An Introduction to Quantum Optics

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Quantum optics is the study that applies quantum mechanics to optics - the field of research in physics that focuses on light’s behavior and interactions. The particular field of quantum optics merges quantum-mechanical and semi-classical physics to understand and observe light’s actions with matter at a submicroscopic level.

As a result of quantum optics studying the way photons, or quantas of light, behave with atoms and molecules, the study of photons goes beyond that of quantum optics. Photons are an instrumental part of understanding quantum mechanics, such as teleportation and quantum entanglement.

Ultimately, quantum optics study of photons helps physicists learn the patterns and behavior of electromagnetic waves.

The Beginning of Quantum Optics

Max Planck, a German physicist who won the Nobel Prize in 1918 for his discovery of energy quanta, was the first to make headway in quantum optics. Planck made his mark with his correct modeling of the blackbody radiation spectrum. The physicist modeled his spectrum based on the hypothesis that light is released in discrete units of energy.

In 1900, Planck wrote a paper on the ultraviolet catastrophe in black body radiation. Approximately five years later, Albert Einstein strengthened these principles by applying them to his understanding of the photoelectric effect, which in turn described the photon theory of light. Both physicists supported the notion that light moved in discrete bundles - providing a foundation for both works and theories.

Throughout the initial half of the twentieth century, science was primarily concerned with quantum physics and its development; but, this is the study of matter’s behavior and not quantas of light. However, the second half of the twentieth century paved way for inventions such as the maser and the laser, both utilizing the property of light. Due to these new inventions and their dependency on light, quantum optics flourished as a new field of physics. As the devices gained more importance, so did the study of light and matter.

Specifics About Quantum Optics

Light that emits from machines like lasers and masers are known to be in what is called a coherent state. Essentially, this means that these waves have a sine curve and are therefore known as sinusoidal waves, while also following an equally dispersed wave function.

Wave-particle duality, a quantum mechanics phenomenon, is the idea that all particles or quantum bodies can be illustrated by both particles and waves. Wave-particle duality provides a foundation for electromagnetic radiation in quantum optics because this light-focused field also views radiation as moving in a wave and particles simultaneously. Furthermore, if photons travel in a series of particles, the patterns those particles present is dependent upon a quantum wave function that will influence the direction of the particle.

Quantum Electrodynamics

Another way to understand quantum optics is through QED, also known as quantum electrodynamics. By taking findings from QED, physicists can observe quantum optics as the creation and destruction of photons. Not only does this QED method explain quantum optics with field operators, but it also applies statistical evidence to help enable different observations of light.

Despite quantum electrodynamics being a useful procedure, there is still some controversy that surrounds its representations. Physicists are unsure if it displays what is taking place in real-time - thus, the approach is commonly seen as a helpful statistic model.


Quantum optics has developed into a subject that applies quantum-mechanical, as well as semi-classical physics to light, and in turn, attempts to analyze light’s interactions with matter. Topics under the umbrella of quantum optics are known as photonics; subjects such as coherent perfect absorbers, parametric oscillation, quantum information, Bose-Einstein condensates, and parametric down-conversion all apply to quantum optics.

Quantum theory still visualizes particles as a wavefunction, but it also suggests that light is a stream of particles, known as photons, and not solely an electromagnetic wave.

Sources and Further Reading

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Sydney Luntz

Written by

Sydney Luntz

Since graduating from the University of York with a BA Hons. in English Literature and Linguistics, Sydney has spent her time interning and freelancing before attending University of Arts College London in the fall, to complete a Master's in Data Journalism. In her spare time, you can catch Sydney reading a book, at a concert, or wandering a gallery!


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