Efficient entanglement generation using a spin bus

The current state-of-the-art quantum computing model realizes quantum circuits using a sequence of quantum gates from a universal one- and two-qubit gate set. Quantum circuits comprised of only those gate operations typically require a very long sequence of such quantum gates, putting some significant restrictions on the quantum coherence and the quantum circuit complexity. For spin qubits in semiconductor quantum dot systems, the exchange interaction between neighboring pairs of spin qubits is the standard mechanism for the two-qubit gates. The very short-range nature of the exchange coupling leads to a large overhead in implementing two-qubit gates between qubits that are far apart. The spin bus, a strongly coupled spin chain, has been proposed to overcome these shortcomings and to provide long-range, multi-qubit gate operations efficiently. We focus on finding the optimal quantum circuits with the spin bus multi-qubit entangling gates by using numerical optimization methods. We compare our results for quantum circuits for the generation of typical entangled states with the conventional exchange-based approach and show that the spin bus can perform the tasks while considerably reducing the depth of the quantum circuits. This work demonstrates the potential of multi-qubit gates for the efficient implementation of large quantum circuits.