The first experiment by Pan Jianwei's team at the University of Science and Technology of China proved that real numbers cannot fully describe standard quantum mechanics, establishing the objective reality of complex numbers.
Recently, Pan Jianwei, Lu Chaoyang, Zhu Xiaobo of the University of Science and Technology of China and Professor Cabello of the University of Seville, Spain, have cooperated to achieve deterministic entanglement exchange using ultra-high-precision superconducting quantum circuits, and with experimental precision of more than 43 standard deviations, standard quantum mechanics in the world has been excluded by experiments in the form of real numbers for the first time.
The relevant paper of the team of the University of Science and Technology of China was published in the "Physics Review Letters"
Fan Jingyun, Yang Shengjun, Li Zhengda of southern university of science and technology, wang zizhu of the university of electronic science and technology of China, and scientists from Spain, Switzerland, Austria and other countries, also confirmed this result in light quantum experiments.
Both research papers were published in the form of "Editor's Recommendation" in the Journal of Physical Review Letters and as highlight articles. The American Physical Society's Physics website and Nature magazine each invited international experts to write relevant review articles for them.
Sustech's team's relevant paper was published in The Physical Review Letters
According to the paper, standard quantum theory was formulated using complex Schrödinger equations, wave functions, operators, and Hilbert spaces. Previous research has attempted to simulate quantum systems that use only real numbers by expanding Hilbert space.
But the question also arises: Are complex numbers really necessary in standard quantum theory?
Physicists have long used mathematics to describe the laws of nature. In classical physics, one can write all the laws using only real numbers, and the complex number is subjectively introduced only as a convenient computational tool (i.e., z = a + bi, where a and b are real numbers).
With the birth of quantum mechanics, complex numbers gradually showed a certain intuitive inevitability: theoretically, the Schrödinger equation and the Heisenberg-to-easy relationship, which are the cornerstones of quantum mechanics, are themselves written by complex numbers; experimentally, the real and imaginary parts of the wave function are directly measured. This shows that the complex number may not be a purely subjective introduction of the calculation symbol, but a physical reality that can be detected experimentally.
Therefore, a team of scientists from Austria, Spain, and Switzerland proposed a test method that uses deterministic entanglement exchanges to verify the bell inequality type of the necessity of complex numbers. Participants who follow quantum physics in real form cannot obtain the limits allowed in standard quantum theory, thus ruling out the possibility of describing standard quantum mechanics only in real form.
According to the above test method, the team of Pan Jianwei of the University of Science and Technology of China completed the experiment for the first time in the world based on the superconducting quantum circuit and high-precision quantum manipulation technology independently designed and developed. In the case of quantum physics, which follows the real form, the boundary of the real form is 7.66. However, the experimental test result is 8.09, which exceeds the criterion by 43 standard deviations, which proves the error of describing standard quantum mechanics in real form and establishes the indispensable role of complex numbers in standard quantum theory.
The experimental results of the team of the University of Science and Technology of China, the picture comes from the official website of the University of Science and Technology of China
The SUSTech team used the photonic system to conduct experimental tests to prove that the quantum entanglement in the optical quantum network with two independent EPR sources and three detectors violated the constraints of quantum physics in real form, exceeding 4.5 standard deviations, thus proving that standard quantum theory in real form is not universal.
The American Physical Society's Physics website commented on this: The two groups have adopted different methods to achieve quantum entanglement.
The team used a superconducting quantum processor in which the qubits are controlled and read out separately. The main challenge with this approach is to make qubits located on the same circuit truly independent and decoupled —a strict requirement of Bell's inequality type testing method.
The SUSTech team chose a photon that is easier to achieve this independence for experimentation. Specifically, they used polarized entangled photons resulting from parametric downconversion and probed them using superconducting nanowires single-photon detectors. However, optical quantum experiments face a different challenge: complete Bell state measurements are required in the experiment, which can be achieved directly using superconducting qubits, but not through linear optical phenomena. Therefore, the SUSTech team can only rely on "partial" Bell state measurements.
Sustech team experimental scene, picture from the paper
"Despite the inherent difficulties of each experiment, both experiments yielded convincing results. Impressively, their data is many standard deviations (43 standard deviations and 4.5 standard deviations, respectively) than theoretical data in real form, which is a powerful proof of the need for complex numbers to describe quantum experiments. Physics commented.
"Interestingly, both experiments are based on the minimal quantum network scheme (two sources and three nodes), which is a promising component of a future quantum internet." The experimental results also prove that the availability of new quantum technologies is closely related to the possibility of testing aspects of the fundamentals of quantum mechanics. Conversely, these new fundamental insights into quantum mechanics could have an unexpected impact on the development of quantum information technology. ”
However, caution must also be exercised when assessing the impact of these results. One might conclude that plurals are essential for describing the physical world of the universe. But this conclusion holds only when accepting the standard framework of quantum mechanics, which is based on several assumptions. These experimental results do not apply to other formulas of quantum mechanics, such as Bohmian mechanics based on different assumptions, but they are enough to inspire people to try to go beyond the standard forms of quantum mechanics.