As a longtime member of the LIGO scientific team since 2014, Dr. Haocun Yu has mainly focused on the enhancement of LIGO sensitivity using quantum techniques, as well as the demonstration of macroscopic quantum phenomena in Advanced LIGO detectors.
From 2017 to 2109, Yu played a leading role in the research team in implementing squeezed vacuum sources in Advanced LIGO. The team built, measured, diagnosed, and optimized the squeezing. Due to their extraordinary efforts, they present the very first implementation of squeezed vacuum states in the Advanced LIGO detectors, which improves the interferometer sensitivity above 50 Hz by up to a factor of 1.4 (3 dB), which enables weekly detections of astrophysical events during the 3rd observing run (O3) of the Advanced LIGO, compared to monthly detections prior to squeezing implementation. This work marks the very first direct observation of GW with quantum-enhanced interferometers.
In 2020, via injecting squeezing in Advanced LIGO detectors, Yu directly observed the first evidence of QRPN contributing to the motion of 40 kg mirrors using 200kW laser beams, proving that quantum backaction and the Heisenberg uncertainty principle persists even at human scales. Furthermore, by exploiting the quantum correlations produced from the strong optomechanical coupling in LIGO, Yu has demonstrated that the positions of the kilogram-mass mirrors can be sensed with quantum noise surpassing the free-mass standard quantum limit (SQL) at room temperature. These achievements are the culmination of decades of research to see quantum phenomena at a macroscopic scale. Revealing quantum noise below the SQL in the Advanced LIGO detector is the first realization of a quantum non-demolition technique in GW detectors, where quantum correlations prevent the measurement device from demolishing the same information one is trying to extract. Exploiting quantum correlations allows a fundamental quantum limit to be manipulated to improve measurement precision.