A hydrogen-filled hollow-core fibre conserves photon statistics during frequency transduction via Raman molecular modulation; weak signals at five hundred and eighty-five nanometers were selectively converted to both seven hundred and seventy-three nanometers, near infrared, and four hundred and seventy-one nanometers, blue, with efficiencies approaching unity. This builds on previous work by proving conservation of more general statistical properties beyond just biphoton correlations. Light can be converted from one colour to another while maintaining its fundamental quantum properties; specifically, faint signals between visible, near-infrared and blue wavelengths shifted with high efficiency using a hydrogen-filled hollow core fibre.
The process relies on ‘molecular modulation’, where vibrations within the gas harness energy to change the frequency of light without introducing significant noise or altering how photons relate to each other. This conversion uses ‘molecular modulation,’ harnessing vibrations within a gas, similar to tiny tuning forks, to change the energy, and therefore colour, of light passing through it. Researchers employed a hydrogen-filled hollow-core fibre, essentially a glass tube filled mostly with air that guides light over long distances with minimal disruption, to achieve this feat.
They selectively shifted faint 585 nanometer (yellow) signals into both near-infrared at 773nm and blue wavelengths at 471nm, achieving efficiencies approaching unity. Key to this is confirmation of preservation of ‘photon-number statistics’, how individual particles of light distribute themselves in a beam, like counting raindrops falling in consistent patterns rather than random bursts.
High Efficiency Wavelength Conversion Preserves Photon Statistics via Molecular Modulation
Near-unity efficiencies, exceeding 95%, were achieved when they selectively converted weak 585nm signals to both 773nm near infrared and 471nm blue wavelengths. This result surpasses previous demonstrations limited to biphoton correlations during frequency conversion. Conservation of photon-number statistics, a more thorough measure of light’s quantum state than previously proven by experiments using Raman molecular modulation within hydrogen-filled hollow-core fibres.
Carefully controlling dispersion, how different colours travel through the fibre, independently selected up or down-conversion processes for maximum efficiency and broad tunability. A flexible platform for linking diverse quantum technologies like single-photon sources and atomic memories in future hybrid networks is now established by preserving these statistical properties alongside large wavelength shifts.
High efficiencies were also achieved converting weak 585nm signals into approximately 471nm blue light, relevant to nitrogen-vacancy centre technology; this extends results beyond earlier work demonstrating similar conversion to 773nm near infrared wavelengths compatible with rubidium-based quantum memories used in sensing applications. Manipulating pump power allowed control over the initial 585nm signal’s statistics, shifting from skewed distributions towards symmetrical ones before transduction within the hollow core fibre.
Wavelength limitations currently hinder scalable quantum networking
This demonstration offers exciting prospects for linking quantum devices, but it remains a ‘proof of concept’. Performance may degrade with different signal characteristics and details regarding how strong this process is beyond 773nm and 471nm are conspicuously omitted.
This limitation raises questions about whether the technique can be readily adapted to accommodate diverse spectral requirements inherent in complex hybrid networks or if further optimisation is needed before widespread implementation becomes viable. They enabled precise phase matching by controlling hydrogen pressure at either ~16.7 bar for up-conversion or ~28.1 bar for down-conversion; these settings maximised efficiency and allowed independent selection of frequency shifts.
Frequency transduction leaves photon-number statistics unchanged, shifting light’s colour without altering its quantum properties, building on earlier work showing preservation applies to more complex statistical behaviours than simpler correlations between photons. Weak signals from yellow (585nm) were efficiently converted to both near-infrared and blue wavelengths (773nm & 471nm) using hydrogen-filled hollow-core fibres, which are glass tubes guiding light with minimal disruption. These findings pave the way towards building robust long distance connections in future quantum networks by overcoming wavelength limitations that currently hinder scalability.
This research demonstrated that a frequency transduction process, converting light of one color to another, can preserve the original photon-number statistics of weak 585 nanometer signals while shifting them to either 773 or 471 nanometers within a hydrogen-filled hollow-core fiber. This means the quantum properties of the light remain consistent during this conversion, an important feature for interfacing different types of quantum systems. By achieving efficient up- and down-conversion with controlled hydrogen pressure, we open new avenues for quantum communication and computation.
👉 More information
🗞 Preservation of photon statistics upon selective molecular modulation in hollow-core fibers
✍️ Arturo Mena, Pau Arcos, María Sánchez-Hernández, Oskar Arrizabalaga, Joseba Zubia and David Novoa (University of the Basque Country (EHU)); Benoit Debord, Frédéric Gérôme and Fetah Benabid (University of Limoges); Nicolas Y. Joly (University of Erlangen-Nürnberg)
🧠 ArXiv: https://arxiv.org/abs/2610.19964
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