Tiny quantum memories may help overcome a key obstacle in optical interferometry—loss of precious photons—by letting telescopes work in unison across long distances. A Harvard-led proof-of-concept experiment linked two “telescopes” 6 meters apart using a 1.5-k
Night sky or lab bench. the problem starts the same way: by the time light from a distant star makes it through Earth’s thick atmosphere and into a telescope. most of it is gone. Even when it arrives, optical systems still lose precious photons, blurring the picture. For astronomers, the answer has long been to build bigger hardware—larger mirrors and more sensitive detectors. But there’s a hard stop in both physics and budgets.
Radio astronomers learned to work around that stop using interferometry. coordinating arrays of smaller telescopes so their combined timing and spacing act like one enormous observatory. In visible light. optical interferometers were invented more than a century ago. yet scaling up across long baselines has remained far harder because getting enough light from one telescope to another is brutally inefficient.
A new quantum approach is trying to fix that bottleneck by holding onto photons with quantum memories—small storage systems that can preserve information without simply discarding it along the way. “I think this could really become a very exciting area where one could do things which classical systems just cannot do. ” says Mikhail Lukin. a physicist at Harvard University overseeing the new research.
Quantum networking as an idea isn’t new. But Lukin’s group began building the foundations for a robust network two years ago. and this year reached a first milestone: team member Maxim Sirotin. a doctoral student at the Massachusetts Institute of Technology. presented the group’s first “proof-of-concept” experiment at the American Physical Society’s Global Physics Summit. A paper describing the result appeared in Nature in February.
“As soon as we realized that we had sufficiently good quantum memories, we wanted to apply it to a real problem,” Sirotin says.
The experiment is designed to emulate telescopes. It uses two quantum receivers separated by six meters, connected by a 1.5-kilometer-long spooled optical fiber. Through that fiber, a weak laser is beamed. At each receiver. a quantum memory chip—built from an atomic-scale defect in a tiny diamond. a so-called silicon vacancy—stores photons’ information. The storage works by encoding the photon information as variations in the spins of an electron and a silicon atom. In this setup. the electron and nucleus inside the atom are each considered qubits. the quantum equivalent of classical computing bits.
The key step comes before measurement. The two quantum memory chips are entangled via light signals before the weak laser beam is measured. That preparation lets the researchers retrieve an interference pattern from both receivers. recreating what two “telescopes” could do when their outputs are combined.
In theory, the same method could be extended beyond a lab laser. Rather than relying on piped-in light. the team’s interference approach could be achieved with starlight—light beamed into the system from real celestial sources—so that small telescopes separated by long distances could collaborate. If the technique reaches the field. two small telescopes separated by 1.5 kilometers could produce image resolution comparable to a single telescope with a 1.5-kilometer-wide mirror. And if astronomers increase the baseline between small telescopes further, the effective “aperture” could expand too.
That matters for targets that demand extreme precision. The Harvard research team says the approach could help astronomers hoping to catch glimpses of exoplanets, and it could also support a more precise understanding of the motions and sizes of distant stars.
Even so, bringing it to the sky remains a distant milestone. The team notes that using its system “on the sky” to create optical interferometric images of actual celestial targets remains a far-off goal.
Outside experts see what’s being attempted—and the novelty in how it’s being attempted. “I would say it’s a breakthrough. ” says John Monnier. an astronomer studying interferometric techniques at the University of Michigan. who was not involved in the new study. “This is really a completely new way to make interferometers work.”.
Monnier also points to the work still ahead. Before quantum-enhanced optical interferometers can be practical for astronomical applications, many hurdles must be overcome. Building the infrastructure for a sufficiently large optical interferometer might take decades. he says. describing the current moment as the “fun early days” of testing multiple different technological approaches.
Lukin frames the result the same way: “People are now really starting to think what quantum machines can do. What we’ve done is a proof of concept. It’s not practical so far, but it really shows a path to a new class of applications.”
quantum astronomy optical interferometry quantum memories silicon vacancy silicon vacancy diamond entanglement telescopes exoplanets Harvard University Nature