Researchers from the Moscow Institute of Physics and Technology (MIPT), joined by a colleague from Argonne National Laboratory, have implemented an advanced quantum algorithm for measuring physical quantities using simple optical tools. The technology could allow for affordable linear optical sensors with high-performance characteristics, with applications in diverse research fields such as astronomy and biology. “We devised and constructed an optical scheme that runs the Fourier transform-based phase estimation procedure,” said study co-author Nikita Kirsanov from MIPT. “This procedure lies at the core of many quantum algorithms, including high-precision measurement protocols.” Until recently, no measurement tool could ensure precision above the so-called shot noise limit, which has to do with the statistical features inherent in classical observations. Quantum technology has provided a way around this, boosting precision to the fundamental Heisenberg limit, stemming from the basic principles of quantum mechanics. The LIGO experiment, which detected gravitational waves for the first time in 2016, shows it is possible to achieve Heisenberg-limited sensitivity by combining complex optical interference schemes and quantum techniques. Apparatus for measuring the position of an object using optical coherence alone. Courtesy of Nikita Kirsanov/MIPT. A specific arrangement of a very large number of linear optical elements — beam splitters, phase shifters, and mirrors — makes it possible to gain information about the geometric angles, positions, velocities, and other parameters of physical objects. The measurement involves encoding the quantity of interest in the optical phases, which are then determined directly. “This research is a follow-up to our work on universal quantum measurement algorithms,” said principal investigator Gordey Lesovik, who heads the MIPT Laboratory of the Physics of Quantum Information Technology. “In an earlier collaboration with a research group from Aalto University in Finland, we experimentally implemented a similar measurement algorithm on transmon qubits.” The experiment showed that despite the large number of optical elements in the scheme, it is nevertheless tunable and controllable. According to the theoretical estimates provided in the paper, linear optics tools are viable for implementing even operations that are considerably more complex. “The study has demonstrated that linear optics offers an affordable and effective platform for implementing moderate-scale quantum measurements and computations,” Argonne Distinguished Fellow Valerii Vinokur said.