With the help of the parallelism of quantum computing to bring exponential acceleration, it will far exceed the speed of existing classical computers. When the era of quantum computing arrives, it will only take 10 seconds to use a quantum computer with a GHz clock frequency to solve a system of linear equations with billions of billions of variables.
5 light qubit entanglement, 6 light qubit entanglement, 8 light qubit entanglement, 10 light qubit entanglement, 18 light qubit entanglement...
In the laboratory numbered "01003" in the Physics and Chemistry Building of the East District of University of Science and Technology of China, there are densely intricate pipelines and various optical and electronic equipment. Professor Pan Jianwei and his team of the University of Science and Technology of China are constantly researching key problems here, refreshing the number of optical qubits entangled World record. A few days ago, Pan Jianwei and his colleagues Lu Chaoyang, Liu Naile, Wang Xilin, etc. realized the entanglement of 18 optical qubits for the first time in the world, and once again broke the world record for the preparation of the largest entangled state in all physical systems.
What is a qubit? What is quantum entanglement again? What is the significance of successively breaking world records?
Quantum entanglement is a special form of quantum superposition under multi-particle conditions
"Quantum is the smallest unit of energy. The well-known changes in the state of molecules, atoms, electrons, and other microscopic particles all involve energy changes. The energy that changes in this process is a piece of quantum. For example, light in daily life, It is composed of a large number of light quanta." said Wang Xilin, a researcher at the University of Science and Technology of China.
What is a qubit? When any information is encoded, manipulated, processed, etc., there is a most basic processing unit called bit. Bit is transliterated from English BIT, it is the unit of measurement of information volume and the smallest unit of information volume. According to the researchers of Pan Jianwei's team, the bits used by people's commonly used mobile phones and computers are called classic bits. Qubit is the most basic unit for quantum information processing.
So, what about qubit entanglement?
"In the macroscopic classical world, 0 is 0, and 1 is 1. In the microscopic quantum world, a state can exist in the superposition of 1 and 0. It is neither 0 nor 1, but it is both 0 and It is 1." Wang Xilin described with the famous "Schrödinger's Cat", "In the classical world, cats are either alive or dead, but in the quantum world, cats may be dead and alive. Superposition state." A classic bit only has two states of 0 or 1. A qubit can not only be in the two states of 0 or 1, but also in the superposition state of "0+1".
Quantum entanglement is a special form of quantum superposition under multi-particle conditions. Wang Xilin picked up two pieces of paper to explain. In the classic bit scenario, one piece of paper faces up and down, and has no relation to another piece of paper. But when there are two qubits, quantum entanglement occurs.
"When two qubits are entangled, even if they are separated far apart, people will find that when one piece of paper is facing up, the other is facing up; when one piece of paper is facing down, the other is also facing up. Down; when three qubits are entangled, it is found that when one piece of paper is facing up, the other two are also facing up; when one piece of paper is facing down, the other two pieces of paper are also facing down; and so on, 18 qubits are entangled , That is, 18 are facing up at the same time, or 18 are facing down at the same time, and they are in a superimposed state of 18 0+18 1." Wang Xilin said.
Quantum computing requires multiple optical qubits to be entangled, the more the number, the better
"Classic bits processed by classical computers can only process one piece of data at a time. In the future, when quantum computers are processing qubits, they can be in a state of coherent superposition of multiple data, which has powerful parallel computing advantages." Wang Xilin described, "Manipulation A quantum computer with N qubits can, in principle, perform mathematical operations on 2 to the Nth power at the same time, which is equivalent to a classical computer repeatedly performing 2 Nth power operations."
The processing of data can achieve parallel computing, and the computing speed will be greatly improved. At the same time, the speed of quantum computing will increase exponentially as the number of entangled bits that can be manipulated in the experiment increases. The coherent manipulation of multiple qubits and the preparation of entangled states are the core indicators for the development of scalable quantum information technology, especially quantum computing. Quantum computing requires entanglement of multiple optical qubits. The more the number, the better.
However, the next step to achieve entanglement of more qubits requires high-precision, high-efficiency quantum state preparation and precise control of the interaction between independent qubits. But as the number of qubits increases, noise, crosstalk, and errors caused by manipulation also increase. This has extremely high requirements for the design, processing and regulation of quantum systems, and poses a huge challenge to the development of quantum entanglement and quantum computing.
How to alleviate the above problems and achieve the goal of increasing the entanglement number of qubits, the research team recently focused on the control method of multiple degrees of freedom of photons. "For example, 1 photon used to be used to encode 1 qubit, and the entanglement of 10 light qubits requires 10 photons. If the number of entangled light qubits is increased, the number of photons must be increased again, but this is too difficult. Big. We are now thinking whether we can use each photon to encode multiple optical qubits." Wang Xilin explained that by manipulating the polarization, path and orbital angular momentum of a photon and other degrees of freedom, one photon can encode 3 Optical qubits, so that 6 photons can encode 18 optical qubits, realizing the entanglement of 18 optical qubits, and effectively alleviating various problems that may be caused by the increase in the number of photons.
Future quantum computers can be applied to scientific problems that require large-scale calculations
"The greater the number of entangled qubits, the stronger the achievable quantum computing capabilities." The team leader said, they hope that through the next 3 to 5 years, they can achieve about 50 entangled qubits in quantum computing. Coherent manipulation makes it comparable to or surpassing the best classic supercomputers in the solution of certain specific problems.
According to theoretical predictions, the prospect of quantum computing is far more than that. Wang Xilin said that the exponential acceleration brought about by the parallelism of quantum computing will far exceed the speed of existing classical computers. When the era of quantum computing arrives, it will only take 10 seconds to use a quantum computer with a GHz clock frequency to solve a system of linear equations with billions of billions of variables. Now, even with the fastest supercomputer in the world, it will take at least a few hundred years.
"If 100 particles can be entangled and manipulated, the computing power of quantum computing can reach 1 million times the total computing power of the world in terms of solving certain specific problems. When quantum computers are applied, the current weather forecasts and medicines Design and other scientific problems that require large-scale calculations are expected to be solved." Wang Xilin gives an example. For example, for current weather forecasts, it may take 100 days to calculate the weather in one month, but after 100 days of calculation, there will be nothing. The meaning of forecasting is improved, but after applying quantum computing in the future, the forecast in one month may be completed within a few seconds of calculation time.
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