One Step Closer to a Quantum Internet
The Internet is a digital Wild West, but with the help of quantum technology, it doesn’t have to be…
There are many mysteries left to solve on this planet we call home, to say nothing of the greater universe. Some of them are large, and some are infinitesimally small. On the smallest side of the scale, we’ve just begun to scratch the surface of quantum mechanics, and what we’ve found could change technology forever.
Quantum computing is becoming less and less radical as it finds its way into numerous applications, but what if we applied these concepts to the World Wide Web? A recent breakthrough has brought us closer to this reality than ever before.
Exploring The Concept of a Quantum Internet
Many of us don’t give any thought to our security online, at least, not on a day-to-day basis. The reality, however, is that you put yourself at risk every time you open a browser. In fact, there’s a cyber attack every 39 seconds.
The dream of a quantum internet would allow us to have greater security than anything we know today. It’s a big promise, but first we need to roll back the concept to its most basic form. What is a quantum internet? Ronald Hanson of Delft University of Technology in the Netherlands, who is part of a team working on quantum networks, describes it like this:
“The main feature of a quantum network is that you are sending quantum information instead of classical information.”
The key difference, of course, is that classical information is encoded in bits that represent a value of either 0 or 1. Quantum information, however, is represented in qubits, which can be in a superposition of both 0 and 1 at the same time.
One of the most basic applications of this concept is quantum key distribution (QKD). In this practice, we consider Alice and Bob (two names that first appeared in a 1978 paper on public key cryptography and have since become the universal names for nodes in a quantum network).
Alice’s goal is to send qubits to Bob, who will measure them and discover the encryption key needed to decode a set of classical data.. These qubits are encoded in the polarization states of photons, but another method uses the spin states of electronics and atomic nuclei.
By using specific types of measurements, Bob will discover the same value that Alice encoded in the photons coming through a fiber cable. They will discuss the method of measurement publicly before, but the actual encryption key will be encoded in the qubit Alice sends over the fiber link.
This method of transmission means that any type of intrusion would, by the principle of quantum mechanics, change the state of the photons and essentially “ruin” the key because someone else would measure it and modify the state of the qubit.
In this situation, Alice and Bob would see the altered state and discard the qubits before starting with a new encryption key. They would repeat the process until no one was intruding on the quantum channel.
While it sounds exciting, QKD is a very basic application of a quantum internet. In order to fully realize the concept in the way that it’s intended, we need to get spooky.
The Dream of an Ultra Secure Internet is Closer Than Ever
QKD relies on measuring the exact state of quantum keys, which requires you to know their exact physical conditions. That’s not practical when we’re talking about multiple nodes and vast distances. Minute physical changes can throw off the measurements completely.
That’s why new experiments are looking to something better suited for our needs. It all depends on a concept that Albert Einstein referred to as “spooky action at a distance.” I refer, of course, to quantum entanglement.
The concept is this: an object can be placed into a quantum superposition state (meaning it exists in multiple states at once: see Schrödinger’s cat), and share that superposition with another object, regardless of the distance between them.
Measuring the state of one entangled object would then reveal the state of the other. Changing one affects the other instantaneously, regardless of the distance. Spooky indeed.
On February 12th, 2020, a paper published in Nature described two experiments conducted by Pan Jian-Wei at the University of Science and Technology in China that utilized entanglement.
Pan, sometimes referred to as the “father of quantum,” worked with his team on two separate experiments: the first of which entangled quantum memory at two facilities 22 kilometers apart, and the second which entangled particles that traveled through 50 kilometers of fiber optic cable.
The first experiment uses clouds of roughly a hundred million atoms each that are in a single quantum state simultaneously. The state of the cloud is read and written using photons that are trapped in a space with them.
The cloud, known as a quantum memory, is set into a specific state using a write photon. The cloud then emits a second photon whose polarization contains information on the state of the atoms.
From here, the team needed to convert the photon’s wavelength into something used in standard communication fibers. This process causes 30 percent of photons to be lost, but the ones that do remain are transmitted across the fiber optic network.
In this experiment, the two sides of the fiber optic cable were 11km apart. One side was at the University of Science and Technology in China, and the other was at the Hefei Software Park.
To conduct the first experiment, the team created two qubits of quantum memory and generated photons from both. These were sent through separate cables to the Software park.
Here, the photons went through a device that would make them indistinguishable from one another by entangling them. Given that they were also entangled with the qubits from the quantum memories, this was the equivalent of entangling two bits of memory 22km apart.
Keep in mind that the previous record here was 1.4km, so despite the loss in efficiency due to the wavelength shift, this is an impressive feat. The second experiment, however, was even more significant.
Go Big or Go Home
The second experiment utilized a spool of fiber optic cable 50km in length. Two photons, entangled with information from the atom clouds, were sent down the cable and entangled with one another as well.
The impressive feat was not without drawbacks, however. The time to create entanglement went up from the prior experiment. At roughly half a second, this doesn’t seem like a long time, but the lifetime of a qubit’s memory using this process is only 70 microseconds, which is far shorter than the time it takes to entangle the particles.
Assuming this wasn’t an issue, you could theoretically spread a single qubit across two facilities using this method and even extend the distance using a technique called entanglement swapping (again, assuming you could preserve their states).
All of this comes down to a significant breakthrough held back by our limitations. The errors and inefficiencies pile up too quickly to make these concepts ready for prime time, but it does show that a quantum internet is possible, at least theoretically.
In the meantime, it will be interesting to see what new breakthroughs come in the future as China pushes ahead with quantum technology and the US continues to catch-up.
While you’re waiting for an ultra-secure quantum internet, make sure your current cybersecurity is up to par.