  The sensitivity of laser interferometers is fundamentally limited by the
quantum nature of light. Recent theoretical studies have opened a new avenue to
enhance their quantum-limited sensitivity by using active parity-time-symmetric
and phase-insensitive quantum amplification. These systems can enhance the
signal response without introducing excess noise in the ideal case. However,
such active systems must be causal, stable, and carefully tuned to be practical
and applicable to precision measurements. In this paper, we show that
phase-insensitive amplification in laser interferometers can be implemented in
a tabletop experiment. The layout consists of two coupled cavities and an
active medium comprised of a silicon nitride membrane and an auxiliary pump
field. Our design relies on existing membrane and cryogenic technology and can
demonstrate three distinct features: (i) the self-stabilized dynamics of the
optical system, (ii) quantum enhancement of its sensitivity in the presence of
the amplifier, and (iii) optical control of the amplifier gain. These features
are needed to enhance the sensitivity of future interferometric
gravitational-wave and axion detectors.
