Quantum memory sidesteps photon loss that limits conventional methods
For generations, astronomers have stretched the boundaries of sight by linking telescopes together, yet visible light has always resisted the long-distance partnerships that radio waves permit so freely. Now a team at Harvard University has demonstrated that quantum memory — devices capable of holding the fragile state of a single photon — can bridge that gap through entanglement rather than transmission, effectively decoupling resolution from the physical limits of light travel. Presented in Denver at the Global Physics Summit, the experiment achieved a combined telescope diameter more than four times that of the world's largest optical interferometer, suggesting that the ceiling on human vision of the cosmos may be far higher than previously imagined.
- Optical interferometry has been bottlenecked for decades by photon loss — the further light must travel between telescopes, the more of it disappears before it can be combined into a useful image.
- Harvard researchers bypassed this constraint entirely by entangling two diamond-chip quantum memories, then using quantum teleportation to reconstruct photon states across 1.5 kilometres of fibre without ever physically routing the light.
- The experiment, conducted with two telescopes just six metres apart in the same building, simulated a baseline that outperformed CHARA's 330-metre array by a factor of four — a result that reframes what 'distance between telescopes' even means.
- The fragility that makes quantum states difficult to store is the same property that makes them immune to the cumulative losses plaguing conventional systems, turning a fundamental weakness into a structural advantage.
- If the technique scales to multiple telescopes and greater separations, astronomers could assemble optical arrays measured in kilometres, resolving details in distant galaxies and probing depths of the universe currently beyond reach.
Astronomers have long worked around the hard physical limits on telescope size by linking separate instruments together — a technique called interferometry that makes them behave as a single, vastly larger eye. Radio astronomers mastered this approach, famously producing the first image of a black hole by coordinating receivers across the entire planet. Optical telescopes, however, have proven far harder to connect. The largest optical interferometer in operation, CHARA at Mount Wilson Observatory, achieves an effective diameter of 330 metres by combining six telescopes — impressive, but still constrained by how much light is lost as it travels between instruments.
Researchers at Harvard University have now demonstrated a fundamentally different path. Rather than routing actual photons between telescopes, they equipped each instrument with a quantum memory built from a nanoscale diamond chip containing a silicon vacancy — a carefully engineered defect where an electron spin and a nuclear spin each act as a qubit. Before observations began, the nuclear spins of the two chips were entangled using light signals, forging a quantum link between them.
When simulated starlight arrived at a telescope, an incoming photon's quantum state was absorbed by the local electron spin, then transferred to the entangled nuclear spin. Because that spin was quantum-mechanically connected to its counterpart in the second telescope, the photon's information could be reconstructed at the distant location through quantum teleportation — producing an interference pattern as though the light had physically made the journey.
The practical gain is considerable. Conventional systems like CHARA lose photons along the path between telescopes, and that loss sets a hard ceiling on how far apart instruments can be placed. The quantum memory method avoids transmission losses entirely, and the Harvard experiment — using telescopes connected by 1.5 kilometres of fibre — achieved an effective combined diameter more than four times CHARA's. Scaled to multiple telescopes and longer baselines, the approach could yield optical arrays spanning kilometres, opening details in distant galaxies and corners of cosmic history that remain invisible to any instrument operating today.
Astronomers have long faced a stubborn problem: the bigger the telescope, the sharper the image, but there are hard limits to how large a single instrument can be built. For decades, they've worked around this constraint by linking multiple telescopes together, a technique called interferometry that lets separate instruments act as though they were parts of one enormous eye. Radio astronomers perfected this approach—the Event Horizon Telescope collaboration used it to photograph a black hole in 2017, effectively creating a receiver the size of Earth itself. But optical telescopes, which observe visible light, have proven far more difficult to link this way. The largest optical interferometer in operation, called CHARA, combines six telescopes at Mount Wilson Observatory in California to achieve an effective diameter of 330 meters. That's impressive, but it remains constrained by the physics of how light travels between instruments.
Now researchers at Harvard University have demonstrated a fundamentally different approach, one that could shatter those constraints. Instead of physically routing light signals between telescopes to create interference patterns, they use quantum memory—devices that store the quantum state of individual photons—to combine observations through quantum entanglement. The method was presented at the Global Physics Summit in Denver, and the results suggest a path toward optical arrays with far greater effective diameters than anything currently possible.
