The motion of a tennis racket in the air can help predict the behaviour of quanta. “Using an analogy from classical physics aids us in more efficiently designing and illustrating control elements for phenomena in the quantum world,” reports Stefan Glaser, professor in the Department of Chemistry at the Technical University of Munich (TUM).
“Controlling the properties of quanta and using them in technical processes has proven difficult thus far because the quanta adhere to their own laws, which often exceed our imagination,” Glaser explains. “Possible applications such as secure networks, highly sensitive measuring equipment and ultrafast quantum computers are thus still in their infancy.”
Quanta under control
“Utilizing quantum effects in a technical manner by influencing the behaviour of particles through electromagnetic fields required the fastest possible methods to develop fault-tolerant control sequences,” says Glaser. “To date, most of the methods build on very complicated computational processes.”
Together with an international team of physicists, chemists and mathematicians, the researcher has now discovered an unexpected, promising and novel approach: Using the “tennis racket effect”, a well-known phenomenon in classical mechanics, the consistent alteration in the spin of quanta via electromagnetic control commands can be visualized.
Tennis racket in motion
The tennis racket effect describes what happens when one tosses a tennis racket into the air while imparting a rotation about an axis. When one spins the racket about its transverse axis a surprising effect appears: In addition to the intended 360-degree rotation about its transverse axis, the racket will almost always perform an unexpected 180-degree flip about its longitudinal axis. When the racket is caught, the initial bottom side will be facing up.
[image shows the sequence of a toss of racket that is intended to produce a single rotation about one axis; and appearance of the un-anticipated “flip”. Shadowed, is the sequence that would result if the extra rotation does not manifest.]