Breaking Lorentz reciprocity to overcome the time-bandwidth limit in physics and engineering
Breaking Lorentz reciprocity to overcome the time-bandwidth limit in physics and engineering
复制标题
打破洛伦兹互易性，克服物理和工程中的时间带宽限制
DOI：
10.1126/science.aam6662
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发表时间：
2017-06-23
期刊：
影响因子：
56.9
通讯作者：
Boyd, R. W.
中科院分区：
文献类型：
--
作者：
Tsakmakidis, K. L.;Shen, L.;Boyd, R. W.
高带宽谐振系统有源系统的性能，无论是光学、电学还是机械，通常都是通过其品质（Q）因子来描述的。通常情况下，人们知道的规则是，Q因子越高，谐振越尖锐，也就是说，器件的带宽减小。Tsakmakidis等人证明了这确实是事实，但仅限于对称系统。然而，对于非对称（或非互易）系统的情况，不需要遵守该规则。从理论上说，高Q值的系统越不对称，带宽就越宽。该效应提高了设计在大带宽上工作的高Q器件的前景。非对称材料为设计高带宽的高品质因数器件提供了前景。物理学和工程学中有一个世纪的原则，即任何类型的系统，具有带宽Δω，可以在与带宽成反比的有限时间段Δt内与波相互作用（Δt·Δω ~ 2π）。这个定律严重限制了光子学、腔量子电动力学和光力学、声学、连续介质力学、原子和光学物理学中所有类型的共振和波导系统的通用能力，但被认为是完全基本的，源于基本的傅立叶互易性。我们建议，这个“基本”的限制，可以克服系统中的洛伦兹互易性被打破。当一个系统的输运性质变得更加不对称时，其极限可以被超越的程度就变得更大。通过例子，我们从理论上证明了如何，在一个巧妙设计的磁化半导体异质结构，上述限制可以通过使用现实的材料参数的数量级超过。我们的研究结果修改了线性时不变谐振系统的流行范式，挑战了高质量谐振必须总是窄带的理论，并提供了开发具有前所未有的高时间带宽性能的设备的可能性。
Resonant systems with high bandwidth The performance of an active system, whether it is optical, electrical, or mechanical, is often described by its quality (Q) factor. Typically, one learns the rule that the higher the Q factor, the sharper the resonance—that is, the bandwidth of the device is reduced. Tsakmakidis et al. show that this is indeed the case, but only for symmetric systems. However, for the case of asymmetric (or nonreciprocal) systems, the rule need not be obeyed. They show theoretically that the more asymmetric a system with high Q is, the wider the bandwidth can be. The effect raises the prospect of designing high-Q devices operating over large bandwidths. Science, this issue p. 1260 Asymmetric materials provide the prospect of designing high–quality-factor devices with high bandwidth. A century-old tenet in physics and engineering asserts that any type of system, having bandwidth Δω, can interact with a wave over only a constrained time period Δt inversely proportional to the bandwidth (Δt·Δω ~ 2π). This law severely limits the generic capabilities of all types of resonant and wave-guiding systems in photonics, cavity quantum electrodynamics and optomechanics, acoustics, continuum mechanics, and atomic and optical physics but is thought to be completely fundamental, arising from basic Fourier reciprocity. We propose that this “fundamental” limit can be overcome in systems where Lorentz reciprocity is broken. As a system becomes more asymmetric in its transport properties, the degree to which the limit can be surpassed becomes greater. By way of example, we theoretically demonstrate how, in an astutely designed magnetized semiconductor heterostructure, the above limit can be exceeded by orders of magnitude by using realistic material parameters. Our findings revise prevailing paradigms for linear, time-invariant resonant systems, challenging the doctrine that high-quality resonances must invariably be narrowband and providing the possibility of developing devices with unprecedentedly high time-bandwidth performance.