Topics: Modern Physics, Quantum Mechanics, Theoretical Physics
Quantum mechanics, the theory that describes the physics of the universe at very small scales, is notorious for defying common sense. Consider, for instance, the way that standard interpretations of the theory suggest change occurs in the quantum turf: shifts from one state to another supposedly happen unpredictably and instantaneously. Put another way, if events in our familiar world unfolded similarly to those within atoms, we would expect to routinely see batter becoming a fully baked cake without passing through any intermediate steps. Everyday experience, of course, tells us this is not the case, but for the less accessible microscopic realm, the true nature of such “quantum jumps” has been a major unsolved problem in physics.
In recent decades, however, technological advancements have allowed physicists to probe the issue more closely in carefully arranged laboratory settings. The most fundamental breakthrough arguably came in 1986, when researchers for the first time experimentally verified that quantum jumps are actual physical events that can be observed and studied. Ever since, steady technical progress has opened deeper vistas upon the mysterious phenomenon. Notably, an experiment published in 2019 overturned the traditional view of quantum jumps by demonstrating that they move predictably and gradually once they start—and can even be stopped midway.
That experiment, performed at Yale University, used a setup that let the researchers monitor the transitions with minimal intrusion. Each jump took place between two energy values of a superconducting qubit, a tiny circuit built to mimic the properties of atoms. The research team used measurements of “side activity” taking place in the circuit when the system had the lower energy. This is a bit like knowing which show is playing on a television in another room by only listening for certain key words. This indirect probe evaded one of the top concerns in quantum experiments—namely, how to avoid influencing the very system that one is observing. Known as “clicks” (from the sound that old Geiger counters made when detecting radioactivity), these measurements revealed an important property: jumps to the higher energy were always preceded by a halt in the “key words,” a pause in the side activity. This eventually permitted the team to predict the jumps’ unfolding and even to stop them at will.
New Views of Quantum Jumps Challenge Core Tenets of Physics, Eleni Petrakou, Scientific American