Gravitational waves imprint apparent Doppler shifts on the frequency of photons propagating between an emitter and detector of light. This forms the basis of a method to detect gravitational waves using Doppler velocimetry between pairs of satellites
. Such detectors, operating in the milli-hertz gravitational frequency band, could lead to the direct detection of gravitational waves. The crucial component in such a detector is the frequency standard on board the emitting and receiving satellites. We point out that recent developments in atomic frequency standards have led to devices that are approaching the sensitivity required to detect gravitational waves from astrophysically interesting sources. The sensitivity of satellites equipped with optical frequency standards for Doppler velocimetry is examined, and a design for a robust, space-capable optical frequency standard is presented.
A two-photon transition in laser-cooled and trapped calcium atoms is proposed as the atomic reference in an optical frequency standard. An efficient scheme for interrogation of the frequency standard is described, and the sensitivity of the clock tra
nsition to systematic effects is estimated. Frequency standards based on this transition could lead to compact and portable devices that are capable of rapidly averaging down to $< 10^{-16}$.
The time evolution of a two-level quantum mechanical system can be geometrically described using the Bloch sphere. By mapping the Bloch sphere evolution onto the dynamics of oscillating electric dipoles, we provide a physically intuitive link between
classical electromagnetism and the electric dipole transitions of atomic & molecular physics.
