  The gravitational waveform of merging binary neutron stars encodes
information about extreme states of matter. Probing these gravitational
emissions requires the gravitational-wave detectors to have high sensitivity
above 1 kHz. Fortunately for current advanced detectors, there is a sizeable
gap between the quantum-limited sensitivity and the classical noise at high
frequencies. Here we propose a detector design that closes such a gap by
reducing the high-frequency quantum noise with an active optomechanical filter,
frequency-dependent squeezing, and high optical power. The resulting noise
level from 1 kHz to 4 kHz approaches the current facility limit and is a factor
of 20 to 30 below the design of existing advanced detectors. This will allow
for precision measurements of (i) the post-merger signal of the binary neutron
star, (ii) late-time inspiral, merger, and ringdown of low-mass black
hole-neutron star systems, and possible detection of (iii) high-frequency modes
during supernovae explosions. This design tries to maximize the science return
of current facilities by achieving a sensitive frequency band that is
complementary to the longer-baseline third-generation detectors: the10 km
Einstein Telescope, and 40 km Cosmic Explorer. We have highlighted the main
technical challenges towards realizing the design, which requires dedicated
research programs. If demonstrated in current facilities, the techniques can be
transferred to new facilities with longer baselines.
