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Table 2 Notations and conventions, used in this review

From: Advanced quantum techniques for future gravitational-wave detectors

Notation and value

Comments

L

Length of the arms of the interferometer

\(\tau =L/c\)

Light travel time at distance L

\(\omega \)

Optical frequencies

\(\omega _0\)

Interferometer resonance frequency

\(\omega _p\)

Optical pumping frequency (laser frequency)

\(\varOmega = \omega -\omega _p\)

Modulation sideband frequency w.r.t. laser frequency \(\omega _p\)

\(\varDelta =\omega _p-\omega _0\)

Optical pump detuning from the cavity resonance frequency \(\omega _0\)

\(\mathcal {E}_{0} = \sqrt{\dfrac{4\pi \hbar \omega _p}{\mathcal {A}c}}\)

Normalisation constant of the second quantisation of a monochromatic light beam

\(A^{in} = \sqrt{\dfrac{2P^{in}}{\hbar \omega _p}}\)

Classical quadrature amplitude of the incident light beam with power \(P^{in}\)

\(T\,(R)\)

Power transmissivity (reflectivity) of the mirror

\(\gamma _{\mathrm{arm}} = cT/4L\)

Arm cavity half-bandwidth for input mirror transsmissivity T and perfect end mirror

\(\delta _{\mathrm{arm}}\)

Arm cavity detuning/differential detuning of the arms of Fabry–Perot–Michelson interferometer

\(\gamma \)

Interferometer effective half-bandwidth

\(\beta (\varOmega )\)

Phase shift acquired by sidebands in the interferometer

\(\mathcal {K}(\varOmega )\)

Optomechanical coupling factor (Kimble factor) of the interferometer

\(P^{in}\)

Incident light beam power

\(P_c = 2P_{\mathrm{arm}}\)

Total power, circulating in both arms of the interferometer (at the test masses)

M

Mass of the mirror

m

Reduced mass of the signal mechanical mode of the interferometer (e.g., dARM mode)\(^\mathrm{a}\)

\(\varTheta = \dfrac{4\omega _p P_c}{mcL}\)

Normalised intracavity power

\(h_{\mathrm{SQL}} = \sqrt{\dfrac{8\hbar }{mL^2\varOmega ^2}}\)

Standard quantum limit of a free mass for GW strain

\(x_{\mathrm{SQL}} = \sqrt{\dfrac{2\hbar }{m\varOmega ^2}}\)

Standard quantum limit of a free mass for displacement

  1. \(^\mathrm{a}\)Here we follow the same definition of the dARM mechanical mode as we adopted in Danilishin and Khalili (2012), i.e., \(x_{\mathrm{dARM}} = (x_{N}-x_{E})/2\), where \(x_{N,E}\) are the corresponding elongations of the arms of the interferometer. When so defined, the dARM-mode has the same reduced mass as a single test mass, \(m=M\). Another popular definition of the dARM as \(\tilde{x}_{\mathrm{dARM}} = (x_{N}-x_{E})\) leads to the new reduced mass equal to \(m=M/4\) and to the correspondent redefinition of the SQL