A galaxy cluster creates gravitational lensing, bending light around it.
NASA, ESA, Michael Gladders (University of Chicago); Thanks: Judy Schmidt
Quantum physics may be the secret ingredient to understanding cosmic objects that our telescopes can't show us in detail, or at all.
To understand space, we collect and analyze the light that travels from objects such as stars into our telescopes, but this light does not always travel in straight lines. Often, when it passes a very massive object such as a planet or black hole, the light's path is bent and creates distorted images, as if an extra lens had been added somewhere along the way.
What about objects that are not cosmic heavyweights and have relatively low mass? Traditional imaging techniques cannot cope with such microlensing phenomena, but Zhenning Liu from the University of Maryland and his colleagues have now demonstrated that a light analysis protocol that takes into account its quantum nature can perform much better.
They focused on using the quantum properties of light to recognize the mass of objects causing microlensing. Liu says the researchers can tell when a microlensing event is happening because the light gets brighter. This allows them to know that there is an object between us and the light source, but unless that object is huge, they cannot infer its mass from the properties of light that telescopes already measure. Such objects may include small isolated black holes and even some rogue planets.
But light is made up of photonswhich are quantum particles, so information about their journey to Earth is also encoded in their quantum properties. Notably, whenever a photon has the opportunity to take several different paths around an object, each requiring a different travel time, this difference changes the quantum properties of the photon. Because quantum particles can sometimes behave like waves, these photons can effectively travel both paths around an object at the same time, like a wave of water meeting a rock. The team's protocol excels at extracting the time difference between both paths, which can then be translated into the object's mass.
Liu says a planet or black hole creating microlensing would not necessarily be invisible in all other observations. But these methods may require collecting much more light, which is equivalent to having to build increasingly larger telescopes. The quantum approach will work with a relatively small number of photons.
For example, his team's mathematical analysis showed that the protocol would work well for stars in the galactic bulge, a part of the Milky Way where dark objects had previously been discovered through gravitational lensing studies. Because the new protocol does not require full as much as a computer and can be implemented using more standard devices that capture and analyze one photon at a time, in combination with conventional computers; it also has a chance to be field tested for several years.
Daniel High at the University of Strathclyde in the UK says the quantum approach offers an exponential improvement in the ability to extract time delay information from light, an advantage it compares to the Holy Grail of quantum technology. Oi says quantum technologies are naturally suited to weak astronomical signals, such as small numbers of photons, since quantum theory is the source of many of the constraints on how precisely something can be measured in physics.
Link: arXiv, DOI: 10.48550/arXiv.2510.07898
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