac monopole – known as a “Dirac string”. The researchers note that – while other teams have previously made analogues of monopoles, their demonstration is the first in a quantum system which can be tested by experiment. “This creation of a Dirac monopole is a beautiful demonstration of quantum simulation,” said Lindsay LeBlanc, of the University of Alberta, a physicist not involved in the study. “Although these results offer only an analogy to a magnetic monopole, their compatibility with theory reinforces the expectation that this particle will be detected experimentally. “As Dirac said in 1931: ‘Under these circumstances one would be surprised if Nature had made no use of it’.” James Morgan- BBC Science
