The AC Stark effect was discovered in 1955 by American physicists Stanley Autler and Charles Townes.
It is the AC equivalent of the static Stark effect which splits the spectral lines of atoms and molecules in a constant electric field.
Compared to its DC counterpart, the AC Stark effect is computationally more complex.
[1] While generally referring to atomic spectral shifts due to AC fields at any (single) frequency, the effect is more pronounced when the field frequency is close to that of a natural atomic or molecular dipole transition.
[3] Alternatively, this can be described as a Rabi oscillation between the bare states which are no longer eigenstates of the atom–field Hamiltonian.
The AC Stark splitting is integral to several phenomena in quantum optics, such as electromagnetically induced transparency and Sisyphus cooling.
[3] The AC Stark effect was discovered in 1955 by American physicists Stanley Autler and Charles Townes while at Columbia University and Lincoln Labs at the Massachusetts Institute of Technology.
Before the availability of lasers, the AC Stark effect was observed with radio frequency sources.
Autler and Townes' original observation of the effect used a radio frequency source tuned to 12.78 and 38.28 MHz, corresponding to the separation between two doublet microwave absorption lines of OCS.
[5] The notion of quasi-energy in treating the general AC Stark effect was later developed by Nikishov and Ritis in 1964 and onward.
[4] Prior to the 1970s there were various conflicting predictions concerning the fluorescence spectra of atoms due to the AC Stark effect at optical frequencies[citation needed].
In 1974 the observation of Mollow triplets verified the form of the AC Stark effect using visible light.
The solution for the joint particle-field system is, therefore, a linear combination of stationary states of energy
[8] Unlike the DC Stark effect, where perturbation theory is useful in a general case of atoms with infinite bound states, obtaining even a limited spectrum of shifted energies for the AC Stark effect is difficult in all but simple models, although calculations for systems such as the hydrogen atom have been done.
[9] General expressions for AC Stark shifts must usually be calculated numerically and tend to provide little insight.
) can be approximated as a two level quantum system since the off resonance states have low occupation probability.
The energy eigenvalues are and for small detuning, The eigenstates of the atom-field system or dressed states are dubbed
Evidence of this shift is apparent in the atom's absorption spectrum, which shows two peaks around the bare transition frequency, separated by
The modified absorption spectrum can be obtained by a pump-probe experiment, wherein a strong pump laser drives the bare transition while a weaker probe laser sweeps for a second transition between a third atomic state and the dressed states.
[10] Another consequence of the AC Stark splitting here is the appearance of Mollow triplets, a triple peaked fluorescence profile.
[3] For ultracold atoms experiments utilizing the optical dipole force from AC Stark shift, the light is usually linearly polarized to avoid the splitting of different magnetic substates with different
,[12] and the light frequency is often far detuned from the atomic transition to avoid heating the atoms from the photon-atom scattering; in turn, the intensity of the light field (i.e. AC electric field)
is the real part of the complex polarizability of the atom,[14][13] with its imaginary counterpart representing the dissipative optical scattering force.
can be omitted; However, in some cases,[16] the ODT light is so far detuned that counter-rotating term must be included in calculations, as well as contributions from adjacent atomic transitions with appreciable linewidth
In applications that utilize the optical dipole force, it is common practice to use a far-off-resonance light frequency.
Quantitatively, the scattering rate is given by:[13] In quantum system with three (or more) states, where a transition from one level,
Adiabatic elimination has been used to create comparatively stable effective two level systems in Rydberg atoms, which are of interest for qubit manipulations in quantum computing.
[17][18][19] Electromagnetically induced transparency (EIT), which gives some materials a small transparent area within an absorption line, can be thought of as a combination of Autler-Townes splitting and Fano interference, although the distinction may be difficult to determine experimentally.
While both Autler-Townes splitting and EIT can produce a transparent window in an absorption band, EIT refers to a window that maintains transparency in a weak pump field, and thus requires Fano interference.
Because Autler-Townes splitting will wash out Fano interference at stronger fields, a smooth transition between the two effects is evident in materials exhibiting EIT.