Optical detection of magnetic resonance

The NV center in diamond is a spin-1 system, with a zero-field splitting (crystal field) of approximately 2.87 GHz at room temperature in the triplet ground state. Upon driving the ms = 0 to ms = ±1 spin state with microwave irradiation, we would observe a drop in fluorescence from the NV. This is known as Optical Detection of Magnetic Resonance, or ODMR [1].

When the electron spin of the NV center is in its ms=0 spin state, exciting it with green (532 nm) laser from the ground state to the excited state results in fluorescence back to the ground state at 637 nm or 1.945 eV.

When the electron spin of the NV center is in its ms= 0 spin state, exciting it with green (532 nm) laser from the ground state to the excited state results in fluorescence back to the ground state at 637 nm or 1.945 eV. When the electron spin of the NV center is in either ms = 1 or ms = -1 spin state (achieved by microwave irradiation), excitation with green laser results in a reduced fluorescence back to the ground state, the reason for which is a higher probability to decay via a non-conserving spin crossing to the singlet state and then to the triplet ground state, which is not visible as red fluorescnce.

 

 

 

 

For a typical microwave power, the ODMR would look like a Lorentzian, with its width determined by both the microwave power and by the dephasing time [2]. If one reduces the power enough, two or three dips emerge in the ODMR where one was before: these additional dips are the result of the hyperfine coupling between the NV's electron spin and the nitrogen

[1] Gruber et al., Science 1997.

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