Quantum Processor Improves Spectroscopy Measurements

Researchers from the University of Warsaw are applying the first quantum processor built in Poland to spectroscopy. A team at the university has demonstrated how quantum information processing can efficiently provide information on matter hidden in light.

The current work stems from a collaboration several years ago, in which 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. The scientists have since developed that technology into a quantum processor.

A research team in Poland has designed a quantum processor, as well as a superresolution spectroscopy system that uses the processor as a component. The spectroscopy system can achieve a high resolution (15 kHz, or 40 parts per trillion) by using a small amount of light from a particular object. The work has implications for telecommunications — a sector in which more efficient data storage and processing in light is becoming essential. Here, the experimental setup with laser-cooled rubidium atoms, which process the quantum data in visible light, is shown on the left. At right is the experimental setup of the laser beam, which programs quantum operations carried out in light trapped inside the atoms. Courtesy of the University of Warsaw.

“Our processor is based on a cloud of cold atoms. They can efficiently store and process information from light,” said Michal Parniak, leader of the Quantum-Optical Devices Laboratory. The processor uses a cloud of several billion cooled rubidium atoms placed in a vacuum field to carry out calculations. If the atoms are placed in a magnetic field and illuminated with a laser, they can be controlled to perform logic operations, such as processing information on the spectrum of light they are illuminated with.

“We came up with the idea of how a quantum processor could be used to solve particular problems in spectroscopy,” Parniak said.

Ph.D. students Mateusz Mazelanik and Adam Leszczynski, with the help of Parniak, showed that the device can solve real-world problems that cannot be worked out with standard processors. Specifically, the device can be used as part of a superresolution spectrometer.

The device the team built can achieve a high resolution (15 kHz, or 40 parts per trillion) 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,” Mazelanik said. “But this is a remarkable achievement because a classical device with a similar resolution doesn’t actually exist.”

There is still a significant limitation to spectroscopy known as the Rayleigh limit, which states that the information from light can’t be obtained with infinite precision. Some of the signals of the spectrum, known as 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,” Parniak said. He noted that the idea could be used in telecommunications as well, where more efficient data storage and processing in light is becoming essential.

While there have been efforts to circumvent the limits of spectroscopy, the researchers of the University of Warsaw demonstrated how to do this in an unconventional way — with the use of solutions from quantum information science. Where classical physics falls short, quantum physics can open a range of possibilities.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-022-28066-5).