How to Quantum Computers Work

quantum computing tutorial
Quantum Computer

Quantum computing is a fundamentally different approach to computation than the kind of computation that laptops, workstations, and mainframes do today. It won’t replace these devices, but by using the principles of quantum physics, it will solve specific, typically very complex, statistical problems that are difficult for today’s computers.

Quantum Computing - How it works

Classic computers are programmed with bits as data units (zeros and ones). Quantum computers, on the other hand, use so-called qubits, which can represent a combination of zero and one simultaneously, based on a principle called superposition.

This difference gives quantum computers the potential to be exponentially faster than today’s mainframes and servers. Quantum computers can perform multiple calculations with multiple inputs simultaneously. Today’s computers can only process one set of inputs and one calculation at a time. When working with a certain number of qubits - let’s take n as an example - a quantum computer can perform calculations with up to 2n inputs simultaneously.

That sounds easy to me. But if you delve into the details of how a quantum computer works, you begin to understand that many challenges have to be solved before quantum computers can exploit this potential in practice. (See box "Quantum computers compared to traditional computers").

Quantum computers - technical challenges

Some of these challenges are technical, for example, qubits are volatile. Every bit in today’s computers must be in a state of one or zero. There is a lot of work being done to ensure that one bit on a computer chip does not interfere with another bit. Qubits, on the other hand, can represent any combination of zero and one, and interact with other qubits. In fact, it is these interactions that make it possible to perform multiple calculations at once.

However, controlling these interactions is very complicated. The volatility of qubits can cause input to be lost or altered, which can affect the accuracy of the results. And now, in order to build a powerful quantum computer, hundreds of thousands or millions of qubits have to be connected coherently. The few quantum computers that exist today cannot process this number nearly.

Software and hardware companies - from unknown start-ups to research institutes to companies like Google, IBM and Microsoft - are trying to overcome these challenges. They are working on algorithms that hardly resemble those used today. Likewise, the hardware may be very different from today’s gray boxes. They are also working on software that helps translate existing data into a qubit-capable format. But companies still have a long way to go.

Although the concept of quantum computing has existed since the early 1980s, it was not until the end of 2019 that the first real proof was that quantum computers can deal with problems that are too complicated for conventional computers: Google announced that its quantum computer has solved such a calculation in just 200 seconds. But this was more of a mathematical exercise than something practical that could be applied in real business - the problem solved had no real benefit.

Quantum Computing - Areas instead of Answers

The nature of quantum mechanics also poses obstacles to exponential speed increases. Today’s computers work in a simple way: they manipulate a limited data set with an algorithm and then output a result. Quantum computers are more complicated.

After several data units have been entered into qubits, these qubits are manipulated to interact with other qubits so that a series of calculations can be performed simultaneously. Quantum computers are much faster in this than today’s machines. But these performance gains are relativized by the fact that quantum computers do not provide a clear answer. Instead, users receive a limited range of possible responses. It may even happen that various arithmetic runs have to take place in order to limit the area even further. However, the simultaneous execution of several calculations can lead to a lack of the expected speed gains.

Quantum Computing Tutorial

Now, if you get blurred or multiple answers, quantum computers seem to be less precise than today’s computers. This is also true for calculations that are limited in scope, which is one reason why quantum computers will not replace today’s systems. Instead, they should be used for new types of problems. These are incredibly complex tasks that restrict a wide range of possibilities, which means enormous time savings. With which ultimately hybrid approaches are conceivable: A complex problem is first limited to a few possibilities by quantum computer and in a final step a classical computer calculates a result.

Quantum computers can do that

Quantum computers have four basic capabilities that distinguish them from today’s classical computers:

  • quantum simulation in which quantum computers model complex molecules;
  • Optimization, the solution of multivariable problems in unprecedented speed;
  • quantum artificial intelligence (AI) with better algorithms that optimize machine learning and
  • the prime factor decomposition that could revolutionize encryption (hi/fm)

Quantum computers in comparison to classical computers

Bits vs Qubits - the concept is completely different

A bit is the essential information unit of today’s computers.

A qubit is the essential information unit for quantum computers.Qubits can store any combination of zeros and ones simultaneously.

Accordingly, their calculations differ: a single result compared to a limited range of possibilities.

The limitations of the bits become apparent when classic computers are supposed to handle a problem with several variables. In such scenarios, the computer must perform a new calculation each time a variable is changed. Each calculation is a single path to a single result.

Quantum computers, on the other hand, have an exponentially larger working space thanks to the nature of the qubits. You can explore a gigantic number of computational paths at the same time, which gives quantum computers the potential to be much faster. They deliver several results in a narrow range and thus approach the answer much faster than conventional computers.

The hybrid approach

Researchers expect that many multivariable problems can be solved in the future by a combination of quantum and classical calculation. For example, by using emerging quantum computers that limit the range of possible solutions for a financial or logistics problem, a company could reach the optimal solution ten percent faster. This kind of incremental progress will be the norm until quantum computers are mature enough to make massive breakthroughs in areas such as drug development or cryptography.

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