A Floquet phase with counterpropagating translation operators localized at the two edges can be built by applying four layers of SWAP gates, as indicated by 1 to 4* [Reprinted under Creative Commons Attribution 4.0 License.]
Topological phases of matter are systems that … have interesting properties at the surfaces that would be impossible if not for the existence of the underlying material. Some of these phases are “chiral,” featuring unidirectional transport of quantities such as electron charge around the edge.
In a recent issue of Physical Review X, Prof. Ashvin Vishwanath and colleagues from UC Berkeley, Stony Brook University, and University of Texas at Austin pose the following question: Can chiral phases exist in settings where neither charge nor energy is conserved? Since those nonconserved properties can just appear and disappear, they cannot be pumped around the system, and the usual description of chiral phases fails. The authors find that, nonetheless, chiral phases are tenable in such systems. Instead of charge or energy, quantum information is pumped around the edges.
The authors developed a theoretical framework in which they can describe chiral phases in a two-dimensional system of bosons – subatomic particles, such as photons, that can occupy a single quantum state. While the main focus of the study is bosons, they found that this can be extended to some systems of fermions, which are subatomic particles (such as electrons), that cannot occupy the same quantum state. The article describes a possible experimental setup in which bosonic atoms are cooled to low temperatures and loaded onto a 2D lattice with lasers. If this description of chiral phases is valid, then particle numbers will remain stable in the bulk of the setup while those at the edge will rotate about the center.
While the age of quantum computing is still a ways off, one-way transport of quantum information could be used to distribute quantum entanglement, a universal resource for any quantum communication protocol.
*Read Hoi Chun Po, Lukasz Fidkowski, Takahiro Morimoto, Andrew C. Potter, and Ashvin Vishwanath, “Chiral Floquet Phases of Many-Body Localized Bosons,” Phys. Rev. X 6, 041070 | DOI: https://doi.org/10.1103/PhysRevX.6.041070