Quantum astronomy could make telescopes bigger and better than ever

Tiny quantum computers could lead to supersized telescopes

Advances in quantum technology could allow astronomers to bypass age-old problems that limit the size of optical observatories

By KR Callaway edited by Lee Billings

For light from stars and distant galaxies to reach and be detected by our telescopes, we must first defy all odds. Of the photons of light that avoid dust clouds and other deep space obstacles to reach our planet, most do not pass through Earth’s thick atmosphere, much less the loss-prone optics of a telescope. Astronomers increase these chances by building telescopes with larger light-collecting mirrors or detectors, which in turn collect more photons and provide sharper, clearer images. But the construction of ever-larger equipment quickly comes up against physical and economic obstacles which limit the size of any telescope and the sharpness of our cosmic views.

Radio astronomy has long relied on an esoteric workaround: using a technique called interferometry to make arrays of smaller telescopes act collectively as a single giant observatory. Using exquisite timing to track the arrival of photons from each telescope, virtually all of the light absorbed by the entire array can be combined to create interference patterns from which images can be extracted. And the greater the “baseline” separation between individual telescopes in an array, the higher the spatial resolution of the array’s resulting images will be; this allowed radio astronomers, for example, to construct networks with a baseline as big as the Earth itselfgaining sufficient resolution and sensitivity to draw the dark boundaries from the supermassive black hole to the distant heart of the Milky Way.

Optical interferometers were invented more than a century ago, but orchestrating and combining signals from multiple telescopes over long baselines has proven much more difficult to accomplish with visible light compared to the relative ease of working with radio waves. One of the main obstacles to making larger optical interferometers has been the loss of valuable photons along the path between them. However, quantum advances now reveal a possible way to solve this problem and create giant optical interferometers using tiny quantum storage systems—quantum memories-to retain incoming photons.

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“I think this could really become a very exciting area where we could do things that classical systems just can’t do,” says Mikhail Lukin, a physicist at Harvard University who is overseeing the new research.

The general idea of ​​​​use a quantum network Improvements in optical interferometry have been around for decades, but the challenge has been making one robust enough to receive and process these incoming photons. Lukin’s research group began creating the foundations for such a network two years ago; Earlier this year, team member Maxim Sirotin, a doctoral student at the Massachusetts Institute of Technology, presented the group’s first project “proof of concept” experiment at the American Physical Society World Physics Summit. An article describing the result appeared in Nature in February.

“As soon as we realized we had good enough quantum memory, we wanted to apply it to a real problem,” Sirotin says.

The team’s experiment involves two quantum receivers, used to emulate telescopes, separated by just six meters but connected by a 1.5 kilometer-long coiled optical fiber, through which a weak laser is sent. At each receiver, a quantum memory chip built from an atomic-scale defect in a tiny diamond – the so-called silicon vacancy– can store information from photons in the form of variations in the spins of an electron and a silicon atom. (In this configuration, the electron and the nucleus inside the atom are each considered qubitsthe quantum equivalent of classical computer bits.)

Tangle The two quantum memory chips via light signals before measuring the faint laser beam allow researchers to recover an interference pattern from the two “telescopes”, a feat that, in theory, could also be achieved with starlight.

If used in the field, the result would be that two small telescopes 1.5 kilometers apart could work together to create images as high resolution as those from a single telescope with a huge 1.5 kilometer wide mirror. The resolution could be further improved by increasing the baseline between the two small telescopes to emulate an even larger light-collecting surface. This technique could help astronomers hoping to capture glimpses of exoplanets or obtain a more precise understanding of the movements and sizes of distant stars. But the Harvard research team notes that using its “in-the-sky” system to create optical interferometric images of real celestial targets remains a distant goal.

Still, other experts are impressed. “I would say it’s a major breakthrough,” says John Monnier, an astronomer studying interferometric techniques at the University of Michigan who was not involved in the new study. “It’s really a whole new way to operate interferometers.”

Many obstacles still need to be overcome, Monnier warns, before quantum-enhanced optical interferometers become truly practical for astronomical applications. Building the infrastructure for a large enough optical interferometer could take decades, he says, adding that it’s still “fun early days” to try and test several different technological approaches.

“People are really starting to think about what quantum machines can do,” says Lukin. “What we’ve done is a proof of concept. It’s not practical yet, but it really shows the way to a new class of applications.”