High-dimensional photon states (qudits) are pivotal to enhance the information capacity, noise robustness, and data rates of quantum communications. Time-bin entangled qudits are promising candidates for implementing high-dimensional quantum communications over optical fiber networks with processing rates approaching those of classical telecommunications. However, their use is hindered by phase instability, timing inaccuracy, and low scalability of interferometric schemes needed for time-bin processing. As well, increasing the number of time bins per photon state typically requires decreasing the repetition rate of the system, affecting in turn the effective qudit rates. Here, we demonstrate a fiber-pigtailed, integrated photonic platform enabling the generation and processing of picosecond-spaced time-bin entangled qudits in the telecommunication C band via an on-chip interferometry system. We experimentally demonstrate the Bennett-Brassard-Mermin 1992 quantum key distribution protocol with time-bin entangled qudits and extend it over a 60 km-long optical fiber link, by showing dimensionality scaling without sacrificing the repetition rate. Our approach enables the manipulation of time-bin entangled qudits at processing speeds typical of standard telecommunications (10 s of GHz) with high quantum information capacity per single frequency channel, representing an important step towards an efficient implementation of high-data rate quantum communications in standard, multi-user optical fiber networks.
Read more at Nature Communications:
https://www.nature.com/articles/s41467-024-55345-0
Photo caption:
Schematics of quantum state generation and processing for 4- and 8-level entangled quDits. (A) Simplified experimental setup for the generation of picosecond-spaced high-dimensional time-entangled photonic quDits. (B) Operation principle for 4-level quantum state processing using the OIC and external phase modulation (see Methods and Supplementary Materials). (C) Simplified scheme for 8-level quantum interference measurements, where the phase of each photon time mode was prepared by applying a phase modulation to the pump before photon generation. The position of the phase modulator (PM*) is indicated in the setup for clarity. We applied temporal filtering to separate the central interference modes to account for the fact that the time mode spacing (i.e., 32 ps) approaches the jitter time (i.e., 45 ps) of the superconducting nanowire single-photon detectors. OIC: on-chip interferometer cascade, SW: spiral waveguide, NF: notch filter, FBG: fiber Bragg grating, PM: phase modulator, IM: intensity modulator, DEMUX: demultiplexer
02 Jan 2025