Resonance fluorescence

[1] Typically the photon contained electromagnetic field is applied to the two-level atom through the use of a monochromatic laser.

In many experiments an atom of lithium is used because it can be closely modeled to a two-level atom as the excited states of the singular electron are separated by large enough energy gaps to significantly reduce the possibility of the electron jumping to a higher excited state.

Spontaneous emission is when an excited electron arbitrarily decays to the ground state emitting a photon.

This allows for the operators which comprise the field to act on the coherent state and thus be replaced with eigenvalues.

is the Rabi frequency, we can see that this is analogous to the rotation of a spin state around the Bloch sphere from an interferometer.

When a strong field is applied to the atom, a single peak is no longer observed in fluorescent light's radiation spectrum.

The sidebands are a result of the Rabi oscillations of the field causing a modulation in the dipole moment of the atom.

This is known as dynamic Stark splitting and is the cause for the Mollow triplet, which is a characteristic energy spectrum found in Resonance fluorescence.

If the Rabi frequency is allowed to become much larger than the rate of spontaneous decay of the atom, we can see that in the strong field limit

Since this correlation function includes the steady state limits of the density matrix, where

Thus the two-time correlation function is a useful tool in the calculation of the energy spectrum for a given system.

The correlation function associated with the spectral density of resonance fluorescence is reliant on the electric field.

in the spectral density due to the delta function, while in the strong field limit a Mollow triplet forms with sideband peaks at

A two-level atom is only capable of absorbing a photon from the driving electromagnetic field after a certain period of time has passed.

Thus resonance is achievable not only about the possible energy-levels of a two-level atom, but also about the sub-levels in the energy created by lifting the degeneracy of the level.

If the applied magnetic field is tuned properly, the polarization of resonance fluorescence can be used to describe the composition of the excited state.

Thus double resonance can be used to find the Landé factor, which is used to describe the magnetic moment of the electron within the two-level atom.

For instance a superconducting loop which can create a magnetic flux passing through it can act as an artificial atom as the current can induce a magnetic flux in either direction through the loop depending on whether the current is clockwise or counterclockwise.

In an artificial atom, the number of possible modes of the field is significantly limited allowing for easier study of squeezed light.

The implication of this study is it allows for resonance fluorescence to assist in qubit readout for squeezed light.

Direct excitation followed by ground state collection was not achieved until recently.

Resonance fluorescence has been seen in a single self-assembled quantum dot as presented by Muller among others in 2007.

In addition to the excitation of the quantum dot that was achieved, they were also able to collect the photon that was emitted with a micro-PL setup.

This allows for resonant coherent control of the ground state of the quantum dot while also collecting the photons emitted from the fluorescence.

[8] Instead of coupling the electric field to a single atom, they were able to replicate two-level systems in dye molecules embedded in solids.

Due to the fact that they could only have one source at a time, the proportion of shot noise to actual data was much higher than normal.

This is a lens that has a much higher numerical aperture than normal lenses as it is filled with a material that has a large refractive index.

The technique used to measure the resonance fluorescence in this system was originally designed to locate individual molecules within substances.

By coupling a two-level atom, such as a quantum dot, to an electric field in the form of a laser, you are able to effectively create a qubit.

For instance true control of spontaneous decay and decoherence of the field pose large problems that must be overcome before two-level atoms can truly be used as qubits.