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Researchers have harnessed nonlocal artificial materials to create optical systems that emulate parallel spaces, wormholes, and multiple realities. A single material acts as two distinct optical media or devices simultaneously, allowing light to experience different properties based on entry boundaries. Demonstrations include invisible optical tunnels and coexisting optical devices, opening new avenues for compact, multifunctional optical devices by introducing nonlocality as a new degree of freedom for light manipulation.

What if a single space could occupy two different objects at once, depending on how photons access this space? Scientists have brought this sci-fi concept to life, creating optical systems that mimic the exotic phenomena of parallel universes and wormholes.

In a study in Nature Communications, researchers in China used nonlocal artificial materials to develop "photonic parallel spaces."

By manipulating shifted dispersion relations in the momentum space, they managed to create a single material that behaves as two distinct optical media or devices simultaneously.

Light entering from one boundary experiences one set of optical properties, while light entering the space from another boundary encounters a completely different set, with no interference between them. This emulates the magical wardrobe from The Lion, the Witch, and the Wardrobe, where different doors lead to separate worlds located at the same place (behind the door).

"This approach lets us emulate higher-dimensional phenomena in a photonic lab," said Yun Lai, professor from the school of physics at Nanjing University.

"It's like hosting two optical realities in one material, opening the door to compact, multifunctional devices that were previously unimaginable."

The team demonstrated two remarkable phenomena. First, in microwave experiments, the researchers designed an elongated nonlocal artificial material acting as a photonic "wormhole," i.e. invisible optical tunnels.

When a Gaussian beam enters the short side, it is confined in the material and transmits as if traveling through a zero-refractive-index waveguide. When a beam is incident upon the long side, the material exhibits near-zero reflection due to the omnidirectional impedance matching in a parallel photonic space, rendering it effectively invisible to external light.

Secondly, they achieved "photonic multiple realities," where the same material mimics arbitrary optical objects or devices based on the entry boundary.

In one example, the material scatters light like a boat-shaped object for light from one boundary, but behaves like a tree-shaped scatterer of light from another. In another example, it simultaneously functions as a convex lens and a concave lens, operating independently as if the two lenses are located in separate dimensions.

"We're not building real wormholes or multiverses, but we're making these concepts practical for engineering," the researcher noted. "This could revolutionize a range of fields, from highly integrated photonic chips and compact optical systems to photonic information processing, by leveraging nonlocality as a new degree of freedom."

This breakthrough could transform integrated photonics by enabling denser optical devices without crosstalk and multiple functions coexisting in the same space.

By emulating high-dimensional physics, this work opens a gateway to multifunctional devices that transcend their dimensional constraints, heralding a new era for photonics and beyond.