There is a revolution going on in astronomy. In fact, you could say there are several. Over the past ten years, studies of exoplanets have made considerable progress, gravitational wave astronomy emerged as a new field, and the first supermassive images black holes (SMBH) were captured.
A related field, interferometry, has also made incredible progress with highly sensitive instruments and the ability to share and combine data from observatories around the world. In particular, the science of very long baseline interferometry (VLBI) opens up whole new realms of possibilities.
According to a recent study by Australian and Singaporean researchers, a new quantum technique could improve optical VLBI. It’s known as Stimulated Raman adiabatic transition (STIRAP), which allows lossless quantum information transfer.
When imprinted in a quantum error-correcting code, this technique could enable VLBI observations in previously unreachable wavelengths. Once integrated into next-generation instruments, this technique could enable more detailed studies of black holes, exoplanets, the solar system and the surfaces of distant stars.
The research was led by Zixin Huang, a postdoctoral researcher at Center for Quantum Systems Engineering (EQuS) at Macquarie University in Sydney, Australia. She was joined by Gavin Brennan, a professor of theoretical physics in the Department of Electrical and Computer Engineering and the University’s Center for Quantum Technologies. national university of singapore (NUS) and Yingkai Ouyang, Principal Investigator at NUS Center for Quantum Technologies.
To put it clearly, the interferometry technique involves combining light from various telescopes to create images of an object that would otherwise be too difficult to resolve.
Very long baseline interferometry refers to a specific technique used in radio astronomy where signals from an astronomical radio source (black holes, quasars, pulsarstar-forming nebulae, etc.) are combined to create detailed images of their structure and activity.
Over the past few years, VLBI has provided the most detailed images of the stars orbiting Sagittarius A* (Sgr A*), the SMBH at the center of our galaxy. It also allowed astronomers with the Event Horizon Telescope (EHT) Collaboration to seize first image of a black hole (M87*) and Sgr A* himself!
But as they pointed out in their study, classical interferometry is still hampered by several physical limitations, including loss of information, noise, and the fact that the light obtained is usually quantum in nature (where photons are entangled ). By addressing these limitations, the VLBI could be used for much finer astronomical surveys.
Dr Huang told Universe Today via email: “State-of-the-art basic imaging systems operate in the microwave band of the electromagnetic spectrum. To do optical interferometry, you need that all parts of the interferometer are stable within a fraction of a wavelength of light, so light can interfere.
This is very difficult to do over large distances: sources of noise can be from the instrument itself, thermal expansion and contraction, vibration, etc. ; and on top of that there are losses associated with the optical elements.
“The idea of this line of research is to allow us to move into the optical frequencies of the microwaves; these techniques also apply to the infrared. We can already do large-baseline interferometry in the microwaves. waves. However, this task becomes very difficult at optical frequencies, because even the fastest electronics cannot directly measure electric field oscillations at these frequencies.”
According to Dr. Huang and his colleagues, the key to overcoming these limitations is to use quantum communication techniques like stimulated Raman adiabatic switching. STIRAP consists of using two coherent light pulses to transfer optical information between two applicable quantum states.
When applied to VLBI, Huang said, it will enable efficient and selective population transfers between quantum states without suffering from the usual noise or loss issues.
As they describe in their article (“Star imaging with quantum error correction“), the process they envision would involve coherently coupling starlight into “dark” atomic states that do not radiate.
The next step, Huang said, is to couple the light with quantum error correction (QEC), a technique used in quantum computing to protect quantum information from errors due to decoherence and other “quantum noise”.
But as Huang points out, this same technique could allow for more detailed and precise interferometry:
“To mimic a large optical interferometer, light must be collected and processed coherently, and we propose to use quantum error correction to smooth out errors due to loss and noise in this process.
“Quantum error correction is a rapidly developing field primarily focused on enabling scalable quantum computing in the presence of errors. In combination with predistribution tanglewe can perform the operations that extract the information we need from the starlight while removing the noise.”
To test their theory, the team considered a scenario where two facilities (Alice and Bob) separated by long distances collect astronomical light.
Each shares a pre-distributed tangle and contains “quantum memories” in which light is captured, and each prepares its own set of quantum data (qubits) in a certain QEC code. The received quantum states are then printed on a shared QEC code by a decoder, which protects the data from subsequent noisy operations.
In the “encoder” stage, the signal is captured in the quantum memories via the STIRAP technique, which allows incoming light to be coherently coupled into a non-radiative state of an atom.
The ability to capture light from astronomical sources that account for quantum states (and eliminate quantum noise and information loss) would be a game-changer for interferometry. Moreover, these improvements would have important implications for other areas of astronomy that are also revolutionizing today.
“By moving to optical frequencies, such a quantum imaging network will improve imaging resolution by three to five orders of magnitude,” Huang said.
“It would be powerful enough to image small planets around nearby stars, details of solar systems, stellar surface kinematics, accretion disks and potentially details around black hole event horizons – no projects currently planned. cannot solve.”
In the near future, the James Webb Space Telescope (JWST) will use its advanced suite of infrared imaging instruments to characterize exoplanet atmospheres like never before. The same goes for ground-based observatories like the Extremely large telescope (ELT), Giant Magellan Telescope (GMT), and Thirty meter telescope (TMT).
Between their large primary mirrors, their adaptive optics, their coronagraphs and their spectrometers, these observatories will allow direct imaging studies of exoplanets, providing valuable information on their surfaces and atmospheres.
By taking advantage of new quantum techniques and integrating them into VLBI, observatories will have another way to capture images of some of the most inaccessible and hard-to-see objects in our Universe. The secrets it might reveal will certainly (last time, promise!) be groundbreaking!
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