Generation and Sampling of Quantum States of Light in a Silicon Chip

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Scientists from the University of Bristol and the Technical University of Denmark have found a promising new way to build the next generation of quantum simulators combining light and silicon micro-chips.

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

In the roadmap to develop quantum machines able to compete and overcome classical supercomputers in solving specific problems, the scientific community is facing two main technological challenges.

The first is the capability of building large quantum circuits able to process the information on a massive scale, and the second is the ability to create a large number of single quantum particles that can encode and propagate the quantum information through such circuits.

Both these two requirements need to be satisfied in order to develop an advanced quantum technology able to overcome classical machines.

A very promising platform to tackle such challenges is silicon quantum photonics. In this technology, the information carried by photons, single particle of lights, is generated and processed in silicon micro-chips.

These devices guide and manipulate light at the nanoscale using integrated waveguides - the analogue of optical fibres at the nanometre-scale.

Image Caption: Researchers at QETLabs working on silicon quantum photonics experiments. From left to right: Professor Anthony Laing, Dr Stefano Paesani and Dr Raffaele Santagati

Crucially, the fabrication of photonic chips requires the same techniques used for fabricating electronic micro-chips in the semiconductor industry, making the fabrication of quantum circuits at a massive scale possible.

In the University of Bristol’s Quantum Engineering Technology (QET) Labs, the team have recently demonstrated silicon photonic chips embedding quantum interferometres composed of almost a thousand optical components, orders of magnitude higher that what was possible just few years ago.

However, the big question that remained unanswered was if these devices were also able to produce a number of photons large enough to perform useful quantum computational tasks. The Bristol-led research, published today in the journal Nature Physics, demonstrates that this question has a positive answer.

By exploring recent technological developments in silicon quantum photonics, the team have demonstrated that even small-scale silicon photonic circuits can generate and process a number of photons unprecedented in integrated photonics.

In fact, due to imperfections in the circuit such as photon losses, previous demonstrations in integrated photonics have been mostly limited to experiments with only two photons generated and processed on-chip, and only last year, four-photon experiments were reported using complex circuitry.

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