The promise of universal quantum computing hinges on scalable single- and inter-qubit control interactions. Photon systems offer strong isolation from environmental disturbances and provide speed and timing advantages while facing challenges in achieving deterministic photon-photon interactions necessary for scalable universal quantum computing.
In this talk, I will present an experimental demonstration of a new mechanism for protecting biphoton coherence time against Zeeman splitting. We generate narrowband entangled biphotons via four-wave mixing in laser-cooled atoms. While nondegenerate biphotons typically suffer an exponential reduction of temporal coherence due to asymmetric absorption losses, we show that this degradation can be avoided for backward-propagating degenerate biphotons through an underlying space–time symmetry. As an additional benefit, the biphoton coherence time is effectively doubled. This enhanced coherence makes degenerate biphotons particularly well suited for integration with quantum memories, which are essential components of quantum networks and require photons with narrow linewidths and long coherence times.
To realize deterministic photonic quantum gates, we are developing a hybrid quantum computing scheme that interfaces photons with atomic-ensemble–based quantum memories. By leveraging the Rydberg blockade effect to mediate strong nonlinear two-qubit interactions, this approach preserves the advantages of photonic qubits while enabling controlled and deterministic quantum gate operations.
Together, these results highlight the potential of photon-atom hybrid systems in addressing scalability challenges and protecting quantum coherence, paving the way for scalable quantum computing architectures.