  There exists the standard quantum limit (SQL), derived from Heisenberg's
uncertainty relation, in the sensitivity of laser interferometer
gravitational-wave detectors. However, in the context of a full
quantum-mechanical approach, SQL can be overcome using the correlation of shot
noise and radiation-pressure noise. So far, signal recycling, which is one of
the methods to overcome SQL, is considered only in a recombined-type
interferometer such as Advanced-LIGO, LCGT, and GEO600. In this paper, we
investigated quantum noise and the possibility of signal recycling in a
differential-type interferometer. As a result, we found that signal recycling
is possible and creates at most three dips in the sensitivity curve of the
detector. Then, taking advantage of the third additional dip and comparing the
sensitivity of a differential-type interferometer with that of a
next-generation Japanese GW interferometer, LCGT, we found that SNR of inspiral
binary is improved by a factor of 1.43 for neutron star binary, 2.28 for 50
M_sun black hole binary, and 2.94 for 100 M_sun black hole binary. We also
found that power recycling to increase laser power is possible in our
signal-recycling configuration of a detector.
