Can quantum tech give telescopes sharper vision?


Quantum memories and networks could help combine light from widely separated mirrors

19 MAR 2024


8m telescopes.jpeg
The Very Large Telescope Interferometer in Chile pools light from 8-meter telescopes and 2-meter ones (foreground) to make sharp pictures.ALBERTO GHIZZI PANIZZA/ESO

When the Extremely Large Telescope is completed in Chile in a few years’ time, its 39-meter mirror will be larger than those of all earlier research telescopes added together. Yet even this titan will see planets around nearby stars as single points of light, with no discernible detail.

What’s an astronomer to do? At a meeting last week organized by NOIRLab, the U.S. national center for optical and infrared astronomy, researchers discussed a possible answer: not one big telescope, but many, their light combined by quantum technologies. If the strategy works, telescopes hundreds of kilometers apart could collectively acquire a vision sharp enough to reveal surface features on exoplanets and disks of matter swirling around supermassive black holes. “We want to jump the shark on this and invent a new technology,” says Heidi Hammel, vice president for science with the Association of Universities for Research in Astronomy, which manages publicly funded U.S. observatories.

Combining signals from widely spaced telescopes, a technique known as interferometry, is familiar to radio astronomers. The Very Large Array in New Mexico pools signals from 27 dishes spaced across tens of kilometers. The Very Long Baseline Array does the same for 10 telescopes spanning the United States. And the first image of the shadow of a black hole, released in 2019, was the product of a worldwide network of radio dishes.

When electromagnetic signals gathered from different locations are merged, the waves interfere—doubling in brightness where wave peak meets peak and canceling out where peak meets trough. By combining and processing the resulting patterns from many pairs of telescopes, an interferometer can assemble a detailed image of the source. Because radio waves are so long, it’s relatively easy to record the precise timing of the phase, or shape, of the waves at each telescope and interfere them later in a computer.

Visible light waves are 1 million times shorter, so such recording isn’t feasible for optical telescopes. Instead, the waves must be interfered in real time, with mirrors and vacuum pipes channeling the light from the telescopes to a central combiner. The light paths from each telescope must all be identical to less than one-millionth of a meter. As a result, today’s experimental optical interferometers struggle to span more than a few hundred meters, enough to measure the diameter of a star but not to see oceans and continents on one of its planets. “We need hundreds of kilometers to get the resolution we want,” says NOIRLab’s Stuartt Corder.

To get there, Corder says, astronomers want to “ride on the coattails” of quantum technologies developed for other uses. One is quantum memory, which can store the exact state of a photon—including its phase information—in the quantum state of an atom in a crystal lattice. Researchers in Australia and China have created such devices with erbium crystals, storing quantum states for several hours. In theory, quantum memories could be filled at distant telescopes and shipped to a central facility where the states could be converted back to photons and interfered, says John Bartholomew of the University of Sydney. “It keeps a model similar to current interferometry.”

But right now, crystals can store a few hundred quantum states, whereas astronomers would need hundreds of millions to assemble any sort of meaningful picture. And today’s delicate quantum devices may not survive outside a laboratory. “You’re going to need a very stable environment while traveling,” Bartholomew says.

Another option is to transmit photons’ exact quantum states over a network of optical fibers and carry out interference in real time. Several teams have created prototype quantum networks to distribute quantum keys for secure, encrypted transactions. But to work across the distances astronomers want will require repeaters that preserve quantum states, a technology that is still experimental.

An alternative would rely on quantum mechanics’ spooky ability to create long-distance connections. In this scheme, a central source would generate “entangled” photon states, which can be shared between two distant telescopes. The shared state provides a phase reference that can be compared with two incoming photons, equivalent to interfering them together. “You get the same information as if you had used a central beam splitter,” says Johannes Borregaard of the Delft University of Technology.

To work, the central source would need to generate and send out 100 million entangled states per second. “It’s very demanding,” Borregaard says. Nevertheless, one team has demonstrated this process in a lab, using a laser as a simulated star. “We showed the principle works and can be put into practice,” says Brian Smith of the University of Oregon. The team is now setting up telescopes on its laboratory roof and hopes in a couple of years to do the same with actual star light.

NOIRLab’s Ryan Lau says the workshop was about starting a conversation between astronomers and quantum technologists and “learning each other’s language.” The goal is a small demonstration leading to a proposal to build something bigger in the 2030s. “We want to bring it out of quantum theory and labs and take it to actual photons from stars,” Lau says.


In recent years, scientists have investigated the possibility of using quantum principles to enable next-generation astronomy. The basic idea is that photons could be transferred between observatories as quantum states, which would allow for instantaneous transfers over greater distances. The key is to take advantage of quantum entanglement, a phenomenon where particles interact and share the same quantum state – despite being separated by considerable distances.