3 Quantum Nature of Light and Quantum Noise

Now is the time to remind ourselves of the word ‘quantum’ in the title of our review. Thus far, the quantum nature of laser light being used in the GW interferometers has not been accounted for in any way. Nevertheless, quantum mechanics predicts striking differences for the variances of laser light amplitude and phase fluctuations, depending on which quantum state it is in. Squeezed vacuum [163Jump To The Next Citation Point, 99Jump To The Next Citation Point, 136Jump To The Next Citation Point, 38Jump To The Next Citation Point, 90Jump To The Next Citation Point] injection that has been recently implemented in the GEO 600 detector and has pushed the high-frequency part of the total noise down by 3.5 dB [151Jump To The Next Citation Point, 1] serves as a perfect example of this. In this section, we provide a brief introduction into the quantization of light and the typical quantum states thereof that are common for the GW interferometers.

 3.1 Quantization of light: Two-photon formalism
 3.2 Quantum states of light
  3.2.1 Vacuum state
  3.2.2 Coherent state
  3.2.3 Squeezed state
 3.3 How to calculate spectral densities of quantum noise in linear optical measurement?

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