High-density time encoding of entangled photons for ultrafast telecom-compatible quantum secure communication

超级量子计算机的快速发展使得经典的加密技术，例如，银行业、国家安全和个人在线身份处于危险之中。量子密码学提供了一个面向未来的解决方案，以实现牢不可破的安全性。然而，低量子密钥传输速率以及缺乏设备无关安全协议所需的电信友好，紧凑和可批量生产的纠缠光子源，阻碍了该领域的进一步发展。 在这里，我们研究多层次（即，qudit）时间仓纠缠受益于其独特的潜力，以提高量子安全通信和大容量信息处理到Gbit/s的速率。时间模式确实被广泛认为是最容易获得和最强大的光子自由度，对科学界和工业界都有重大影响，正如最近在大城市距离上以Mbit/s密钥速率的量子加密协议的演示所证明的那样。在这里，通过使用纠缠光子qudits的源，我们将通过增加每个光子的信息容量，在甚至更低的重复率下展示类似的性能。在这方面，所要求的设备-电信设施中使用的具有2个通道、模拟带宽> 20 GHz、定时抖动< 10 ps的任意波形发生器-将适用于密集间隔光子时间仓的相干和精确量子态处理。我们将通过使用专门的片上光学设备来生成和处理具有可扩展维度的量子点，然而，这需要至少几十皮秒的操作速度来进行量子态操纵。所要求的超快AWG将使我们能够执行多级时间仓投影，这对纠缠验证至关重要，否则不可能以创纪录的GHz调制速度完成。该仪器将使我们能够在短期内确认第一代芯片上的时间仓纠缠量子数达到4甚至8个级别，以及在更长的时间内，首次展示4级和8级光子的全光纤集成隐形传态。这些目标的实现将极大地推动量子光子学的进步，并将为魁北克和加拿大创造知识产权，以提升下一代量子技术的市场潜力。我们的系统旨在超越其他光子平台：1）量子信息处理速率达到电信级Gbit/s，2）在更高的噪声鲁棒性下增强每个光子的信息容量，3）通过使用芯片集成和电信兼容组件提高稳定性，可扩展性和可访问性。所要求的设备还将大大提升PI和合作者其他活跃项目的影响力，并有助于HQP在神经形态光子学和超快信号处理等极具影响力的领域的培训。

The rapid thrive towards supreme quantum computers puts the classical encryption techniques, used for, e.g., banking, national security, and personal online identity, at risk. Quantum cryptography offers a future-proof solution towards unbreakable security. However, low quantum key transfer rates as well as the lack of telecom-friendly, compact, and mass-producible entangled photons sources, needed for device-independent secure protocols, hamper further advances in this field. Here, we investigate multilevel (i.e., qudit) time-bin entanglement to benefit from its unique potential to boost quantum secure communication and large-capacity information processing to Gbit/s rates. Time modes are indeed widely recognized as the most accessible and robust photon degree of freedom, with significant impact on both the scientific and the industrial communities, as witnessed by the recent demonstrations of quantum encryption protocols at Mbit/s key rates over metropolitan distances. Here, by using sources of entangled photon qudits, we will demonstrate similar performances at even lower repetition rates by increasing the information capacity per photon. In this context, the requested equipment an arbitrary waveform generator (AWG) with 2 channels, analog bandwidth > 20 GHz, and timing jitter < 10 ps, as used in telecom facilities will be adapted for coherent and precise quantum state processing of densely-spaced photon time bins. We will generate and process such qudits with scalable dimensionality by using specialized on-chip optical devices, which however require operational speeds of at least few tens of picosecond for quantum state manipulation. The requested ultrafast AWG will allow us to perform multilevel time-bin projections that are critical for entanglement verification and that would be otherwise impossible to accomplish at record-fast GHz modulation-speeds. The instrument will enable us to confirm, in a short term, the first on-chip generation of time-bin entangled qudits up to 4 and even 8 levels, as well as, in a longer term, to demonstrate first-time all-fiber-integrated teleportation of 4- and 8-level photons. The accomplishment of these objectives will critically boost advances in quantum photonics, as well as will create intellectual property for Quebec and Canada towards elevating market potential for next-generation quantum technologies. Our system aims to outperform other photonic platforms in terms of 1) quantum information processing rates towards telecom-level Gbit/s, 2) enhanced information capacity per photon at higher noise robustness, and 3) increased stability, scalability, and accessibility by using chip-integrated and telecom-compatible components. The requested equipment will also greatly elevate the impact of other active projects of the PI and collaborators, as well as contribute to HQP training in highly impactful fields such as neuromorphic photonics and ultrafast signal processing.