physics

Nonclassical light

Nonclassical light is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nonclassical light rather than just read about it. In short: In optics, nonclassical light is light that cannot be described using classical electromagnetism; its characteristics are described by the quantized electromagnetic field and quantum mechanics. The most common described forms of nonclassical light are the following: Photon statistics of nonclassical light is sub-Poissonian in the sense that the average number of photons in a photodetection of this kind of light show…

Key takeaways

Nonclassical light belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nonclassical light to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nonclassical light from memory before moving on to harder problems.

Reference excerpt

In optics, nonclassical light is light that cannot be described using classical electromagnetism; its characteristics are described by the quantized electromagnetic field and quantum mechanics. The most common described forms of nonclassical light are the following:

Photon statistics of nonclassical light is sub-Poissonian in the sense that the average number of photons in a photodetection of this kind of light shows a standard deviation that is less than the mean number of the photons. Squeezed light exhibits reduced noise in one quadrature component. The most familiar kinds of squeezed light have either reduced amplitude noise or reduced phase noise, with increased noise of the other component. Fock states (also called photon number states) have a well-defined number of photons (stored e.g. in a cavity), while the phase is totally undefined.

Glauber–Sudarshan P representation

The density matrix for any state of light can be written as:

ρ ^ = ∫ P ( α ) | α ⟩ ⟨ α | d 2 α , {\displaystyle {\widehat {\rho }}=\int P(\alpha )|{\alpha }\rangle \langle {\alpha }|{\rm {{d}^{2}\alpha ,}}}

where | α ⟩ {\displaystyle \scriptstyle |\alpha \rangle } is a coherent state. A classical state of light is one in which P ( α ) {\displaystyle \scriptstyle P(\alpha )\,} is a probability density function. If it is not, the state is said to be nonclassical. Aspects of P ( α ) {\displaystyle \scriptstyle P(\alpha )\,} that would make it nonclassical are:

a negative value at any point; being more singular than a Dirac delta function. The matter is not quite simple. According to Leonard Mandel and Emil Wolf's book Optical Coherence and Quantum Optics: "The different coherent states are not [mutually] orthogonal, so that even if P ( α ) {\displaystyle \scriptstyle P(\alpha )\,} behaved like a true probability density [function], it would not describe probabilities of mutually exclusive states."

References

Citations

Citation bibliography

General references Glauber, Roy J. (1963-09-15). "Coherent and Incoherent States of the Radiation Field". Physical Review. 131 (6). American Physical Society (APS): 2766–2788. doi:10.1103/physrev.131.2766. ISSN 0031-899X.

Worked examples

Example 1 — a first encounter with Nonclassical light

Start with the simplest possible case. Write down what Nonclassical light claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nonclassical light before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nonclassical light ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nonclassical light

In research: Nonclassical light appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nonclassical light in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nonclassical light is common in secondary-school and first-year university syllabi. It links to neighbouring topics Quantum optics, Quantum physics stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Nonclassical light outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Nonclassical light in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nonclassical light means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nonclassical light out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nonclassical light in simple terms?

Why does Nonclassical light matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nonclassical light?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nonclassical light.