Nonlinear THz dynamics and quantum vacuum radiation from squeezed quantum vacua

控制光与电子激发的相互作用定义了现代量子电动力学的一个关键方面。在强光-物质耦合结构中，真空拉比频率表征了电子共振对空腔光子的连续发射和再吸收，这导致了代表耦合系统新特征态的空腔极化子的形成。在太赫兹（THz）纳米谐振器中，光与物质的相互作用可以变得非常强，以至于真空拉比频率等于光的载流子频率。在这种情况下，量子基态包含有限数量的压缩、相关光子对，预计当耦合强度被快速调制时，这些光子对将被释放。预期的物理学类似于尚未观测到的动态卡西米尔效应或黑洞的昂鲁-霍金辐射。在这里，我们提出探索自定义切割太赫兹纳米结构的量子真空光子学，这些结构与半导体中与回旋加速器共振耦合的超强光物质、超出玻色子近似的少量朗道电子系统以及石墨烯中的朗道电子。新的研究领域将在三个工作流程中开创：(i)利用我们团队开发的光-物质相互作用的飞秒控制方案，我们将使用宽带太赫兹光谱研究gaas基结构中压缩量子真空的强亚周期切换动力学。该工作流程将为工作流程（ii）和（iii）中更复杂结构的量子真空光子学奠定基础。（ii）我们将针对由定制设计的具有微小模式体积的太赫兹谐振器的三维纳米结构制造的少数朗道电子结构中超越玻色子近似的超强耦合的量子极限。高灵敏度太赫兹量子探测将在极低太赫兹幅值下追踪非摄动非线性动力学和量子真空特征，为压缩量子真空的少光子太赫兹非线性提供了前景。（iii）超越大质量电子系统，我们将研究石墨烯基结构中的超强耦合，其中量子真空的不稳定性被预测会发生。石墨烯及其超强耦合结构的朗道电子由于其非等距能量级数、拉比跳变和非调和朗道阶梯爬升，其反应明显比它们的质量对应物更加非线性。我们将使用我们最灵敏的二维太赫兹光谱和量子探测来研究这些结构中的量子真空光子学。我们的工作为非绝热量子电动力学开辟了一个新的方向，将最复杂的超强耦合结构和最近开发的一些最先进的太赫兹光子学结合在一起。

Controlling the interaction of light with electronic excitations defines a key aspect of modern quantum electrodynamics. In strongly light-matter coupled structures, the vacuum Rabi frequency characterizes the continuous emission and re-absorption of a cavity photon by the electronic resonance, which leads to the formation of cavity polaritons representing the new eigenstates of the coupled system. In terahertz (THz) nanoresonators, light-matter interaction can be made so strong that the vacuum Rabi frequency becomes equal to the carrier frequency of light. In such a setting, the quantum ground state contains a finite population of squeezed, correlated photon pairs, which is predicted to be released when the coupling strength is rapidly modulated. The anticipated physics is similar to the yet unobserved dynamical Casimir effect or Unruh-Hawking radiation of black holes. Here, we propose to explore quantum vacuum photonics of custom-cut THz nanostructures ultrastrongly light-matter coupled to cyclotron resonances in semiconductors, few-Landau-electron systems beyond the bosonic approximation, and Landau electrons in graphene. The novel research field will be pioneered in three work streams:(i) Exploiting femtosecond control schemes for light-matter interaction developed in our groups, we will investigate the strongly sub-cycle switching dynamics of squeezed quantum vacua in GaAs-based structures using broadband THz spectroscopy. This work stream will set the stage for quantum vacuum photonics in the more complex structures of work streams (ii) and (iii).(ii) We will target the quantum limit of ultrastrong coupling beyond the bosonic approximation in few-Landau-electron structures fabricated by three-dimensional nanostructuring of custom-designed THz resonators with tiny mode volumes. Highly sensitive THz quantum detection will trace the non-perturbatively nonlinear dynamics and quantum vacuum signatures at extremely low THz amplitudes, holding the prospect of few-photon THz nonlinearities of squeezed quantum vacua. (iii) Going beyond massive electron systems, we will investigate ultrastrong coupling in graphene-based structures, where an instability of the quantum vacuum is predicted to occur. Landau electrons of graphene and its ultrastrongly coupled structures are expected to react distinctly more nonlinear than their massive counterparts due to their non-equidistant energy progression, Rabi flopping, and anharmonic Landau ladder climbing. We will pursue quantum vacuum photonics in these structures using our most sensitive two-dimensional THz spectroscopy and quantum detection.Our work opens a new direction in non-adiabatic quantum electrodynamics, bringing together the most sophisticated ultrastrongly coupled structures and some of the most advanced THz photonics recently developed.