Quantum computers 101

We explain quantum computers with the help of cats and light bulbs.

Google claims to have achieved quantum supremacy. We ponder how quantum computers work, and what that has to do with data protection

Last fall, Google announced that it had achieved quantum supremacy. If that sounds a bit abstract and not relevant to the average user, think again. What the Google team did, essentially, was use a quantum computer to solve a problem that would have bamboozled even the snazziest supercomputer. Impressive, wouldn’t you agree?

What’s more, the state of quantum computing has a direct bearing on the security of your data. After all, many protection methods in the digital world are based not on being uncrackable, but on being uncrackable within a reasonable amount of time. Here, we take a look at Google’s new toy and consider whether we should worry about cybercriminals one day using it to hack into our lives.

What is a quantum computer?

The main difference between quantum computers and the traditional transistor kind that we all use today is how they handle data. The devices that we are familiar with — from smartphones and laptops to the Deep Blue chess supercomputer — store everything in bits, which is the name given to the smallest unit of information. A bit can take one of two values: 0 or 1.

Consider the light bulb: It’s either on (1) or off (0). A file on a computer disk looks like a set of light bulbs, some on, the others off. Armed with many such light bulbs, you can encode information, such as the phrase “Albert was here” or an image of the Mona Lisa.

When a two-state device solves a problem, it has to turn those light bulbs on and off continuously, writing and erasing the results of intermediate calculations to prevent them from clogging up its memory. That takes time, so if the task is very complex, the computer will think for a long, long time.

Quantum computers, unlike their elder cousins, store and process data using quantum bits, or qubits for short. These can not only be turned “on” and “off” but be in a transitional state or even on and off at the same time. Continuing the light bulb analogy, a qubit is like a lamp that you turned off but continues to blink. Or like Schrödinger’s cat, which is considered simultaneously both alive and dead.

The light bulbs in a quantum computer being both on and off saves a huge amount of time. Therefore, a quantum computer can solve complex problems much faster than even the most powerful traditional device. Google claims that its quantum machine, Sycamore, performed calculations in a bit over 3 minutes that would have taken an ordinary supercomputer 10,000 years. That’s where the term “supremacy” comes in.

Quantum computers in real life

We’ve established that quantum computers are pretty sharp when it comes to solving highly complex problems. So, why hasn’t the transistor age been consigned to the history books already? Because quantum technology is still young, and the state of the “blinking light bulb” is very unstable — not to mention that the more qubits a system contains, the more difficult it is to maintain stability. And the feasibility of complex calculations depends, inter alia, on the number of qubits: With two bulbs, even top-end ones, you won’t draw the Mona Lisa.

Other reasons prevent quantum computers from totally supplanting their predecessors. Keep in mind that they process information in a fundamentally different way. That means software for them has to be developed from scratch. You can’t just install Windows on a quantum computer; you’d need a wholly new quantum operating system and quantum applications.

Although scientists and IT giants are dipping their toes into quantum waters, for the time being quantum computers work approximately like external hard drives, connected to and controlled by regular computers. They are used to solve a narrow range of problems, such as modeling a hydrogen atom or searching databases. Despite quantum computing’s power, you can’t yet use it to go online and watch a video of skateboarding cats.

Nevertheless, many believe the future belongs to quantum computing. The first quantum computers appeared on the market back in 1999. Today, large organizations such as Google, Honeywell, and IBM (the latter already offers customers cloud access to its quantum computer), Toshiba, Alibaba, and Baidu are investing heavily in this area.

However, it’s worth pointing out that the task Google solved has no practical use, except to demonstrate the capabilities of quantum computing. We will not delve into the nitty-gritty, because it really is very complex and not very necessary for the everyday user. But if you want to study the details, take a look at Google’s report.

Incidentally, not everyone agrees with Google’s 10,000-year claim. IBM, for example, is sure that a supercomputer could solve the same task, if not in 3 minutes, then in not much more than 48 hours. But still, even if this estimate is more accurate, even non-mathematicians will spot a noticeable speed difference between quantum and traditional computers.

Quantum computers not (yet) a threat

As you can see, quantum computers are still more of a plaything for scientists than they are consumer devices or hacker tools. But that of course doesn’t mean that they won’t become more practical (and dangerous) down the line. With that in mind, data security experts are already drawing up battle plans. But more about that next time.