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Standard Quantum Limit

Author: the photonics expert (RP)

Acronym: SQL

Definition: a limit for noise levels set by quantum mechanics

Categories: article belongs to category quantum photonics quantum photonics, article belongs to category fluctuations and noise fluctuations and noise

Related: quantum noisesqueezed states of lightshot noise

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DOI: 10.61835/tpi   Cite the article: BibTex BibLaTex plain textHTML   Link to this page!   LinkedIn

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What is the Standard Quantum Limit?

The standard quantum limit for the noise of some optical measurement scheme usually refers to the minimum level of quantum noise which can generally be obtained — without the use of squeezed states of light. Some examples are:

  • The standard quantum limit for high-frequency intensity noise of a laser is the shot noise limit. A lower intensity noise level can be obtained only with amplitude-squeezed light.
  • There is also a standard quantum limit for phase noise, which is reached by a laser only at high noise frequencies. (See the article on the Schawlow–Townes linewidth.)
  • The sensitivity of various optical measurements, e.g. of length measurements with interferometers [2], has a standard quantum limit.
  • The same applies to certain correlations e.g. of intensity noise between two optical beams.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What is the standard quantum limit (SQL)?

The standard quantum limit is the minimum level of quantum noise that can be achieved in an optical measurement without using squeezed states of light.

What is a common example of the standard quantum limit?

A common example is the shot noise limit for the high-frequency intensity noise of a laser. Lower noise can only be achieved with amplitude-squeezed light.

Does the standard quantum limit apply to phase noise?

Yes, there is also a standard quantum limit for phase noise. For a laser, this is related to the Schawlow–Townes linewidth and is typically reached only at high noise frequencies.

Bibliography

[1]C. M. Caves, “Quantum-mechanical radiation-pressure fluctuations in an interferometer”, Phys. Rev. Lett. 45 (2), 75 (1980); doi:10.1103/PhysRevLett.45.75
[2]M. T. Jaekel and S. Reynaud, “Quantum limits in interferometric measurements”, Europhys. Lett. 13, 301 (1990); doi:10.1209/0295-5075/13/4/003
[3]H. M. Wiseman, “Light amplification without stimulated emission: beyond the standard quantum limit to the laser linewidth”, Phys. Rev. A 60 (5), 4083 (1999); doi:10.1103/PhysRevA.60.4083
[4]V. Giovannetti, S. Lloyd and L. Maccone, “Quantum-enhanced measurements: beating the standard quantum limit”, Science 306 (5700), 1330 (2004); doi:10.1126/science.1104149

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