Perovskite Design Boosts Light-Matter Interaction over Twentyfold

Amir Rahmani and colleagues at the Institute of Physics present a new approach to achieving slow light, where photon density increases and nonlinear effects become more pronounced. Their design uses a dielectric superlattice structure to create conditions for key light-matter interaction between photons and semiconductor excitons. This results in a more than 20-fold enhancement of the single-particle phase shift. The findings offer a promising pathway towards realising strong, accessible interactions for solid-state integrated optics and potentially advances the field towards few-photon quantum technologies.

Dielectric superlattice design enables strong light-matter interaction and phase shift enhancement

Researchers Amir Rahmani and colleagues at the Institute of Physics, Polish Academy of Sciences achieved a single-particle phase shift exceeding 20 times that of a regular waveguide. This breakthrough surpasses a vital threshold for accessing the few-photon quantum regime, enabling advanced quantum technologies where individual photons strongly influence each other. The enhancement resulted from designing a dielectric superlattice, a carefully structured material that slows light and amplifies its interaction with semiconductor excitons, bound pairs of electrons and holes behaving as single particles. The significance of exceeding this threshold lies in the ability to create scenarios where photon-photon interactions become appreciable, a cornerstone of quantum computation and communication protocols. Traditional approaches to enhancing light-matter interaction often suffer from limitations in scalability and efficiency, hindering the development of practical quantum devices.

A nearly-flat band within the superlattice was characterised by low group velocity and minimal group velocity dispersion, both fundamental for amplifying nonlinear effects using ultrashort pulses. Group velocity describes the speed at which the envelope of a wave packet propagates, while group velocity dispersion dictates how different wavelengths within that packet spread out as it travels. Minimising dispersion is crucial for maintaining the integrity of ultrashort pulses, preventing them from broadening and losing their effectiveness in nonlinear processes. Simulations predict a sharp increase in local field intensity, stemming from spatial compression of the optical mode, and contributing to an additional enhancement of nonlinear response proportional to the inverse square of the group velocity. This inverse square relationship highlights the substantial benefit of achieving extremely low group velocities; even a modest reduction in velocity translates to a significant amplification of nonlinear effects. Room-temperature operation and scalable production, however, remain key challenges for practical device implementation. Maintaining performance at room temperature is essential for widespread adoption, while scalable fabrication techniques are needed to move beyond laboratory prototypes.

Structural dispersion engineering underpins this design, differing from approaches reliant on bound states in the continuum which can be sensitive to material imperfections. Bound states in the continuum, while offering another route to slow light, are often highly susceptible to variations in material quality and fabrication tolerances. This sensitivity can lead to unpredictable performance and limit the reliability of devices. The perovskite-based structure facilitated this enhancement, exhibiting a single-particle phase shift exceeding 20 times that of a standard waveguide, representing a substantial advance towards manipulating individual photons. Purely periodic structures exhibit fast pulse spread, a limitation this approach circumvents. Periodic structures, lacking the carefully engineered defect bands of the superlattice, typically allow pulses to broaden rapidly due to dispersion, diminishing their utility for nonlinear optics

Perovskite Fishbone Superlattice for Enhanced Nonlinear Optical Interactions

A layered dielectric superlattice, designed to manipulate light propagation, was fabricated utilising a perovskite-based material. Perovskites, a class of materials with a specific crystal structure, are increasingly favoured in photonics due to their high refractive index and strong light absorption properties. The structure featured a corrugated ‘fishbone’ design with a period of 0.13μm and a defect created by altering the width of one cell to achieve a supercell length, L. This ‘fishbone’ geometry, resembling the skeletal structure of a fish, is specifically engineered to create a photonic band gap, a range of wavelengths that are forbidden from propagating within the structure. The introduction of a defect, by modifying a single cell within the periodic structure, creates a localised state within the band gap, forming a resonant cavity for light. This configuration created a photonic band gap and a nearly-flat defect band, crucial for slowing light and minimising group velocity dispersion. The flatness of the defect band is directly related to the low group velocity, as a flat band implies a minimal change in the energy of photons within that band, reducing their tendency to disperse.

Nanoscale phase manipulation demonstrates significant progress towards compact optical devices

Current research increasingly focuses on manipulating light at the nanoscale to create more efficient and compact optical devices. This work offers a pathway to stronger interactions between light and matter than previously attainable in solid-state systems, potentially revolutionising fields like telecommunications and sensing. The current demonstration enhances a single-particle phase shift, a subtle change in light’s wave, but does not yet demonstrate actual quantum behaviour. The single-particle phase shift represents the accumulated phase change experienced by a photon as it propagates through the structure, and its enhancement is a crucial step towards achieving the strong light-matter coupling necessary for quantum effects.

Deliberately reducing light’s velocity, known as slow light, increases photon density and amplifies nonlinear effects, important for manipulating light at a small scale. This new design provides stronger control of light within solid materials, exceeding previous limitations in integrated optics. Integrated optics aims to miniaturise optical circuits onto a single chip, analogous to electronic microchips, offering advantages in terms of size, weight, and power consumption. Engineering a carefully structured material has demonstrated a significant enhancement of how light interacts with semiconductor excitons, bound pairs of electrons and holes behaving as single, temporary particles. This achievement unlocks potential for manipulating photons on a nanoscale, paving the way for more compact and efficient optical devices. The ability to confine light and enhance its interaction with matter at the nanoscale is essential for developing advanced optical functionalities, such as all-optical switching, signal processing, and quantum information storage.

The researchers successfully demonstrated an enhancement of the single-particle phase shift by a factor of more than 20 using a perovskite-based dielectric superlattice structure. This achievement represents a significant step towards stronger light-matter interactions within solid-state integrated optics, allowing for greater control of light at a small scale. By slowing light and increasing photon density, the design enhances nonlinear effects crucial for manipulating light on a nanoscale. The work provides a blueprint for accessible strong interactions, potentially enabling the development of more compact optical devices.