光子动量-偏振两自由度逻辑Bell态测量

Logical Bell state measurement for photon system in momentum and polarization degrees of freedom

量子逻辑编码是提高量子系统抗噪声能力的一种有效方法.相较于单自由度多光子逻辑编码方式,单光子多个自由度的逻辑编码方式更为简洁且能够节约光子资源.本文利用线性光学元件提出了两种光子动量-偏振两自由度逻辑Bell态测量方案:辅助W态的逻辑Bell态测量方案和自辅助逻辑Bell态测量方案.在第一个方案中,通过辅助四光子W态对两光子的两个自由度同时进行宇称测量,并根据光子探测器的响应情况得到偶宇称逻辑Bell态的测量结果,成功率为12.5%.在第二个方案中,利用简单的线性光学元件和光子探测器能够从四个逻辑Bell态中完全区分出两个偶宇称逻辑Bell态,且成功率提高为50%.相较于非线性光学方案,这两种基于线性光学的逻辑Bell态测量方案更加容易实验实现,因此在量子通信中有非常重要的应用.

Quantum logic coding efficiently enhances the noise immunity of quantum systems.A quantum logical qubit using multiple degrees of freedom(DOFs)of a photon is concise,and it can reduce resource consumption compared with a quantum logical qubit using multiple photons in one DOF.In this study,two logical Bell state measurement schemes are proposed for photon systems in momentum and polarization DOFs with linear optical elements,namely,momentum polarization logical Bell state measurement assisted by W-state and self-assisted momentum polarization logical Bell state measurement.In the first scheme,parity measurements on momentum and polarization DOFs are performed simultaneously using an auxiliary four-photon W-state.The even-parity logical Bell states can be distinguished by photon detector results,resulting in a success rate of 12.5%.The second scheme does not require an auxiliary entangled photon state,and the even-parity logical Bell states can be completely distinguished by simple linear optical elements and photon detector results with a success rate of 50%.These two linear optical momentum polarization logical Bell state measurement schemes are easier to implement experimentally than the nonlinear optical schemes,and their applications in quantum communication protocols are crucial.