High-Fidelity Hybrid Universal Quantum Controlled Gates on Photons and Quantum-Dot Spins

Both photons and semiconductor quantum-dot (QD) spins are promising candidates for quantum information science and technology. It is of critical significance to realize high-fidelity quantum controlled gates on photon-spin hybrid systems. In this paper, based on the novel balance condition for the interaction between a single input photon and a singly charged QD embedded in an optical single-sided microcavity, we present three schemes for implementing three universal quantum controlled gates, i.e., the two-qubit controlled-NOT (CNOT) gate, the three-qubit Toffoli gate, and the three-qubit Fredkin gate, on composite hybrid quantum systems consisting of flying photons and QD-confined electron spins. By exploiting the balance condition, the noise caused by the unbalanced reflectance of the coupled and uncoupled QD-cavity systems can be efficiently suppressed, so that the fidelity of each quantum gate operation can be raised to unity in principle. The balance condition can be met without the strict requirement of strong coupling, making the high-fidelity quantum gates easier to be demonstrated in experiments. These features can improve the fidelity and feasibility of these schemes, which can be applied to large-scaled quantum computing and quantum information networks.