Time-entanglement is a promising resource for the implementation of quantum communications over standard fiber networks. In particular, photonic qudits can enhance the performance of quantum communication, including quantum key distribution, in terms of noise robustness, quantum information content, distance reach, as well as security and secret key rates. However, time-entangled photonic qudits are not ready yet to be fully exploited for quantum communications in fiber networks that are fully compatible with standard telecommunication architecture. Here, we demonstrate the implementation of telecommunication-compatible quantum communications based on picosecond-spaced time-entangled qudits. To this end, we make use of an integrated photonic chip comprising a cascade of programmable interferometers and a spiral waveguide. We use entangled qudits to implement high-speed quantum key distribution, chip-to-chip entanglement distribution, and quantum state propagation over 60 km of standard fiber. Our results show the potential of time-entangled qudits for high-speed quantum communications in telecommunication-compatible architecture.
Quantum technologies harness nonclassical features of particles, here, photons, to develop novel, efficient, and precise devices for information processing applications. Superposition, entanglement, as well as the coherent manipulation of quantum states are at the heart of the second quantum revolution (quantum 2.0) which targets the development of secure cryptographic systems, complex computation protocols, and more. Emerging quantum architectures rely on the realistic implementation of photonic schemes which are scalable, resource-efficient, and compatible with CMOS technologies as well as fiber networks. This work demonstrates current schemes utilized for time-/frequency-bin entanglement generation and processing by leveraging existing telecommunications and integrated photonics infrastructures.
KEYWORDS: Quantum optics, Picosecond phenomena, Temporal resolution, Dispersion, Time correlated single photon counting, Electro optics, Single photon detectors, Signal detection, Signal processing
High temporal resolution detection for time-correlated single-photon counting (TCSPC) is critical for a broad range of applications, such as sensing, bio-imaging and quantum information. To harness non-classical advantages, high temporal resolution TCSPC is necessary to capture the unique properties of quantum entanglement, in which the precise time delays between two photons are used to reconstruct the biphoton distribution. However, current state-of-the art, high-resolution TCSPC systems, such as superconducting nanowires, have large footprints and require cryogenic cooling to liquid helium temperatures. They are not well equipped to be conveniently mounted on a satellite or transported within a health care facility. Small footprint, simple, low energy consuming single photon detection systems are therefore needed in order for high temporal resolution TCSPC applications to move beyond the research laboratory. In this direction, we demonstrate a proof-of-concept experiment for improving the temporal resolution of single-photon and biphoton detection schemes that is simple, fiber-based, and readily chip integrable. The principle relies on electrooptic gating of fast single-photon and biphoton signals using a high-speed RF pulse which drives an electro optic intensity modulator. As such, the instrument response function (IRF) of the detection scheme takes on the temporal profile of the electro-optic gate. Experimentally, we improve the IRF of our detection scheme from ~1.54 ns to <100 ps, allowing high resolution detection of ultrafast single photon TCSPC signals as well as to observe nonlocal dispersion cancellation effects in ultrafast biphoton distributions. This technique could allow for practical and simplified access to rapid temporal dynamics at the single photon scale.
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