Advanced LIGO A Quantum Limited Interferometer LIGO I Ad LIGO Seismic Suspension thermal Test mass thermal Quantum

Why use squeezed states? Heisenberg  minimum uncertainty Equal uncertainty in both quadratures Squeezing  reduce uncertainty in one quadrature at the expense of increased uncertainty in orthogonal quadrature Area in quadrature phase space conserved Uncertainty circle  ellipse How to squeeze? Correlate quadratures Why is it useful Line up signal phasor with narrowest part of ellipse Noise in measurement of that signal lower than the quantum noise limit

Sub-quantum-limited Advanced LIGO X+ X- Quantum correlations (Buonanno and Chen) Input squeezing

One way to squeeze Vacuum seeded OPO ANU group  quant-ph/0405137