One aspect of quantum optics concerns how light and atoms interact such that certain properties like coherence are altered. Researchers use laser-cooled alkali atoms coupled to a cavity to facilitate the light-matter interactions. By injecting light into a cavity/atom system the quantum properties of photons emerge. The study of this is called quantum electrodynamics (QED).
As an alternative to laser-cooled atoms, scientists can use devices called quantum dots, which are “artificial atoms.” Quantum dots are nanocrystals of semiconductor wherein an electron-hole pair can be trapped. The nanometer size is comparable to the wavelength of light and so, just like in an atom, the electron can occupy discrete energy levels. The dots are confined in a photonic crystal cavity, where they can be probed with laser light.
Quantum dots can also be used for quantum information technology. Because the devices are small and made of semiconductor material, they could be integrated onto chips. In this way, they allow for a scalable way to integrate optics or couple photons with quantum matter.
Because quantum opticians are interested in the properties of photons, they often investigate single photon sources, as well as correlated photons. “On demand” single photon sources include quantum dots, ions, neutral atoms. Probabalisitic photon sources exist as well, such as, those from parametric downconversion and four-wave mixing.
Detecting single photons is challenging and improving technology for accomplishing this is critical for this research. Single photon detectors are technology that has widespread applications outside of quantum metrology. These applications range from DNA sequencing to various forms of spectroscopy to light detection and ranging (LIDAR).
Related review papers:
- Single-photon sources and detectors, M.D. Eisaman, J. Fan, A. Migdall, and S.V. Polyakov, Rev. Sci. Instr. 82, 071101, (2011)
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