I’m a quantum computing skeptic. The first time I came into contact with the subject, back in 2007 during my physics degree, I was already hearing that quantum computers were near and that encryption as we knew it was over. Eighteen years later, we’re still using the same cryptographic algorithms and still hearing the same story: encryption is going to end. I’ve talked about this topic in another article, but here I’d like to address a less discussed aspect.

To be honest, quantum computing bores me these days. Not the concept itself, but the way it’s being handled today. When people talk about quantum computing, the topic that dominates the discourse is Shor’s algorithm: factoring large numbers more efficiently and declaring the end of public-key cryptography as we know it. Ok, this is mathematically proven, but in practice I have my doubts about the scalability of quantum processors and the practicality of their applications.

But there’s another topic that doesn’t get much attention and has applications I find much more curious, interesting and anything but boring: Quantum Information.

Quantum Information for the Impatient

(with all due respect to Neil deGrasse Tyson’s “Astrophysics for People in a Hurry”)

Quantum Information explores unique properties of the quantum world, like the impossibility of copying data without altering it, opening doors to applications that go beyond traditional computing. In quantum computing, we explore the properties of quantum mechanics to perform information processing in quantum states, with potential applications that are impossible in classical computing and, in some cases, gains in efficiency.

In quantum information, we use the same properties of quantum mechanics to define the concept of information and the means to store, transmit, process and protect that information. Some of the characteristics that only appear in the quantum world can be leveraged to do truly new things, which are not just quantum versions of classical concepts.

The No-Cloning Theorem

One of these innovative concepts derives directly from the no-cloning theorem, which is a consequence of Heisenberg’s Uncertainty Principle. This principle states that merely observing or measuring a property of a quantum system will inevitably disturb it, altering its state. Consequently, any attempt to intercept a quantum system will result in a detectable alteration to that state.

It is this impossibility of copying an unknown quantum state without affecting the original, formalized by the no-cloning theorem, that becomes the basis for practical applications like Quantum Key Distribution.

Quantum Information in Action

Recently, Swisscom and the German startup Quantum Optics Jena conducted a proof-of-concept experiment in Quantum Key Distribution (QKD) for symmetric encryption (https://www.quantum-photonics.de/en/c/swisscom-and-german-start-up-test-quantum-security-solution.63411). The test used entangled photon pairs transmitted over existing fiber optic infrastructure. No details were disclosed such as transmission distance, limitations or difficulties encountered. Even so, this already shows that quantum information concepts are moving beyond mathematical demonstration and into real-world implementation.

This experiment uses quantum information concepts: entanglement and no-cloning to encode classical information into a quantum state and transmit it securely. During the test, entangled photons were generated: particles of light whose states are correlated in such a way that any attempt to intercept them alters the system and exposes the eavesdropping.

This is one of the applications I find most interesting in quantum information: security doesn’t depend on external layers added to protect the information, it is a direct consequence of the laws of physics. And there’s no bypass here, breaking this kind of property would mean breaking the very functioning of the universe. Or discovering a flaw in the model physics uses to describe our reality. Either possibility would be fascinating.

The Challenge of Cryptographic Key Exchange

Quantum key distribution helps solve a major problem in cryptography. Imagine our old friends, Alice and Bob, needing to exchange secret messages between them, but they don’t have a reliable channel free from interference and eavesdropping. For that, encryption is used: the message will be encrypted with cryptographic keys that will be used to encode and decode the message, making it unreadable to anyone who doesn’t have the key. Now, regardless of the algorithm used, whether symmetric or asymmetric keys, for this encrypted communication to happen, the cryptographic keys must be distributed between the participants before the actual communication begins.

To give an example that combines both types of keys, symmetric and asymmetric, we can use the TLS protocol, used in “https” connections that protect a large part of the internet. During the TLS handshake, before transmitting actual data, asymmetric cryptography is used: the server presents a certificate containing its public key, which the client verifies using a trusted Certificate Authority. The server may also prove possession of the private key by signing parts of the handshake messages. The matter of initial trust in the certificate and public key is a challenge in itself (and would deserve another article!), but for the purposes of this discussion, let’s assume that proper security protocols were followed to establish that trust.

This process enables the secure negotiation of a symmetric session key. Yes, TLS doesn’t use asymmetric algorithms all the time. They’re used basically for the initial exchange of the symmetric keys that will be used during the entire communication session, which is unique for that moment. From there, encrypted communication can proceed normally between the two parties using symmetric encryption.

Quantum Key Distribution – QKD

So how does QKD help in this scenario? Simple! Or, at least, as simple as quantum mechanics allows. In QKD, using the no-cloning theorem, transmission security is guaranteed by quantum properties. Any attempt at interception alters the quantum state of the entangled photons (or any other implementation of an entangled system, photons are not the only possibility). This alteration can be immediately detected by the participants, who can then discard the key and interrupt the communication.

In practice, this creates a key distribution channel in which the very act of eavesdropping exposes the eavesdropper. It doesn’t matter if the adversary has a supercomputer, or even a quantum computer, they will run into the fundamental laws of the universe. Security stops being an additional layer and becomes a property of the medium itself.

Superdense Coding

Quantum information also has other characteristics that feel strange. After all, as Niels Bohr, Nobel Prize winner in Physics in 1922, once said: those who are not shocked when they first come across quantum theory cannot possibly have understood it. Using the same idea of transmitting quantum information over a classical channel, there’s another fascinating topic that can bring a lot of utility to classical information: superdense coding.

Imagine being able to send double the classical information using the same number of information “carriers”. That’s what superdense coding promises, using quantum entanglement to optimize the amount of data transmitted. In a classical scenario, to send two bits of information (for example, “00”, “01”, “10” or “11”), you would need two physical bits. With superdense coding, if Alice and Bob share a previously entangled pair of photons, Alice can manipulate just one of her photons in a specific way to encode those two bits of classical information. By sending this single manipulated photon to Bob, he can perform a measurement on his entangled pair and, with that information, decode the two bits Alice sent.

This concept is fascinating because it shows how quantum properties can be used for other purposes beyond security, in this case to increase the efficiency of data transmission. Quantum information doesn’t just aim to solve the same problems as classical computing. It opens doors to entirely new capabilities, going far beyond the “cryptographic apocalypse” and the simple race for faster machines.

Conclusion

Quantum information goes far beyond quantum key distribution and superdense coding. We are also talking about applications such as:

• Quantum teleportation: where the state of a quantum system can be instantly transferred to another, regardless of distance.
• Distributed quantum computing: processing quantum information across networks, surpassing the limits of a single processor.
• Communication in noisy channels: leveraging quantum properties to enable communication in highly noisy environments, something impossible under the current model.
• Simulation of physical systems: implementations closer to the real world, challenging classical modeling and opening the way for advances in materials chemistry and drug development.

While the spotlight remains fixed on quantum processors, perhaps the real revolution is happening quietly, in the foundations of information. The next big shift may not come from a machine that breaks keys, but from the way we choose to represent and protect what we call data.