Quantum computers are much faster than classic computers, and the key reason is quantum parallel computing.
Editor’s note: This article is from WeChat public number “PingWest product play” (ID: wepingwest), author Decode.
On October 23, 2019, Nature officially published Google’s paper on “Using Quantum Superiority,” “Quantum Advantages Using Programmable Superconducting Processors.”
This paper was leaked a month ago, but it was quickly deleted.
“Quantum superiority” means that quantum computers can do things that classic computers (which today’s popular computers) can’t do.
This concept was first proposed by John Preskill, a professor of theoretical physics at the California Institute of Technology in 2012.
In theory, classic computers can solve any calculable problem as long as you give enough time.
Therefore, the standard of “quantum superiority” is that quantum computers have significant (exponential) acceleration over the same computing task.
Google’s papers show that they created 53 quantum bit quantum computers with superb computing power.
With the same amount of computation, the quantum computer is completed in 200 seconds, and the current most powerful classic supercomputer takes 10,000 years to complete.
IBM researchers have different opinions on this.
On October 21st, IBM researchers wrote a question about Google’s experimental approach:
Google has a problem in estimating estimates that classic supercomputers need to calculate in 10,000 years, and IBM’s approach allows supercomputers to perform the same computing tasks with higher fidelity in 2.5 days.
This is still a “conservative, worst-case estimate”, and other studies can further reduce time.
No matter 10,000 years or 2.5 days, the speed of quantum computers is far more than the classic computer, the key reason behind this isQuantum parallel computing.
Explain quantum parallel computing, starting with the properties of quantum.
“Quantum” is not a specific particle, but a general term for a material object in a quantum world. It can be a microscopic particle such as a photon, an electron, an atom, a nucleus, or an elementary particle, or a quantum system at a macroscopic scale. For example, “Schrödinger cat”.
In our daily experience, the physical quantities and states of macroscopic world objects are always determined at some point.
For example, a light bulb is either open or closed, and it cannot be opened and closed.
But in the quantum world, “a light bulb that is turned on and off” exists because quantum has a superposition state.
Quantum superposition means that a quantum system can be in a superposition state of different quantum states.
In short, the two states are superimposed.
“Schrodinger’s Cat” is a thought experiment that explains quantum superposition:
Keep the cat in an opaque box with a device that releases poison gas.
If you do not open the box to observe (measure), the cat is stuck in a dead/live superimposed state.
In addition to the superposition state, quantum has another important property – quantum entanglement.
Quantum entanglement means that two particles can have interconnected properties even if they are separated by several light years. 
In 1981, American physicist Chad Feynman suggested that in principle, one could design a computer that works through quantum mechanical properties, simulates quantum systems, and uses quantum equations to obtain solutions.
Because quantum systems have natural parallel processing capabilities, computers that are implemented with them are likely to go far beyond classical computers.
The information unit of a classic computer is a bit, which is generally represented by “0” and “1”.
One bit, either “0” or “1”.
The unit of information in a quantum computer is “qubit bit.”
As mentioned above, quantum has the property of superposition, so the qubit can be at “0” at the same time.The status of “1”.
Someone has done a metaphor:
The classic bits are “switches”, with only two states (0 and 1) on and off, and the qubits are “knobs”, just like the knobs on the radio, there are infinite states.
Classical computers operate by manipulating classical bits, and quantum computers manipulate quantum bits, essentially to rotate them.
▲ (picture from the source quantum)
Because of this superposition, quantum computers can have powerful parallel computing capabilities.
When designing a quantum computer, the characteristics of quantum entanglement are usually used to entangle one particle with other particles, further improving the parallel computing power.
In short, the use of quantum superposition and quantum entanglement can increase the computational power exponentially.
Making quantum computers is not an easy task.
Since the quantum state of quantum bits is very fragile, one of the main difficulties in building quantum computers is to maintain the ultra-low temperature of the quantum states.
The slightest vibration of a “noise” or a change in temperature disturbance can cause the quantum behavior to decay before the particle is properly completed. This is known as the “Decoherence” phenomenon.
The quantum computer must therefore operate at extremely low temperatures to try to protect the quantum bits from the external environment.
Secondly, because of the instability of quantum bits, the accuracy of quantum computing is also problematic, and the fidelity is not high.
A lot of researchers believe that Google’s results have pushed quantum computing a big step forward, but everyone knows that the application of quantum computing is still very limited.
At present, classic computers are still the simplest and most economical solution to most problems.
Quantum computers are used in materials science, pharmaceutical research, and cryptography, and companies have been experimenting with them in the automotive and pharmaceutical industries.
In addition, the core optimization process and quantum computing in machine learning is a natural fit. It is not surprising that Google has spent so much effort to develop quantum computers.
The cover image is from pexels