1 - The Ugly Duckling of Quantum Computing

To those of you who are familiar with Quantum Computing, and to those who are just curious, I would like to introduce you to the fascinating world of Quantum Error Correction.

The big buzz around Quantum Computing is very nice, but what many people don't know, is that Quantum Computing, just like Classical Computing, will not be possible without the core idea of Error Correction.

Noise and Errors

Our world is noisy, and noise is causing communication to suffer from errors. Think of yourself trying to hear your roommate while you are taking a shower, or try talking on the phone while your friend is shredding paper.

In classical communication, noise is added to 0 / 1 bits and may lead to incorrect 0 / 1 identification. The solution to these errors is encoding. For example, you can replace every 0 with four zeros. In this way, even with some low chance of 0-1 flipping, the decoder will understand if the origin was 0 or 1.

Qubits (quantum bits) are suffering from similar issues. Qubit, like a bit, is a creature that stores a basic unit of 0/1 information. Unlike a bit, a qubit can store both 0 and 1 at the same time (a superposition of 0 and 1), where each of the states is stored with some probability of being determined as 0 or 1 at the time of measuring the qubit.

When noise is added to a qubit, those 0 / 1 probabilities are changed. The values of those 0/1 probabilities are crucial for quantum computation. The interesting algorithms that are using those qubits are relying on those probabilities information. Therefore we cannot allow for errors to misrepresent these crucial probabilities.

How is it affecting the whole Quantum Computer?

The noisier a quantum computer is, the more qubits it will need to compensate for its noise. Think of the classical repetition code that I mentioned just earlier, where the addition of extra bits helped us mitigate the introduction of noise.

Ok, but how many more qubits? It may reach up to thousands of times more than the silent case! Let's see an example. You might have heard of Shor's Algorithm which is a quantum solver that can crack RSA encryption by decomposing numbers into primary factors.

To decompose a 2000 bits number, in ~24 hours Shor's algorithm will need a total amount of ~300,000 silent qubits (logical qubits). For today's noise rate of 1/1000, each one of these 300,000 logical qubits will be replaced by 3,600 physical qubits, which will result in ~1 Billion (1Giga) physical qubits!

It might sound huge, but don't forget that a classical computer hard disk contains ~x1000 times bit than 1 Billion. Anyway, the only reason that those algorithms are even possible, is only thanks to the Quantum Error Correction schemes.

The Ugly Duckling

Quantum Computing has received much attention around the globe. The spotlight is focused mainly on advanced applications like simulating molecules, solving optimization problems, financial use cases, and quantum machine learning.

"The quantum community proceedes under the assumption that it already has a fault-tolerant quantum computer, while the reality is that we are far from it."

The community assumes that each logical qubit is one silent physical qubit, somewhat overlooking the reality of noise. This wrong way of thinking has huge implications on products are designed, whether it is hardware, algorithm, or software.

Founders have invested more than 100,000,000$ to develop applications that may (or may not) be relevant just in more than 10 years. Yet there is a severe lack of knowledge, courses, and infrastructures among researchers, engineers, and developers about the foundation concepts surrounding the creation of a fault-tolerant quantum computer.

The ugly duckling of error correction needs more attention. Don't forget who saved the chicks at the end of the story.

Soon, quantum computer companies will start to publish that they have a fully connected quantum computer with more than 1000 physical qubits. Don't forget that this is equivalent to only one logical qubit! In order to build useful architectures for a quantum computer, those companies will have to dive into the world of error correction and include it as a part of their solution.

So, are you a chick or a duck? Would you like to be among the ducks that know how to build a fault-tolerant quantum computer? In the next article, I will explain the fundamentals of Quantum Computing Theory that are a prerequisite to understanding how Quantum Error Correction works.

Stay tuned... Don't be a chick...

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