Quantum limits of laser interferometric gravitational-wave detectors

Current ground-based gravitational-wave detectors, e.g., Advanced LIGO, are kilometre scale Michelson-type laser interferometers with kilogram mirror-endowed test masses. Even though they are macroscopic in size, quantum mechanics plays an important role in determining their sensitivity. In particular, quantum fluctuation of the optical field not only sets the measurement imprecision in terms of shot noise, but also induces quantum back action noise that perturbs the motion of test masses. The trade-off between these two types of quantum noise gives rise to the so-called Standard Quantum Limit (SQL). For the first part of this talk, we will walk through different approaches to surpassing the SQL, which leads to a more stringent sensitivity limit---the Fundamental Quantum Limit (FQL). For the second part, we will present current understanding of the FQL and its implications for enhancing detector sensitivity. The discussions here are not limited to gravitational-wave detectors, and can be applied to general linear quantum measurement devices.

References: arXiv:1305.3957 for the first part and arXiv:1608.00766 for the second.