Although quantum networks may one day connect computers and sensors across cities, distance remains a major engineering barrier. Quantum signals in optical fiber attenuate quickly, making long-distance connections difficult.
According to ITNA and citing Interesting Engineering, Chinese researchers have demonstrated a method that keeps quantum systems connected over much longer fiber distances.
The experiment used two quantum memory systems containing laser-cooled rubidium atoms, the result of which could give engineers a practical platform to develop quantum networks beyond urban areas.
Quantum signals lose strength as they travel through fiber, and this issue becomes more severe as the distance between network nodes increases. The researchers used clouds of rubidium atoms as quantum memories that can store quantum states.
The experiment preserved entanglement over 420 kilometers of fiber, surpassing the roughly 320-kilometer threshold associated with direct transmission through an attenuating fiber channel. Accordingly, direct transmission beyond that point becomes increasingly impractical, and quantum memories can provide a way to circumvent this limit by dividing longer networks into smaller segments.
Synchronizing these memories posed another challenge. Temperature fluctuations and mechanical vibrations can disrupt the quantum effects required to establish entanglement. The research team developed an active stabilization system to compensate for these oscillations, continuously adjusting settings to keep quantum states aligned across the fiber link.
They also tuned the operational wavelength of the quantum memories, which reduced signal losses during transmission and helped preserve the fragile quantum connection.