Physicists Discover Quantum Speed Limit

The speed of light is the cosmic speed limit, according to physicists’ best understanding: No information can be carried at a greater rate, no matter what method is used. But an analogous speed limit seems to exist within materials, where the interactions between particles are typically very short-range and motion is far slower than light-speed. A new set of experiments and simulations by Marc Cheneau and colleagues have identified this maximum velocity, which has implications for quantum entanglement and quantum computations.

In non-relativistic systems, where particle speeds are much less than the speed of light, interactions still occur very quickly, and they often involve lots of particles. As a result, measuring the speed of interactions within materials has been difficult. The theoretical speed limit is set by the Lieb-Robinson bound, which describes how a change in one part of a system propagates through the rest of the material. In this new study, the Lieb-Robinson bound was quantified experimentally for the first time, using a real quantum gas.