[Space] NASA is funding a quantum trick to detect gravitational waves without connecting spacecraft with lasers

[Voyager17]

A new NASA Innovative Advanced Concepts grant is backing a proposal from a team led by Paul Stankus at Brookhaven National Laboratory that could sidestep one of the biggest engineering headaches in gravitational wave astronomy, the need to maintain a flawless laser link between spacecraft separated by millions of kilometers. Current space based interferometer concepts like LISA require exactly that kind of continuous physical connection, bouncing a laser beam between precisely floating mirrors, and keeping that link stable across such vast distances is close to an engineering nightmare.

Ground based detectors like LIGO, which made the first gravitational wave detection back in 2015, can only pick up relatively high frequency waves in the 10 to 10,000 hertz range, typically caused by stellar mass black hole and neutron star collisions. Pulsar timing arrays cover the opposite extreme, detecting nanohertz level background hums by tracking pulsar timing over decades. That leaves a substantial gap around the microhertz range that existing and planned detectors, including LISA, still can't cleanly reach without solving that laser link problem first.

Stankus's proposal throws out the laser connection requirement entirely. Instead of measuring the distance between two spacecraft directly, the team wants to watch for the subtle wobble a passing gravitational wave induces in the apparent position of background stars, using a quantum effect called the Hanbury Brown and Twiss effect that the team has already demonstrated in what they call a two photon amplitude interferometer. Two independent, uncabled spacecraft would each watch the same set of stars, timestamp every photon detected with ultra fast single photon detectors, and beam that raw timing data back to Earth for supercomputers to compare.

According to the underlying quantum mechanics, photons arriving separately at each spacecraft should show correlated arrival patterns, a phenomenon called quantum bunching, even though the two photons never actually interact with each other directly. If a gravitational wave passes through and subtly shifts a star's apparent position, that shift should show up as a detectable phase change in those correlations. The team now has nine months of NIAC funding to prove the underlying concept actually scales to real satellites floating in space, and if it works, it could open up an entirely new frequency window for probing black hole mergers and the broader evolution of the cosmos

Gravitational Wave Detectors Turn to Quantum Mechanicsspectrum.ieee.org