For years, quantum computing has been talked about as a future challenge for cybersecurity, something to worry about once powerful quantum machines actually materialise. But that future is arriving faster than many expected. While we’re still some way from large-scale, fault-tolerant systems, progress in quantum hardware is already forcing governments, operators, and security specialists to rethink how we protect the data we rely on every day.
One technology now moving steadily from the lab into real-world networks is Quantum Key Distribution (QKD). Unlike traditional cryptography, which depends on certain mathematical problems staying hard to solve, QKD relies on the behaviour of individual photons to share encryption keys securely. If anyone tries to intercept those photons, their quantum state changes and the intrusion is immediately detectable. It’s a brilliantly simple principle, but until recently, one that was difficult to engineer into practical systems.
But that picture is changing. Advances in sensing technologies, particularly high-sensitivity infrared detectors, are giving QKD the practical boost it has long needed. These detectors act as the ‘eyes’ of the system, spotting incredibly faint quantum signals, often just a single photon at a time. Improvements here translate directly into longer distance communications, higher key rates and lower error levels, all of which are essential if QKD is to operate alongside conventional telecoms equipment.
Within this wider sensing landscape, avalanche photodiodes (APDs) have become especially important. Because they amplify the tiny electrical signal generated by an individual photon, APDs effectively set the performance limits of many QKD receivers. As APD technology has advanced, with lower noise, higher gain and more stable operation, the gap between laboratory demonstrations and deployable QKD has narrowed significantly. The detector advances emerging from research groups and companies, including Phlux Technology, are a key factor in this progress.
Why QKD is gaining traction now
Several forces are converging. First, there’s growing recognition that ‘harvest now, decrypt later’ attacks are a real concern. Data intercepted today may remain sensitive for decades – long enough for future quantum computers to threaten it. Second, large-scale investment is arriving through national quantum-secure communication initiatives, from Europe’s EuroQCI programme – which aims to build a secure quantum communication infrastructure spanning the EU – to UK projects such as Marconi – an Innovate UK-backed initiative exploring how quantum-secure links could be delivered over both terrestrial and satellite networks. However, the most decisive shift is technological. Historically, QKD systems were limited by detector noise, sensitivity and strict cooling requirements. Today’s APDs are far more capable. With lower noise floors and improved gain, they can detect single-photon events with far greater clarity. This isn’t just a modest improvement – it fundamentally changes what QKD links can achieve. Crucially, many modern APDs also operate reliably at higher temperatures, reducing system complexity, not least in terms of thermal management, and making deployments in data centres or telecoms environments far more realistic.
Fibre links, free space, and the role of satellites
Most commercial QKD demonstrations today use optical fibre, with distances of around 100-200km increasingly routine. Fibre attenuation remains a challenge, though: every decibel of loss matters when dealing with single photons. This is where high-performance detectors prove their worth, extending the practical reach of QKD systems and improving their resilience.
At the same time, a fast-moving effort is underway to take QKD above the atmosphere. Free-space and satellite-based QKD help bypass fibre’s range limitations entirely. China, Europe and others have already demonstrated intercontinental quantum-secure key exchanges using satellite downlinks, and the technology is maturing rapidly.
These systems place even greater demands on detectors, which must cope with low photon fluxes, atmospheric turbulence, background light, and extreme environmental conditions. Continued improvements in infrared sensing and APDs make these links increasingly robust, helping bring global quantum-secure communication within reach.
Beyond the hype: how QKD fits into real-world security
It’s important to recognise that QKD won’t replace all existing cryptography. Instead, it complements post-quantum cryptography (PQC), which strengthens software-based encryption schemes against quantum attack. PQC provides broad, scalable protection; QKD offers physics-based security for the most sensitive or long-lived data.
We’re likely heading toward hybrid architectures where PQC, QKD and classical encryption operate together. Telecom operators are already experimenting with these approaches. The real question is not whether QKD or PQC ‘wins’, but where each provides the most value. For government, defence, critical infrastructure and high-value commercial links, QKD is becoming increasingly attractive.
Looking ahead
Over the next decade, several trends will shape QKD’s evolution:
• Deeper integration with classical optical systems, allowing QKD to be deployed with minimal disruption
• Further advances in detector technology, still one of the biggest levers for performance and cost
• Growing standardisation, giving operators confidence in interoperability and long-term support
The overarching story is one of maturation. QKD is no longer a theoretical curiosity or a niche physics experiment. With better detectors, more reliable components and substantial government backing, it is steadily becoming a practical tool for securing tomorrow’s networks. We may still be at the early stages, but the direction of travel is clear: quantum-secure communication is moving out of the lab and into infrastructure – and advances in infrared sensing technology are helping to open that door.
About the author:
Christian Rookes is VP Marketing at Phlux Technology, a manufacturer of avalanche photodiode (APD) infrared sensors based on Sheffield, UK. He has over 25 years’ experience in technical marketing in semiconductor and optical communication fields. Christian holds a BSc in Engineering and Physics from Loughborough University and an MBA Essentials Certificate from the London School of Economics. He holds two patents, including one related to impedance matching for laser diode circuits.
