Widely flexible and finely adjustable nonlocal dispersion cancellation with wavelength tuning

In fiber-based quantum information processing with energy-time entangled photon
pairs, optimized dispersion compensation is vital to preserve the strong temporal correlation of
the photon pairs. We propose and experimentally verify that, by simply tuning the wavelength
of the entangled photon pairs, nonlocal dispersion cancellation (NDC) can provide a widely
flexible and finely adjustable solution for optimizing the dispersion compensation, which cannot
be reached with the traditional local dispersion cancellation (LDC) instead. By way of example,
when a 50 km-long single-mode fiber (SMF) is dispersion compensated by a 6.2-km-long
commercial dispersion compensating fiber (DCF) based on the LDC configuration, it will lead
to an almost invariant over-compensation in the wavelength range of 1500-1600 nm which
restricts the observed temporal coincidence width of the self-developed energy-time entangled
photon-pairs source to a minimum of ∼110 ps. While in the NDC configuration, the dispersion
compensation can be readily optimized by tuning the signal wavelength to 1565.7 nm and a
minimum coincidence width of 86.1 ± 0.7 ps is observed, which is mainly limited by the jitter
of the single-photon detection system. Furthermore, such optimized dispersion compensation
can also be achieved as the fiber length varies from 48 km to 60 km demonstrating the wide
flexibility of NDC. Thanks to these capabilities, elaborate dispersion compensation modules are
no longer required, which makes NDC a more versatile tool in fiber-based quantum information
and metrology applications.

在基于光纤的能量-时间纠缠光子对（energy-time entangled photon pairs）量子信息处理中，优化的色散补偿对于维持光子对的强时间相关性至关重要。我们提出并通过实验验证：仅通过调谐纠缠光子对的波长，非局域色散抵消（nonlocal dispersion cancellation, NDC）即可为色散补偿优化提供一种兼具宽灵活性与精细可调性的解决方案，而这是传统局域色散抵消（local dispersion cancellation, LDC）无法实现的。举例来说，当采用基于局域色散抵消配置的6.2 km长商用色散补偿光纤（dispersion compensating fiber, DCF）对50 km长单模光纤（single-mode fiber, SMF）进行色散补偿时，会在1500 nm至1600 nm的波长范围内产生近乎恒定的过补偿效应，将自研能量-时间纠缠光子对源的实测时间符合宽度限制至约110 ps的最小值。而在非局域色散抵消配置中，仅需将信号波长调谐至1565.7 nm即可完成色散补偿优化，此时测得的最小符合宽度为86.1±0.7 ps，该值主要受限于单光子探测系统的抖动。进一步研究显示，当光纤长度在48 km至60 km范围内变动时，仍可实现此类优化的色散补偿，这充分体现了非局域色散抵消的宽灵活性优势。得益于上述特性，无需再依赖复杂的色散补偿模块，这使得非局域色散抵消成为一种在基于光纤的量子信息处理与计量应用中更具通用性的工具。