Strongly long-range interacting quantum systems—those with interactions decaying as a power law $1/r^{\alpha }$ in the distance $r$ on a $D$-dimensional lattice for $\alpha \le D$—have received significant interest in recent years. They are present in leading experimental platforms for quantum computation and simulation, as well as in theoretical models of quantum-information scrambling and fast entanglement creation. Since no notion of locality is expected in such systems, a general understanding of their dynamics is lacking. In a step towards rectifying this problem, we prove two Lieb-Robinson-type bounds that constrain the time for signaling and scrambling in strongly long-range interacting systems, for which no tight bounds were previously known. Our first bound applies to systems mappable to free-particle Hamiltonians with long-range hopping, and is saturable for $\alpha \le D/2$. Our second bound pertains to generic long-range interacting spin Hamiltonians and gives a tight lower bound for the signaling time to extensive subsets of the system for all $\alpha <D$. This many-site signaling time lower bounds the scrambling time in strongly long-range interacting systems.

• Received 12 June 2019
• Accepted 9 June 2020

DOI:https://doi.org/10.1103/PhysRevA.102.010401