Hybrid Biphoton Spectrometer Captures Three-Fold Non-Degenerate Joint Spectra for Time-Resolved Quantum Spectroscopy

Understanding the properties of entangled photons is fundamental to advances in quantum technologies and spectroscopy, and Ozora Iso, Koya Onoda, and Nicola J. Fairbairn, from The University of Electro-Communications, alongside Masahiro Yabuno, Hirotaka Terai, and Shigehito Miki from the National Institute of Information and Communications Technology, have developed a new instrument that significantly enhances our ability to study these correlations. Their work addresses a key challenge in the field, namely the difficulty of simultaneously achieving both high spectral purity and the time-resolved measurements needed to observe rapid molecular processes. The team constructed a hybrid biphoton spectrometer capable of capturing a three-fold non-degenerate joint spectrum across both visible and near-infrared wavelengths, and crucially, it achieves a temporal resolution of approximately 150 picoseconds. This innovative approach provides a powerful new tool for characterising entangled photon pairs and unlocking deeper insights into dynamic molecular behaviour, bridging a critical gap in current spectroscopic techniques.

This research focuses on improving the precision and efficiency of biphoton state characterisation, enabling more robust quantum systems and offering new insights into molecular processes.

Time-Resolved Entangled Photon Spectroscopy System

This study introduces a novel hybrid spectrometer capable of capturing time-resolved joint spectral intensity, a significant advancement in quantum spectroscopy. Researchers engineered a system that simultaneously measures the time and frequency of entangled photon pairs, achieving a temporal resolution of approximately 150 picoseconds. This breakthrough allows observation of fast molecular dynamics previously inaccessible with static techniques. The system employs two distinct spectrographs, one utilising a superconducting nanowire single-photon detector for near-infrared photons and another employing a delay-line-anode single-photon imager for visible photons.

Visible photons are converted into amplified signals, and their timing directly corresponds to the photon’s arrival time, while near-infrared photons undergo temporal stretching before detection. This hybrid detection scheme overcomes spectral limitations while capitalising on the efficiency of superconducting nanowire detectors. Data processing relies on second-order correlation functions to reconstruct time-resolved joint spectral intensity. Researchers validated the system by generating and measuring entangled photon pairs, comparing simulated and experimental data to confirm performance. This innovative methodology establishes a foundational capability for observing quantum-correlated dynamics in real-time, promising significant advancements in quantum-enhanced sensing and spectroscopy.

Entangled Photons Enhance Fluorescence Spectroscopy Resolution

This research presents a novel approach to two-dimensional fluorescence spectroscopy using quantum entangled photons and time-and frequency-resolved two-photon coincidence detection. The goal is to enhance the resolution and sensitivity of fluorescence spectroscopy, potentially revealing subtle dynamics in complex systems like photosynthetic complexes, organic materials, and biological samples. The system utilises a source of entangled photons generated through Spontaneous Parametric Down-Conversion, exhibiting strong correlations in their properties. A two-photon coincidence detection system identifies correlated photon pairs with time and frequency resolution, providing detailed information about sample dynamics.

This allows creation of a two-dimensional map of fluorescence emission, revealing correlations between different fluorescence frequencies and providing insights into the energy landscape and dynamics of the sample. The use of entangled photons and coincidence detection is expected to improve resolution and sensitivity, enabling study of samples with low fluorescence yields. Potential applications include studying energy transfer dynamics in photosynthetic complexes, investigating excited-state dynamics in organic semiconductors, analysing fluorescence properties of biomolecules, and studying interactions between excited states in materials.

Time-Resolved Biphoton Spectra with High Fidelity

This research demonstrates a novel methodology for capturing biphoton spectra, successfully generating a three-fold non-degenerate joint spectrum encompassing both visible and near-infrared photons. The team achieved this by employing a unique hybrid system incorporating two non-scanning spectrographs and a time-tagging acquisition strategy, enabling measurements with approximately 150 picosecond temporal resolution. This advancement bridges a critical gap between the need for highly pure biphoton states in quantum information science and the demand for time-resolved capabilities in spectroscopic investigations of molecular dynamics. The system’s performance represents a significant step forward compared to traditional scanning techniques, which often suffer from low signal contrast and lengthy acquisition times.

Researchers confirmed photon count conservation between time-resolved and static measurements, validating the accuracy and reliability of the technique. Future work will likely focus on optimising components and exploring the application of this hybrid spectrometer to a wider range of chemical and physical dynamics. This work establishes a proof of principle, opening new avenues for integrating quantum information science with advanced spectroscopic analysis.