  The Juggled interferometer (JIFO) is an earth-based gravitational wave
detector using repeatedly free-falling test masses. With no worries of seismic
noise and suspension thermal noise, the JIFO can have much better sensitivity
at lower frequencies than the current earth-based gravitational wave detectors.
The data readout method of a JIFO could be challenging if one adopts the
fringe-locking method. We present a phase reconstruction method in this paper
by building up a complex function which has a fringe-independent
signal-to-noise ratio. Considering the displacement noise budget of the
Einstein Telescope (ET), we show that the juggled test masses significantly
improve the sensitivity at 0.1-2.5$\,$Hz even with discontinuous data. The
science cases brought with the improved sensitivity would include detecting
quasi-normal modes of black holes with $10^4-10^5\,M_{\odot}$, testing
Brans-Dicke theory with black-hole and neutron-star inspirals, and detecting
primordial-black-hole-related gravitational waves.
