Of course, to observe the time dependence given in (27), we also need a

Larmor frequency larger than the frequency of H; that is, [[omega].sub.L] > [omega].

It is used to generate a signal at the Larmor frequency for generation of RF pulses and for downconversion of received signals.

The first step in this process is demodulation to remove the carrier, the Larmor frequency, such that only the audio frequency excursions remain.

When the RF pulse is turned off, [M.sub.xy] begins to rotate (at the

Larmor frequency) around the z-axis, as the net magnetization begins to realign with [B.sub.0].

However, at low [[tau].sub.NRSE], [DELTA][[omega].sub.BS] can be a significant fraction of the

Larmor frequency.

This results in a decoherent precession of the atom ensemble in the presence of a magnetic field, which makes the measurement of the Larmor frequency difficult.

The Cs atoms in the dark states precess around the magnetic field axis at the Larmor frequency that is proportional to the field magnitude: [w.sub.L] = [gamma][absolute value of [B.sub.0]], where [gamma] is the gyromagnetic constant that for cesium is 2[pi] ?

To maintain this coherence and synchronize the precession of atomic spins, the rf driving magnetic field must be resonant with the Larmor frequency, that is, [w.sub.rf] = [w.sub.L].

The signature of a finite EDM is a change of the neutron Larmor frequency synchronous with the rever sal of the relative orientations of the magnetic and electric fields.

The detection of the modulated transmission by a photodetector allows a direct and real time measurement of the magnetic field in terms of the Larmor frequency.

The basic adiabaticity requirement is that the rate of a change of the field direction, has to be smaller compared to the

Larmor frequency [omega] = [mu]B/h ([mu] is the magnetic moment of the neutron) then the projection of the spin on the field direction is approximately conserved; the projection of the neutron spin on the field direction is an adiabatic invariant.

In this method, the magnetization is tipped away from the quantization axis by applying a short pulse of radiation at the

Larmor frequency (85 kHz for our typical operating field of 2.6 mT).