Programmable frequency-bin quantum states in a nano-engineered silicon device

International audiencePhotonic qubits should be compatible with easy on-chip manipulation and noise-tolerant transmission over optical networks to find practical use across the whole spectrum of quantum technologies. Furthermore, the source of qubits should grant programmable control over the emitted state and high brilliance, in order to provide quantum algorithms with resilience to losses. However, encoding schemes demonstrated so far only combine at most two of the aforementioned properties, restricting the full potential of photonic quantum technologies. In this work, we finally overcome this hurdle by demonstrating a programmable silicon nano-photonic chip capable of generating frequency-bin entangled photons, a type of qubit encoding compatible with long-range transmission over optical links. Our device emits quantum states that can be manipulated using existing telecommunication components, including active devices that can be integrated in silicon photonic technology. Remarkably, our design also overcomes the state-of-art trade-off between brightness and operation bandwidth. As a powerful demonstration, we programmed our chip to generate the four computational basis states, and the four maximally-entangled Bell states, of a two-qubit system. For each state we perform quantum state tomography, confirming high brightness, fidelity, and purity. Such a device combines all the key properties of on-chip quantum state reconfigurability and dense integration