Chapter 201 of the Science Fiction World Text Volume of Academic Masters, Quantum Algorithm and Physics Implementation In the next few days, Pang Xuelin focused his main energy on learning quantum computers.

The so-called quantum computer is a physical device that stores quantum information and realizes quantum computing according to the laws of quantum mechanics.

Generally speaking, the input of a quantum computer can be described as a quantum system with a finite energy level.

Such as a two-level system, it is called a qubit.

The qubit Ψ>=a0>+β1> can be any combination of 0> state and 1> state, where a and β represent the proportional coefficients in the coherent superposition state, respectively.

Based on the quantum coherence effect, there are infinite sets of conditional coefficient values ​​of a^2+β^2=1, so the information represented by qubits is greatly enriched.

According to the composition of qubits, quantum computers can be divided into the following types.

Use photon polarization to construct quantum bits, the so-called optical quantum computer.

In 2017, the world's first optical quantum computer was born at the University of Science and Technology of China.

The energy level of captured ions or atoms is used to construct quantum bits, the so-called ionic quantum computer.

Ionic quantum computers have not been manufactured yet. Scientists in Sweden and Austria have collaborated to create basic components of ionic quantum computers, but it is still a while before they can make real ionic quantum computers.

The last type is a superconducting quantum computer, which uses superconducting lines, including cooper pairs and left/right rotation circulation superposition states related to the circulation direction, to construct quantum bits.

Currently, companies such as ibm, Google, and Microsoft are in fierce competition in this field.

The superposition and quantum coherence of quantum are the most essential features of quantum computers.

The transformation implemented by a quantum computer on each superimposed component is equivalent to a classical calculation. All these classical calculations are completed at the same time and are superimposed at a certain probability amplitude to give the output result of the quantum computer.

Therefore, quantum computers are essentially a kind of parallel computing that can solve problems that can only be solved within the exponential time of the classical computer under parallel conditions.

For example, a quantum computer can decompose a 250-bit large number into the product of two prime numbers in a few seconds, and it takes a million years for the current computer to complete this work.

Because of this, there are countless top scholars in the world from mathematics, physics, chemistry and other fields who have become interested in quantum computers.

It also aroused the interest of government departments and business circles.

But so far, the so-called quantum computer is just an expensive toy.

There are non-scientific competitions carried out by large companies such as Google, ibm, and Microsoft to dominate the industry.

For example, the so-called quantum hegemony announced by Google a few months ago was more due to commercial interests than to that level.

At present, there are two main branches in the field of quantum computer research.

They are quantum algorithms and physical implementations respectively.

Practical quantum algorithms can be divided into three major categories. The first category is the problem of finding periodicity based on quantum fourier transformation method represented by the shor algorithm, which can be further attributed to the problem of Abel's hidden subgroup.

The second type of algorithm is called the governor algorithm.

The governor algorithm constructs a basic framework for a type of problem based on the probability amplification method, including improved governor algorithms, collision problems, quantum genetic algorithms, quantum simulation annealing algorithms, quantum neural networks, etc.

The third type is an algorithm that simulates or solves quantum physics problems, including Feynman's original idea of ​​using quantum computers to accelerate quantum physics simulations. Recently, there are algorithms based on quantum random walks, especially continuous time quantum random walks, including the Boolean logic calculation algorithm of Nand Tree proposed by Edward Farry, director of the Center for Theoretical Physics of MIT and Gutman.

The physical implementation of quantum computers is much more difficult than quantum algorithms.

First of all, the physical system of quantum computers must meet the following requirements.

First, it has scalable and good characteristics qubits.

Second, it can initialize qubits to a reference state, such as 000…>.

Third, it must have a coherence time long enough, which is much longer than the operation time of completing the quantum gate.

Fourth, it has a general set of quantum gates.

Fifth, the measurement of specific qubits can be achieved.

In order to be able to physically realize quantum computing, the researchers have conducted in-depth research in two major directions based on the above requirements.

The first type is a quantum computer based on solid-state electromagnetic circuits.

This solution also includes different solutions such as spin systems, superconducting systems, quantum dot systems, and nuclear magnetic resonance systems.

The second type is a quantum computer based on quantum optical systems.

Including ion traps, cavity quantum electrodynamic systems, linear optical systems, photonic crystals and photonic crystal-bound cold atomic systems, etc.

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After spending a full half month, Pang Xuelin brushed all the 100 papers and the technical manuals of quantum computers given by the system, and gained a basic understanding of quantum computers.

Then he found that it is unlikely that the quantum computer that the system gave to be made in reality in a short period of time.

Because the quantum computer given by the system is a topological quantum computer, the number of quantum bits in the quantum chip is as high as 10 million, and the computing power is several orders of magnitude higher than that of all computers in the world.

To make such a quantum chip, it is necessary to use a quasi-particle with a 1/4 charge, which behaves very differently from those with an odd-particle with a quasi-particle. When electrons, photons or particles with an odd-particle with a particle exchange position with another particle, there will be no large overall effect.

In contrast, the position exchange of 1/4 charge quasi-particles can weave a "braid" that can retain particle historical information, showing "non-Abel" characteristics.

Although Israeli scientists have discovered the existence of this quasi-particle in the real world as early as 2008.

However, to accurately find the corresponding materials, the manpower and material resources required are basically astronomical figures.

However, although there is no way to use the quantum chip of this quantum computer, through this technical manual, Pang Xuelin found a way to use the nearest neighbor effect of graphene materials and conventional superconductors to construct Majorana fermions.

Mayorana fermions are precisely the most critical step in realizing quantum topological computing in the true sense.

"Perhaps, what Google calls quantum supremacy can be realized in my hands."
Chapter completed!