Editing Quantum optics (section)

== History ==
Light propagating in a restricted volume of space has its [[energy]] and [[momentum]] quantized according to an integer number of particles known as [[photons]].  Quantum optics studies the nature and effects of light as quantized photons. The first major development leading to that understanding was the correct modeling of the [[blackbody radiation]] spectrum by  [[Max Planck]] in 1899 under the hypothesis of light being emitted in discrete units of energy. The [[photoelectric effect]] was further evidence of this quantization as explained by [[Albert Einstein]] in a 1905 paper, a discovery for which he was to be awarded the [[Nobel Prize]] in 1921. [[Niels Bohr]] showed that the hypothesis of optical radiation being quantized corresponded to his theory of the [[quantized energy levels of atoms]], and the [[spectrum]] of [[Gas-discharge lamp|discharge emission]] from [[hydrogen]] in particular. The understanding of the interaction between light and [[matter]] following these developments was crucial for the development of [[quantum mechanics]] as a whole. However, the subfields of quantum mechanics dealing with matter-light interaction were principally regarded as research into matter rather than into light; hence one rather spoke of [[atom physics]] and [[quantum electronics]] in 1960. [[Laser science]]—i.e., research into principles, design and application of these devices—became an important field, and the quantum mechanics underlying the laser's principles was studied now with more emphasis on the properties of light{{dubious|date=May 2013}}, and the name ''quantum optics'' became customary.

As laser science needed good theoretical foundations, and also because research into these soon proved very fruitful, interest in quantum optics rose. Following the work of [[Paul Dirac|Dirac]] in [[quantum field theory]], [[John R. Klauder]], [[George Sudarshan]], [[Roy J. Glauber]], and [[Leonard Mandel]] applied quantum theory to the electromagnetic field in the 1950s and 1960s to gain a more detailed understanding of photodetection and the [[statistical mechanics|statistics]] of light (see [[degree of coherence]]). This led to the introduction of the [[coherent state]] as a concept that addressed variations between laser light, thermal light, exotic [[squeezed state]]s, etc. as it became understood that light cannot be fully described just referring to the [[electromagnetic field]]s describing the waves in the classical picture. In 1977, [[H. Jeff Kimble|Kimble]] et al. demonstrated a single atom emitting one photon at a time, further compelling evidence that light consists of photons. Previously unknown quantum states of light with characteristics unlike classical states, such as [[Squeezed coherent state|squeezed light]] were subsequently discovered.

Development of short and [[ultrashort pulse|ultrashort]] laser pulses—created by [[Q switching]] and [[modelocking]] techniques—opened the way to the study of what became known as ultrafast processes. Applications for solid state research (e.g. [[Raman spectroscopy]]) were found, and mechanical forces of light on matter were studied. The latter led to levitating and positioning clouds of atoms or even small biological samples in an [[optical trap]] or [[optical tweezers]] by laser beam. This, along with [[Doppler cooling]] and [[Sisyphus cooling]], was the crucial technology needed to achieve the celebrated [[Bose–Einstein condensation]].

Other remarkable results are the [[Bell test experiments|demonstration of quantum entanglement]], [[quantum teleportation]], and [[quantum logic gate]]s. The latter are of much interest in [[quantum information theory]], a subject that partly emerged from quantum optics, partly from theoretical [[computer science]].<ref>{{cite book|last1=Nielsen|first1=Michael A.|last2=Chuang|first2=Isaac L.|title=Quantum computation and quantum information|date=2010|publisher=Cambridge University Press|location=Cambridge|isbn=978-1107002173|edition=10th anniversary}}</ref>

Today's fields of interest among quantum optics researchers include [[parametric down-conversion]], [[Optical parametric oscillator|parametric oscillation]], even shorter (attosecond) light pulses, use of quantum optics for [[quantum information]], manipulation of single atoms, [[Bose–Einstein condensate]]s, their application, and how to manipulate them (a sub-field often called [[atom optics]]), [[coherent perfect absorber]]s, and much more. Topics classified under the term of quantum optics, especially as applied to engineering and technological innovation, often go under the modern term [[photonics]].

Several [[Nobel Prize]]s have been awarded for work in quantum optics. These were awarded:
* in 2022, [[Alain Aspect]], [[John Clauser]] and [[Anton Zeilinger]] "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science".<ref>[https://www.nobelprize.org/prizes/physics/2022/summary/ "The Nobel Prize in Physics 2022"]. Nobel Foundation. Retrieved 9 June 2023.</ref>
* in 2012, [[Serge Haroche]] and [[David J. Wineland]] "for ground-breaking experimental methods that enable measuring & manipulation of individual quantum systems".<ref>[https://www.nobelprize.org/nobel_prizes/physics/laureates/2012/index.html "The Nobel Prize in Physics 2012"]. Nobel Foundation. Retrieved 9 October 2012.</ref>
* in 2005, [[Theodor W. Hänsch]], [[Roy J. Glauber]] and [[John L. Hall]]<ref>{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/2005/ |title=The Nobel Prize in Physics 2005 |publisher=Nobelprize.org |access-date=2015-10-14}}</ref>
* in 2001, [[Wolfgang Ketterle]], [[Eric Allin Cornell]] and [[Carl Wieman]]<ref>{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/2001/ |title=The Nobel Prize in Physics 2001 |publisher=Nobelprize.org |access-date=2015-10-14}}</ref>
* in 1997, [[Steven Chu]], [[Claude Cohen-Tannoudji]] and [[William Daniel Phillips]] for [[laser cooling]]<ref>{{cite web|url=https://www.nobelprize.org/prizes/physics/1997/summary/ |title=The Nobel Prize in Physics 1997 |publisher=Nobelprize.org |access-date=2015-10-14}}</ref>