Photonic quantum computing encodes quantum information in properties of individual photons — typically their polarization, path, or timing. Photons have a unique advantage: they naturally resist decoherence because they interact very weakly with their environment. Unlike superconducting qubits, photonic systems can operate at room temperature, potentially reducing the infrastructure requirements for quantum computing.
PsiQuantum is the highest-profile photonic quantum computing startup, having raised over $700 million with a strategy focused on building a million-qubit fault-tolerant photonic quantum computer using silicon photonics manufacturing. Xanadu, based in Canada, takes a different photonic approach using squeezed states of light in a continuous-variable encoding scheme and has made its Strawberry Fields software platform open source. In China, research groups at USTC have demonstrated photonic quantum systems with over 100 detected photons for quantum computational tasks.
The central challenge for photonic quantum computing is that photons do not naturally interact with each other, making two-qubit gates — which require qubit-qubit interactions — extremely difficult. Approaches include measurement-based quantum computing (where entanglement is created through photon detection) and nonlinear optical effects. Photon loss is another major concern, as losing a single photon mid-computation destroys the information it carried. Despite these challenges, the potential for room-temperature operation and compatibility with existing telecommunications infrastructure keeps photonic approaches among the serious contenders for scalable quantum computing. For deeper coverage, see DeepTechIntel's quantum computing section.