A year ago this week, Chinese physicists launched the world’s first quantum satellite. Unlike the dishes that deliver your Howard Stern and cricket tournaments, this 1,400-pound behemoth doesn’t beam radio waves. Instead, the physicists designed it to send and receive bits of information encoded in delicate photons of infrared light. It’s a test of a budding technology known as quantum communications, which experts say could be far more secure than any existing info relay system.
They’ve kept the satellite busy. This summer, the group has published several papers in Science and Nature in which they sent so-called entangled photons between the satellite—nicknamed Micius, after an ancient Chinese philosopher—and multiple ground stations. If quantum communications were like mailing a letter, entangled photons are kind of like the envelope: They carry the message and keep it secure. Jian-Wei Pan of the University of Science and Technology of China, who leads the research on the satellite, has said that he wants to launch more quantum satellites in the next five years. By 2030, he’s hoping that quantum communications will span multiple countries. In 13 years, you can expect quantum internet.
Which means … what exactly? In the simplest terms, it will involve multiple parties pinging information at each other in the form of quantum signals—but experts haven’t really figured out what it will do beyond that. “‘Quantum internet’ is a vague term,” says physicist Thomas Jennewein of the University of Waterloo. “People, including myself, like to use it. However, there’s no real definition of what it means.”
That’s because so much of the technology is still in its infancy. Physicists still can’t control and manipulate quantum signals very well. Pan’s quantum satellite may have been able to send and receive signals, but it can’t really store quantum information—the best quantum memories can only preserve information for less than an hour. And researchers still don’t know what material makes the best quantum memory.
They also aren’t sure how they’d transmit signals efficiently between the nodes of the future quantum web. Blanketing Earth in quantum satellites is expensive—Pan’s cost $100 million. Ground-based transmission via optical fiber isn’t perfect either: Quantum signals die out after about 60 miles of transmission. The signals can’t be amplified like an electronic signal, either. So researchers are developing special devices known as quantum repeaters that can transmit signals over long distances.
That research will take time. Even if Pan gets his international network up and running by 2030, it’s not like it’ll be handling your social media feed by then. And maybe we wouldn’t want it to, either. Just because something is “quantum” doesn’t mean it’s automatically better, says physicist Kai-Mei Fu of the University of Washington. “In many cases, it doesn’t make a lot of sense to communicate quantum mechanically,” she says. Quantum signals have weird properties like superposition, where a particle’s location is a probability distribution, and it has no precise location. Most communication between humans would still be far easier to express by encoding regular old 1’s and 0’s in blips of electricity.
So what’s the point of it? In the near future, the quantum internet could be a specialized branch of the regular internet. Research groups all over the world are currently developing chips that might allow a classical computer to connect to a quantum network. People would use classical computing most of the time and hook up to the quantum network only for specific tasks.
For example, says physicist Renato Renner of ETH Zurich, you might connect a classical personal computer to a quantum network to send a message using quantum cryptography—arguably the most mature quantum technology. In quantum cryptography, a sender uses a cryptographic key encoded in a quantum signal to encrypt a message. According to the laws of quantum mechanics, if someone tried to intercept the key, they would destroy it.
The quantum internet could also be useful for potential quantum computing schemes, says Fu. Companies like Google and IBM are developing quantum computers to execute specific algorithms faster than any existing computer. Instead of selling people personal quantum computers, they’ve proposed putting their quantum computer in the cloud, where users would log into the quantum computer via the internet. While running their computations, they might want to transmit quantum-encrypted information between their personal computer and the cloud-based quantum computer. “Users might not want to send their information classically, where it could be eavesdropped,” Fu says.
But it’ll take a while—if ever—before a quantum network gets as big or as versatile as our current internet. “To get to the point where billions of quantum devices are connected to the same network, where any connected device can talk to any other device, we’d be lucky to see it in our lifetime,” Jennewein says.
The incremental progress doesn’t bother Renner. He’s just excited that these experiments inspire physicists to think about quantum mechanics in new ways. “All these developments will certainly help our understanding of physics,” he says. “As a physicist, I want to stress that we are not only application-driven, but also driven by our search for understanding.” As consumers, though, we’ll be waiting for our new gadgets.
On May 11, the Nature Publishing Group released Nature Publishing Index 2010 China, remarking “a dramatic rise in the quality of research being published by China”. University of Science and Technology of China is ranked 3rd of TOP 10 Institutions in Index 2010 China.
This article came from News Center of USTC.