Skip to Content

Linear optics quantum circuits


Quantum information science addresses how uniquely quantum mechanical phenomena such as superposition and entanglement can enhance communication, information processing, and precision measurement. Photons are appealing for their low-noise, light-speed transmission and ease of manipulation using conventional optical components. However, it has been very difficult to achieve the necessary two-qubit operations since the physical interaction between photons is much too small. In a breakthrough, Knill, Laflamme, and Milburn (KLM) showed that effective nonlinear interactions can be achieved using only linear optical elements, auxiliary photons, and measurement. Inspired by the KLM approach, a number of quantum logic gates using heralded photons and event postselection have been proposed and demonstrated. Furthermore, optical quantum circuits combining these gates have been demonstrated . We experimentally demonstrate a two photon quantum gate (controlled-NOT gate) based on the KLM approach. This result confirms the first step in the original KLM “recipe” for all-optical quantum computation, and should be useful for on-demand entanglement generation and purification. Our other recent progress on linear optics quantum circuit will also be introduced.