New photonic chip offers route to specialized quantum computing

03 Oct 2023

University of Washington device employs eight photonic cavities as quantum simulator.

Development of quantum computing devices promises to be transformational in multiple applications, including security, drug discovery and material fabrication.

One facet of current research involves the creation of specialized quantum computer devices termed "quantum simulators," special purpose devices dedicated to the tackling of defined specific problems rather than act as generally programmable computing devices.

Various approaches to quantum simulators suitable for practical real-world tasks have been tried, based on exotic quantum operations, trapped ions, cold atoms and superconducting qubits.

A project at the University of Washington (UW) has now demonstrated that a new kind of silicon photonic chip could function as the foundation of a practical quantum simulator, and published its findings in Nature Communications.

"We have shown that photonics is a leading contender for quantum simulation, and photonic chips are a reality," commented Arka Majumdar from UW. "We believe that these chips can play a very important role in building a quantum simulator."

The work builds on the use of photonic coupled cavities arranged in arrays, where coupling effects between cavities constrain the movement of photons for long enough that useful non-linear effects can occur. UW's new implementation employs a lattice made up of eight photonic resonators, where photons can be confined, raised and lowered in energy through the application of thermal energy, and moved around in a controlled manner, essentially forming circuits.

In practice this involved UW designing an algorithm that to map the chip in detail, and designing a new kind of architecture for heating and independently controlling each cavity in the array in order to program the device. Successfully implementing both of these two innovations on a silicon photonic chip has never been accomplished before, according to the UW team.

Using quantum simulators for common applications

In trials the UW team showed that its device could successfully program, create and maintain quantum functions named Hamiltonians, an indication of the total energy of a particular system, with only half the thermal crosstalk between neighboring cavities that traditional versions of the same cavity principle suffer from.

"The fabrication process that we have for this chip can directly latch onto the already well-matured silicon fabrication that we use for transistors and other computer chips,” said UW's Abhi Saxena said. "For other quantum simulator platforms that's not feasible, even though many of them have already demonstrated prototypical devices."

Future work will involve fine tuning of the device's behavior and of the photon interaction taking place within the cavities, but UW believes its device can now be a solid foundation for a platform that demonstrates photonics and a semiconductor-based technology as viable alternatives for the creation of quantum simulators.

"I think that up until now, many in the scientific and engineering communities have generally avoided considering photonics for this purpose," said Saxena. "But our work shows that it is realistically possible, so it is a very good incentive for more people to begin moving in this direction."