Several years ago, physicists from the Centre for Quantum Optical Technologies and the Faculty of Physics of the University of Warsaw designed and built the first quantum memory in Poland, which was further developed into a quantum processor. “Our processor is based on a cloud of cold atoms. They can efficiently store and process infor­mation from light,” describes Michal Parniak, leader of the Quantum-Optical Devices Labora­tory. Now, PhD students Mateusz Mazelanik and Adam Leszczynski with Michal Parniak show that the device can solve real-world problems, which can’t be worked out with standard processors; it can be used as part of a super­resolution spectro­meter.

“We squeeze out as much information as we can from individual photons, so the measure­ment becomes very efficient,” says Mateusz Mazelanik. When we pass light through a solution or a substance, we’re able to determine what it’s composed of, i.e. whether it contains toxins. Such methods of spectro­scopy are used by biologists, physicists, astronomers, chemists and medical doctors on a daily basis. But there’s a signi­ficant limitation in spectro­scopy, the Rayleigh limit, which states that the information from light can’t be obtained with infinite precision. Some of the spectral lines can be so similar that traditional optical spectro­meters can’t differentiate between them.  

“Our device and algorithm allow us to not only gather information from light more effi­ciently, but it could also improve cramming information into light,” says Parniak. He notes that this idea could be used in telecommunications as well, where more efficient data storage and processing in light is becoming essential. Although there have been efforts to circumvent the limits of spectro­scopy, the researchers demons­trated how to do this in a completely uncon­ventional way – with the use of solutions from quantum information science. Because where classical physics can’t cope, quantum physics sometimes offers a whole spectrum of possi­bilities.

The physicists have built a device that can achieve a high resolution in spectro­scopy by using a small amount of light from a particular object. “Our spectro­meter beats the classical limit using 20 times less photons than the hypothetical traditional spectro­meter,” says Mazelanik, “But this is a remarkable achievement because a classical device with a similar reso­lution doesn’t actually exist.” The processor uses a cloud of several billion cooled rubidium atoms placed in a vacuum field, in order to carry out calcu­lations. If the atoms are placed in a magnetic field and illu­minated with a laser, they can be controlled to perform particular logic operations, such as process infor­mation on the spectrum of light that they are illuminated with.

Quantum effects are used in the calcu­lations, so calculations in the cold atomic cloud don’t substitute conven­tional binary calcu­lations, but add a new level of quality. “We came up with the idea of how a quantum processor could be used to solve particular problems in spectro­scopy,” says Michal Parniak. And he emphasises that, up until this point, finding practical appli­cations for quantum processors and designing devices like these with unique solu­tions in mind wasn’t at all obvious. (Source: U. Warsaw)

Reference: M. Mazelanik et al.: Optical-domain spectral super-resolution via a quantum-memory-based time-frequency processor, Nat. Commun. 13, 691 (2022); DOI: 10.1038/s41467-022-28066-5

Link: Centre for Quantum Optical Technologies, University of Warsaw, Warsaw, Poland