One of the biggest challenges for astronomers is capturing images of objects and phenomena that are difficult to see with optical (or visible) telescopes. This problem has been largely addressed by interferometry, a technique in which multiple telescopes collect light that is then combined to create a complete image.
Examples include the Event Horizon Telescope, which is drawing on observatories from around the world to capture the first images of the supermassive black hole (SMBH) at the center of the M87 galaxy and Sagittarius A* at the center of the Milky Way.
However, classical interferometry requires maintaining optical links between observatories, which imposes limitations and can result in drastically increased costs. In a recent study, a team of astrophysicists and theoretical physicists proposed how these limitations could be overcome through the use of quantum mechanics. Instead of relying on optical links, they propose how the principle of quantum entanglement could be used to share photos between observatories. This technique is part of a growing area of research that could one day lead to ‘quantum telescopes’.
The study was conducted by researchers from Brookhaven National Laboratory (BNL) and Stony Brook University in New York, New York. Additional support was provided by Stephen Vintskevich, a theoretical physicist and independent researcher currently based in the United Arab Emirates. The paper describing their findings recently appeared online and is under review for publication in the scientific journal optics.
In classic Michelson interferometry, a light beam is split in such a way that one beam hits a fixed mirror and the other hits a moving mirror. When the reflected rays are recombined, an interference pattern is created.
For astronomical purposes, the two beams are collected by two telescopes that are some distance apart (called baseline interferometry). However, despite its effectiveness, classical interferometry is subject to some limitations. Andrei Nomerotsky, astrophysicist at BNL and co-author of the paper, explained this universe today by email.
“Interferometry is a way to increase the effective aperture of telescopes and improve angular resolution, or astrometric precision,” he said. “The main difficulty here is maintaining the stability of this optical path with very high precision, which should be much smaller than the photon wavelength to preserve the photon’s phase. This limits practical baselines to a few hundred meters.”
goal of quantum astronomy
In recent years, scientists have explored the possibility of using quantum principles to enable next-generation astronomy. The basic idea is that photons could be transmitted between observatories without physical connections, which are expensive to build and maintain. The key is to use quantum entanglement, a phenomenon where particles interact and share the same quantum state – despite being separated by a deliberate distance.
Quantum telescopes were originally proposed by researchers Daniel Gottesman, Thomas Jennewein and Sarah Croke from the Perimeter Institute for Theoretical Physics and the Institute for Quantum Computing at the University of Waterloo.
The interferometer proposed by the BNL team borrows features from the Gottesman-Jennewein-Croke (GJC) proposal and the Narrabri Stellar Intensity Interferometer (NSII). Said Nomerotski:
“The proposal was to use an entangled photon source and use correlations of photon numbers in two stations, thereby largely eliminating the photon phase stability problem. The intensity interferometers are used to measure stellar diameters using a technique based on the Hanbury Brown-Twiss (HBT) effect of photon bunching. In our scheme we use the same effect, only its phase-dependent part, to measure the aperture angle between two stars, which may now be separated by a significant angle. On the other hand, Nomerotski said, the second star can also be viewed as a source of coherent photons for the first star, hence the connection to the Gottesman-Jennewein-Croke proposal.”
The team is developing a physical description, Nomerotski said, that would include both options. This could be generalized to multiple stations and quantum protocols to process quantum information in a “noisy” environment. To test their concept, the team built a benchtop version of the two-photon interferometer that used a narrow spectral line in two argon lamps (to simulate two stars). As predicted based on previous theoretical investigations, the team noted HBT peaks and channel correlations and measured their dependence on photon phase.
The main advantage of this technique is the improved angular resolution (the ability to see details in objects) in telescopes. But as Nomerotski explained, the long-term benefits could be immeasurable:
“There could be several scientific possibilities that would benefit from significant improvements in astrometric precision. To name a few: testing theories of gravity by direct imaging of black hole accretion disks, precision parallax and the cosmic distance ladder, mapping microlensing events, exoplanets, peculiar motions, dark matter and others.
“All of this is of course quite long-term and requires proof of principle and, importantly, improved sensitivity compared to what is achievable now. These improvements are based on advances in the development of quantum networks and quantum repeaters as in the original GJC proposal. Many of these developments are now being driven by companies for very different purposes and are well advanced, so they could become a reality in the foreseeable future.”
This proposal for two-photon interferometry is one of many proposals for quantum telescopes in recent years. Other examples include a proposal by an MIT team to combine interferometry with quantum teleportation to dramatically increase the resolution of observatories (without using larger mirrors). There is also the more recent idea of combining Stimulated Raman Adiabatatic Passage (STIRAP) and pre-distributed entanglement to create a virtual Very-Long Baseline Interferometry (VLBI) telescope the size of planet Earth.
These quantum techniques could enable observations at previously inaccessible wavelengths and more detailed studies of black holes, exoplanets, the solar system and the surfaces of distant stars. And as efforts to advance the technology behind quantum computing continue, applications are sure to spill over into other research areas (like quantum astronomy). As Nomerotski added:
“There are a lot of interesting conceptual ideas in this area, but most of them are theoretical and therefore quite futuristic. We believe our work is one of the few that addresses the experimental difficulties of the approach and we have made good progress there. Some of us will organize a one-day workshop, a side meeting ahead of the Quantum 2.0 conference in Denver in June, to gather these ideas.”
This article was originally published on universe today by Matt Williams. Read the original article here.