ChatGiant laser observatories like LIGO are blinded at low frequencies by the rumbling vibrations of Earth's seismic waves; dropping clouds of ultra-cold strontium atoms in a ten-meter vacuum tower allows quantum wave interference to measure gravitational ripples with zero seismic interference. Published in Nature, this prototype differential atom interferometer opens the uncharted "mid-band" gravitational wave frequency window, creating an ultra-sensitive quantum sensor to hunt for ultralight dark matter.
While gravitational wave detectors like LIGO have heard dozens of high-frequency black hole collisions, they are deaf to mid-frequency cosmic rumbles (between 0.1 and 10 Hz) because the rumble of ocean waves, traffic, and Earth's tectonic plates drowns out delicate laser beams.
Quantum physicists at MAGIS and AION designed an atomic solution: dropping laser-cooled clouds of strontium atoms down a ten-meter vertical vacuum tube. By splitting each atom into a quantum superposition so it travels along two paths simultaneously, laser pulses measure the difference in gravitational pull with atomic clock accuracy, canceling out Earth's background seismic noise.
The prototype demonstrated record-breaking quantum strain sensitivity. By bridging the observational gap between ground-based LIGO and future space-based LISA detectors, by hunting for ultralight axion dark matter waves, and by testing Einstein’s equivalence principle, atom interferometry pioneers the future of quantum gravity sensing.
A prototype differential atom interferometer for fundamental physics
Gravitational waves and ultralight dark matter are among the most compelling frontiers in fundamental physics, motivating proposals for very-long-baseline atom interferometerssuch as AION1, MAGIS2, AICE3 and AEDGE4 that aim to detect at frequencies at which ground-based5 and space-borne6 laser interferometers lose sensitivity. Very-long-baseline atom interferometers look for signals by comparing the quantum phase evolution of widely separated atomic ensembles interrogated by a common laser. However, their performance depends critically on suppressing noise sources, particularly laser phase noise. The experimental validation of such noise rejection remains an important challenge. Here we demonstrate a prototype differential atom interferometer based on the single-photon clock transition of fermionic 87Sr. Thus, we obtain a gradiometer configuration with a species intrinsically suited to kilometre-scale and space-baseline operation. The instrument operates at the standard quantum limit7 with no excess noise beyond atom shot noise. The differential configuration maintains quantum-limited sensitivity in the presence of several radians of artificially injected laser phase noise per shot, which emulates the conditions expected in a very-long-baseline atom interferometer. We also demonstrate the recovery of coherent oscillatory signals across a broad frequency range under fully phase-randomized conditions, a capability that is inaccessible to a single interferometer operating in the same regime. These results provide an experimental validation of the noise-immune measurement principle underlying very-long-baseline atom interferometers and mark an important step towards next-generation quantum sensors for gravitational-wave detection and searches for ultralight dark matter8,9. A prototype differential atom interferometer operates at the standard quantum limit with no excess noise beyond atom shot noise, achieving performance in line with the specifications for future long-baseline atom interferometers.
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