Ramsey interferometry

Ramsey interferometry, also known as Ramsey–Bordé interferometry or the separated oscillating fields method, is a form of atom interferometry that uses the phenomenon of magnetic resonance to measure transition frequencies of atoms. It was developed in 1949 by Norman Ramsey, who built upon the ideas of his mentor, Isidor Isaac Rabi, who initially developed a technique for measuring atomic transition frequencies. Ramsey's method is used today in atomic clocks and in the S.I. definition of the second. Most precision atomic measurements, such as modern atom interferometers and quantum logic gates, have a Ramsey-type configuration. A modern interferometer using a Ramsey configuration was developed by French physicist and is known as the Ramsey–Bordé interferometer. Bordé's main idea was to use atomic recoil to create a beam splitter of different geometries for an atom-wave. The Ramsey–Bordé interferometer specifically uses two pairs of counter-propagating interaction waves, and another method named the "photon-echo" uses two co-propagating pairs of interaction waves.

A main goal of precision spectroscopy of a two-level atom is to measure the absorption frequency ${\displaystyle \omega _{0}}$ between the ground state |↓⟩ and excited state |↑⟩ of the atom. One way to accomplish this measurement is to apply an external oscillating electromagnetic field at frequency ${\displaystyle \omega }$ and then find the difference ${\displaystyle \Delta }$ (also known as the detuning) between ${\displaystyle \omega }$ and ${\displaystyle \omega _{0}}$ ${\displaystyle (\Delta =\omega -\omega _{0})}$ by measuring the probability to transfer |↓⟩ to |↑⟩ . This probability can be maximized when ${\displaystyle \Delta =0}$, when the driving field is on resonance with the transition frequency of the atom. Looking at this probability of transition as a function of the detuning ${\displaystyle P(\Delta )}$, the narrower the peak around ${\displaystyle \Delta =0}$ the more precision there is. If the peak were very broad about ${\displaystyle \Delta =0}$ then it would be difficult to distinguish precisely where ${\displaystyle \Delta =0}$ is located due to many values of ${\displaystyle \Delta }$ having close to the same probability.

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