Physics Colloquium

Optical interferometer observatories, namely LIGO, have begun a new era of astrophysics by measuring the length of their vast, 4km arms to such precision that gravitational waves from distant collisions of black holes and neutron stars are now regularly observed. The global gravitational wave network recently entered another era, whereby every detector has enhanced sensitivity using quantum squeezed states of light, limited by optical loss and quantum mechanical back-action. With squeezing, LIGO operates in a regime long predicted and studied within quantum measurement theory, where the act of strongly measuring its mirrors' positions pushes and rumbles them. Two decades ago, Kimble et al[1], derived "Frequency-dependent squeezing" as a means to suppress radiation pressure back-action, bypassing trade-offs seemingly implied by Heisenberg uncertainty.

LIGO is now realizing Frequency-dependent squeezing[2] to achieve a broadband noise improvement and utilize "quantum nondemolition" to accelerate observational astrophysics. I will overview LIGO, describing how gravitational wave interferometers achieve their quantum noise limits and surpass them using squeezed states of light. Looking forward, I will conclude with next-generation detector concepts and further prospects where quantum measurement and astrophysics should collide.

[1] H. J. Kimble, Y. Levin, A. B. Matsko, K. S. Thorne, and S. P. Vyatchanin, "Conversion of conventional gravitational-wave interferometers into quantum nondemolition interferometers by modifying their input and/or output optics," Phys. Rev. D, vol. 65, no. 2, p. 022002, Dec. 2001, doi: 10.1103/PhysRevD.65.022002.
[2] LIGO O4 Detector Collaboration, "Broadband Quantum Enhancement of the LIGO Detectors with Frequency-Dependent Squeezing," Phys. Rev. X, vol. 13, no. 4, p. 041021, Oct. 2023, doi: 10.1103/PhysRevX.13.041021.

Join via Zoom:
https://caltech.zoom.us/j/81866929019
Meeting ID: 818 6692 9019

The colloquium is held in Feynman Lecture Hall, 201 E. Bridge.