Quantum surprise: Scientists uncover how matter enables ultrastrong photon coupling

As advances in the quantum realm continue, scientists have found a new way for photon coupling – using matter as the middleman – helping to unlock faster, more energy-efficient technologies for quantum computing and communications.

Specifically, the team at Rice University has created a special 3D structure called a photonic-crystal cavity, which traps light between tiny reflective surfaces, making it bounce around in particular ways, and allowing them to study how light behaves when interacting with electrons, per a recent study.

Light, electrons, and a little bit of quantum magic

Typically, photons don’t interact with each other. However, in this setup, when light bounced around inside the cavity and passed through a thin layer of free-moving electrons exposed to a magnetic field, something new happened – the light and matter became so closely linked that they formed hybrid states, called polaritons.

As Junichiro Kono, the Karl F. Hasselmann Professor in Engineering, professor of electrical and computer engineering and materials science and nanoengineering, and the study’s corresponding author, explained:

“It is well known that electrons strongly interact with each other, but photons do not. (…) This cavity confines light, which strongly enhances the electromagnetic fields and leads to strong coupling between light and matter, creating quantum superposition states — so-called polaritons.”

These polaritons let photons interact indirectly – essentially ‘talking’ to one another through the electrons. This kind of interaction, known as ultrastrong coupling, is so intense that energy bounces back and forth between light and matter before it can escape, creating a deeply entangled state.

What’s more, the study has shown that the way the photons interact depends on polarization – the direction in which the light waves oscillate. In some cases, the light modes remained separate, but in others, they merged into entirely new patterns.

Stronger photon coupling as a step toward quantum tech of the future

With this discovery, the scientists have opened up the possibility of developing new materials where light modes can be controlled through electron interactions – a big deal for quantum computers, which rely on strange quantum states to work. 

By exploring how matter can mediate light interactions, the Rice team may have laid the groundwork for the next generation of quantum technologies and, as Kono said, it “can lead to new protocols and algorithms in quantum computation and quantum communications.”

Elsewhere, scientists have developed a breakthrough method to more easily identify diamonds with certain optically active defects for highly sensitive sensors called qubits, which store quantum data in the electron spin state of the color centers for use in quantum computers.