Jianjia Fei, Dong Zhou, Yun-Pil Shim, Sangchul Oh, Xuedong Hu, Mark Friesen
In a typical quantum circuit, non-local quantum gates are often applied to non-proximal qubits. If the underlying physical interactions are short-range (e.g., exchange interactions between spins), intermediate swap operations must be introduced, thus reducing the efficiency of the circuit. Here we develop a new class of "mediated" gates for spin qubits, which act on non-proximal spins via intermediate ancillae qubits. At the end of the operation, the ancillae return to their initial states. We provide examples of mediated gates for a triple-quantum-dot system, and we show that these gates provide equal or improved efficiency compared to swap-based protocols. Our method can be extended to a spin bus, further improving the circuit efficiency.
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http://arxiv.org/abs/1207.6063
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