Recently, mainland scientists and international researchers have achieved superconducting multi-qubit entanglement to approach the Heisenberg limit, demonstrating the ability of superconducting quantum computing technology to accurately manipulate multi-qubits, which is expected to be applied to quantum metrology.
The asterisk pointed by the arrow is the advantage of quantum metrology achieved by the institute, and the results show that the entangled state prepared by using 19 superconducting quanta is closer to the Heisenberg limit shown by the shadow boundary than other experiments, picture from the Beijing Institute of Quantum Information Science
The Heisenberg limit is the final limit of accuracy that is limited by the uncertainty principle of quantum mechanics. The uncertainty principle in quantum mechanics, also known as the uncertainty principle, was proposed by the German physicist Heisenberg, one of the founders of quantum mechanics.
In recent years, superconducting quantum computing has developed rapidly, and the implementation of quantum algorithms and the nature of quantum analog multibody systems have attracted attention. The use of superconducting qubits to achieve multi-particle entanglement can demonstrate the ability of the system to control multiple qubits at the same time, and quantum entanglement is a useful resource for quantum computing, and its convenient preparation will reduce the difficulty of implementing quantum algorithms. However, there is less exploration of the use of quantum entanglement to break through the standard quantum limit of classical methods of measuring accuracy and further approach the Heisenberg limit, which is the content of the field of quantum metrology.
Quantum metrology has broad application prospects, the purpose of which is to use entangled states to achieve breakthroughs in the accuracy limits of classical technology, in order to achieve ultra-high-precision measurements of certain physical quantities. If it is difficult to measure the thickness of a piece of paper directly with calipers, but it is easier to measure the thickness of a stack of paper by dividing the number of paper layers to obtain the thickness of a piece of paper, quantum metrology is based on this naïve idea.
For example, considering the phase information of measuring optical qubits, if these photons are independent of each other, according to the statistical central limit theorem, the accuracy of multiple measurements can only reach the shot noise limit, that is, the standard quantum limit. However, if the photons are all entangled to form a special multi-particle entangled state, their phase information is enlarged, just like stacking multiple layers of paper, then measuring the phase information can break through the standard quantum limit and can approach the Heisenberg limit, which can be called the advantage of quantum metrology.
The degree of approximation to the Heisenberg limit is related to the degree of entanglement of the multiparticle state that enables the detection, but the measure of the entanglement size of the multiparty is more complex and depends on the application. The advantages of quantum metrology can be measured with quantum Fisher information and are also directly related to the size of entanglement. Although the entanglement and quantum metrology advantages of Gaussian compressed states can be characterized by linear compression coefficients, for non-Gaussian entangled states in the overcompressed region, the linear compression coefficient cannot determine whether there is multibody entanglement.
In recent years, the compression coefficient can be generalized from the linearity of the original concept to the nonlinear compression coefficient, which can better characterize the entanglement of non-Gaussian states, and is directly related to the advantages of quantum metrology. However, subject to the experimental difficulty of multi-qubit single-engine measurements, the measurement of nonlinear compression coefficients is not realized in various multi-particle entanglement systems.
If multiparticle entanglement can be achieved with superconducting qubits, can a special entangled state with the advantages of high quantum metrology be obtained?
This time, Xu Kai, associate researcher of solid state quantum information and computing laboratory of institute of physics of Chinese academy of sciences/Beijing National Research Center of Condensed Matter Physics, researcher Fan Juan, researcher Zheng Dongning, researcher of state key laboratory of superconductivity, wang haohua team of professor of Zhejiang University, and Japanese researchers cooperated to successfully prepare non-Gaussian compression states that approached the Heisenberg limit in quantum metrology by using 10 and 19 superconducting qubits in multi-qubit devices, and realized the measurement of nonlinear compression coefficients in entangled states for the first time. Among them, the quantum measurement advantage obtained by the entangled state of 19 qubits is significantly better than that of other series of work, creating a world record for the quantitative advantage of the same magnitude of bits. The results were recently published in the Physical Review Letters.
Image courtesy of Physical Review Letters
Previously, the Institute of Physics of the Chinese Academy of Sciences and the Quantum Computing Cloud Platform team of the Beijing Institute of Quantum Information Science have long been committed to the research of superconducting quantum computing, and have cooperated to prepare 20 superconducting qubits Schrödinger cat state, refreshing the world record of multi-particle entanglement in solid-state systems.
The research team continues to use the above-mentioned devices with fully connected 20 superconducting qubits, using 10 and 19 superconducting qubits respectively, to prepare a compressed state with quantum metrology advantages and a non-Gaussian compression state in the superconducting quantum computing platform newly built by the Institute of Physics of the Chinese Academy of Sciences, and measured the nonlinear compression coefficient of this non-Gaussian compression state, which is the first successful measurement of nonlinear compression coefficient in the experiment.
There are 19 qubit positions in the device, which are coupled to each other intensity information, as well as experimental operation steps when measuring linear and nonlinear compression coefficients, quantum Fisher information, picture from the Institute of Physics, Chinese Academy of Sciences
Experimental results show that the non-Gaussian compressed state of superconducting qubits has approached the final precision limit that can be achieved in quantum metrology, the Heisenberg limit. Based on the advantages of quantum metrology, the entangled state prepared in this experiment is the best in the year-on-year specials, which shows the ability of superconducting quantum computing technology to accurately manipulate multiple qubits, as well as the characteristics of strong versatility, and is expected to be applied to quantum metrology, and at the same time lays a technical foundation for the quantum computing cloud platform based on this experimental system.
The above research was completed by Fan Juan, Xu Kai, Zheng Dongning, Song Xiaohui and other members of the quantum computing cloud platform team in cooperation with professor Wang Haohua of Zhejiang University and Dr. Zhang Yuran and Professor Nori of Riken in Japan, and supported by the National Natural Science Foundation of China and the Pilot Special Project B of the Chinese Academy of Sciences.