How fast can quantum computers process information?

(JerusalemPost) A new peer-reviewed study by physicists at the University of Bonn in Germany and the Technion – Israel Institute of Technology examines which factors determine the speed at which calculations can be performed by a quantum computer. The study draws on previous research by Soviet physicists Leonid Mandelstam and Igor Tamm.
Dr. Andrea Alberti of the Institute of Applied Physics at the University of Bonn and one of the study’s authors explained that “They (quantum computers) require a minimum amount of time to transform the wave function and the information this contains.” Mandelstam and Tamm theoretically deduced this required minimum time in their research, and this new study investigates the limit they determined.
To investigate that limit, this study’s authors initially observed the motion of cesium atoms as they rolled “like marbles” down a light bowl, though this method proved to have variables that hindered the researchers’ ability to identify information changes. “We therefore devised a different method to detect the deviation from the initial state,” Alberti explained.
Gal Ness, a doctoral student at the Technion and the lead author of the study explained that the team “used fast light pulses to create a so-called quantum superposition of two states of the atom. Figuratively speaking, the atom behaves as if it had two different colors at the same time.” Each copy of the atom “takes a different position in the light bowl: One is high up on the edge and ‘rolls’ down from there. The other, conversely, is already at the bottom of the bowl. This twin does not move – after all, it cannot roll up the walls and so does not change its wave function.”
The height above the bottom of the light bowl was varied at the start of the experiment to control the atom’s “position energy.” Technion Prof. Yoav Sagi explained: “We were able to demonstrate that the minimum time for the matter wave to change depends on this energy uncertainty. The greater the uncertainty, the shorter the Mandelstam-Tamm time.”
When the physicists increased the energy uncertainty “until it exceeded the average energy of the atom, then the minimum time did not decrease further – contrary to what the Mandelstam-Tamm limit would actually suggest.” The new findings proved that there is a speed limit imposed by the atom’s average energy.