Understanding quantum memory requires grasping what makes it different from ordinary storage. A quantum memory captures and preserves the quantum state of a photon or other elementary particle, holding that information until it's needed. The catch is that quantum states are fragile; they collapse easily, and the act of reading them destroys the information. This makes quantum memories inherently volatile—they can't hold data indefinitely the way a hard drive can. But that fragility is precisely what makes them useful for this astronomical application.
The Harvard team's experiment used two telescopes separated by 1.5 kilometers of fiber optic cable, though they were physically located just six meters apart in the same building. Each telescope was equipped with a quantum memory made from a diamond chip engineered at the nanometer scale. The key feature was a silicon vacancy—a defect where two carbon atoms in the diamond lattice had been replaced by a silicon atom and a hole. Within this defect, an electron spin and a nuclear spin each functioned as a qubit, the basic unit of quantum information. Before observations began, the researchers entangled the nuclear spins of the two diamond chips using light signals, creating a quantum connection between them.
During the experiment, a weak laser beam simulated starlight entering both telescopes. When a photon arrived at the first telescope, it interacted with an electron in that quantum memory. The electron spin then transferred the photon's quantum information to the nuclear spin. Because that nuclear spin was entangled with the nuclear spin in the second quantum memory, the researchers could reproduce the photon's quantum state at the distant location by measuring the electron and nuclear spins. This process—quantum teleportation—allowed them to combine signals from the two telescopes and generate an interference pattern as if the photons had been physically routed between them.
The advantage over conventional interferometry is substantial. In systems like CHARA, light must travel from each telescope to a central location where it's combined. This journey causes photon loss—some light is absorbed or scattered along the way. That loss fundamentally limits how far apart the telescopes can be; beyond a certain distance, too many photons are lost to create a usable interference pattern. The quantum memory approach sidesteps this problem entirely. By storing and teleporting quantum information rather than transmitting actual photons, the system avoids the losses that plague conventional methods. The two telescopes in the Harvard experiment, separated by 1.5 kilometers of fiber, achieved an effective combined diameter more than four times larger than CHARA's 330 meters.
The implications are striking. If this technique can be scaled up to multiple telescopes and longer distances, it could enable optical interferometry arrays with effective diameters of kilometers or more. That would translate directly into sharper images and the ability to observe fainter, more distant objects. Astronomers could resolve details in distant galaxies that are currently invisible, peer deeper into the universe's history, and potentially detect phenomena that remain hidden to today's instruments. The quantum memory approach doesn't replace conventional telescopes; rather, it offers a way to multiply their collective power by linking them in ways that were previously impossible.
Citações Notáveis
Quantum memories can be used to create low loss and high effective diameter arrays of optical telescopes to increase the resolution of the effective telescope and let us see deeper into our universe.— Harvard researchers, presented at Global Physics Summit in Denver
A Conversa do Hearth Outra perspectiva sobre a história
So quantum memory is just storage, like a hard drive?
Not quite. A hard drive holds data passively—you can read it a thousand times and it stays the same. Quantum memory holds the quantum state of a particle, which is fragile. The moment you measure it, the state collapses. It's volatile by nature, which sounds like a weakness, but for this application it's actually the point.
Why would you want something that disappears when you read it?
Because you're not trying to preserve the information forever. You're trying to synchronize two distant telescopes in a way that avoids losing photons in transit. The quantum state gets teleported, not transmitted. The information never travels as light through fiber; it travels as quantum entanglement.
And that's faster or more efficient?
Neither, really. It's lossless. When you send actual photons down a fiber, some get absorbed or scattered. Over long distances, you lose too much signal. With quantum memory and entanglement, you avoid that loss entirely. You can link telescopes that are kilometers apart and still combine their observations cleanly.
So this is just about distance?
Distance is part of it, but the real payoff is resolution. Bigger effective diameter means sharper images. The Harvard experiment achieved four times the baseline of the largest optical interferometer in existence. Scale that up, and you're looking at the ability to see things we can't see now.
What's the catch?
The technology is still experimental. Diamond chips with silicon vacancies, quantum entanglement between distant qubits—it's all cutting edge. Making it work reliably, scaling it to many telescopes, integrating it with real observatories—that's years of work. But the physics works. The proof is there.