Quantum experiment with two slits gives hope for the creation of a telescope the size of the Earth

The new proposal will use quantum hard drives to combine light from multiple telescopes, allowing astronomers to create incredibly high-resolution optical images.

In the experiment with two slits, a photon passes through both slits at once and interferes with itself on the other side. The wave represents the possible positions of the photon; white indicates where it is most likely to be found. Astronomers hope to present optical telescopes as separate slits. Imagine being able to see the surface of an Earth-like planet orbiting another star, or watch a star burst into a black hole.


Such precise observations are currently not possible. However, scientists are proposing ways to quantum-mechanical linking optical telescopes around the world to see space in mind-blowing levels of detail.

The trick is to transfer fragile photons between telescopes so that the signals can be combined or “interfered” to create much sharper images. Researchers have already lot have known for years that this kind of interferometry is possible with a futuristic network of teleportation devices called the quantum Internet… However, while the quantum Internet is a distant dream, a new proposal outlines a scheme for implementing optical interferometry using quantum memory devices that are currently being developed.

This approach would represent the next phase of astronomers’ obsession with size. Wider mirrors create sharper images, so astronomers continually design larger telescopes and reveal more and more details of the cosmos. Today they are building an optical telescope with a mirror nearly 40 meters wide, 16 times the width (and therefore the resolution) of the Hubble Space Telescope. However, there is a limit to the growth possibilities of mirrors.

“We are not going to build a 100-meter telescope with one aperture. This is madness! – exclaims Lisa Prato, an astronomer at Lowell Observatory in Arizona. – So what is the future? The future belongs to interferometry ”.

Earth-sized telescope

Radio astronomers have been involved in interferometry for decades. The first in history picture black hole, published in 2019, was obtained by synchronizing signals received by eight radio telescopes scattered around the world. Collectively, the telescopes had the resolution of a single telescope with a mirror equal to the distance between them, that is, the effective telescope was the size of the Earth.

To capture this image, the radio waves entering each telescope were converted to accurate time-stamped data and stored. This data was later stitched together. This procedure is relatively straightforward in radio astronomy, since radio-emitting objects are usually extremely bright and radio waves are relatively large and therefore easy to align.

Optical interferometry is much more complex. The visible wavelengths are measured in hundreds of nanometers, which leaves much less room for errors when superimposing waves depending on the time they arrive at different telescopes. What’s more, optical telescopes capture photon-by-photon images from very dim sources. Such grainy signals cannot be stored on conventional hard drives without losing information vital to interferometry.

Astronomers were able to directly connect nearby optical telescopes with fiber optic cables – an approach that led to the first direct observation exoplanets. “However, connecting telescopes more than 1 kilometer or so is extremely cumbersome and expensive,” says Theo ten Brummelaar, head of CHARA Array, an optical interferometric array in California. “If there was a way to register photon events in an optical telescope using some kind of quantum device, it would be a great boon for science.”

Young’s slits

Joss Bland-Hawthorne and John Bartholomew from the University of Sydney and Matthew Sellars from Australian National University recently offered scheme for the implementation of optical interferometry using quantum hard disks.

The principle behind the new proposal dates back to the early 1800s, before the quantum revolution, when Thomas Jung developed an experiment to test if light is composed of particles or waves. Jung passed light through two closely spaced, separate slits and saw that a pattern of regular bright stripes had formed on the screen behind. He argued that this interference pattern arose from the fact that light waves from each slit extinguish each other and add up in different places.

And then things got weirder. Quantum physicists have found that the interference pattern for the two slits persists even if photons are sent to the slits one at a time. Point by point, they gradually create the same light and dark stripes on the screen. However, if someone can trace through which slit each photon passes, the interference pattern will disappear. Unperturbed particles behave only like waves.

Now imagine that you have two telescopes instead of two slits. When a single photon from space arrives at Earth, it can hit any telescope. Without measurement – as is the case with Young’s double slits – a photon is a wave that enters both slits.

Blend-Hawthorne, Bartholomew, and Sellars propose connecting a quantum hard disk to each telescope that can record and store the wave-like states of incoming photons without disturbing them. Over time, the hard drives are transferred to one location, where the signals are superimposed on each other to create an incredibly high resolution image.

Quantum memory

For this to work, quantum hard drives must store a lot of information over a long period. One of the turning points came in 2015 when Bartholomew, Sellars and colleagues have developed a storage device made of europium nuclei embedded in a crystal, which could store fragile quantum states for six hours, with the possibility of extending this period to several days.

Then, earlier this year, a team from the University of Science and Technology of China in Hefei demonstrated the ability to store photon data in similar devices and then read them out.

“It is very interesting and surprising to see that quantum information methods can be useful for astronomy,” said Zong-Quan Zhouwho was a co-author recently published articles. Zhou describes a world in which high-speed trains or helicopters quickly move quantum hard disks between distant telescopes. However, it remains to be seen if these devices can work outside of laboratories.

Bartholomew believes that hard drives can be protected from accidental electric and magnetic fields that disrupt quantum states. However, they also have to withstand pressure drops and acceleration. Researchers are also working to create hard drives that can store photons at different wavelengths – necessary for capturing images of space.

Not everyone thinks it will work. “In the long term, if these technologies are implemented in practice, they will need a quantum network,” says Mikhail Lukin, a specialist in quantum optics at Harvard University. Instead of physically transporting quantum hard drives, Lukin proposed a scheme that will rely on the quantum Internet – a network of devices called quantum repeaters that teleport photons between sites without disrupting their state.

Bartholomew counters, saying, “We have good reason to be optimistic about quantum hard drives. I think that within 5-10 years we will be able to see preliminary experiments in which we will actually begin to observe real [астрономические] sources “. On the contrary, the creation of the quantum Internet, in the words of Bland-Hawthorne, “is decades away from reality.”

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