Patent ID: 6359916
Filing Date: 2002-03-19
Classification: G04F,H03L

Abstract:
A method for generating a frequency standard, the method comprising:providing a quantum absorber that generates a coherent population trapping state with high efficiency and has a transition between a lower quantum state and an upper quantum state, in which: the lower quantum state is split by hyperfine interaction into two lower sub-state groups of at least one lower sub-state, the upper quantum state is split by hyperfine interaction into upper sub-state groups of at least one upper sub-state, none of the upper sub-state groups is a cycling transition sub-state group having at least one allowed electric dipole transition to one of the lower sub-state groups but having no allowed electric dipole transitions to the other of the lower sub-state groups, and the upper quantum state differs in energy from a first lower sub-state in one of the lower sub-state groups and from a second lower sub-state in the other of the lower sub-state groups by energy differences that correspond to transition frequencies of &ohgr;1 and &ohgr;2, respectively; generating incident electro-magnetic radiation including two main frequency components having frequencies respectively equal to &ohgr;1 and &ohgr;2, and differing in frequency by a frequency difference; irradiating the quantum absorber with the incident electro-magnetic radiation; detecting electro-magnetic radiation from the quantum absorber to generate a detection signal; controlling the frequency difference to obtain an extremum in the detection signal, the extremum indicating that the frequency difference corresponds to an energy difference between the first lower sub-state and the second lower sub-state; and providing a frequency standard signal related in frequency to the frequency difference.