Omnidirectional Suppression of Light Scattering Demonstrated in Three-Dimensional Atomic Arrays

The collective interaction between atoms and light underpins many areas of science and technology, and researchers are continually seeking ways to control this interaction with increasingly precise structures. Yu-Kun Lu, Hanzhen Lin, and Jiahao Lyu, all from the Massachusetts Institute of Technology, alongside colleagues, have now demonstrated the suppression of coherent light scattering within a fully three-dimensional atomic array. This achievement is significant because previous studies largely confined their investigations to lower dimensions, whereas a true three-dimensional arrangement is essential for achieving complete suppression of light scattering in all directions. By creating a three-dimensional array in the form of a Mott insulator, the team not only observes this omnidirectional suppression, but also reveals how residual scattering arises from atomic movement and other processes, opening new avenues for photon storage and the investigation of complex quantum systems.

It is fundamental to both basic science and the design of light-matter interfaces in quantum technologies. Numerous studies over the past decades have focused on arranging atoms in ordered arrays and utilising constructive, or destructive, interference to enhance, or suppress, the coupling to electromagnetic fields, thereby tailoring collective light-matter interactions. These investigations have primarily concentrated on one- and two-dimensional arrangements, but only three-dimensional (3D) arrays can demonstrate destructive interference of coherent light scattering in all directions. This omnidirectional suppression of coherent light scattering in 3D atomic arrays has, thus far, not been experimentally demonstrated.

Light Scattering Probes Ultracold Atomic Gases

Light scattering provides a powerful method for investigating the properties of ultracold atomic gases trapped within optical lattices. This technique extends beyond simple coherent scattering to account for the effects of density fluctuations, atomic interactions, and multiple atoms occupying the same lattice site. The goal is to understand how light scattering reveals information about the complex behaviour of these systems, including transitions between different quantum states. The scattering process is influenced by the arrangement of atoms and their interactions, creating a measurable signal that reflects the system’s properties.

The distinction between coherent and incoherent scattering is crucial; coherent scattering arises from the ordered arrangement of atoms, while incoherent scattering results from density fluctuations and multiple occupancy of lattice sites. A key quantity in this analysis is the structure factor, which represents the total scattering intensity as a function of momentum transfer and directly relates to the density correlations within the system. Interactions between atoms and the discrete nature of the lattice lead to density fluctuations, contributing to incoherent scattering. When multiple atoms occupy a single lattice site, it introduces additional incoherent scattering due to their relative motion.

The Debye-Waller factor accounts for the reduction in scattering intensity caused by thermal or quantum fluctuations. Different factors are used for sites occupied by single or multiple atoms. Light scattering can also be used to probe the superfluid-to-Mott insulator transition, a quantum phase transition where the system changes its behaviour. The Mott insulator phase is characterised by localised atoms and suppressed density fluctuations, while the superfluid phase exhibits long-range coherence. The presence of vacancies, or holes, in the lattice also affects the scattering. Theoretical models are used to calculate density fluctuations and predict the scattering intensity.
D Atomic Arrays Suppress Light Scattering

Researchers have demonstrated a significant reduction in light scattering from a unique three-dimensional arrangement of atoms, a feat not previously observed in experiments. Unlike lower-dimensional atomic arrays where some light scattering always occurs, this 3D arrangement effectively suppresses light scattering in all directions, behaving similarly to a perfect crystal. This suppression arises from the way light waves interfere within the 3D structure, leading to a near-complete cancellation of scattered light. The team created this 3D array using optical lattices, which are light-based traps that hold atoms in precise positions.

Measurements reveal that the observed suppression isn’t due to a lack of atoms, but rather a fundamental property of the 3D arrangement itself. Any residual scattering is attributable to minor imperfections and atomic motion within the lattice, allowing researchers to probe the characteristics of these complex systems. The degree of suppression was quantified by observing how the scattering diminished as the atoms were released from the lattice, confirming the theoretical predictions without needing to adjust any parameters. This breakthrough has important implications for several areas of physics and technology.

The ability to control light scattering in this way opens possibilities for creating highly efficient photon storage devices, where light can be trapped and held for extended periods. Furthermore, the sensitivity of the light scattering measurements to even slight changes in the atomic arrangement provides a powerful new tool for studying the behaviour of atoms in complex, many-bodied systems, including the transition between different quantum states and the identification of defects within the lattice. The observed suppression is substantial, and the method offers a sensitive way to characterise the properties of these quantum materials.

Suppressed Light Scattering Reveals Atomic Fluctuations

Researchers have successfully demonstrated the suppression of light scattering in three-dimensional arrangements of atoms, a phenomenon fundamentally different from what occurs in lower-dimensional systems. This suppression arises from the way atoms collectively interact with light, minimising scattering in all directions, and was observed within a Mott insulator created using optical lattices. The remaining, residual light scattering originates from both the movement of individual atoms and fluctuations in the density of atoms within the many-body system, providing a sensitive probe of these fluctuations. This work establishes a new method for characterising complex quantum systems, particularly those exhibiting superfluidity and Mott insulating behaviour.

The degree of light scattering directly correlates with the density of defects within the atomic array, allowing researchers to map the system’s state and even measure the speed at which phase transitions occur. The technique is minimally disruptive to the system being studied and complements existing microscopy techniques. Future research could utilise this suppression of light scattering to create subradiant states, potentially useful for storing photons, and to further investigate correlations within many-body systems. The team also suggests the method could be applied to a broad range of systems, including those inaccessible to conventional microscopy due to their three-dimensional nature or extremely small spacing.