$XNDU - Quantum meets Photonics 🔥

Photonics offers a promising platform for quantum computing owing to the availability of chip integration for mass-manufacturable modules, fibre optics for networking and room-temperature operation of most components.

However, experimental demonstrations are needed of complete integrated systems comprising all basic functionalities for universal and fault-tolerant operation.

Here we construct a (sub-performant) scale model of a quantum computer using 35 photonic chips to demonstrate its functionality and feasibility.

This combines all the primitive components as discrete, scalable rack-deployed modules networked over fibre-optic interconnects, including 84 squeezers and 36 photon-number-resolving detectors furnishing 12 physical qubit modes at each clock cycle.

We use this machine, which we name Aurora, to synthesize a cluster state entangled across separate chips with 86.4 billion modes, and demonstrate its capability of implementing the foliated distance-2 repetition code with real-time decoding.

The key building blocks needed for universality and fault tolerance are demonstrated: heralded synthesis of single-temporal-mode non-Gaussian resource states, real-time multiplexing actuated on photon-number-resolving detection, spatiotemporal cluster-state formation with fibre buffers, and adaptive measurements implemented using chip-integrated homodyne detectors with real-time single-clock-cycle feedforward.

We also present a detailed analysis of our architecture’s tolerances for optical loss, which is the dominant and most challenging hurdle to crossing the fault-tolerant threshold.

This work lays out the path to cross the fault-tolerant threshold and scale photonic quantum computers to the point of addressing useful applications.