Department of Optics, Palacký University, 17. listopadu 1192/12, 771 46 Olomouc, Czech Republic.
Sci Rep. 2016 Sep 20;6:33475. doi: 10.1038/srep33475.
We experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit. Our robust and versatile scheme exploits encoding of two qubits into polarization and path degrees of single photons and involves two crossed inherently stable interferometers. This approach allows us to design a complex quantum logic circuit that combines a genuine four-qubit C(3)Z gate and several two-qubit and single-qubit gates. The C(3)Z gate introduces a sign flip if and only if all four qubits are in the computational state |1〉. We verify high-fidelity performance of this central four-qubit gate using Hofmann bounds on quantum gate fidelity and Monte Carlo fidelity sampling. We also experimentally demonstrate that the quantum logic circuit can generate genuine multipartite entanglement and we certify the entanglement with the use of suitably tailored entanglement witnesses.
我们实验演示并描述了一个四量子比特线性光学量子逻辑门。我们的稳健而通用的方案利用单个光子的偏振和路径自由度对两个量子比特进行编码，并涉及两个交叉的固有稳定干涉仪。这种方法使我们能够设计一个复杂的量子逻辑门电路，该电路结合了真正的四量子比特 C(3)Z 门和几个两量子比特和单量子比特门。只有当所有四个量子比特都处于计算态 |1〉时，C(3)Z 门才会引入符号翻转。我们使用量子门保真度的霍夫曼界和蒙特卡罗保真度抽样来验证这个中心四量子比特门的高保真度性能。我们还通过使用适当设计的纠缠见证实验证明了量子逻辑门可以生成真正的多体纠缠，并证明了纠缠的存在。
