Quantop > Quantum Optics Lab > Research > Mesoscopic cold atomic ensembles > Ramsey Spectroscopy

Ramsey Spectroscopy

We want to compare the frequency of our reference oscillator $\nu_{osc}$ with the atomic transition frequency $\nu_{clock}$ using microwave pulses and measurements.

This can be done with the following 3-step algorithm (Ramsey spectroscopy):

1. Prepare the atom in $|\downarrow\rangle$.
   
2. A microwave $\pi/2$-pulse performs a $90^\circ$-rotation around the $y$-axis.
   
3. Now we wait during the interrogation time $\tau$. During this time the state evolves and precesses around the $z$-axis until $\varphi = \tau \Delta \nu$.
   
4. After the interrogation time a second microwave $\pi/2$-pulse is sent - but this time with a phase such that it performs a $90^\circ$-rotation around the $x$-axis.
   
5. Finally we measure whether the atom is in the $\downarrow-$ or $\uparrow$-state. This way - depending on whether $\Delta \nu$ was positive or negative - the probability find the atom in either the upper or the lower state is larger and we can adjust the frequency of the reference oscillator $\nu_{osc}$ accordingly.
   

Of course this experiment is not just performed with a single atoms but rather with about $100000$ atoms simultaneously.