Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
(a) A generic level scheme for the experiments considered here. (b) A closed-time path-loop diagram for a four-wave mixing experiment. The loop describes the propagation of the wave function by moving clockwise, first forwards in the left branch and then backwards in the right branch.
