Tiny quantum computers could lead to supersized telescopes
Advances in quantum technology might allow astronomers to circumvent age-old issues that limit the size of optical observatories
A laser shoots into the night sky from an 8.2-meter optical telescope at the European Southern Observatory’s Paranal Observatory in Chile. In the future, quantum technology could allow arrays of optical telescopes to work in unison, effectively acting as a single giant observatory.
Alberto Ghizzi Panizza/Science Photo Library/Getty Images
Light from distant stars and galaxies faces significant challenges to be captured by telescopes on Earth. Many photons are blocked by cosmic dust clouds, and even fewer penetrate Earth’s dense atmosphere and a telescope’s imperfect optics. To improve the odds of capturing these elusive photons, astronomers construct telescopes with larger mirrors and detectors to gather more light, resulting in sharper images. However, the physical and financial constraints of building increasingly larger telescopes limit their size and the clarity of the observations.
Radio astronomy has long utilized a technique known as interferometry, which allows multiple smaller telescopes to function as a single large observatory. By meticulously timing the arrival of photons at each telescope, the collected light can be combined into interference patterns from which images are derived. The greater the distance between individual telescopes in an array, known as the “baseline,” the higher the spatial resolution of the images produced. This method has enabled radio astronomers to create arrays with baselines as large as Earth, achieving the resolution necessary to map the edges of the Milky Way’s supermassive black hole.
Although optical interferometers were developed over a century ago, coordinating and merging signals from multiple telescopes over long distances is more challenging with visible light than with radio waves. A significant hurdle in expanding optical interferometers is the loss of photons between telescopes. Recent advancements in quantum technology offer a potential solution, enabling the creation of large optical interferometers through the use of tiny quantum storage systems, known as quantum memories, to store incoming photons.
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“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.
The concept of enhancing optical interferometry through a quantum network has been considered for years, but the challenge has been to develop a system capable of reliably handling incoming photons. Lukin’s team embarked on building the foundation for such a network two years ago. Earlier this year, Maxim Sirotin, a doctoral student at the Massachusetts Institute of Technology, presented their initial proof-of-concept experiment at the American Physical Society’s Global Physics Summit. Their findings were published 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.
In their experiment, two quantum receivers stand in for telescopes and are placed six meters apart but connected by 1.5 kilometers of spooled optical fiber, through which a weak laser beam is sent. Each receiver contains a quantum memory chip made from an atomic-scale defect in a tiny diamond, termed a silicon vacancy, capable of storing photon information as variations in the spins of an electron and a silicon atom. In this configuration, the electron and nucleus within the atom function as qubits, the quantum version of classical computing bits.
By entangling the two quantum memory chips using light signals before measuring the laser beam, researchers can extract an interference pattern from both “telescopes.” This method, in theory, could also be applied to starlight.
If applied practically, this would enable two small telescopes separated by 1.5 kilometers to generate images with the same resolution as a single telescope equipped with a large 1.5-kilometer-wide mirror. Increasing the baseline between the small telescopes could further enhance resolution, simulating a larger light-gathering surface. This approach could be valuable for astronomers aiming to observe exoplanets or better understand the movements and dimensions of distant stars. However, the Harvard team acknowledges that applying their system to create optical interferometric images of actual celestial targets remains a distant goal.
Despite the challenges, the research has garnered attention. “I would say it’s a breakthrough,” comments John Monnier, an astronomer specializing in interferometric techniques at the University of Michigan, who was not part of the study. “This is really a completely new way to make interferometers work.”
Monnier cautions that significant obstacles must be surpassed before quantum-enhanced optical interferometers can be utilized for astronomical purposes. Establishing the infrastructure for a large optical interferometer could take decades, he notes, adding that these are still the “fun early days” of exploring and testing various technological methods.
“People are now really starting to think what quantum machines can do,” Lukin says. “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.”
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