Five things you need to know about quantum computers

Any discussion of quantum computing sounds like a leap in science fiction. Although there are many complex principles behind quantum computers, you should know the following five facts.

The work of quantum computers depends on "quantum bits", which is equivalent to bits in modern classical computers. When we talk about the number of qubits in a quantum computer, we are more concerned about the number of logical qubits than the number of physical qubits. In fact, due to the high error rate of current qubits, a large number of physical qubits are required to create a "functional" logical qubit.

More clearly, imagine an old robot, you can ask it a question. When you ask it your question, it only replies 7 out of 10 times and often crashes. Therefore, it is necessary to ask him the same question many times in order to finally determine the answer. Another option is to let thousands of old robots be used by you. You can ask the same questions. Then take the average value of the answers and select the answers most often given by the robot. This is the general situation of qubits.

When designing quantum algorithms, researchers imagine perfectly stable qubits, which can fully meet their expectations. So you need a lot of physical qubits to get some logical qubits. For example, researchers estimated in 2019 that 20 million noisy physical qubits or 6189 logical qubits are needed to solve the RSA algorithm, and the RSA algorithm is largely responsible for the security of the Internet [1].

Obviously, doubling the number of physical qubits is not enough to increase the power of quantum computers. The multiplication of qubits creates a lot of problems, such as it is difficult to cool them all or isolate them all.

When we talk about the capabilities of quantum computers, we usually only talk about how many qubits they have, or how many qubits they need to complete a specific task. However, in computing, for a classical computer, one 64 bit computer may not be as good as another 64 bit computer. The same is true of quantum computers.

In a typical computer, the ability of the processor to process these bits is more important than the number of bits. High performance processors can process and perform more operations faster than poorly designed processors.

Similarly, a 10 qubit quantum computer is not equal to another quantum computer with the same number of qubits. Similarly, a 4000 qubit computer with poor quality is actually not much better than a computer with only 50 qubits, because the quality of a 50 qubit computer is very good.

Finally, we also need to consider the communication between all these qubits, as well as the error rate or the number of operations that can be performed in parallel. In short, quantum computers are not just about qubits.

In order to work, our modern computers use transistors, and there are many transistors. Modern computers usually contain billions of transistors. Small switches that store '0' and '1' for computers that use power. Servers and supercomputers use a lot of transistors and power, which leads to many environmental problems. According to the researchers [2], due to the design of quantum processor, it can significantly reduce the energy consumption by 100 to 1000 times.

"Because [quantum computers] take much less time to calculate, they will also be more energy-efficient," said Tamar Elam, an IBM researcher who studies how to reduce the impact of cloud computing. If quantum computers are limited today, such as the need to cool them to extreme temperatures, current research shows that the total power consumption of quantum computers is still lower than that of computers used today.

Scientists at Oak Ridge National Laboratory (ORNL) also believe that [3] quantum computers will consume less energy than today's supercomputers. "Today's high-performance computers with thousands of processors require a lot of energy to perform complex scientific computing. In addition to their unprecedented ability to solve major problems, we also find that quantum computers have the potential to reduce energy consumption by more than 1 million kwh," said Travis humble of ORNL.

This seems obvious, but it should be noted that quantum computers are fundamentally different from classical computers. Although quantum computers can run traditional algorithms, they are not as efficient as traditional computers. It will stand out only when you get a special quantum algorithm to solve it. As a theoretical concept, quantum algorithm has been studied for more than 20 years.

In addition to quantum algorithms, such as shor and Grover algorithms, there are many programming languages for quantum computers. Each of them has its own characteristics. For example, in 2020, the Federal Institute of technology in Zurich developed the high-level programming language "Silq" [4] to promote the learning of quantum computers.

To facilitate learning, companies like IBM provide cloud access to quantum computers. Researchers can use quantum computers to train themselves in quantum programming.

Quantum computers have different quantum programming languages and different technologies to realize the creation of qubits and related computers. They have very different capabilities and requirements for each qubit.

"You have to understand that there are many different skills in dueling," explains Olivier ezrate, author of understanding quantum computing [5]. "There are at least six competing technologies that are not related to each other. This is different from the difference between computer processors and smartphone processors. The processors of computers and smartphones are the same technology to some extent. On the other hand, the differences between different branches of quantum computing are huge."

The materials and technologies used vary widely. For example, we have found a quantum computer composed of superconductors, semiconductors, entangled photons, silicon isotopes, mayora nanofermions and ion traps. Recently, researchers proposed to use carbon nanotubes to realize qubits [6]. At present, research is in full swing to determine the best model.

"The advantage is that it creates diversity. It's a bit Darwinian," Olivier ezrate concluded. "They have very different characteristics. We don't know which one will work or won't work in advance."

Link:
[1] https://arxiv.org/abs/1905.09749
[2] https://arxiv.org/abs/1609.02732
[3] https://www.ornl.gov/news/energy-quantum-computing-efficiency
[4] https://silq.ethz.ch/
[5] https://www.oezratty.net/wordpress/2020/comprendre-informatique-quantique-edition-2020/
[6] https://arxiv.org/abs/2008.10524
[7] https://technewsinc.com/5-things-you-didnt-know-about-quantum-computers/