As new quantum devices grow in size and complexity, it is crucial to develop reliable methods to certify and identify quantum resources that provide a real computational advantage, in order to outline the best way to use them.

A new study published in Science Advances has shown exactly how to certify the different quantum properties of integrated photonic devices of increasing complexity.

The study is the result of a long-standing scientific collaboration in the field of quantum certification between Sapienza in Rome, the Institute for Photonics and Nanotechnologies of the National Research Council in Milan (CNR-Ifn), the Politecnico di Milano and the International Iberian Nanotechnology Laboratory (INL).

Programmable optical integrated circuits are among the main candidate platforms for quantum information processing based on qubits. On the one hand, they allow experiments to be carried out to verify the fundamental properties of quantum mechanics, and on the other hand, they make it possible to implement devices for future applications in the fields of metrology, cryptography and computation.

The experiments, led by Fabio Sciarrino of Sapienza University and carried out at Sapienza's Quantum Lab, confirmed the presence of genuine quantum properties such as contextuality and coherence in a programmable optical integrated circuit. The methodology used was developed by the theoretical team led by Ernesto Galvão of the INL in Portugal.

"The use of a fully integrated and programmable photonic chip improves the accuracy and coherence of the characterisation process, offering the potential for implementing these devices in practical applications," says Dr Roberto Osellame, Research Director at CNR-IFN.

"Our work," adds Taira Giordani, a researcher at Sapienza University and member of the Quantum Lab team, "is the first experimental application of this technique to quantify the computational resources provided by quantum mechanics in optical devices".

However, the techniques developed also made it possible to verify the quantum advantage in practical applications such as quantum imaging. Imaging systems, thanks to certain quantum correlations, make it possible to achieve a resolution that goes beyond the limits of classical optics and find application in various fields of metrology and sensor technology.

"Our results," concludes Fabio Sciarrino, head of Quantum Lab at Sapienza University, "motivate research into new techniques for studying non-classical resources. We expect that this work will stimulate research into the future certification of optical devices that exploit increasingly complex quantum states of light".

This line of research is supported by the National Quantum Science and Technology Institute (NQSTI), Italy's funding for fundamental research on quantum technologies, the ERC Advanced Grant QU-BOSS, the Horizon Europe FoQaCiA project and Portugal's FCT - Fundação para a Ciência e a Tecnologia.

References: 

Experimental certification of contextuality, coherence, and dimension in a programmable universal photonic processor - Giordani T, Wagner R, Esposito C, Camillini A, Hoch F, Carvacho G, Pentangelo C, Ceccarelli F, Piacentini S, Crespi A, Spagnolo N, Osellame R, Galvão EF, Sciarrino F. - Sci Adv. 2023. doi: 10.1126/sciadv.adj4249

Further Information

Fabio Sciarrino 
Department of Physics
fabio.sciarrino@uniroma1.it