Micro-wave assisted transparency in a M-system

In this work we theoretically study a five level M-system whose two unpopulated ground states are coupled by a micro-wave (MW) field. The key feature which makes M-systems more efficient in comparison to closed loop $\Lambda$ systems is the absence of MW field induced population transfer even at high intensities of the later. We examine lineshape of probe absorption as a function of its detuning in the presence of both control and MW fields. The MW field facilitates the narrowing of the probe absorption lineshape in M-systems which is in contrast to closed loop $\Lambda$-systems. Hence this study opens up a new avenue for atom based phase dependent MW magnetometry.