The reliable manipulation of the speed at which light travels through objects could have valuable implications for the development of various advanced technologies, including high-speed communication systems and quantum information processing devices. Conventional methods for manipulating the speed of light, such as techniques leveraging so-called electromagnetically induced transparency (EIT) effects, work by utilizing quantum interference effects in a medium, which can make it transparent to light beams and slow the speed of light through it.

Despite their advantages, these techniques only enable the reciprocal control of group velocity (i.e., the speed at which the envelope of a wave packet travels through a medium), meaning that a light beam will behave the same irrespective of the direction it is traveling in while passing through a device. Yet the nonreciprocal control of light speed could be equally valuable, particularly for the development of advanced devices that can benefit from allowing signals to travel in desired directions at the desired speed.

Researchers at the University of Manitoba in Canada and Lanzhou University in China recently demonstrated the nonreciprocal control of the speed of light using a cavity magnonics device, a system that couples microwave photons (i.e., quanta of microwave light) with magnons (i.e., quanta of the oscillations of electron spins in materials).

Among the crystalline materials whose edges host exotic quantum states are the Dirac semimetal and the Chern insulator. In the semimetal, the edge states are localized and not protected from perturbations by their topology; in the insulator, they move in one direction and are protected. Proposed by theorists in 2011, a hybrid phase called a Chern semimetal simultaneously hosts localized and one-way edge states, both with topological protection (see Synopsis: Quantum Hall Anomaly in 3D). Now Jianfeng Chen and Cheng-Wei Qiu at the National University of Singapore and their colleagues have realized this phase in a two-dimensional photonic metamaterial [1]. The researchers say that their system provides a platform for nanophotonic applications and a playground for topological physics.

The researchers built a honeycomb-shaped, single-layer array of millimeter-sized magnetic rods. They then applied a carefully tuned, spatially varying magnetic field to this array, creating a pattern in which only specific rods were magnetized. Lastly, they placed a source of microwaves at the array’s boundary and observed how the microwave radiation traveled through the structure. The team found that the magnetization pattern caused some radiation to localize at the array’s boundary and other radiation to move in one direction around the boundary. All these edge states were topologically protected in that they were immune to scattering caused by slight differences in the alignment, shape, and size of the rods and other material imperfections.

Thanks to the coexistence and potential hybridization of localized and one-way states, a photonic Chern semimetal can reduce the speed of transmitted radiation. The researchers found that their metamaterial exhibited a slowdown factor of up to 30 while preserving the radiation’s topological protection. They say that this capability could be useful for nanophotonic technology.

Quantum materials exhibit remarkable emergent properties when they are excited by external sources. However, these excited states decay rapidly once the excitation is removed, limiting their practical applications.

A team of researchers from Harvard University and the Paul Scherrer Institute PSI have now demonstrated an approach to stabilize these fleeting states and probe their quantum behavior using bright X-ray flashes from the X-ray free electron laser SwissFEL at PSI. The findings are published in the journal Nature Materials.

Some materials exhibit fascinating quantum properties that can lead to transformative technologies, from lossless electronics to high-capacity batteries. However, when these materials are in their natural state, these properties remain hidden, and scientists need to gently ask for them to pop up.

A project led by the University of Melbourne’s Dr. Manjith Bose and Professor Jeff McCallum, who are also members of the ARC Center of Excellence for Quantum Computation and Communication Technology, has identified a promising class of superconductors that may potentially avoid the need for high levels of cryogenic cooling. These advanced materials can be manufactured, be integrable and be compatible using standard silicon and superconducting electronics approaches.

To optimize the growth of these silicide superconductors, Dr. Bose and Prof. McCallum are making extensive use of high–temperature neutron reflectometry on the Spatz reflectometer at ANSTO’s Australian Center for Neutron Scattering.

Neutrons are an ideal tool for exploring extreme sample environments, such as the high pressure, temperatures or fields that are present when manufacturing circuit elements. This is because neutrons can penetrate through most common metals, allowing one to see reflective thin films deep inside furnaces, magnets and cryo-chambers.