Quantum teleportation brings to mind Star Trek’s transporter, where crew members are disassembled in one location to be reassembled in another. Real quantum teleportation is a much more subtle effect where information is transferred between entangled quantum states. It’s a quantum trick that could give us the ultimate in secure communication. While quantum teleportation experiments have been performed countless times in the lab, doing it in the real world has proved a bit more challenging. But a recent experiment using a dark fibre portion of the internet has brought quantum teleportation one step closer to real world applications. 

The backbone of the internet is a network of optical fibre. Everything from your bank transactions to pictures of your cat travel as beams of light through this fibre network. However there is much more fibre that has been laid than is currently used. This unused portion of the network is known as dark fibre. Other than not being currently used, the dark fiber network has the same properties as the web we currently use. This new experiment used a bit of this dark web in Calgary to teleport a photon state under real world conditions.

The basic process of quantum teleportation begins with two objects (in this case photons) that are quantumly entangled. This basically means the state of these two objects are connected in such a way that a measurement of one object affects the state of the other. For quantum teleportation, one of these entangled objects is measured in combination with the object to be “teleported” (another photon). The result of this measurement is then sent to the other location, where a similar combined measurement is made. Since the entangled objects are part of both measurements, quantum information can be “teleported.” This might seem like an awkward way to send information, but it makes for a great way to keep your messages secret. Using this method, Alice can basically encrypt a message using the entangled objects, send the encrypted message to Bob, who can then make his own measurement of the entangled state to decode the message.

Using dark fibre to teleport photons. Credit: Raju Valivarthi, et al.

This new experiment used a variation of this method using three observers rather than two. Using the Bob and Alice analogy, Bob and Alice each make measurements of an entangled state and a photon, about 8 kilometers from each other. Their results are then sent to Charlie, who combines the two results to achieve quantum teleportation. This method assures that the experiment extends beyond a single lab location, and it was done using existing dark fibre and wavelengths of light commonly used in current fibre internet.

Overall the experiment demonstrates that quantum teleportation can be used as a way to encrypt messages over the web. The next big challenge will be to find a way to make it practical enough for everyone to use.

Paper: Raju Valivarthi, et al. Quantum teleportation across a metropolitan fibre network. Nature Photonics 10, 676–680 (2016) DOI:10.1038/nphoton.2016.180

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If you want to keep information hidden, you’ll probably want to encrypt it. We do this all the time for things like credit card transactions, the data on your phone, and even this website. Encryption is a way to ensure that only the the intended recipient can get access to your information. That is, unless someone is able to crack the code.

One of the more common methods of encryption is known as public key encryption, where a large random number is entered into a key generator algorithm to create a pair of public and private keys. The public key can be used to encrypt a message which can only be decrypted with the private key. As long as the private key is kept private, this works pretty well. One one catch is that you need a large random number, and ideally it needs to be truly random. If someone could predict your random number, they could generate the same public and private key, and you’re out of luck.

But often “random” numbers are only pseudo-random. They look like random numbers, but use a particular algorithm to simulate randomness. To get better random numbers, you can use thermal fluctuations in your computer, or noise in weather data. Or, as in the case of a new paper, data from the cosmic microwave background. It might seem like the CMB is a really bad choice. After all, it can be seen by everyone, so if you use CMB data to create a random number why can’t someone else get the same number? But it turns out that’s not a problem.

The basic idea is to take a patch of sky and measure the distribution of energy from the CMB, specifically what’s known as the power spectrum. That spectrum is then compared to the theoretical ideal, and the difference creates a random number. Even if someone measured exactly the same patch of sky, they wouldn’t get the exact same result, and therefore wouldn’t get the same number. While the authors use the CMB as an example, they point out a similar method could be used to generate random numbers from the 21 centimeter line, supernova remnants, radio galaxies and other astrophysical phenomena. All you need is a basic radio telescope, and you have a random number generator.

It’s not likely that this astrophysical method is any better than what we use now. Thermal variations and weather patterns are pretty random as it is. But it’s an interesting idea to use the secrets of the universe to keep your own secrets.

Paper: Jeffrey S. Lee and Gerald B. Cleaver. The Cosmic Microwave Background Radiation Power Spectrum as a Random Bit Generator for Symmetric and Asymmetric-Key Cryptography.  arXiv:1511.02511 [cs.CR] (2015)

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