Researchers have developed a quantum-inspired protocol to measure the masses of small cosmic objects that subtly bend light through microlensing. This approach leverages the quantum properties of photons to extract precise information from faint signals. It could detect elusive entities like rogue planets and isolated black holes without needing massive telescopes.
Light from distant stars does not always travel in straight lines; massive objects can bend it, creating gravitational lensing effects. While dramatic lensing from heavyweights like black holes is detectable, subtler "microlensing" from smaller masses poses challenges for traditional methods. Zhenning Liu at the University of Maryland and his colleagues propose a protocol that accounts for the quantum nature of light to overcome this.
Microlensing events are identifiable because the light temporarily brightens, indicating an intervening object. However, inferring the object's mass from conventional telescope data is difficult for small bodies, such as rogue planets or isolated black holes. Liu explains: "Researchers can tell when a microlensing event happens, because the light becomes brighter. This allows them to know there is an object between us and the light’s source, but if that object is not huge, they cannot infer its mass from the properties of the light that telescopes already measure."
The innovation lies in photons, the quantum particles of light. When a photon encounters a lensing object, it can take multiple paths with different travel times, altering its quantum properties. Like waves splitting around a rock, photons effectively explore both routes simultaneously. The team's algorithm extracts the time delay between these paths, which directly relates to the object's mass.
This quantum approach requires few photons, making it feasible with existing detectors and conventional computers, without a full quantum computer. Mathematical analysis shows it performs well for stars in the Milky Way's galactic bulge, where prior lensing studies have found dark objects. Implementation could be testable within a few years.
Daniel Oi at the University of Strathclyde praises the method: it offers "an exponential improvement in the ability to extract time delay information from light," calling it a "holy grail of quantum technology." Quantum tools suit weak astronomical signals, as they address fundamental measurement limits in physics.
The protocol, detailed in a recent arXiv paper (DOI: 10.48550/arXiv.2510.07898), promises to unveil cosmic objects invisible to other observations, enhancing our understanding of the universe's hidden masses.