A team of researchers from the University of Ottawa’s Nexus for Quantum Technologies Institute (NexQT) [1], led by Dr. Francesco Di Colandrea and supervised by Professor Ebrahim Karimi, has developed an innovative method for assessing the performance of quantum circuits. This groundbreaking advancement, recently published in the esteemed journal npj Quantum Information, marks a significant progress in the realm of quantum computing.

Figure 1. FQPT compared with traditional maximum likelihood (ML) methods. (Credit: University of Ottawa)

Figure 1 shows the schematic of a high-dimensional quantum photonics system generation and implementation of Fourier quantum process tomography (FQPT) compared with traditional maximum likelihood (ML) methods.

In the fast-developing field of quantum technologies, ensuring the reliability and functionality of quantum devices is paramount. Accurately and swiftly characterizing these devices is essential for their seamless integration into quantum circuits and computers, influencing both fundamental research and practical applications.

Characterization is crucial for verifying device operations, especially when anomalies or errors occur. Identifying and addressing these issues is vital for the advancement of future quantum technologies.

Historically, scientists have used Quantum Process Tomography (QPT) [2], a method requiring a large number of “projective measurements” to fully reconstruct a device’s operations. However, the number of measurements needed in QPT scales quadratically with the operation's dimensionality, posing significant experimental and computational challenges, particularly for high-dimensional quantum information processors.

The University of Ottawa team has introduced an optimized method called Fourier Quantum Process Tomography (FQPT). This technique enables the complete characterization of quantum operations with a minimal number of measurements. Instead of numerous projective measurements, FQPT employs the Fourier transform to perform a portion of the measurements in two different mathematical spaces. The physical relationship between these spaces enhances the information extracted from single measurements, drastically reducing the number of measurements needed. For example, for processes with dimensions 2d (where d can be arbitrarily high), only seven measurements are required.

To validate their technique, the researchers conducted a photonic experiment using optical polarization to encode a qubit. The quantum process was implemented as a complex space-dependent polarization transformation, using advanced liquid-crystal technology. This experiment showcased the method’s flexibility and robustness.

“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,” said Francesco Di Colandrea, a postdoctoral fellow at the University of Ottawa.

This novel technique signifies a remarkable advancement in quantum computing. The research team is now working on extending FQPT to arbitrary quantum operations, including non-Hermitian and higher-dimensional implementations, and employing AI techniques to increase accuracy and reduce measurements. This new method represents a promising pathway for further advancements in quantum technology.

Source: University of Ottawa

References:

1. https://www.sciencedaily.com/releases/2024/06/240620194011.htm
2. https://www.eurekalert.org/news-releases/1048809

Cite this article:

Hana M (2024), University of Ottawa Researchers Pioneer Revolutionary Quantum Circuit Evaluation Technique, AnaTechMaz, pp. 138