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 , has a standard quantum limit.
- The same applies to certain correlations e.g. of intensity noise between two optical beams.
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