On-chip quantum memories based on erbium dopants in silicon waveguides

通过量子中继器实现全球量子网络是当前量子科学中最热门的话题之一。量子存储器不仅可以为量子理论的基础和精确测试提供新的便利，而且可以在量子信息处理中实现许多应用。为了实现大型量子网络，需要满足严格标准的量子存储器。首先，他们需要提供足够的存储时间，大约为1秒。其次，它们必须以高效率和保真度促进量子比特的存储和按需检索。第三，它们必须作为低损耗电信波段的单光子源（或与源兼容）。最后，它们应该提供一个简单的策略来实现高效的多路复用，这通常需要多模容量，低成本材料，鲁棒性和可扩展的制造技术。尽管在不同的物理平台上做出了许多努力，但实现这种量子存储器仍然是一个突出的挑战。特别是，后两个标准在以前的实验中已经证明是困难的。因此，一种克服现有物理系统瓶颈的新技术似乎是强制性的。为此，我们计划在由晶体硅制成的纳米光子波导中研究铒掺杂剂。总的来说，基于掺杂剂的存储器特别有前途，因为它们提供了任何量子系统中最长的相干时间（长达6小时），并且它们为可扩展性提供了明确的途径。在迄今为止研究的所有掺杂剂中，铒突出，因为它的发射波长福尔斯落在1530 nm和1565 nm之间的光通信的主波长带内。这有两个优点：首先，硅在该波长范围内的透明性确保了与硅纳米光子学的成熟平台的兼容性，为多路复用提供了清晰的路径。其次，光纤在该波长下的最小损耗是跨越全球距离的量子网络的关键要求。我们的新实验平台建立在半导体行业的标准工艺基础上，与所有其他正在研究的平台相比，大大降低了实验开销。通过利用硅纳米纤维的潜力来实现集成纳米光子量子存储器，我们期望建立一种可证明安全的通信和基于网络的量子信息处理的关键能力。

The realization of global quantum networks via quantum repeaters is one of the most intensely pursued topics in current quantum science. It would not only facilitate novel fundamental and precision tests of quantum theory, but also enable numerous applications in quantum information processing.To implement a large quantum network, quantum memories that fulfil stringent criteria are required. First, they need to offer sufficient storage time, on the order of 1 s. Second, they have to facilitate storage and on-demand retrieval of qubits with high efficiency and fidelity. Third, they must act as a source (or be compatible with sources) of single photons in the low-loss telecom bands. Finally, they should provide a simple strategy for efficient multiplexing, which typically requires multimode capacity, low-cost material, robustness and scalable fabrication techniques.In spite of numerous efforts in different physical platforms, the realization of such quantum memory is still an outstanding challenge. In particular, the latter two criteria have proven difficult in previous experiments. Therefore, a new technology that overcomes the bottlenecks of existing physical systems seems mandatory. To this end, we are planning to investigate erbium dopants in nanophotonic waveguides made of crystalline silicon.In general, memories based on dopants are particularly promising as they offer the longest coherence times of any quantum system – up to six hours – and they provide a clear path towards scalability. Among all dopants studied to date, erbium stands out because its emission wavelength falls within the main wavelength band of optical telecommunication between 1530 nm and 1565 nm. This has two advantages: first, the transparency of silicon in this wavelength regime ensures compatibility with the mature platform of silicon nano-photonics, providing a clear path for multiplexing. Second, the minimal loss of optical fibers at this wavelength is a key requirement for quantum networks that span global distances.Our new experimental platform builds on standard processes of the semiconductor industry, which dramatically reduces the experimental overhead compared to all other platforms under investigation. By harnessing the potential of silicon nanofabrication towards the realization of integrated nanophotonic quantum memories, we thus expect to establish a critical capability for provably-secure communication and for network-based quantum information processing.