Universal quantum computing relies on high-fidelity entangling operations. Here, we demonstrate that four coupled qubits can operate as a quantum gate, where two qubits control the operation on two target qubits (a four-qubit gate). This configuration can implement four different controlled two-qubit gates: two different entangling swap and phase operations, a phase operation distinguishing states of different parity, and the identity operation (idle quantum gate), where the choice of gate is set by the state of the control qubits. The device exploits quantum interference to control the operation on the target qubits by coupling them to each other via the control qubits. By connecting several four-qubit devices in a two-dimensional lattice, one can achieve a highly connected quantum computer. We consider an implementation of the four-qubit gate with superconducting qubits, using capacitively coupled qubits arranged in a diamond-shaped architecture.

通用量子计算依赖于高保真纠缠操作。在这里，我们证明了四个耦合的量子位可以用作量子门，其中两个量子位控制着两个目标量子位（一个四量子位）的操作。这种配置可以实现四个不同的受控二量子位门：两个不同的纠缠交换和相位运算，区分不同奇偶性状态的相位运算和标识运算（空闲量子门），其中门的选择由状态决定。控制量子位。该设备利用量子干扰来控制目标量子位，使其通过控制量子位彼此耦合。通过在二维晶格中连接几个四量子位器件，可以实现高度连接的量子计算机。