Scientists have discovered a new intelligent way to control the light emitted by quantum points – tiny crystals that can release individual photons.
The advance could lead to faster, cheaper and more practical quantum technologies, ultra-secure communication systems to experiences that explore the strange foundations of quantum physics.
The challenge of unique photon sources
Quantum points are tiny semiconductive structures capable of freeing unique photons on demand, making solid candidates for future quantum photonic computers. The difficulty is that two quantum points are not exactly the same, and everyone can emit light to slightly different colors. This variation prevents researchers from combining several points to create multi-photos states.
To get around this, scientists generally count on a single quantum point, then divide its light into different spatial and temporal modes using a rapid electro-optical modulator. The downside is that these modulators are expensive, often require highly personalized and can be ineffective, resulting in energy loss within the system.
An elegant optical solution emerges
A research collaboration led by Vikas Remesh of the photonics group of the Experimental Physics Department, the University of Innsbruck, as well as partners from the University of Cambridge, Johannes Kepler Linz University and other institutions, has now demonstrated a way to get around these challenges. Their method is based on a fully optical process known as the excitement stimulated with two photons. This technique allows quantum points to issue photon flows in separate polarization states without the need for electronic switching equipment.
In tests, researchers have successfully produced states with two high quality photons while keeping excellent characteristics of unique photons.
How the technique works in practice
“The method works by first exciting the quantum point with laser impulses drawn precisely to create a biexciton state, followed by stimulation impulses controlled by polarization which trigger deterministicly photon Establishment in the desired polarization, ”explains Yusuf Karli and Iker Avila Arenas, the first authors of the study.
“It was a fantastic experience for me to work in the photonics group for my master’s thesis,” recalls Iker Avila Arenas, which was part of the 2022-2024 cohort of the Erasmus Mundus joint master’s program in photonics for reliability and safety of security and spent 6 months in Innsbruck.
Complexity moved to the optical step
“What makes this approach particularly elegant is that we have moved the complexity of expensive electronic components and loss inductors after the issue of unique photons at the stage of optical excitement, and it is a significant step to make quantum sources more practical for applications of the real world,” notes Vikas Remesh, the main study of the study.
For the future, researchers plan to extend the technique to generate photons with arbitrary linear polarization states using specially designed quantum points.
Quantum applications of the real world
“The study has immediate applications in secure quantum keys distribution protocols, where several independent photon flows can allow simultaneous secure communication with different parts, and in multi-photo interference experiences which are very important to test even the fundamental principles of quantum mechanics”, explains Gregor Weihs, head of the photonic research group in Innsbruck.
Research, published in Quantum information NPJrepresents an effort of collaboration involving expertise in quantum, the physics of semiconductors and photonics engineering.
Reference: “State generation with two passive multiplected photons from a quantum point” by Yusuf Karli, Iker Avila Arenas, Christian Schimpf, Ailton Jose Garcia Junior, Santanu Manna, Florian Kappe, René Schwarz, Gabriel Undeutsch, Maximilian Aigner, Melilin Gregor Weihs and Vikas and Vikas Remesh, August 11, 2025, Quantum information NPJ.
DOI: 10.1038 / S41534-025-01083-0
The work was supported by the Austrian Sciences Fund (FWF), the Austrian research promotion agency (FFG) and the European Union research programs.
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