A new on-demand photon source reaches nearly 92% interference visibility in the telecom C-band, overcoming a decade-long challenge.
A long-standing bottleneck in photonic quantum technology may finally be easing. Researchers in Germany have demonstrated a deterministic photon source that operates in the telecom C-band while delivering record-high photon indistinguishability.
The advance targets a problem that has frustrated quantum optics laboratories for more than a decade.“The lack of a high-quality on-demand C-band photon source has been a major problem in quantum optics laboratories for over a decade — our new technology now removes this obstacle,” says Prof. Stefanie Barz.The work comes from scientists at the University of Stuttgart. The team reports a source that produces single photons on demand at 1550 nanometers. That wavelength aligns with global fiber-optic communication networks.The result brings deterministic photon sources closer to practical quantum computing and networking systems.Quantum technologies rely on photons behaving in exactly the same way. Identical photons interfere with one another, allowing quantum systems to amplify or suppress measurement outcomes.This interference underpins protocols in quantum computing, sensing, and secure communications.If photons differ even slightly, interference degrades. That loss directly limits system performance. High-quality interference therefore becomes a strict requirement, not a bonus feature.Nico Hauser, a scientist at the University of Stuttgart and first author of the study, explains that practical quantum systems need photons that arrive together and behave identically.Many existing sources struggle to meet both conditions at once, especially at telecom wavelengths.Telecom wavelength barrierTelecom networks operate most efficiently in the C-band near 1550 nanometers. Optical fibers show minimal loss in this region. Any scalable photonic quantum system must work there.Quantum dots have delivered near-perfect photon properties at shorter wavelengths. Extending that performance into the telecom range proved difficult. Previous deterministic quantum dot sources in the C-band reached interference visibilities near 72 percent. That level fell short of what demanding quantum protocols require.Probabilistic sources, such as spontaneous parametric down-conversion, offer higher indistinguishability. However, they cannot guarantee when a photon appears.That randomness prevents synchronization across multiple sources.“Our new device now lifts this roadblock,” says Stefanie Barz.Deterministic breakthroughThe Stuttgart team built its source using indium arsenide quantum dots embedded in indium aluminium gallium arsenide. They integrated the structure into a circular Bragg grating resonator. The resonator boosts photon emission efficiency.The researchers tested multiple excitation methods. They found that lattice vibration-mediated excitation outperformed higher-energy optical pumping. This approach reduced noise and preserved photon coherence.Using this scheme, the device achieved a raw two-photon interference visibility of nearly 92 percent.That figure marks the highest reported value for any deterministic single-photon source operating in the telecom C-band.The result places deterministic sources in the same performance class as probabilistic ones, while retaining on-demand operation.“Our ability to simultaneously achieve deterministic single-photon generation, emission in the telecom C-band, and high photon indistinguishability will now enable applications that require large numbers of synchronized photons, from measurement-based quantum computing to quantum repeaters for long-distance communication,” says Hauser.The advance removes a key technical barrier. It also brings large-scale photonic quantum systems closer to deployment on existing fiber networks.The study is published in the journal Nature Communications.
Quantum Computing Quantum Networking Quantum Optics Single-Photon Sources
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