ИСТИНА

Laser GW antenna is the unique displacement meter measuring distance 4 km between 40-kg masses with unique sensitivity about 10−19 m. We present analysis of main fundamental reasons, which determine sensitivity of GW detectors. Current sensitivity is close to Standard Quantum Limit (SQL). We discuss the reasons of SQL (measurement noise and back action) and methods to surpass it: quantum non-demolition measuremens (QND), quantum variational measurements, speedmeter and usage of optical rigidity. We also consider the methods of broadband variational measurement for mechanical oscillator, so called “system free from quanum mechanics” (SFQM) and “negative mass”.