August 25, 2025 – A new approach using innovative encryption protocols applied to quantum dots to send encrypted information securely that doesn’t require perfect optical hardware has been developed by researchers at the Hebrew University of Jerusalem (HU). 

For four decades, the holy grail of quantum key distribution (QKD)—the science of creating unbreakable encryption using quantum mechanics—hinged on perfectly engineered single-photon sources, tiny light sources that can emit one particle of light (photon) at a time. In practice, building such devices with absolute precision has proven extremely difficult and expensive. 

Laser light is the current standard to transmit faint light pulses that contain a small, but unpredictable, number of photons, a compromise that limits both security and the distance over which data can be safely transmitted. A smart eavesdropper can “steal” the information bits that are encoded simultaneously on more than one photon. 

In the research published in PRX Quantum, the breakthrough concept in quantum encryption makes private communication more secure over significantly longer distances, surpassing state-of-the-art technologies. Real-world tests show it can outperform even the best of current systems, potentially bringing quantum-safe communication closer to everyday use. 

The research was led by Ph.D. students Yuval Bloom and Yoad Ordan, under the guidance of Professor Ronen Rapaport from the Racah Institute of Physics at the Hebrew University, in collaboration with researchers at the Los-Alamos National Labs. 

“This is a significant step toward practical, accessible quantum encryption,” said Prof. Rapaport. “It shows that we don’t need perfect hardware to get exceptional performance—we just need to be smarter about how we use what we have.” 

Co-Lead author Yuval Bloom added, “We hope this work helps open the door to real-world quantum networks that are both secure and affordable. The cool thing is that we don’t have to wait, it can be implemented with what we already have in many labs worldwide.” 

Developing a Better Approach with Imperfect Tools 

The researchers developed two new protocols—sub-Poissonian photon sources based on quantum dots, which are tiny semiconductor particles that behave like artificial atoms. By dynamically engineering the optical behavior of these quantum dots and pairing them with nanoantennas, the team was able to tweak how the photons are emitted. This fine-tuning allowed them to suggest and demonstrate two advanced encryption strategies: 

• A truncated decoy state protocol: A new version of a widely used quantum encryption approach, tailored for imperfect single photon sources, that weeds out potential hacking attempts due to multi-photon events. 
• A heralded purification protocol: A new method that dramatically improves signal security by “filtering” the excess photons in real time, ensuring that only true single photon bits are recorded. 

In simulations and lab experiments, these techniques outperformed even the best versions of traditional laser-based QKD methods—extending the distance over which a secure key can be exchanged by more than three decibels, a substantial leap in the field. 

A Real-World Test and a Step Toward Practical Quantum Networks 

To prove it wasn’t just theory, the team built a real-world quantum communication setup using a room-temperature quantum dot source. They ran their new reinforced version of the well-known BB84 encryption protocol—the backbone of many quantum key distribution systems—and showed that their approach was not only feasible but superior to existing technologies. 

What’s more, their approach is compatible with a wide range of quantum light sources, potentially lowering the cost and technical barriers to deploying quantum-secure communication on a large scale.

The research paper titled “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 and can be accessed here.

Researchers:

Yuval Bloom, Yoad Ordan, Tamar Levin, Kfir Sulimany, Eric G. Bowes, Jennifer A. Hollingsworth, and Ronen Rapaport

Institutions:

Racah Institute of Physics, Hebrew University of Jerusalem