Shulou(Shulou.com)11/24 Report--

The experience of time flowing in a certain direction from the past to the future is deeply rooted in our minds. At the micro level, however, the laws of nature seem indifferent to the difference between the past and the future. In both classical mechanics and quantum mechanics, the basic equations of motion are reversible, and changing the time symbol will still produce effective dynamics.

Recent research has found that in well-designed circuits, photons seem to move forward and backward at the same time, which can not only help scientists improve quantum computing and understand quantum gravity, but also help us figure out some of the most mysterious phenomena in the universe.

The "time reversal" effect of the two quantum principles stems from the fusion of two strange principles. The first is quantum superposition: quantum superposition is the basic principle of quantum mechanics. It points out that, like waves in classical physics, any two (or more) quantum states can be superimposed together, and the result will be another valid quantum state; on the contrary, each quantum state can be expressed as the sum of two or more different states. Mathematically, it refers to the properties of the solution of the Schrodinger equation. Because the Schrodinger equation is linear, any linear combination of solutions is also a solution. This means that tiny particles, such as electrons, can exist in many different states at the same time, called superposition states. The second principle is charge, parity and time inversion symmetry (CPT), which states that any system containing particles will obey the same physical laws, even if the charge, spatial coordinates and time motion of the particles are inverted.

Quantum time reversal (quantum time flip)

By combining these two principles, physicists produce a kind of photon that seems to move along both the time arrow and the reverse time arrow.

In a 2013 paper, physicist Giulio Chiribela proposed a circuit that places events in a temporal superposition that transcends the superposition of spatial positions. In 17 years, Chiribela's idea was confirmed by experiments.

The researchers sent a photon to the superposition of two paths: one experienced event A, then event B, the other experienced event B, and then event A. In a sense, each event seems to lead to another event, a phenomenon later known as infinite causality.

Arrow of time time seems to have a direction-the past is behind, fixed, while the future is in front, not necessarily fixed. In most cases, however, the laws of physics do not specify a time arrow and allow any process to proceed forward or backward. This is usually the result of modeling time by parameters in the system being analyzed, where there is no "inherent time": the direction of the time arrow is sometimes arbitrary.

Chiribela designed a quantum device in which time enters a superposition from the past to the future, and vice versa-an infinite arrow of time.

To do this, Chiribela needs a system that can change in the opposite direction. He envisions putting such a system in a superposition state.

The game of photons

Chiribela designed a device in which a laser emits photons to two crystal devices An and B. When a photon passes forward through a small device, its spin polarization depends on the setting of the device; through this device, the electron polarization rotates in exactly the opposite way.

The researchers set up circuits so that photons move in only one direction in each device. Then, even if An and B are in an uncertain causal order, the detector matches the device settings for up to 90% of the time. A photon is only successful when it goes through a superposition that causes it to move forward and backward in both devices (quantum time inversion).

Last year, the team of the University of Science and Technology of China and the team of Vienna established a quantum time inversion circuit. In more than 1 million rounds of tests, the success rate of the Vienna team was 99.45 per cent. The success rate of the team of China University of Science and Technology is 99.6%. Both teams have broken the 90% theoretical limit, which proves that photons experience the superposition of two opposite transformations, so there is an infinite time arrow.

The future of time reversal is obvious that this experiment does not achieve the reversal of the time arrow. Reversal time requires the superposition of the spatio-temporal structure itself into two geometric figures pointing in different directions.

At the same time, if the photon passes through the real superposition of the two space-time geometry, the measurable properties of the photon will change exactly the same. In the quantum world, there is no reality beyond the measurable range.

Physicists hope that the ability to design quantum circuits that flow in both directions may provide new equipment for quantum computing, communications and metrology. Although time flip circuits break through the theoretical performance limits, this is a highly artificial task, only to highlight their advantages over unidirectional circuits.

Anton Cailinger, a famous physicist, once thought that quantum entanglement was not good for anything. Today, quantum entanglement connects the nodes in the newborn quantum network with the qubits in the prototype quantum computer. Nothing is known about the reversible nature of quantum time.

This article comes from the official account of Wechat: Lao Hu Shuo Science (ID:LaohuSci). Author: I am Lao Hu.

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