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Although the "spooky superposition effect" has been verified between two particles in the entangled state, in the traditional quantum mechanics, this superposition effect cannot be used to transmit information at superluminal speed. However, the research team of China University of Science and Technology succeeded in verifying through experiments: In the world of PT symmetry theory, entanglement can be used to realize superluminal information transmission.
Since the birth of quantum mechanics for more than 100 years, it has achieved great success in almost all fields of physics. However, for the foundation of quantum mechanics, especially how it is integrated with general theory of relativity, until now, quantum mechanics theory has not been able to give satisfactory answers. A few days ago, researchers from the University of Science and Technology of China published a study in the British Journal of Nature and Photonics. They successfully simulated the phenomenon of superluminal in the parity-time (PT) symmetric world, or answered this question. A step has been taken on the road to a problem.
Incredible overreach effect
The formulation of Bell's inequality has changed the completeness of quantum mechanics from philosophical speculation to experimental verification. Later, more and more experiments support the role of superposition, and do not support local realism.
In the 1920s, several quantum physicists represented by Bohr, Heisenberg, etc. established an interpretation method that divided the world into two distinct areas, one classic and one quantum. In the quantum world, everything is governed by a specific field or wave that tells us what the probability of a real state is. When this quantum wave touches something in the classical field through a measurement or other interaction, the wave function will immediately "evaporate" or collapse, eliminating all other states and leaving only one real state. Scholars such as Bohr believe that before the measurement, all we can know about this world is a series of probabilities.
Einstein always believed that Bohr's interpretation was incomplete. In this protracted debate, he has always played the role of an opponent. At the 5th Solvay meeting in 1927, at the Solvay meeting of physics, Einstein pointed out that, for example, what is happening to an electron, Bohr's theory gives the probability of finding this electron in a certain position at a certain moment in time. However, if it appears in A, it will prevent the electron from appearing in B. That is, a function that appears in "here" makes it impossible for this effect to appear there. Einstein believes that "this process assumes a very peculiar, ultra-distance mechanism of action", in other words, either admits the existence of superposition or Bohr's theory is incomplete.
Throughout his life, Einstein advocated local causality, that is, objects could not be transmitted at superluminal speed, negating the role of superposition. In the 1960s, the Irish physicist John Bell demonstrated in an influential paper that the “setting a measuring device will affect the reading of another device, no matter how far†in the theory of quantum mechanics, and made famous Bell's inequality, he said: "This theorem undoubtedly suggests that Einstein's time-space concept of being neatly divided into different regions by the speed of light is not flawless."
The formulation of Bell's inequality has changed the completeness of quantum mechanics from philosophical speculation to experimental verification. Later, more and more experiments support the role of superposition, and do not support local realism. Until 2015, the Delft University of Technology team in the Netherlands announced that they have designed and conducted the most rigorous experiments to date, verifying for the first time that the Bell inequality has been destroyed without holes, thus demonstrating that the "super-distance effect" of quantum mechanics is real. of. This study was included in the Global Science magazine as one of the top 10 scientific news of 2015.
When PT symmetry theory meets quantum mechanics
Physicists predict that the non-Hermitian Hamiltonian system in PT symmetry theory will also bring about new physical phenomena - entanglement can be used to achieve superluminal information transmission.
Although the "spooky superposition effect" has been verified between two particles in the entangled state, in the traditional quantum mechanics, this superposition effect cannot be used to transmit information at superluminal speed. The research team of the University of Science and Technology of China successfully verified this experiment: In the world of PT symmetry theory, entanglement can be used to achieve superluminal information transmission.
First of all, what is PT symmetry theory? It is related to the physical quantity that a physicist often encounters in solving a job. "We know that quantum mechanics itself is established by a series of assumptions. One of them involves the description of the basic physical quantity of quantum systems - the Hamiltonian," one of the correspondents of the research paper, and a key experiment in quantum information of the Chinese Academy of Sciences, University of Science and Technology of China. Room professor Han Yongjian explained to the reporter of Science and Technology Daily: “The nature of a physical system is determined by Hamiltonian.â€
The traditional quantum mechanics public establishment has its physical roots, but one of them is the requirement of pure mathematics—that is, the Hamiltonian of the required system must be “Hermioneâ€. The so-called Hermione means that the matrix is ​​the same as the original matrix after both "Transpose" and "Conjugate" transformations; and if the transformed matrix is ​​different from the original matrix, it is non-Hermitian. Hermione's Hamiltonian indicates that the energy of the system is real and the total probability is conserved.
At the beginning of this century, American physicists Carl Bender and others proposed different opinions. They believe that the mathematic requirement that Hamilton must be Hermite is too strict and should be relaxed. But how should we relax?
"The two transforms of transpose and conjugate can be replaced by two weaker and more 'physical' transforms - the inversion of space (P) and time (T)," said Han Yongjian, "reducing the amount of Hamiltonian The Hermite condition—this mathematical requirement—is symmetrical to the PT, and although this mathematical condition is relaxed, its corresponding physical requirements—the real nature of energy and the conservation of total probability—are still maintained.†Hamilton The quantity only needs to satisfy the space and time inversion symmetry at the same time. The real energy of the system and the conservation of the total probability can still be maintained.
In this way, under the PT's assumption, some non-Hermitian Hamiltonian also becomes legal, and also meets the physical requirements of energy and the general probability of conservation. For more than a decade, the PT symmetry theory has made great achievements in the field of classical optics. In the quantum world, physicists predict that non-Hermitian Hamiltonian systems in PT symmetry theory will also bring about novel physical phenomena - entanglement It is used to achieve superluminal information transmission. The experiment of the Chinese Academy of Sciences Key Laboratory of Quantum Information successfully validated this theoretical prediction.
Make information "fly" at 1.9 times the speed of light
The PT symmetry theory may open up new fields for quantum mechanics. Interestingly, metrics can be introduced into the PT symmetry theory to provide a possibility to introduce gravity under the quantum mechanics framework.
In order to simulate the superluminal phenomenon in the PT symmetry theory world, the team used quantum simulators to perform complex experiments.
"We first need to distribute a pair of entangled photon pairs to two labs 25 meters apart," said Han Yongjian. In one of the labs, the researchers used a series of quantum logic gates and a post-selection operation, making One photon in an entangled photon pair is subjected to non-parametric evolution under PT symmetry control. Then, simultaneous measurements are made on two photons separated by a class of space. “Spatiality needs fast measurements to ensure that our measurement time is 43.5 nanoseconds.â€
The measurement results show that the information encoded in the symmetric world of PT can be transmitted from one laboratory to another at a speed of light exceeding 1.9 times.
"Of course, in our experiment, the PT symmetric world is probabilistically realized (50% probability)," Han Yongjian said. Therefore, additional information is needed to determine if the system is in the PT world. If we add the information needed in this part, there will be no superluminal phenomena in the entire system, which is consistent with the world we are in and the existing quantum mechanics.
The PT symmetry theory may open up new fields for quantum mechanics. Han Yongjian said that Einstein's theory of general relativity was described using geometric metrics; in traditional quantum mechanics, metrics did not play any role. "Interestingly, metrics can be introduced into the PT symmetry theory to provide a possibility to introduce gravity under the quantum mechanics framework."
In the future, will the PT symmetry theory help promote the integration of quantum mechanics and general relativity theory? Han Yongjian stated objectively that it is still far from that step and the current work remains at the stage of researching the phenomenon of PT symmetry. "Even if PT symmetry theory exists in nature and is correct, whether it can fuse general relativity, there is still a long way to go." (Text, reporter Liu Suiyu)
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