An international group of researchers from the University of Ottawa's Nexus for Quantum Technologies Institute, led by Dr. Francesco Di Colandrea and Ebrahim Karimi, Associate Professor of Physics, has created a novel method for assessing the performance of quantum circuits. This important development marks a major achievement in the field of quantum computing. This study was published in the journal npj Quantum Information.
The research team in their laboratory. From left to right: Professor Karimi, Francesco Di Colandrea, Nazanin Dehghan, and Allesio D’Errico. Image Credit: University of Ottawa
Ensuring the operation and dependability of quantum devices is crucial in the quickly developing field of quantum technologies. High-speed and accurate characterization of these devices is necessary for their effective integration into quantum circuits and computers, which will influence fundamental research and real-world applications.
When a device displays anomalies or mistakes, characterization is important to ascertain whether it performs as planned. It is imperative to recognize and resolve these problems to progress the development of upcoming quantum technologies.
To fully reconstruct a device's activities, scientists have depended on Quantum Process Tomography (QPT), a technique that calls for many “projective measurements.” Unfortunately, in QPT, the number of measurements needed scales quadratically with the dimensionality of the operations. This presents serious computational and experimental difficulties, particularly for high-dimensional quantum information processors.
Fourier Quantum Process Tomography (FQPT) is an optimal technology that was developed by a research team at the University of Ottawa. With only a few measurements, this technique enables the complete characterization of quantum operations.
Rather than carrying out an extensive series of projective measurements, FQPT performs a subset of the measurements in two distinct mathematical spaces using a well-known Fourier transform map.
The physical relationship between these regions improves the information that can be gleaned from a single measurement, dramatically lowering the number of measurements required. For processes with dimensions 2d, where d can be arbitrarily high, just seven measurements are needed.
To confirm their method, the researchers used optical polarization to encode a qubit in a photonic experiment. The quantum process was achieved using cutting-edge liquid-crystal technology as a complicated space-dependent polarization change. This experiment illustrated the method's adaptability and stability.
The experimental validation is a fundamental step to probe the technique’s resilience to noise, ensuring robust and high-fidelity reconstructions in realistic experimental scenarios.
Dr. Francesco Di Colandrea, Postdoctoral Fellow, University of Ottawa
This new method is an excellent development in the field of quantum computing. The research team is currently focusing on implementing AI approaches to reduce measurement errors and boost accuracy and expanding FQPT to arbitrary quantum operations, including non-Hermitian and higher-dimensional implementations. This novel method offers a viable path forward for developing quantum technologies.
Journal Reference:
Colandrea, D. F., et al. (2024) Fourier Quantum Process Tomography. npj Quantum Information. doi.org/10.1038/s41534-024-00844-7.