Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
Sci Rep. 2014 Feb 18;4:4118. doi: 10.1038/srep04118.
Chip-based photonic quantum computing is an emerging technology that promises much speedup over conventional computers at small integration volumes. Particular interest is thereby given to polarisation-encoded photonic qubits, and many protocols have been developed for this encoding. However, arbitrary wave plate operation on chip are not available so far, preventing from the implementation of integrated universal quantum computing algorithms. In our work we close this gap and present Hadamard, Pauli-X, and rotation gates of high fidelity for photonic polarisation qubits on chip by employing a reorientation of the optical axis of birefringent waveguides. The optical axis of the birefringent waveguide is rotated due to the impact of an artificial stress field created by an additional modification close to the waveguide. By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations. Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides. The implemented gates are tested with classical and quantum light.
基于芯片的光子量子计算是一种新兴技术，有望在小集成体积上比传统计算机实现更大的速度提升。因此，人们对偏振编码的光子量子比特特别感兴趣，并且已经为这种编码开发了许多协议。然而，到目前为止，芯片上还没有任意的波片操作，这阻止了集成通用量子计算算法的实现。在我们的工作中，我们通过重新定向双折射波导的光轴，在芯片上实现了对光子偏振量子比特的高保真度的 Hadamard、Pauli-X 和旋转门，从而弥补了这一差距。由于在波导附近的附加修改产生的人工应力场的影响，双折射波导的光轴会发生旋转。通过调整缺陷沿着波导的长度，普通和异常场分量之间的延迟可以精确地调节，包括半波片和四分之一波片操作。我们的方法展示了对诱导双折射的方向和强度的全面控制，从而允许进行任意的波片操作，而不会影响偏振度或向波导引入额外的损耗。所实现的门使用经典和量子光进行了测试。
