Abstract Semiconductor quantum‐dot (QD) spins hold great promise in quantum information science and technology. The implementation of high‐fidelity quantum gates on QD‐spin qubits is of great importance. Here, two schemes are presented to implement two universal quantum controlled gates, that is, the two‐qubit controlled‐not gate and the three‐qubit Toffoli gate, on stationary electron‐spin qubits in QDs inside single‐sided optical microcavities, based on the cavity‐assisted photon scattering under the balance condition. Compared with the previous schemes based on the ideal giant circular birefringence, the present schemes use the balance condition of the single‐sided QD‐cavity system, which can be achieved in both the weak‐ and strong‐coupling regimes of cavity quantum electrodynamics. Under the balance condition, the noise caused by the unbalanced reflectance between the coupled and uncoupled QD‐cavity systems can be efficiently depressed, so that the fidelity of each quantum gate operation can be increased to unity in principle. The schemes exhibit the possibility of realizing high‐fidelity and scalable quantum computing with single QD spins and single photons using the feasible and robust light–matter quantum interface. These high‐fidelity quantum controlled gates can lead to more efficient construction of quantum circuits for quantum computing, and provide a convenient avenue for quantum networking.
We present some deterministic schemes to construct universal quantum gates, that is, controlled- not, three-qubit Toffoli, and Fredkin gates, between flying photon qubits and stationary electron-spin qubits assisted by quantum dots inside double-sided optical microcavities. The control qubit of our gates is encoded on the polarization of the moving single photon and the target qubits are encoded on the confined electron spins in quantum dots inside optical microcavities. Our schemes for these universal quantum gates on a hybrid system have some advantages. First, all the gates are accomplished with a success probability of 100
in principle. Second, our schemes require no additional qubits. Third, the control qubits of the gates are easily manipulated and the target qubits are perfect for storage and processing. Fourth, the gates do not require that the transmission for the uncoupled cavity is balanceable with the reflectance for the coupled cavity, in order to get a high fidelity. Fifth, the devices for the three universal gates work in both the weak coupling and the strong coupling regimes, and they are feasible in experiment.