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腔光子通过电子共振的连续发射和再吸收，从而导致代表耦合系统新本征态的腔极化激元的形成。在太赫兹（THz）纳米谐振器中，光与物质的相互作用可以变得如此强烈，以至于真空拉比频率变得等于光的载波频率。在这样的设置中，量子基态包含有限的压缩的相关光子对，这被预测为当耦合强度被快速调制时被释放。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Unruh-Hawking辐射。在这里，我们建议探索定制的太赫兹纳米结构的量子真空光子学超强轻物质耦合到半导体中的回旋共振，少数朗道电子系统超出玻色子近似，和朗道电子在石墨烯。新的研究领域将在三个工作流中开创：（i） 利用我们小组开发的飞秒光-物质相互作用控制方案，我们将利用宽带THz光谱研究GaAs基结构中压缩量子真空的强子周期开关动力学。这一工作流将为工作流（ii）和（iii）的更复杂结构中的量子真空光子学奠定基础。（二） 我们的目标是通过三维纳米结构的定制设计的太赫兹谐振器与微小的模式体积制造的少数朗道电子结构中的玻色子近似之外的超强耦合的量子极限。 高灵敏度的太赫兹量子探测将在极低的太赫兹振幅下追踪非微扰非线性动力学和量子真空特征，从而为压缩量子真空的少光子太赫兹非线性提供了前景。（三） 超越大质量电子系统，我们将研究基于石墨烯的结构中的超强耦合，其中预计会发生量子真空的不稳定性。石墨烯及其超强耦合结构的朗道电子由于其非等距离的能量级数、拉比跳跃和非谐朗道爬梯，预期比它们的大质量对应物明显更非线性地反应。我们将利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。我们的工作开辟了非绝热量子电动力学的新方向，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.