In June 23, 2017, research fellow State Key Laboratory of modern optical instrumentation Zheng Xiaodong School of Optoelectronics Zhejiang University completed Breaking Lorentz reciprocity to overcome the time-bandwidth limit in physics and Engineering "(breaking Lorenz reciprocity to overcome the time limit of bandwidth in physics and Engineering) in the" Science ". In this study, a system of asymmetric wave packet entry and exit was designed, which successfully broke the limitation of time bandwidth in more than 100 years. The higher the degree of asymmetrical system is, the higher the degree of exceeding the "limit". This research will play a profound role in the development of new devices and systems. The famous science news website Phys.org reports on the theme of "A 100-year-old physics problem has been solved", and has triggered a lot of attention and discussion.
According to reports, the original research work at Zhejiang University State Key Laboratory of national optical instrument teacher Shen Linfang (now a researcher at Nanchang University Space Institute) as the first author, Zhejiang University and the Nanchang University professor Zheng Xiaodong Deng Xiaohua is co-author of the article. The whole team is composed of 9 researchers from 6 universities, Canada, China, the United States and Switzerland. The key system used in the design of asymmetric system in the study is the hybrid resonant cavity / waveguide system of magneto optic materials, which is studied by Nanchang University and Zhejiang University.
The following are the interpretations of this progress by Mr. Zheng Xiaodong, who was involved in the study.
What is the "time bandwidth limit"?
Resonance is a common phenomenon in the fields of light, electricity, sound wave, machinery and other related fields. The resonators and systems are widely used in all walks of life in modern society. For example, a laser resonator, a variety of waveguides, etc. Leave the resonance, the computer is no longer computing, mobile phone, TV can display images, Shuabing can not watch radio radio, unable to support social operation timing, physical and engineering systems are used in a large number of various types of resonator. For a long time, the design of the resonant system is considered to be constrained by a basic limit, that is, the time that the energy stored by the resonator is inversely proportional to its bandwidth, or the product of the storage capacity and the system bandwidth is fixed, and there is a "time bandwidth limit".
This rule is proposed by K. S. Johnson in 1914: a resonant cavity has a longer storage time and a wide narrow band, or a larger bandwidth, but a short energy storage time. It is impossible to store large data in a resonant cavity for a long time. Because long time means taking narrow and vice versa. This time bandwidth limit rule has never been challenged for more than 100 years. Physicists and engineers have been designing and constructing optical, acoustic, and electronic resonance systems (see Figure 1). From the frontiers of micro / slow optical waveguides, to the vibrational relations between atoms and molecular structures, all types of resonators, crystal oscillators and so on are limited by the time bandwidth limit.
Figure 1 a number of optical and electrical systems that are limited by time bandwidth.
Break the "magic"
Now, the limit is in theory the past. So, how is this magic spell broken? The solution to the paper is to break the "Lorentz reciprocity". The Lorentz reciprocity theorem is the basic theorem of the electromagnetic field. It describes: "in linear and isotropic media, if we exchange the location of the source and the observation point without changing the source, the field at the new observation point is equal to the field at the original observation point before switching." A metaphor that is not very accurate but can be understood is that if the cavity is compared to a room, the energy oscillation of the traditional resonator is like a row of people swing on the door, which is reciprocity from the house to the outside and from the outside room. The reciprocal cavity can only be allowed to move in and out of the same person, and it can stay in the house for a long time. If the speed is fast or slow, it can only stay for a very short time. It is the limit of time bandwidth in physics and engineering. How can the adults, the children, the fast and slow people go in, and how long can they stay in the house?
The article's plan is to let people swing into the house side by side at normal speed, and from inside to outside, it will no longer be side by side, but will reverberate in a sequential order in a controllable speed. That is to say, using the control energy to enter and leave the resonant cavity at different rates, or designing the resonant system with asymmetric time and time, successfully broke the limitation of the time bandwidth in the past more than 100 years. The higher the degree of asymmetrical system is, the higher the degree of exceeding the "limit".
Figure 2 asymmetric resonator / waveguide system.
The next question is how to make the energy entering and leaving the resonance system freely adjustable, which is the key to achieve the design of asymmetric system. The use of the exclusive secrets is Nanchang University and the Zhejiang University cooperation on magneto-optical material / hybrid resonator waveguide system (see Figure 2). With this system, we can freely control the energy transmission rate of the backpropagation electromagnetic wave freely. In terahertz wave band, the traditional time bandwidth limitation has been increased thousands of times. In theory, there is no upper limit in these (time) asymmetrical systems, and the bandwidth is no longer subject to the storage time of energy.
The breakthrough of the time bandwidth limit of the resonant system will have a far-reaching impact on many fields of physics and engineering, and the potential application prospect is very extensive, including communication, light detection, energy acquisition and information storage. For example, people