Important step towards on-chip quantum simulators

Monday 01 Jul 19

Scientists from the DNRF Centre for Silicon Photonics for Optical Communications (SPOC), at DTU and the Centre for Nanoscience and Quantum Information (NSQI) at Bristol University have collaborated on creating a silicon photonic chip, which demonstrates a simulation task that classical computers find extremely hard to do (and for large complexity even impossible), but which a quantum simulator can easily perform. The principle is experimentally proven using 4 photon pairs on a chip, and a theoretical consideration suggests that this principle is scalable to more than 48 photons, entering the so called quantum supremacy region, where quantum technology outperforms classical technology.

The Paper on this photonic quantum simulator on a silicon chip came out in Nature Physics this week. Nature Physics even issued a News&Views article about our paper, which highlights the potential of the scheme:

The full article may be found here:

As explained in the News&Views article, the researchers have taken a big step towards beating classical computers. A special class of problems known as boson sampling, is notoriously hard to solve by classical means. On the contrary, using a number of single quantum particles, like photons, in a quantum circuit is very well suited for this type of problem. When the number of photons becomes large, approaching 50, classical supercomputers have to give in—it simply gets too complicated to find a solution. On the other hand, photonic quantum simulations can perform the task, as the Nature Physics paper demonstrates. Indeed, the principle is demonstrated for 8 photons, and theoretical considerations show that the system is scalable to 48-70 photons.

Performing useful quantum computational tasks

“In this work, by improving the design of each integrated component, we have shown that even simple circuits can produce experiments with up to eight photons, doubling the previous record in integrated photonics. Moreover, our analysis shows that by scaling up the circuit complexity, which is an essential capability of the silicon platform, experiments with more than 20 photon pairs are possible. With that many quantum particles, in this case photons, we would be entering a regime where photonic quantum machines are expected to surpass the best classical supercomputers”, explains Leif K. Oxenløwe, Professor at DTU Fotonik and leader of the SPOC centre.

The experiment demonstrated an example of quantum simulations known as Gaussian Boson Sampling, which is a world-first. The team also demonstrated that, using such protocols, silicon quantum devices will be able to solve relevant problems. For instance, the chemical problem of finding the vibrational transitions in molecules undergoing an electronic transformation can be simulated on this type of chip using Gaussian Boson Sampling. 

Lead author Dr. Stefano Paesani from the University of Bristol’s NSQI Centre says: “Our findings show that photonic quantum simulators surpassing classical supercomputers are a promising prospect for the silicon quantum photonics platform. The development of such quantum machines can have potentially ground-breaking impact on industrially relevant fields such as chemistry, molecular designing, artificial intelligence, and big-data analysis. Applications include the design of better pharmaceuticals and the engineering of molecular states able to generate energy more efficiently.”

Senior Researcher Dr. Yunhong Ding from the SPOC Centre who fabricated the chip elaborates: “It is thrilling to see how silicon photonic integrated chips are useful for advanced quantum applications. There are competitive technologies, such as trapped ion systems, solid-state spin systems, and superconducting systems. So far there is no winner yet. The photonic approach has some unique advantages, and superconducting and other systems have other advantages, perhaps lending different technology systems to different types of problems, which make it all the more promising and exciting to follow in the future.”


‘Generation and sampling of quantum states of light in a silicon chip’ by S. Paesani, Y. Ding, R. Santagati, L. Chakhmakhchyan, C. Vigliar, K. Rottwitt, L. Oxenløwe, J. Wang, M. Thompson and A. Laing in Nature Physics, July 2019, DOI


By exploring complex integrated circuits, photonic states can be generated and processed at larger scales. Credit: Dr Stefano Paesani, University of Bristol
16 DECEMBER 2019