New Structural Quantum Circuit Simulating a Toffoli Gate
  A Toffoli gate ($C^{n}$-NOT gate) is regarded as an important unitary gate in quantum computation, and is simulated by a quantum circuit composed of $C^{2}$-NOT gates. This paper presents a quantum circuit with a new configuration of $C^{2}$-NOT gates simulating a $C^{2m+1}$-NOT operation under the condition $m=2^{n}$ ($n=1,2,...$). The circuit is composed of units called multi-qubits gates (MQGs), each of which performs $m$ $C^{2}$-NOT operations simultaneously on $3m$ qubits. Simultaneous operations eliminate the need to manipulate qubits individually, as required in conventional quantum circuits. The proposed circuit thus represents a more realistic mode of operation for practical computing systems. A nuclear magnetic resonance implementation of the circuit is presented as a demonstration of the feasibility of MQG operations for practical systems. 
Masanari Asano and Chikara Ishii