  We analyze the sensitivity of gravitational-wave antenna with stable double
optical spring created by two independent pumps. We investigate regime of three
close eigen frequencies (roots of characteristic equation) which appears to
provide more wide frequency band in which sensitivity of antenna can beat
Standard Quantum Limit (SQL) than previously considered regime with two close
eigen frequencies. We take into account optical losses and show that they do
not degrade sensitivity significantly. We also demonstrate possible application
of considered regime to Einstein Telescope.
