Quantum correlAtions in TerAhertz qcl COMBs (QATACOMB)

量子技术(Qt)平台能够利用原子、光和固态系统的非经典状态，最近在通信、计算、信息、传感和计量等各种战略领域实现了这一平台。在电磁光谱的可见光和近红外部分取得的成功成就导致了最近在小型化和紧凑几何方面的进展。这反过来又使得一方面实现了高度集成的量子平台，另一方面使其扩展到非常规光谱区域，这些区域的特殊功能仍未得到充分利用。在这方面，Qt向太赫兹(THz)频率范围的迁移在技术上具有挑战性，尽管具有巨大的技术潜力。事实上，连续变量纠缠THz态的制备可以成为未来实现量子计算协议、量子隐形传态或增加选定的自由空间量子通信信道的容量、健壮性和安全性的基础。例如，太赫兹辐射的特殊特性、对其他不透明材料的透射率或对瑞利散射的稳健性，可能会允许过多的前沿应用，例如不透明或恶劣环境(尘埃、烟雾、颗粒)中的量子安全快速数字数据传输，或光谱和计量太赫兹设置中的量子增强型灵敏度。QATACOMB的目标是开发一个小型化的固态平台，用于产生、检测和完全表征THz频率光的非经典压缩态。这将利用太赫兹量子级联激光器(QCL)频率梳(FCS)作为非线性光源，与石墨烯纳米级联量子传感器和腔耦合超快相干探测器相结合。QCL是迄今为止太赫兹频率下最有效的小型化激光器。它们的宽增益和可控群速度色散最近实现了基于增益介质内发生的四波混频(FWM)过程的紧凑型FC产生。因此，由于量子相关边带模式的存在，QCL是产生多模压缩光的理想候选者。特别值得一提的是，在可见光/近红外光谱学和计量学中，以及在引力波和目标探测方面的应用中，双模压缩态所提供的量子灵敏度确实得到了证实，这引发了THz量子传感的类似方法，其中双模压缩态可以通过使用THzQCL谐波梳子来实现。此外，通过太赫兹辐射控制分子的转动自由度可以为利用冷分子样品进行量子理论研究提供新的途径。项目目标的成功实现将是颠覆性的，评估太赫兹光子学和QT战略领域的基础知识。

Quantum technology (QT) platforms, capable of exploiting non-classical states of atoms, light and solid-state systems, have been recently realised in a variety of strategic fields, such as communication, computation, information, sensing and metrology. Successful achievements in the visible and near-infrared parts of the electromagnetic spectrum have led to recent advancements in miniaturized and compact geometries. This, in turn, has enabled, on one hand, the implementation of highly-integrated quantum platforms and, on the other hand, the extension to non-conventional spectral regions, whose peculiar features are still underexploited. In this regard, QT migration to the terahertz (THz) frequency range is technologically challenging, although of huge technological potential. In fact, continuous-variable entangled THz states preparation can become the founding blocks for future implementation of quantum computation protocols, quantum teleportation or to increase capacity, robustness and security of selected free-space quantum communication channels. For example, the peculiar features of THz radiation, transmissivity through otherwise opaque materials, or robustness with respect to Rayleigh scattering, can potentially allow a plethora of frontier applications, such as quantum-secured fast digital data transfer in opaque or harsh environments (dust, smog, particulate) or quantum-enhanced sensitivity in spectroscopic and metrological THz setups. The goal of QATACOMB is to develop a miniaturized solid-state platform for generation, detection and complete characterization of non-classical squeezed states of THz frequency light. This will exploit THz quantum cascade laser (QCL) frequency combs (FCs) as nonlinear sources, coupled with graphene nanoscale quantum sensors and cavity-coupled ultrafast coherent detectors. QCLs are, to date, the most efficient miniaturized lasers at THz frequencies. Their broad gain and controlled group velocity dispersion has recently enabled compact FC generation, based on four-wave mixing (FWM) processes that take place within the gain medium. As a consequence, QCLs are ideal candidates for the generation of multi-mode squeezed states of light, due to the presence of quantum-correlated side-band modes. In particular, quantum-enhanced sensitivity, provided by two-mode squeezed states has been indeed demonstrated in visible/NIR spectroscopy and metrology setups, as well as in applications for gravitational waves and target detection, motivating a similar approach for THz quantum sensing, where two-mode squeezed states can be achieved by employing THz QCL harmonic combs. Moreover, control of rotational degrees of freedom in molecules by THz radiation can provide novel ways to exploit cold molecular samples for QT. The successful achievement of the project goals will be disruptive, assessing fundamental knowledge in the strategic fields of THz photonics and QT.