近日，德国亚琛工业大学的
该研究团队开发了一种描述短一维电磁脉冲的光子语言，特别是在电力传输线中。在当前的量子技术实践中，使用任意波形发生器可以在极低噪声和低温环境下轻松生成非常短且周期少的脉冲。研究人员认为这些系统已经达到了产生纯相干量子态的极限，其中真空在短时间内被置换，因此仅在短空间范围内。当脉冲为双极时，即脉冲的积分电压为零，可以用单模态的有限位移来描述其状态。因此，光子的平均数目是确定的，但它们既没有明确的频率，也没有明确的位置。
由于佩利-维纳定理，这种模式的双组分光子“波函数”虽然有些局域化，但在空间上并不是严格有界的，即使定义它的真空位移是有界的。当脉冲为单极时，无法进行光子描述，因为光子数被认为是发散的。
为了在几个示例脉冲中最佳地转换和检测光子，研究人员考虑了光子计数器和量子非破坏探测器必须具备的特性。他们开发了一个概念验证系统，用于实现短脉冲量子密钥分发，该系统基于最近在低温微波装置中实现的贝尔定理检验的设计。
附：英文原文
Title: The photonic content of a transmission-line pulse
Author: Varvelis, Evangelos, Biswas, Debjyoti, DiVincenzo, David P.
Issue&Volume: 2024-1-16
Abstract: We develop a photonic description of short, one-dimensional electromagnetic pulses, specifically in the language of electrical transmission lines. Current practice in quantum technology, using arbitrary waveform generators, can readily produce very short, few-cycle pulses in a very-low-noise, low-temperature setting. We argue that these systems attain the limit of producing pure coherent quantum states, in which the vacuum has been displaced for a short time, and therefore over a short spatial extent. When the pulse is bipolar, that is, the integrated voltage of the pulse is zero, then the state can be described by the finite displacement of a single mode. Therefore there is a definite mean number of photons, but which have neither a well-defined frequency nor position. Due to the Paley–Wiener theorem, the two-component photon “wavefunction” of this mode, while somewhat localized, is not strictly bounded in space even if the vacuum displacement that defines it is bounded. When the pulse is unipolar, no photonic description is possible—the photon number can be considered to be divergent. We consider properties that photon counters and quantum non-demolition detectors must have to optimally convert and detect the photons in several example pulses. We develop a conceptual test system for implementing short-pulse quantum key distribution, building on the design of a recently achieved Bell’s theorem test in a cryogenic microwave setup.
DOI: 10.1073/pnas.2314846121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2314846121