  The quantum noise of light fundamentally limits optical phase sensors. A
semiclassical picture attributes this noise to the random arrival time of
photons from a coherent light source such as a laser. An engineered source of
squeezed states suppresses this noise and allows sensitivity beyond the
standard quantum limit (SQL) for phase detection. Advanced gravitational wave
detectors like LIGO have already incorporated such sources, and nascent efforts
in realizing quantum biological measurements have provided glimpses into new
capabilities emerging in quantum measurement. We need ways to engineer and use
quantum light within deployable quantum sensors that operate outside the
confines of a lab environment. Here we present a photonic integrated circuit
fabricated in thin-film lithium niobate that provides a path to meet these
requirements. We use the second-order nonlinearity to produce a squeezed state
at the same frequency as the pump light and realize circuit control and sensing
with electro-optics. Using a 26.2 milliwatts of optical power, we measure (2.7
$\pm$ 0.2 )$\%$ squeezing and apply it to increase the signal-to-noise ratio of
phase measurement. We anticipate that on-chip photonic systems like this, which
operate with low power and integrate all of the needed functionality on a
single die, will open new opportunities for quantum optical sensing.
