The Science Fiction World of Xueba

In the next few days, Pang Xuelin focused his energy on the study of quantum computers.

The so-called quantum computer is a type of physical device that stores quantum information and implements quantum calculations in accordance with the laws of quantum mechanics.

In general, the input of a quantum computer can be described by a quantum system with finite energy levels.

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

The qubit -Ψ> = α-0> + β-1> can be any combination of the -0> state and the -1> state, where α and β represent the proportionality coefficients in the coherent superposition state, respectively.

Based on the quantum coherence effect, there are infinitely many sets of conditional coefficient values ​​for α ^ 2 + β ^ 2 = 1, so the information represented by qubits can be greatly enriched.

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

The qubits are constructed using the polarization of photons, so-called optical quantum computers.

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

The qubits are constructed using the energy levels of captured ions or atoms, so-called ionic quantum computers.

At present, ionic quantum computers have not been manufactured. Scientists from Sweden and Austria have cooperated to create the basic components of ionic quantum computers. However, it is still a while before the actual ionic quantum computers are manufactured.

The last one is the superconducting quantum computer, which uses superconducting lines, including Cooper pairs and left / right-handed circular current superposition states related to the circulation direction, to construct qubits.

At present, companies such as IBM, Google, and Microsoft are fiercely competing in this field.

Quantum superposition and quantum coherence are the most essential characteristics of quantum computers.

The transformation that a quantum computer implements for each superposition component is equivalent to a classic calculation. All these classic calculations are completed at the same time and are superimposed with a certain probability amplitude to give the output result of the quantum computer.

Therefore, a quantum computer is essentially a kind of parallel computing. Under parallel conditions, it can solve problems that can only be solved in classical computer exponential time in polynomial time.

For example, a quantum computer can break a large 250-bit number into a product of two prime numbers in a matter of seconds, and current computers take one million years to complete this task.

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

At the same time, it has also attracted the interest of government departments and the business community.

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

In the middle is a mix of non-scientific competition by major companies such as Google, IBM, and Microsoft in order to dominate the industry.

For example, a few months ago, the so-called quantum hegemony announced by Google was more derived from commercial interests than technically.

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

They are quantum algorithms and physical implementations.

Practical quantum algorithms can be divided into three major categories. The first category is based on the quantum Fourier transform method represented by the Shor algorithm to find periodic problems, and it can be further reduced to the problem of Abel implicit subgroups.

The second type of algorithm is called the Gover algorithm.

The Gover algorithm builds a basic framework for a class of problems based on the method of probability amplitude amplification, including improved Gover algorithm, collision problem, quantum genetic algorithm, quantum simulated annealing algorithm, quantum neural network, and so on.

The third category is algorithms that simulate or solve quantum physics problems, including Feynman's original idea of ​​accelerating quantum physics simulation with quantum computers. Recently, there are also algorithms based on quantum random walk, especially continuous-time quantum random walk. It includes the Boolean logic calculation algorithm of NAND tree proposed by Edward Fary, 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, the physical system of a quantum computer must meet the following requirements.

First, it has scalable qubits with good characteristics.

Second, it can initialize the qubit to a certain reference state, such as -000 ...>.

Third, it must have a sufficiently long coherence time, much longer than the time required to complete the operation of the quantum gate.

Fourth, it has a universal set of quantum gates.

Fifth, it is possible to measure specific qubits.

In order to enable quantum computing in physics, researchers have conducted in-depth research in two directions based on the above requirements.

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

This scheme includes different schemes such as spin system, superconducting system, quantum dot system, and nuclear magnetic resonance system.

The second is a quantum computer based on a quantum optical system.

Including ion traps, cavity quantum electrodynamic systems, linear optical systems, photonic crystals, and photonic crystal-bound cold atom systems, etc. ~ www.NovelMTL.com ~ It took a full half month. Brushed the technical manual of the quantum computer all over, and got a basic understanding of the quantum computer.

Then he found that it was unlikely that he would want to make this quantum computer provided by the system in reality in a short time.

Because the quantum computer provided by the system is a topological quantum computer, the number of qubits in its 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 combined.

To make this kind of quantum chip, you need a quasi-particle with 1/4 charge. The behavior of this kind of particle is very different from those of quasi-particles with an odd number of charges. When a half-charged particle exchanges position with another particle, there is not much overall effect.

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

Although the real world dates back to 2008, Israeli scientists have discovered the existence of such quasiparticles.

But to find the corresponding material accurately, the manpower and material resources required are basically an astronomical figure.

However, although there is no way to integrate the quantum chip of this quantum computer, through this technical manual, Pang Xuelin has found a way to construct the Mayorana fermion using the close-knit effect of graphene materials and conventional superconductors.

And Mayorana Fermion is exactly the most critical step in realizing quantum topology calculations.

"Perhaps what Google calls quantum hegemony can be achieved in my hands."

Pang Xuelin murmured to himself.