New forms of photons open the door to advanced optical technologies

New forms of photons open the door to advanced optical technologies
New forms of photons open the door to advanced optical technologies

Researchers at the University of Twente in the Netherlands have gained important insights into photons, the elementary particles that make up light. They “behave” in a surprisingly greater variety than the electrons that surround atoms, but they are also much easier to control.


Photons: the elementary particles that make up light

These new insights have broad applications, from smart LED lighting to new photonic bits of information driven by quantum circuits to sensitive nanosensors. Their findings were published in Physical Review B.

In atoms, tiny elementary particles called electrons occupy regions around the nucleus in shapes called orbitals. These orbitals indicate the probability of finding an electron in a certain region of space. Quantum mechanics determines the shape and energy of these orbitals. Like electrons, researchers also describe the region of space where a photon is most likely to be found using orbitals.

Researchers from the University of Twente have studied these photonic orbitals and discovered that by carefully designing specific materials, they can create and control these orbitals with a wide variety of shapes and symmetries. These findings have potential applications in advanced optical technologies and quantum computing.

First author Kozon explains: “In chemistry textbooks, electrons always orbit the small atomic nucleus in the middle of the orbital. So the shape of an electron orbital cannot deviate much from a perfect sphere. With the photon, orbitals can have any arbitrary shape that you design by combining different optical materials in designed spatial arrangements.”


The researchers conducted a computational study to understand how the photon behaves when confined in a specific 3D nanostructure consisting of tiny pores (a photonic crystal). These voids are intentionally designed to have defects, creating a superstructure that isolates the photonic states from their surroundings.

Physicists Vos and Lagendijk say: “Given the rich toolbox of nanotechnology, it is much easier to design ingenious nanostructures with new photonorbitals than to modify atoms to create new electronic orbitals and new chemistries.”

Photonic orbitals are important for the development of advanced optical technologies, such as efficient lighting, quantum computing, and sensitive photonic sensors. Researchers have also studied how these nanostructures enhance the local density of optical states, which is important for applications in cavity quantum electrodynamics.

They found that structures with smaller defects showed greater improvement than structures with larger defects, making them more suitable for integrating quantum dots and creating single-photon networks.

New device precisely controls photon emissions for more efficient wearable displays

Recently, a team of chemists, mathematicians, physicists and nano-engineers at the University of Twente in the Netherlands developed a device to control the emission of photons with unprecedented precision. This technology could lead to more efficient miniature light sources, sensitive sensors and stable quantum bits for quantum computing.

The part of your smartphone that consumes the most energy is the screen. By reducing unwanted energy leaking from the screen, you extend the life of your smartphone. Imagine if your smartphone only had to charge once a week. However, to increase efficiency, you need to be able to emit photons in a more controlled way.

The researchers developed the “MINT toolbox”: a set of tools from the scientific disciplines of mathematics, computer science, natural sciences and technology. This toolbox included advanced chemical tools. The most important were polymer brushes, small chemical chains that can hold photon sources in a certain place.


First author Andreas Schulz explains: “The polymer brushes are grafted in solution onto porous surfaces in a so-called silicon photonic crystal. A rather complicated experiment. We were therefore very excited when we saw in separate X-ray imaging studies that the photon sources were placed in the right positions on top of the brushes.”

By adding nanophotonic tools, the team showed that excited light sources are inhibited by almost 50 times. In this situation, a light source remains excited for 50 times longer than normal. The spectrum matches the theoretical spectrum calculated with advanced mathematical tools very well. Second author Marek Kozoň says: “The theory predicts zero light because it is an infinitely extended fictitious crystal. In our real finite crystal, the emitted light is not zero, but so small that it is a new world record.”

The new results promise a new era for efficient lasers and miniature light sources, for qubits in photonic circuits with greatly reduced disturbances (due to elusive vacuum fluctuations). Willem Vos says: “Our multi-toolbox opens up possibilities for completely new applications that benefit from highly stabilized excited states. These are fundamental for photochemistry and could become sensitive chemical nanosensors.”

Many photons are better than one for advancing quantum technologies

Quantum objects, such as electrons and photons, behave differently from other objects in ways that make quantum technology possible. Therein lies the key to unlocking the mystery of quantum entanglement, in which multiple photons exist in multiple modes or frequencies.

In the pursuit of photonic quantum technologies, previous studies have demonstrated the usefulness of Fock states. These are multiphoton, multimodal states made possible by cleverly combining a number of single-photon inputs using so-called linear optics. However, some essential and valuable quantum states require more than this photon-by-photon approach.

Now, a team of researchers from Kyoto University and Hiroshima University has theoretically and experimentally confirmed the unique advantages of non-Fock states, or iNFSs, complex quantum states that require more than a single photon source and linear optical elements. The study was published in the journal Science Advances.

“We successfully confirmed the existence of the iNFS using a multi-photon optical quantum circuit,” said corresponding author Shigeki Takeuchi of the Graduate School of Engineering.


“Our research will lead to breakthroughs in applications such as optical quantum computers and optical quantum sensors,” adds co-author Geobae Park.

The photon is a promising carrier because it can be transmitted over long distances while maintaining its quantum state at a constant room temperature. Harnessing many photons in multiple modes would realize long-range optical quantum cryptography, optical quantum sensing, and optical quantum computing.

“We have painstakingly generated a complex type of iNFS by utilizing our Fourier transform photonic quantum circuit to manifest two photons in three different paths, which is the most difficult conditional coherence phenomenon to achieve,” explains co-author Ryo Okamoto.

In addition, this study compared another phenomenon with the widely used quantum entanglement, which appears and disappears by simply passing through a single linear optical element. Quantum entanglement is a quantum state with two or more states entangled in a superposition between two separate systems.

“Remarkably, this study shows that the properties of the iNFS do not change when passed through a network of many linear optical elements, which represents a leap forward in quantum optical technology,” said co-author Holger F. Hofmann of Hiroshima University.

Takeuchi’s team hypothesizes that the iNFS exhibits conditional coherence, a somewhat mysterious phenomenon in which the detection of even a single photon implies that the remaining photons are in a superposition of multiple paths.

“Our next step will be to realize large-scale multi-mode, multi-photon and quantum optical circuit chips,” Takeuchi announces.