Demonstration of displacement-noise-free interferometry using bi-directional Mach–Zehnder interferometers

We have demonstrated displacementand frequency-noise-free laser interferometry (DFI) by partially implementing a recently proposed optical configuration using bi-directional Mach–Zehnder interferometers (MZIs). 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 that cancels the displacement noise of the mirrors and beam splitters while maintaining gravitational-wave signals. The attained maximum displacement noise suppression was 45 dB. PACS numbers: 04.80.Nn, 06.30.Ft, 95.55.Ym (Some figures in this article are in colour only in the electronic version)