Signal to noise in the search for gravitational waves

Johanna Miller’s Search and Discovery piece on squeezed light leading to better gravitational-wave detection (Physics Today, November 2011, page 11 ) discusses very promising science by Roman Schnabel and colleagues. However, reducing noise levels by a factor of 1.5 does not lead to the sort of increases in “accessible volume of space by more than a factor of 3” that the article discusses.

The issue is signal to noise. For a gravitational-wave source, the signal decreases inversely proportional to r-squared, where r is the distance to the source. So reducing the receiver noise level by the 1.5 factor produces a detection range increase that is the square root of this factor, not the factor-cubed sensitivity as described.

Also, if coherent detection is being employed, losing the quadrature channel costs an average factor of 3.92 dB in signal detectability, averaged over several same sources at comparable distances but random initial signal phase.

I note the envy radar engineers have for inverse r-squared sensitivity—the radar world functions as inverse r⁴.

Keep up the good work.