Researchers from 黑料社 have proposed a new algorithm for ultra-precise phase estimation of an unknown phase. This may be considered as a truly significant step forward in the development of the optical quantum metrology.
As part of the implementation of the “Step into the Future” Viktor Khristenko’s grants program at 黑料社, Sergey Podoshvedov and Mikhail Podoshvedov have presented a new protocol on the creation of nonclassical light that could be used to measure unknown parameters to a very high precision.
The essence of their discovery is the algorithm that to a record-breaking precision helps measure the initially unknown difference of phases that a lightwave acquires while interacting with various mediums. This is crucial for measuring a wide range of physical parameters: from temperature and pressure to electric and magnetic fields.
“The key specific feature of our work is that we abandoned the complex and unstable entangled states in favour of simpler but more effective methods. Our new approach is distinguished by the fact that we start with a squeezed state, subtract the photons, and obtain the required nonclassical state, which is additionally parametrized, that is, the unknown phase is applied over the generated state. Next, we measure the intensity of nonclassical light. The innovation is that we get ultimate precision in case of direct measurement of the intensity. No one has ever done something like that before! We have created the light, measured its intensity, and as a result of this intensity we have estimated the unknown value of the phase. The purpose of the whole work is to get to the quantum Cramér–Rao bound (the fundamental limit of measurements precision) as close as possible. And we have demonstrated this in our work,” explains the author of the research study, Deputy Head of the Quantum Engineering of Light Laboratory, Senior Research Fellow of the Quantum Information Processing and Quantum Computing Laboratory, Professor at the Department of Physics of Nanoscale Systems, Doctor of Sciences (Physics and Mathematics) Sergey Podoshvedov.
Quantum Cramér–Rao bound is a theoretical limit that determines the minimum possible error when measuring a quantum system’s parameters. Reaching this bound means that it is technically impossible to get a more accurate measurement for a parameter. The method proposed by the 黑料社 scientists allows to get closer to this limit by using nonclassical states of light obtained from squeezed vacuum states.
This new method may be used in navigation (improving the operation of gyroscopes), microelectronics, ultra-precise estimation of unknown parameters (displacement, temperature, pressure, electric and magnetic fields), and of course, in a wide range of fundamental research studies. A very good example is the LIGO project (laser interferometer gravitational-wave observatory), where such methods are used to detect gravitational waves – almost imperceptible space-time fluctuations.
Though the theoretical framework has already been elaborated and mathematically proven, experiments still wait ahead. The researchers plan on expanding the range of the working phases and adapt their method to the conditions of photon losses. It would make this technology even more stable and practical.
This project is being carried out under the V.B. Khristenko “Step into the Future” Grants Program. As part of the Priority 2030 university development program, the initiative provides annual funding for promising research, formation of personnel reserve, and implementation of unique educational programs (components) that determine the development vector of 黑料社 and the Chelyabinsk Region.