Scientists have found a intelligent new strategy to management the sunshine emitted by quantum dots — tiny crystals that may launch particular person photons.
The advance might result in quicker, cheaper, and extra sensible quantum applied sciences, from ultra-secure communication methods to experiments that discover the unusual foundations of quantum physics.
The Challenge of Single-Photon Sources
Quantum dots are tiny semiconductor constructions able to releasing single photons on demand, making them sturdy candidates for future photonic quantum computer systems. The issue is that no two quantum dots are precisely the identical, and every can emit gentle at barely totally different colours. This variation prevents researchers from combining a number of dots to create multi-photon states.
To work round this, scientists usually depend on a single quantum dot after which cut up its gentle into totally different spatial and temporal modes with the assistance of a quick electro-optic modulator. The downside is that these modulators are expensive, usually require extremely custom-made designs, and could be inefficient, resulting in vitality losses throughout the system.
An Elegant Optical Solution Emerges
A analysis collaboration led by Vikas Remesh of the Photonics Group on the Department of Experimental Physics, University of Innsbruck, along with companions from the University of Cambridge, Johannes Kepler University Linz, and different establishments, has now demonstrated a strategy to bypass these challenges. Their methodology depends on a completely optical course of referred to as stimulated two-photon excitation. This method permits quantum dots to emit streams of photons in distinct polarization states with out the necessity for digital switching {hardware}.
In exams, the researchers efficiently produced high-quality two-photon states whereas sustaining glorious single-photon traits.
How the Technique Works in Practice
“The methodology works by first thrilling the quantum dot with exactly timed laser pulses to create a biexciton state, adopted by polarization-controlled stimulation pulses that deterministically set off photon emission in the desired polarization,” explain Yusuf Karli and Iker Avila Arenas, the study’s first authors.
“It was a fantastic experience for me to work in the photonics group for my master’s thesis, remembers Iker Avila Arenas, who was part of 2022-2024 cohort of the Erasmus Mundus Joint Master’s program in Photonics for Security Reliability and Safety and spent 6 months in Innsbruck.
Moving Complexity to the Optical Stage
“What makes this approach particularly elegant is that we have moved the complexity from expensive, loss-inducing electronic components after the single photon emission to the optical excitation stage, and it is a significant step forward in making quantum dot sources more practical for real-world applications,” notes Vikas Remesh, the study’s lead researcher.
Looking ahead, the researchers envision extending the technique to generate photons with arbitrary linear polarization states using specially engineered quantum dots.
Real-World Quantum Applications
“The study has immediate applications in secure quantum key distribution protocols, where multiple independent photon streams can enable simultaneous secure communication with different parties, and in multi-photon interference experiments which are very important to test even the fundamental principles of quantum mechanics,” explains Gregor Weihs, head of the photonics research group in Innsbruck.
The research, published in npj Quantum Information, represents a collaborative effort involving expertise in quantum optics, semiconductor physics, and photonic engineering.
Reference: “Passive demultiplexed two-photon state generation from a quantum dot” by Yusuf Karli, Iker Avila Arenas, Christian Schimpf, Ailton Jose Garcia Junior, Santanu Manna, Florian Kappe, René Schwarz, Gabriel Undeutsch, Maximilian Aigner, Melina Peter, Saimon F. Covre da Silva, Armando Rastelli, Gregor Weihs and Vikas Remesh, 11 August 2025, npj Quantum Information.
DOI: 10.1038/s41534-025-01083-0
The work was supported by the Austrian Science Fund (FWF), the Austrian Research Promotion Agency (FFG), and the European Union’s research programs.
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