Light is composed of photons, but only recently has it become
relatively common, albeit still challenging, to manipulate single or few photons.
This special issue presents state-of-the-art theory and experiment
concerning the production of few-photon states of light, processing the states,
and performing highly sensitive low-noise detection at the single-photon
level.
In many cases, the connection between photon manipulation and quantum
information science is apparent. Few-photon sources have applications for
quantum cryptography and optical quantum computing. Photon processing
can involve producing entangled states of light as resources for
quantum information processing, performing optical gates for example by
interferometry, and realizing quantum memory to store information and synchronize gate
operations. Ultimately the photons are carriers of information, and
this information is acquired by detectors, which have to be reliable,
highly sensitive, fast and operate with low noise. Many of these photon
generation, processing and detection issues are exemplified in the papers
presented here.
This special issue thus serves as a compendium of recent results in
the area of few-photon optics, covering the development of new sources,
the characterization and improvement of detection schemes, and the
analysis and proposal of processing protocols. We trust that this issue will
serve as a valuable resource for the community for years to come.