Breaking Lorentz Reciprocity To Overcome the Time-bandwidth Limit in Physics and Engineering


    Resonance is a universal phenomenon in relevant fields such as optics, electricity, acoustic waves and mechanics. Resonant devices and systems have wide applications in various domains in modern society. 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.

    Zheng Xiaodong, from the State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, is a member of the research team that breaks Lorentz reciprocity to overcome the time-bandwidth limit in physics and engineering. The research team proposes that as a system becomes more asymmetric in its transport properties, the degree to which the limit can be surpassed becomes greater. By way of examples, they 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. Their 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.

    The findings of the research team were published in Science—one of the world’s top academic journals on June 23(doi: 10.1126/science.aam6662).