Physicists at the Hebrew University of Jerusalem have set a new benchmark in quantum encryption, developing an innovative concept that makes private communication far more secure over much greater distances—surpassing today’s leading technologies.
For decades, experts believed that major advances in quantum encryption could only be realised with perfect optical hardware, specifically light sources capable of emitting single photons at a time. Yet, such sources are exceptionally difficult and costly to build.
The Hebrew University team has upended this notion. Their approach applies pioneering encryption protocols to quantum dots—tiny, engineered semiconductor materials—to transmit encrypted information securely, even with less-than-perfect light sources. Real-world tests have demonstrated that this method outperforms even the best current systems. This breakthrough brings quantum-safe communication much closer to everyday use.
The research, led by PhD students Yuval Bloom and Yoad Ordan, under the guidance of Professor Ronen Rapaport from the Racah Institute of Physics at Hebrew University, was conducted in collaboration with scientists from Los Alamos National Laboratory. Their findings, published in PRX Quantum, introduce a practical solution that dramatically improves quantum encrypted information transfer using light particles—even when equipment is not flawless.
Cracking a Four-Decade Challenge
Quantum key distribution (QKD), long regarded as the holy grail of secure communication, promises unbreakable encryption through the laws of quantum mechanics. However, it has always depended on perfectly engineered single-photon light sources—devices that emit precisely one photon at a time. In practice, creating such devices with absolute accuracy has proven extremely challenging, and prohibitively expensive.
As a workaround, most research has relied on lasers, which are more practical but imperfect. Lasers emit weak light pulses containing a small, unpredictable number of photons—a compromise that limits both security and transmission distance. Security vulnerabilities arise when an eavesdropper intercepts multiple photons in a single pulse, potentially extracting encoded information.
Making the Most of Imperfect Tools
Bloom, Ordan and their colleagues tackled this issue head-on. Rather than waiting for perfect photon sources, they developed two new protocols that work with available technology—sub-Poissonian photon sources based on quantum dots, which are nanoscale particles that mimic the properties of atoms.
By dynamically engineering the optical behaviour of quantum dots and pairing them with nanoantennas, the researchers improved how photons are emitted. They introduced:
A truncated decoy state protocol: An updated version of a widely used quantum encryption technique, adapted for imperfect single-photon sources. This method weeds out hacking attempts that exploit multi-photon emissions.
A heralded purification protocol: A strategy that dramatically enhances signal security, “filtering” excess photons in real time and ensuring only single-photon data is recorded.
Simulations and laboratory experiments revealed these protocols outperform traditional laser-based QKD approaches, extending secure key distribution by more than three decibels—a notable advance in the field.
Turning Theory into Practice
To validate their innovation, the team built an operational quantum communication system using a room-temperature quantum dot source. They implemented a reinforced version of the well-known BB84 protocol—the foundation of many QKD systems—and demonstrated their approach is both practical and superior to established methods. What makes this work especially significant is its broad compatibility: their approach can be used with a wide range of quantum light sources, reducing costs and technical barriers to large-scale quantum-secure communication.
“This is a significant step towards practical, accessible quantum encryption,” said Professor Rapaport. “It shows that we don’t need perfect hardware for superior performance—we simply need to be more inventive with what we have.”
Co-lead author Yuval Bloom added:
“We hope this work opens the door to real-world quantum networks that are both secure and affordable. The exciting thing is it can be implemented now, in many labs around the world.”
The research paper, “Decoy state and purification protocols for superior quantum key distribution with imperfect quantum-dot based single photon sources: Theory and Experiment,” is now available in PRX Quantum.
Researchers: Yuval Bloom, Yoad Ordan, Tamar Levin, Kfir Sulimany, Eric G. Bowes, Jennifer A. Hollingsworth, Ronen Rapaport
Institutions: Racah Institute of Physics, Hebrew University of Jerusalem; Los Alamos National Laboratory