PRL develops compact device for hack-proof communication

Ahmedabad: Scientists at the Physical Research Laboratory (PRL) in Ahmedabad have built a small box — about the size of a tablet and weighing just 1.5kg — that creates pairs of linked light particles for unbreakable, secure communication. Called Jonaki, which means firefly in Bengali, it is India's first homegrown, ready-to-use device that aims to make intercepting secret messages impossible and to enable very precise scientific measurements. Jonaki is designed to support drone-based and other free-space quantum communication deployments and precision sensing, scientists said. While simple international systems cost over Rs 30 lakh, Jonaki is built to be far more advanced yet accessible for undergraduate research."The goal is to move quantum tech from elite labs to Indian educational institutions. By providing an affordable, hands-free device, PRL is empowering undergraduate colleges to train the next generation of scientists," Dr Goutam Samanta, research leader at PRL's Photonic Sciences Laboratory, told TOI during an interaction at the Student Conference on Optics and Photonics - Optical Society of India Symposium (SCOPOSIS).At its core, Jonaki is an entangled photon source. It fires a laser through a specialized crystal to create pairs of tiny light particles called photons (wavelength of 810 nanometres) that are linked to each other — like twins. Whatever happens to one particle instantly affects its twin. This linking phenomenon is one of the most important concepts in modern physics. If a hacker tries to "look" at one, the delicate link breaks instantly, alerting the sender of the message."This property forms the basis of entanglement-based quantum key distribution (QKD), where any attempt at interception of the communication alters the quantum state of the photons, revealing the presence of an eavesdropper," Samanta said."In a drone-based set-up, Jonaki would act as the source of entangled photons. One photon from each pair could be transmitted via a free-space optical link to a ground station while its twin is retained at another node, allowing secure key generation or correlation tests over an airborne link," Samanta added.Another promising sector is Jonaki's use in precision measurements. "Entangled photons respond to minute changes in optical properties with sensitivities unattainable by conventional light sources. This allows high-precision measurements and sensing capabilities that surpass classical optical techniques," Samanta said.According to PRL, Jonaki produces at least 10 lakh linked light-particle (photon) pairs every second per milliwatt of power, placing it among the best such devices in the world. It scores over 98% on key accuracy tests used globally to judge quantum devices. "The system also demonstrates Bell-state fidelity exceeding 98% along with a strong Bell-inequality violation — benchmarks required for high-quality quantum communication and metrology experiments," Samanta added. Unlike most quantum set-ups that occupy entire tables and require constant manual adjustment, Jonaki operates at room temperature, stays stable on its own, and connects directly to optical fibres, making it practically plug-and-play.