Gravitational wave astronomy is entering a new chapter thanks to a recent NASA Institute for Advanced Concepts grant. Current detection methods like LIGO and Pulsar Timing Arrays cover significant frequency ranges, but they leave a gap in the micro-Hertz spectrum. Space-based interferometers like LISA represent the next step, yet they face the immense engineering hurdle of maintaining laser links between spacecraft separated by millions of kilometers.
Paul Stankus from Brookhaven National Laboratory proposes a different approach that removes the need for physical or optical links between satellites. Instead of measuring distance between craft, this concept relies on tracking the astrometric signature of stars. As gravitational waves pass through the solar system, they warp spacetime, creating a tiny, coordinated wobble in the positions of background stars. Detecting this subtle motion requires a fresh application of quantum physics.
The research team aims to deploy two spacecraft in independent orbits. Rather than connecting them with a laser, each craft uses ultra-fast single-photon detectors to monitor the same set of stars. By recording precise timestamps of incoming photons, the team can analyze quantum correlations known as quantum bunching. Supercomputers on Earth process this data to calculate phase interference without the need for the photons to interact directly. This allows researchers to observe the apparent star wobbles caused by passing gravitational waves.
While the concept relies on complex quantum mechanics, the team has already successfully demonstrated a tabletop version of this two-photon amplitude interferometer in a laboratory setting. The current nine-month project focuses on scaling this technology for space-based operations. Proving this method works with satellites in orbit could unlock a new way to map events in the universe that remain hidden from current detectors. This transition from ground-based laser interferometry to quantum-based astrometry addresses the engineering limitations inherent in deep space observation.