Is the randomness of quantum mechanics overthrown？ Don’t worry, God still rolls dice.
Yale University scientists revealed the gradual process of quantum transition through a high-speed photography technology. Quantum jump has once again become a buzzword, and it has set off a debate about whether quantum mechanics is random or continuous.
As a theory to understand the atomic scale world, quantum mechanics has a core concept that is extremely radical, bold and counterintuitive, and even becomes a buzzword, that is "quantum transition". Most pioneers of quantum mechanics believe that quantum transitions are "random and instantaneous".
A new experiment shows that this is not the case. The research was completed by Zlatko Minev, a graduate student of Mike de Vorreith Laboratory of Yale University. He and his colleagues revealed the gradual process of quantum transition through a high-speed photography technique. This achievement was recently published in the journal Nature.
The significance of the experiment may be far more than that: researchers use the high-speed detection system to "catch" the quantum transition when it is about to be marked, and then reverse it to restore the system to its initial state.
As a result, the inevitable stochastic processes in quantum physics are now proved to be controllable — — Can people really control quantum?
Debate on quantum transition
Unlike Bohr and Heisenberg’s quantum theory, Schrodinger believes that there is no quantum transition.
In the mid-1920s, physicists niels bohr, Werner Heisenberg and colleagues established quantum theory. Bohr first proposed the concept of quantum transition, but it was not observed in the laboratory until the 1980s. This theory is collectively called Copenhagen interpretation.
Bohr proposed earlier that the energy levels (i.e. energy states) of electrons in atoms are quantized, that is, electrons can only use certain energy levels, while all intermediate energy levels are forbidden. He assumes that electrons change their energy by absorbing or releasing light quantum particles, that is, photons, and the energy of photons matches the energy gap between the allowed electronic States. This explains why atoms and molecules can absorb or release light with specific wavelengths. For example, many copper-containing salts are blue, while sodium lamps emit yellow light.
In a set of mathematical theories developed by Bohr and Heisenberg, which can explain quantum phenomena, Heisenberg listed all the allowed quantum states, suggesting that the transitions between these quantum states are instantaneous and discontinuous. The concept of instantaneous quantum transition has become a basic concept in Copenhagen.
However, the Austrian physicist Erwin Schr?dinger, another founder of quantum mechanics, did not agree with this view. In Schrodinger’s theory, he represented quantum particles by wave-like entities of wave functions. Their changes were gentle, and they changed continuously with time, just like gentle waves on the vast sea.
Schrodinger believes that things in the real world will not suddenly change greatly without spending a little time, and discontinuous quantum transitions are just an illusion in my mind. In an article entitled "Is there a quantum jump" published in 1952, Schrodinger firmly replied: "No."
The focus of the debate between them is not just whether Schrodinger likes sudden changes, but that Bohr and others claim that quantum transitions will occur randomly, but they can’t say why it is that particular time. This is like a result without reason, which is undoubtedly a great challenge to the law of natural causality.
In order to explore deeply, people need to observe a single quantum transition. In 1986, three international research teams reported that they observed quantum transitions in a single atom suspended by an electromagnetic field: the atom switches back and forth between a "bright" state and a "dark" state, in which the atom emits a photon, while in a "dark" state it does not emit photons randomly; The atom stays in one of these states for a few tenths of a second to a few seconds, and then jumps again.
Since then, people have observed such transitions in different systems, including the transition of photons between different quantum states and the transition of atoms of solid materials between quantized magnetized states. In 2007, a French research team reported that a transition was found, which was in line with what they described as the process of "a single photon from birth, activity to death".
In these experiments, the transition really seems to be sudden and random, because even if the quantum system is monitored, no one can tell when the transition will occur, and there is no specific image showing the transition.
Capture quantum transition
The experiment of Yale University can not only predict the transition, but also reverse it.
How exactly did Yale University do this experiment?
Generally speaking, they use a special method to indirectly monitor superconducting artificial atoms, that is, three microwave generators are used to irradiate atoms enclosed in an aluminum three-dimensional cavity. This dual indirect monitoring method developed for superconducting circuits enables researchers to observe atoms with unprecedented efficiency. They found that every time a quantum jump occurs, a tiny photon disappearance phenomenon will occur, which can be regarded as an early warning signal.
Minev, the first author of the paper, said: "Using this phenomenon, we can not only predict the transition, but even reverse the transition."
The researchers said that although quantum transitions are discrete and random in the long run, preventing quantum transitions means that the evolution of quantum States is deterministic to some extent, rather than completely random; Transitions always occur from their random starting points in the same and predictable way.
The quantum system used by researchers is much larger than atoms, and it is composed of cables made of superconducting materials, sometimes called "artificial atoms" because they have discrete quantum energy states, similar to the electronic states in real atoms. Transitions between energy states can be induced by absorbing or releasing a photon, just like electronic transitions in atoms.
Some scientists believe that this research may also be applied to quantum computing error correction. However, the real value of the experimental results lies not in any practical application, but in our understanding of the quantum mechanical system.
