A quantum "smartcard."

In an era where every other day seems to bring to light a new cyber-attack, secure communications are a premium. And one key ingredient to the future of cybersecurity is quantum cryptography.

The way quantum cryptography works is not at all simple, but here's the basic idea: in quantum mechanics, it's possible for two photons of light to become entangled. Meaning that when you change the quantum "spin" of one of the photons, the spin of the other photon changes almost instantaneously (it's been clocked at a speed at least four magnitudes greater than that of light).

In quantum cryptography, that entanglement is used to create an encryption key for a message that I send through normal channels. If somebody were to try to eavesdrop on that quantum communication, the connection is so fragile that it would disrupt the entanglement - letting both me and the person I was trying to send a message to know that someone is eavesdropping.

The main problem with quantum communications is that so far, they've only been successful with point-to-point communications. So if you want to send a quantum encrypted email, you can only send it to somebody that you have a quantum connection of entangled photons with. And even then, you can only send it short distances - the record right now is about 100 kilometers.

Researchers at the Los Alamos National Laboratory are trying to change that, though. In a paper they submitted to arXiv, the researchers described a prototype quantum network that they've built and have been working with the past two and half years. Although it's not operational yet in the sense of being able to send messages, it's provided a demonstration that doing so would be possible.

"We're trying to come up with better scaled architecture for quantum networks," lead researcher Richard Hughes explained to me. "And by scaling I mean, in our approach, if you have many clients and one server. However, you don't have to actually send secure communications through the central server. Secure communications can go by any path you like. There are quantum links between each end client and the server, and the server manages the encryption keys."

The end result is something similar to public key encryption. The server in the middle has quantum links to each end user, and sends non-secret information to both that lets them derive the encryption key. That allows the users to send communications to each other without having a quantum link with each other.

"Let's say you want to send encrypted email to me," Hughes explained. "You and I are each doing quantum communications separately with server. So you tell the server you need a key to encrypt the message. The server knows both your quantum key and mine, and uses those keys to produce a secret key."

This method isn't limited to encryption, either. It also lets you know if someone's listening. "Along with encrypting message, it also authenticates it," said Hughes. "If somebody tampered with message, the authentication value wouldn't match. So I could tell that someone was impersonating me or tampering with my messages in transit."

Another benefit of the system is that unlike conventional cryptography, which relies on computers having to crunch large mathematical operations on each end, quantum cryptography literally moves at the speed of light - so there's very little latency between operations.  That's crucial for securing basic infrastructure like electric grids, where too much latency can make basic operations impractical.

The other major benefit of the Los Alamos setup is that it should be easy to scale up once its fully operational. "We think with new silicon photonic chips, we can get per unit costs way down. We could construct networks using fabrication techniques that are amenable to mass production," said Hughes. "The next generation of devices that we want to build will be smaller and could even be built into tablets or smartphones."

There are two big next steps for the team working on this network. The first is installing a working communications network within their own lab. But the next challenge is literally bigger - Hughes and his team will be working on getting successful quantum communications from the current range of 100km to about 1000 km.

"Once you're at the 1,000 kilometer range," said Hughes. "You can have continental or even intercontinental quantum communications."
