Atomic clocks based on the microwave oscillator have reached the so-called “quantum projection noise limit.” Current atomic clocks use the Ramsey method to measure the phase difference between local oscillator (LO) and atomic phase. As a result, the stability of the frequency is reduced as t^-1/2. In theory, one can achieve the stability reduction as t^-1, if LO is genuinely phase locked to atomic phase. What prevents us from this atomic phase lock is the fact that we perform projection measurement after the Ramsey sequence and the phase of the atom is demolished completely.
By the use of weak measurement, phase of the atom is conserved and the stability will be reduced as t^-1. We are preparing the proof of the principle experiment, using microwave clock referenced to a cloud of ions trapped in a linear rf-trap.