How can Schrodinger’s cat be saved
Through correct monitoring, we can observe an early warning signal and take action.
Schrodinger’s cat paradox explains the concept of "superposition" in quantum physics (that is, two opposite states can coexist) and unpredictability: a cat is placed in a sealed box with a radioactive source and a poison in it. If one atom of radioactive material decays, it will release poison. According to the superposition theory of quantum physics, before someone opened the box, the cat in it was both alive and dead, that is, in the superposition state of two States. Once the box is opened and the cat’s life and death are observed, its quantum state will change immediately and become one of "dead" or "alive".
Yale University’s research shows that an early warning signal can be observed during quantum transition, which makes Schrodinger’s cat saved.
Because the decay of nuclear is a random event, physicists only know the probability of its decay, and can’t know when it decays. If the nucleus decays, releasing alpha particles, triggering the electronic switch, the hammer falls, smashing the poison bottle and releasing cyanide gas, the cat will be poisoned.
If physicists don’t open the lid of the secret room, it is uncertain whether the cat is dead or alive, and it is in a superposition state of both death and life. Only when the lid is lifted can we know for sure whether the cat is dead or alive. In this way, the microscopic uncertainty principle has become a macroscopic uncertainty principle.
Yale University researchers use an indirect observation method in the experiment, which is also a "weak measurement" method widely used in the field of quantum information, and will not disturb the observed object. Researchers believe that the transition of a particle is neither as sudden nor as random as previously thought, and the evolution of quantum state is deterministic rather than random to some extent. Theoretically, through correct monitoring, we can definitely find the warning of the coming disaster, and take action before the disaster, and remove the poison bottle at the moment when the nuclear decay is predicted, so Schrodinger’s cat was saved. Minev said: "The quantum transition of atoms is somewhat similar to volcanic eruption. In the long run, they are completely unpredictable. Nevertheless, through correct monitoring, we can accurately get the early warning of the impending disaster and take action before it happens. "
The foundation of quantum mechanics has not been affected.
The paper clearly shows that the experimental results are in good agreement with the theory of quantum mechanics.
According to von Neumann’s summary, quantum mechanics has two basic processes, one is deterministic evolution according to Schrodinger equation, and the other is random collapse of quantum superposition state caused by measurement. Schrodinger equation is the core equation of quantum mechanics, which is deterministic and has nothing to do with randomness. Then the randomness of quantum mechanics only comes from measurement.
This randomness of measurement is what Einstein can’t understand. He used the metaphor that "God can’t roll the dice" to oppose randomness of measurement. However, countless experiments have confirmed that the result of directly measuring a quantum superposition state is random. In order to solve this problem, many interpretations of quantum mechanics have been born, among which three mainstream interpretations are Copenhagen interpretation, multi-world interpretation and consistent historical interpretation.
According to Copenhagen interpretation, measurement will lead to the collapse of quantum state, that is, quantum state will be destroyed instantly and fall to an eigenstate randomly; According to the multi-world interpretation, every measurement is a division of the world, and the results of all eigenstates exist, but they are completely independent of each other and do not interfere with each other. We are just randomly in a certain world; Consistent historical interpretation introduces quantum decoherence process, which solves the problem from superposition state to classical probability distribution. However, in choosing which classical probability, it still goes back to the debate between Copenhagen interpretation and multi-world interpretation.
Professor Li Chuanfeng from the Key Laboratory of Quantum Information of China Academy of Sciences told the Science and Technology Daily reporter that these interpretations predicted the same physical results, and they could not be falsified, so the physical meanings were equivalent. Therefore, the academic circles mainly adopted Copenhagen interpretation, that is, the word collapse represented the randomness of measuring quantum states.
"The experiment of Yale scholars has not affected the foundation of quantum mechanics, that is, the inherent uncertainty of quantum mechanics." Li Chuanfeng said that the quantum transition is certain for the wave function itself, just like a dice, and it is certain that it can’t roll 7 points. The wave function can calculate how the particle probability cloud in quantum state evolves, but once the measurement problem is involved, the Schrodinger equation cannot be solved. The only way is to calculate the probability of particles, such as position probability, momentum probability and so on.
"In fact, as early as 1986, a research team confirmed through experiments that quantum transitions take time. Yale University found that quantum transitions not only take time, but also send out an early warning signal before each transition. " Li Chuanfeng said that this is like saying that someone wants to jump long, but it is impossible to predict when he will take off, but before jumping forward, his body will lean forward and raise his arm to swing back and forth, and there is a definite causal relationship between these two things. Just hit him as soon as he raises his arm, and he won’t jump. However, when this early warning signal appears is still probabilistic. As for the "overturning quantum mechanics and overturning the uncertainty principle of quantum mechanics" circulating on the Internet, it is not involved in the experiment at all, and it is clearly stated in the paper that the experimental results are in good agreement with the theory of quantum mechanics.
