Realization of a Knill-Laflamme-Milburn C-NOT gate -a photonic quantum circuit combining effective optical nonlinearities

摘要

Quantum information science addresses how uniquely quantum mechanicalphenomena such as superposition and entanglement can enhance communication,information processing and precision measurement. Photons are appealing fortheir low noise, light-speed transmission and ease of manipulation usingconventional optical components. However, the lack of highly efficient opticalKerr nonlinearities at single photon level was a major obstacle. In abreakthrough, Knill, Laflamme and Milburn (KLM) showed that such an efficientnonlinearity can be achieved using only linear optical elements, auxiliaryphotons, and measurement. They proposed a heralded controlled-NOT (CNOT) gatefor scalable quantum computation using a photonic quantum circuit to combinetwo such nonlinear elements. Here we experimentally demonstrate a KLM CNOTgate. We developed a stable architecture to realize the required four-photonnetwork of nested multiple interferometers based on a displaced-Sagnacinterferometer and several partially polarizing beamsplitters. This resultconfirms the first step in the KLM `recipe' for all-optical quantumcomputation, and should be useful for on-demand entanglement generation andpurification. Optical quantum circuits combining giant optical nonlinearitiesmay find wide applications across telecommunications and sensing.