July 13, 2020
RIKEN
Keio University
A joint research team, consisting of Researcher Tomotaka Kuwahara of the Mathematical Science Team, Generic Technology Research Group at the RIKEN Center for Advanced Intelligence Project, and Professor Keiji Saito of the Department of Physics, Faculty of Science and Technology, Keio University, has discovered a new physical law governing information propagation in quantum many-body systems.
These research findings are expected not only to provide new insights into the dynamics of many particles interacting quantum mechanically but also to contribute to the understanding of fundamental constraints in information processing technologies such as quantum computers.
In quantum many-body systems, long-range interacting forces can transmit effects instantaneously between particles, no matter how far apart they are. This means that even if the interaction decays quickly, the speed of information propagation could potentially be infinite. The question of under what conditions the speed of information propagation becomes finite is known as the "linear light cone problem," which has been a significant unsolved problem in physics.
The joint research team has now mathematically derived a general condition under which the speed of information propagation is finite when long-range forces exist between particles in a quantum many-body system. This condition is formulated mathematically as a condition for the finiteness of the information propagation speed, known as the "Lieb-Robinson bound." They also proved that the condition provided in this study is the optimal solution to the linear light cone problem.
This research will be published soon in the online open-access scientific journal "Physical Review X."
*Note added on July 14:
This research was published in "Physical Review X" (July 13 issue) and was selected for a Viewpoint.
Please see below for the full press release.