This award supports tabletop experiments to study methods for mitigating quantum noise in gravitational-wave interferometers. An experimental setup limited by both radiation pressure and shot noise in a low noise cryogenic environment will be developed. To achieve this in a small scale prototype, micro-fabricated mechanical resonators (of order 100 nanograms) will be used as one mirror of a high finesse optical cavity inside a low vibration cryostat, cooled to below 10K. A series of experiments will then be performed to verify models of quantum noise, and to test methods for its reduction. Specifically, a homodyne detector will be used to perform a variational readout of the resonator's position, to exploit the ponderomotive squeezing, and to evade the radiation pressure noise at a single frequency. A filter cavity will then be introduced to evade the radiation pressure noise in a wide frequency band. Advanced LIGO and other second generation gravitational wave detectors are expected to be limited by quantum noise across the majority of their detection frequency band. At low frequencies, the test masses are driven by radiation pressure and at high frequencies, shot noise limits the phase precision of the measurement. Together, the radiation pressure and shot noise represent a significant limit on the sensitivities of future gravitational-wave detectors. Collaboration with other groups within the LIGO Scientific Collaboration will provide access to a source of squeezed vacuum states, which will be used to directly reduce the radiation pressure noise. Alternative topologies, such as the speedmeter and dual-carrier readout, will also be explored. By using a combination of optical trapping and cooling, the mechanical resonators will be placed into low noise states, with decoherence rates less than their oscillation frequency, allowing for the resonators to be placed in non-classical states, as a test of quantum mechanics.
This research program will substantially enhance the on-campus research activities of the experimental gravitational physics program at Louisiana State University. Because of LSU's proximity to the LIGO Livingston Observatory, and the PI's other research activities within the LIGO project, there will be substantial personnel and intellectual overlap between LIGO commissioning, other on-site work, and R&D activities. Integration among these activities will strengthen the LIGO project and reduce risk, as well as advance the frontier of gravitational-wave science. Students and post-docs with experience in both small scale lab experiments and large scientific collaborations will be trained. The nature of this work naturally leads to collaboration between the GW community and the fields of quantum optics and quantum information. The thermal noise characterization experiments will have wide ranging applications to many systems limited by thermal noise. A summer research and education program aimed at undergraduate juniors will be developed, with the goal of encouraging and helping underrepresented groups in the region enter and succeed in graduate school within the LIGO Scientific Collaboration. This program will contain both a research and an education component, and will work strongly with existing programs including the LIGO Science Education Center, Southern University Baton Rouge's Timbuktu Academy, and the outreach group in the LIGO Scientific Collaboration to develop the educational program and to attract students.