Demonstration of displacement- and frequency-noise free laser interferometry using bi-directional Mach-Zehnder interferometers

We have demonstrated displacement- and frequency-noise free laser interferometry (DFI) by partially implementing a recently proposed optical configuration using bi-directional Mach-Zehnder interferometers (MZI). This partial implementation, the minimum necessary to be called DFI, has confirmed the essential feature of DFI: the combination of two MZI signals can be carried out in a way which cancels displacement noise of the mirrors while maintaining gravitational wave signals. The attained maximum displacement noise suppression allowed a simulated-SNR of 45dB.