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

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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.