Experimental realization of quantum overlap tomography

Quantum tomography is a process of reconstructing and characterizing a quantum state using a series of collected measurements. In recent years, many physicists have been trying to use this process to learn more about quantum states, as this could also advance the development of quantum technologies.

Researchers at Nanyang Technological University in Singapore recently demonstrated quantum overlap tomography (QOT), a recently theoretically constructed subtype of quantum tomography, in an experimental setting. Their paper, published in Physical Review Lettersit could inform future quantum physics research by offering an efficient new tool to probe these systems.

“We experimentally implement QOT with a linear optical system and demonstrate its advantage compared to the widely accepted whole-state tomography,” Zhengning Yang, one of the researchers who conducted the study, told Phys.org. “QOT is a method for reconstructing subsystems of an unknown large quantum body state with a small data set, first proposed theoretically by Jordan Cotler and Frank Wilczek at Stanford and MIT.”

The recent work of Yang and his colleagues builds on a 2020 study by Cotler and Wilczek, who proposed that the state of unknown employees could be fully characterized by leveraging a series of single-qubit measurements, through a process they named QOT. The team at Nanyang Technological University wanted to turn this theoretical idea into reality in an experimental setting.

“We built an optical platform to reproduce a 4/6-qubit quantum state by reproducing individual photon qubits,” explained Yang. “The copies of states are then measured in a complete set of quantum bases. We then used the measurement data set to statistically estimate the quantum state with two different methods, whole state tomography (FST) and QOT, to compare which as well as they perform.”

The results of the researchers’ experiments were very promising, as they suggested that QOT is a more reliable method for characterizing quantum states than FST, the conventional quantum tomography process used to characterize core quantum states. Furthermore, QOT can accurately characterize quantum states using far fewer measurements.

“​​​​We found that QOT can obtain much more accurate results than FST with the same number of measurements without introducing apparent systematic errors,” Yang said.

The results collected by Yang and his colleagues show the remarkable ability of QOT to study quantum states. In the future, they could encourage the use of this quantum state characterization method in both research and industrial settings, for example helping the development of more advanced quantum computers or other quantum technologies.

“Going through all the works on QOT, we see that ‘overlap’ is a powerful tool to efficiently extract information from a quantum state,” Yang said. “So we now plan to find out how well it can be done to evaluate the whole system rather than just the subsystems. We hope that it will be the most effective quantum tomography protocol possible for most of the systems.”

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