Breakthrough Quantum Photon Source Delivers On-Demand Identical Light in Telecom Band
Record-Quality Single Photon Mark Major Step Toward Scalable Quantum Computing
A research team from the University of Stuttgart and Julius-Maximilians-Universität Würzburg, led by Professor Stefanie Barz of the University of Stuttgart, has unveiled a new single-photon source that delivers both on-demand performance and record-breaking photon quality in the telecommunications C-band.
The breakthrough marks a significant advance towards scalable photonic quantum computing and secure quantum communication.
"For more than ten years, the absence of a high-quality, on-demand C-band photon source has posed a serious challenge for quantum optics laboratories," Professor Barz says. "Our technology now overcomes this long-standing barrier."
The Key: Identical Photons on Demand
In everyday life, standing out is often seen as a virtue and few people aspire to be exactly the same as everyone else. In the world of quantum technology, however, the opposite is true. Here, perfect indistinguishability is essential.
Quantum particles such as photons must be identical in every measurable property to interfere with one another, much like noise-cancelling headphones use precisely inverted sound waves to eliminate unwanted background noise.
When photons behave in perfect synchrony, the likelihood of certain measurement outcomes can be enhanced or suppressed. These uniquely quantum effects underpin some of the most powerful emerging technologies, including quantum computing and quantum networking. For such systems to function reliably, extremely high-quality photon interference is a fundamental requirement.
High-Quality Photon Generation Demonstrated
Now, Nico Hauser, a researcher at the University of Stuttgart and lead author of the study, together with his colleagues, has demonstrated a photon source that meets these demanding criteria.
The system generates highly indistinguishable photon on demand and operates at wavelengths fully compatible with today's telecommunications infrastructure, making it especially promising for real-world applications.
The Telecom Challenge in Quantum Technologies
For photonic quantum technologies to scale beyond the laboratory, they must connect seamlessly with the fiber-optic networks that underpin today's data-driven society.
In practical terms, this demands photon sources that operate in the telecommunications C-band, at around 1,550 nanometers, where signal losses in silica fibers are at their lowest.
Meeting this requirement has proved challenging. Although quantum dot sources—nanoscale structures that behave like artificial atoms—have delivered near-perfect photon performance at shorter wavelengths between 780 and 960 nanometers, reproducing the same quality within the telecom range has remained an elusive goal.
Photon Made to Order
Deterministic vs Probabilistic Sources
The most widely used alternative, known as spontaneous parametric down-conversion (SPDC), is capable of producing photons of exceptionally high quality, but only in a probabilistic manner.
In simple terms:
- There is no way to know precisely when a photon will be generated
- Synchronization between multiple sources becomes impossible
This unpredictability makes it impossible to synchronize multiple photons from different sources for protocols that require them to arrive at the same time.
Deterministic sources, by contrast, emit a photon each time they are triggered.
Overcoming a Long-Standing Performance Barrier
While quantum-dot devices capable of producing C-band photons do exist, they have so far achieved two-photon interference visibilities of only around 72% —a key indicator of photon indistinguishability.
This falls well short of the performance routinely delivered by SPDC and is insufficient for the most demanding quantum applications.
"Our new device removes this long-standing roadblock," says Stefanie Barz.
Toward Scalable Photonic Quantum Systems
The newly developed photon source created by Hauser and colleagues is built around:
- Indium arsenide quantum dots
- Indium aluminium gallium arsenide structures
- A circular Bragg grating resonator
This design significantly boosts photon emission.
By systematically testing multiple excitation strategies, the researchers discovered that triggering through elementary vibrations in the crystal lattice—rather than using higher-energy optical pumping—delivered superior performance.
Operating in this regime, the device achieved a raw two-photon interference visibility approaching 92%, the highest ever reported for a deterministic single-photon source in the telecommunications C-band.
New Applications for Perfectly Synchronized Photons
The new results elevate deterministic quantum dot sources into the same performance class as probabilistic SPDC approaches, without sacrificing the ability to produce photons exactly when required.
According to Hauser, combining:
- On-demand single-photon generation
- Telecom C-band operation
- Exceptional photon indistinguishability
opens the door to technologies that rely on many perfectly synchronized photons, including:
- Measurement-based quantum computing
- Quantum repeaters for secure long-range communication
The study appears in Nature Communications.
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