How does a quantum computer work?
© IBM/Andrew Lindemann
Franziska Bechtold
In recent years, news of new breakthroughs in the quantum technology always processed. If you want to explain the achievements, fallen terms like qubits, overlay and restriction. But what do they mean, how are quantum computers structured and what can you actually do with them? The futurezone asked.
What distinguishes a normal computer from a quantum computer?
A regular computer, which most people use on a daily basis, processes information in bits. You can either state 1 or 0 accept. ALL INFORMATION CAN BE PRESENTED WITH THIS. 8 bits are one byte. The more bytes a computer has, the more information it can store.
A quantum computer uses against it qubits. Like normal bits, they can do that state 0 or 1 accept. However, they are not in either one state or the other, but in both at the same time (superposition). This enables enormous computing power to be achieved very quickly, which a normal computer could not provide.
What does the term “quantum” even mean?
In quantum physics and thus the basis for quantum computers, the smallest particles are examined. At the molecular level, these particles behave according to other physical laws. For example, that they can assume several states at the same time, so-called die overlay. The well-known thought experiment – Schrödinger’s cat – one of the founders of quantum mechanics, Erwin Schrödinger, Exactly this idea. The cat is in two states at the same time – one alive and one dead.
But now it was found that these particles can be irradiated, for example with photons. This creates an interaction and their state is measured. Through the measurement, the particles randomly “decide” for one of these two states.
How does a quantum computer work?
With the rules of this quantum mechanics it is possible to qubits (two state system) create. Among other things, are used electrons, ions or photons. For a certain time they remain stable, die so-called coherence time. Then they are in the state of superposition, i.e. 0 and 1 at the same time.
Once a qubit IS measured, it “chooses” a state. If this measurement is made often enough, a clear result emerges. For example, if you want a prime factorization of the number 15, one measurement will give a result of 3 and another a result of 5.
Prime factor analysis is the mathematical process of representing a natural number as prime numbers. Prime numbers are natural numbers that can only be divided by 1 and itself (e.g. 2, 3, 5, 7, 11…). So a prime factorization of 9 would result in 3×3, with 20 you get 2x(2×5).
If you do the measurement again and again, you can see which possible results are spit out. In this simple example, you could 1,000 measurements die 499 times 3 find, and die 501 times 5 and knows: 3 and 5 are the right answers.
Here the measurements are still error-prone on a large scale and it is necessary to discover whether smaller deviations are further results or errors of the computer. If you stay with the above simplified example of the prime factorization of 15, this means that you get: 50 percent 5to 49.9 percent 3 and to 0.1 percent another number. Validating whether you have found 2 or 3 correct answers is currently an area of research.
Unlike a normal computer, the qubits can die multiple bills at the same time perform and are not only much faster, they make possible what was previously unthinkable. If you want the state of 300 atoms store, a normal computer would need as much storage space as there are atoms in the universe.
A quantum computer that has 300 qubits can easily map those 300 atoms, like a miniature. In an interview with futurezone, the Quantum physicist Gerhard Kirchmair Compare a comparison: “For example, when I design an airplane or car, I test a 1:1 miniature in a wind tunnel. This is how you can imagine it in a quantum computer.”
What different construction methods are there?
When you look at images of quantum computers, you always come across a golden structure that looks like a chandelier looks. Most of it is the “refrigerator“. The actual processor is a chip of a few square centimeters that hangs at the bottom.
It is a quantum computer with superconducting circuits. As the name suggests, in the first case the qubits are built from superconductors, like electrical circuits.
There is another type of quantum computer that is showing a lot of potential at the moment: the ion traps. Here ions in a vacuum chamber trapped with a laser and electric fields. Instead of being attached to a “chandelier” as below, the processor is in a steel canister.
“Both technologies have advantages and disadvantages,” explains Kirchmair, who works at the University of Innsbruck a superconducting circuit researches. Ion traps are about less calculablebut could one better coherence time have, i.e. the duration during which the qubits remain stable.
Also, with ion traps, you can bet that you will always die anywhere in the world exactly the same quantum bits used. “That’s an advantage because they don’t have to become ingredients anymore. It’s different with superconducting circuits, but here I can design my system myself,” says Kirchmair.
But it doesn’t have to be one or the other. “In my opinion, there will not be one quantum computer in the future, but there could be several different platforms connected to each other in a data center,” the physicist assumes.
Google shows at his Labor Tour on YouTube exactly how his quantum computer is built.
What do I need it for – and what not?
The big question, of course, is: what do you do with the quantum computer once you have it? In research, for example, you can do that Simulate behavior of molecules. You can examine their properties and what reactions take place.
But in the future you could also use them for encryption insert. That’s what we’re using today Public key encryption, for example in browsers or bank transactions. Key pairs are exchanged, some of which are secret, but some are public. This works because it would take a normal computer far too long to identify each key. However, quantum computers can do this much more efficiently – and thus crack this protection in the shortest possible time.
With the means of quantum physics, however, one can unbreakable system create. That’s what death is used for restrictionso the connection, of qubits. If the qubit on the quantum computer of the sender of the message has the value 1, then so does the qubit on the quantum computer of the recipient. You can Interlock security keys. The random value of the sender’s key is therefore always the same random value of the recipient’s key.
Theoretically, this works over long distances. The principle has already been successfully tested with photons, including by the University of Vienna and the University of Innsbruck. this quantum communication IS THE BASIS FOR THIS uncrackable quantum internet. However, there are still problems in maintaining the entanglement.
Another area of application is Optimization of processes. Kirchmair explains this using the “Problem of the traveling salesman“: “You imagine a delivery man who has to deliver packages with a given city map. The best route is sought, which can be the fastest or the first route. A Classic computers would try all paths and take a very long time to do so. However, quantum computers can test all paths at the same time.”
How many qubits do you need?
Researchers keep coming up with milestones: Quantum computers in China should 66 qubits check, IBM builds a quantum computer 127 qubits. But how many qubits do you actually need? “I can’t say that yet. In research, you first have to agree on certain benchmarks. A qubit is not just a qubit either. One speaks more of quantum volume,” says Kirchmair. When it comes to volume, it’s not just the sheer number of qubits that matters, but also how good the connections between them are.
Several hundred qubits would be sufficient for research projects, for example to answer fundamental physics questions. But if you want algorithms or optimization problems, then the number of qubits required would already solve Hundreds of thousands to millions climb.
Is the quantum revolution here yet?
While the solution of complex algorithms and optimization processes is still far in the future, quantum computers are already being used in research. At least on a small scale, theorists can use the quantum computers of many companies via the cloud. “In the next few years, this will also be possible for larger processors,” says Kirchmair.
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