New quantum technology could change how we study the universe

(ORDO NEWS) — A revolution is taking place in astronomy. In fact, we can say that there are several of them. Over the past ten years, exoplanet research has advanced significantly, gravitational wave astronomy has become a new field, and the first images of supermassive black holes (SMBHs) have been obtained.

A related field, interferometry, has also advanced incredibly 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 entirely new possibilities.

According to a recent study by scientists from Australia and Singapore, a new quantum technique could improve optical VLBI. It is known as Stimulated Raman Adiabatic Transition (STIRAP), which allows lossless transmission of quantum information.

Embedded in a quantum error correction code, this technique could allow VLBI observations to be made at previously inaccessible wavelengths. When integrated with next-generation instruments, this technique could enable more detailed studies of black holes, exoplanets, the solar system, and the surface of distant stars.

The study was led by Zixin Huang, Postdoctoral Research Fellow at the Center for Engineering Quantum Systems (EQuS) at Macquarie University in Sydney, Australia.

She was joined by Gavin Brennan, Professor of Theoretical Physics, Department of Electrical and Computer Engineering and Center for Quantum Technology, National University of Singapore (NUS), and Ingkai Ouyang, Senior Research Fellow, NUS Center for Quantum Technology.

In simple terms, interferometry combines light from different 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 astronomical radio sources (black holes, quasars, pulsars, star forming nebulae, etc.) are combined to create detailed images of their structure and activity.

In recent years, VLBI has provided the most detailed images of the stars orbiting Sagitarrius A* (Sgr A*), SMBH at the center of our galaxy. It also allowed astronomers from the Event Horizon Telescope (EHT) collaboration to get the first image of a black hole (M87*) and Sgr A* itself!

But as they pointed out in their study, classical interferometry is still hampered by a number of physical limitations, including information loss, noise, and the fact that the resulting light is typically quantum in nature (when the photons are entangled). By removing these limitations, VLBI can be used for much finer astronomical research.

Dr. Huang told Universe Today via email: “Modern long baseline imaging systems operate in the microwave range of the electromagnetic spectrum. To implement optical interferometry, all parts of the interferometer must be stable to within fractions of a wavelength of light so that light can.

This is very difficult to do over long distances: sources of noise can come from the instrument itself, thermal expansion and contraction, vibration, etc., and there are also losses associated with optical elements.

“The idea behind this line of research is to allow us to move into optical frequencies from the microwave range; these methods are equally applicable to the infrared range. We can already do long baseline interferometry in the microwave range.

However, in optical frequencies, this challenge becomes very difficult, since even the fastest electronics cannot directly measure the electric field fluctuations at these frequencies.”

The key to overcoming these limitations, according to Dr. Huang and her colleagues, is the use of quantum coupling techniques such as stimulated Raman adiabatic passage. STIRAP consists of using two coherent light pulses to transfer optical information between two applicable quantum states.

Applied to VLBI, Huang says, this will allow efficient and selective transfer of populations between quantum states without suffering from the usual problems of noise or loss.

As they describe in their paper (“Imaging Stars with Quantum Error Correction”), the process they envision involves the coherent coupling of starlight with “dark” atomic states that do not radiate.

The next step, Huang says, will be to couple 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, the same technique could allow for more detailed and accurate interferometry:

“In order to simulate a large optical interferometer, light must be collected and processed coherently, and we propose using quantum error correction to mitigate errors due to loss and noise in this process.”

“Quantum error correction is a rapidly developing field, mainly aimed at enabling scalable quantum computing in the presence of errors. Combined with pre-distributed entanglement, we can perform operations to extract the information we need from starlight while suppressing noise.”

To test their theory, the team considered a scenario in which two objects (Alice and Bob) separated by large distances collect astronomical light.

Each of them has pre-distributed entanglement and contains a “quantum memory” that light hits, and each prepares its own set of quantum data (qubits) in some QEC code. The resulting quantum states are then imprinted onto a common QEC code by a decoder that protects the data from subsequent noisy operations.

At the “encoder” stage, the signal is captured into quantum memory using the STIRAP technique, which allows the incoming light to be coherently coupled into a non-radiative state of the atom.

The ability to capture light from astronomical sources while taking into account quantum states (and eliminate quantum noise and information loss) would be a game changer in interferometry. Moreover, these improvements will have significant implications for other areas of astronomy, which are also undergoing revolutionary changes today.

“By switching to optical frequencies, such a quantum imaging network would improve image resolution by three to five orders of magnitude,” says Huang.

“It will be powerful enough to image small planets around nearby stars, details of solar systems, kinematics of stellar surfaces, accretion disks, and possibly details around black hole event horizons – none of which currently planned projects can’t resolve.”

In the near future, the James Webb Space Telescope (JWST) will use its advanced infrared imaging toolset to characterize exoplanet atmospheres like never before. The same applies to ground-based observatories such as the Extremely Large Telescope (ELT), the Giant Magellanic Telescope (GMT) and the Thirty Meter Telescope (TMT).

With their large primary mirrors, adaptive optics, coronagraphs and spectrometers, these observatories will enable direct imaging of exoplanets, providing valuable information about their surfaces and atmospheres.

By taking advantage of new quantum technologies and integrating them with VLBI, observatories will have another way to image some of the most inaccessible and hard-to-observe objects in our universe. The secrets this might uncover are sure to be (for the last time, I promise!) revolutionary!

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