III. Electron Spin Resonance Results

ODMR scheme


The ODMR scheme uses  circularly polarized pump laser light (σ+ and σ) to  selectively address the electron spin states. The four ESR transitions take place between the eight hyperfine ground levels when a π-pulse in the fixed frequency cavity is applied.


Electronic levels of rubidfium 87

87Rubidium energy levels. In a magnetic field the fine structure splits into several hyperfine levels.

In the indermediate magnetic field neither mF nor {mI, mJ} is a good quantum number. The diagonalization of  the Hamiltonianleads to linear combinations (mixing) of the basis set. The eigenenergies are given by the Breit-Rabi formula, which uses the hyperfine constant aHFS, and the Landé gJ factor as parameters.


Electronic Paramagnetc Resonance


The influence of the droplet is immediately apparent as shift of the ESR lines of 87Rb monomers on HeN to the respective free atom peak by up to 129 μT in the spectrum.


ESR spectrum of rubidium doped helium nano-droplets

ESR spectrum of 87Rb: Embedded monomers on helium droplets are shifted with respect to the free atom peak


This effect is droplet size dependent. By changing the nozzle source conditions we were able to record a different shift for different mean droplet sizes. By using the Breit-Rabi formula we report the change of the Fermi contact term  dependence on the mean droplet size. The results are in excellent agreement with previous measurements on 85Rb.[1]


rubodoium 87 ESR on superfluid helium nano-droplets

The shift in the EPR spectrum is droplet size dependent.


The change of aHFS can by interpreted as a compression of the radial part of the Rb valence electron wave function due to the helium droplet:
δaHFS / aHFS = δ|ψ(0)|2 / |ψ(0)|2


Fermi contact term droplet size dependence

The Fermi contact term for Rubidium on helium nano-droplets is a measure for the modification of the wave function.

No evidence within  experimental uncertainty was found for a change of the Landé factor gJ.


II. Optical Pumping of Rubidium IV. Simple Pump model

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