In the future, communication networks could be based on the bizarre world of quantum mechanics, and now we’re a step closer to that reality. Researchers in China have demonstrated a quantum network where entangled photons are beamed between drones and ground stations, successfully maintaining their quantum link over a distance of 1 km (0.6 miles).
Quantum entanglement involves pairs of particles becoming so intertwined that it becomes impossible to describe them individually. By measuring a property of one of them, such as its polarization, you’ll be able to tell the same property of its partner. Weirder still though, it appears to be the case that you’re actually changing the state of the partner instantly, no matter how much distance separates them.
That bizarre phenomenon can be taken advantage of to make fast and secure quantum communication networks. Entangled pairs of photons are generated, then one photon is passed to each user to allow them to communicate instantly by measuring their photons. Most experimental setups so far have tested this using fiber optic cables, but the photons can lose their entanglement over long distances as they bounce off the sides of the optical fibers.
Transmitting them through the air may boost the distances that quantum communications can work. In the past, that’s been done using satellites such as Micius, which a few years ago smashed records by transmitting quantum information between two ground stations 1,200 km (746 miles) apart.
But access to satellites isn’t always available, and there can be some technical difficulties. So in the new study, researchers from Nanjing University in China experimented with a similar setup that’s a bit closer to the ground – drones.
In this experiment, the researchers wanted to connect two ground stations, one nicknamed Alice and the other Bob. Each station collects photons using a telescope with a 26-mm-wide aperture and a single-photon detector. But it wasn’t a direct link between the stations – there were two drones hovering in the sky above them.
The first drone generates entangled pairs of infrared photons, then sends one of them to the Alice station and the other to the second drone. This drone uses an optical fiber to collimate the photons it receives, effectively “focusing” them so they can then be passed on to the Bob station on the ground.
The drones were about 200 m (656 ft) apart, and each was 400 m (1,312 ft) from the station it was passing the photons to, meaning the message was effectively traveling 1 km total. Alice recorded about 25 percent of the photons sent its way, while Bob only caught about four percent. That may sound low, but it’s a decent step up from previous fiber optic experiments where only around one percent of the photons completed the journey.
The team compared the polarizations of the photons received by the Alice and Bob stations, and found that they did remain entangled over the entire trip.
The next steps, the researchers say, are to add more drones to increase the size of the network, potentially providing quantum links across a city. Unlike satellites or optical fiber networks, swarms of drones could eventually be rolled out relatively quickly when needed, almost anywhere. They could connect two points that don’t have direct line of sight and, unlike towers, they can move to avoid obstacles or inclement weather.
The research was published in the journal Physics Review Letters.
Source: Nanjing University via Physics