COLMAR: Collaborative Optics in Layered Materials

Spontaneous emission, an inherent process in which excited emitters release incoherent photons into undesired channels, fundamentally limits the efficiency of light-matter interaction. Overcoming this barrier is crucial for advancing technologies in quantum optics, communication, sensing, and imaging. One of the most promising approaches involves collective quantum effects, particularly superradiance and superfluorescence (SF). Superradiance occurs when a dense ensemble of quantum emitters, usually confined to a volume smaller than the emission wavelength, interacts coherently to emit light in a fast, intense and coherent pulse. In SF, coherence emerges spontaneously, making the process highly sensitive to environmental decoherence and thus difficult to achieve, especially in solid-state systems. An important counterpart to superradiance is subradiance, a collective effect in which emitters interfere destructively, leading to suppressed and prolonged emission, offering further control over light-matter interactions.

Recent discoveries in two-dimensional materials, particularly hexagonal boron nitride (hBN), offer a promising new direction. Specific defects in hBN, most notably the « blue » (435 nm) and « green » (565 nm) defects, exhibit ideal characteristics such as strong isolation in a wide bandgap host, nearly identical bright emisssion, long photoluminescence lifetimes, and coherence times close to the theoretical limit. These defect ensembles can also be arranged deterministically with sub-wavelength precision, enabling detailed exploration of collective emission phenomena.

This project proposes to investigate collective effects in hBN defects and ultimately tailor the defects’ emission rates using a novel strategy that combines:

1. The use of stable hBN defects arranged in subwavelength-scale arrays,
2. Tip-Enhanced Photoluminescence for nanometer-scale spatial and spectral mapping, and
3. Integration into waveguides, enabling long-range interactions between emitters. mediated by guided optical modes.

A metallic scanning probe tip is used to locally enhance the photoluminescence signal from individual defects within a cluster in hexagonal boron nitride . By scanning the tip across the sample surface while collecting the enhanced emission, spatially resolved spectral information is obtained with nanometer precision. This technique enables high-resolution 3D mapping of the emitters’ positions, emission wavelengths, and polarization characteristics, providing critical insight into the spatial arrangement and optical properties of defects for studying collective effects.

Research project selected under the 2025 call for proposals

Principal Investigator : Andrea BALOCCHI

Involved Teams :

• LPCNO/OPTO
• CEMES/NeO

Research project selected under the 2025 call for proposals