Quantum-enhanced THz spectroscopy and imaging

量子力学有望成为下一次技术革命的驱动力，而量子密码学为最终安全提供了商业解决方案，很可能被认为是这一变化的先驱。通过这个提议，我们的目标是展示量子力学如何能够克服长波长辐射检测所面临的限制，特别是在太赫兹频率。太赫兹是电磁频谱的一部分，既非常难以获得，又从技术角度来看非常重要。它确实是安全（爆炸物，毒品和无危险隐藏武器检测），电信（增加短距离无线通信的数据速率），监控和质量控制（光谱学）的关键参与者。尽管其潜力很大，但缺乏有效的源和检测器阻止了太赫兹时域光谱和成像的广泛商业应用。然而，一些高科技公司正在投资太赫兹技术，最近的市场研究表明，与这项技术相关的营业额每年增长40%。因此，现在确定克服当前太赫兹探测器局限性的策略至关重要。该提案旨在开发这样一种策略，利用光的量子纠缠态的独特性质。纠缠光子在空间中分离，但共享一个共同的波函数，可以由商业非线性晶体产生，并增强经典方法无法获得的不寻常特性。这些属性中的两个，即在传播时获得经典状态的两倍相位的能力和低于经典散粒噪声极限的减小的幅度噪声，提供了用于增加太赫兹时域检测器的灵敏度的手段，其实际上作为差分相位传感器操作。将这种改进与最近的超分辨成像概念相结合，也将提高长波长映射的分辨率。首次将量子光学概念（被认为是我们未来技术的主要支柱）与太赫兹光子学概念相结合，促进了许多尚未开发的应用潜力，这一提议符合英国研究委员会制定的研究战略，并承诺对生物学和材料科学等多个不同学科以及质量控制和安全检查活动产生影响。

Quantum mechanics promises to be the driving force underneath the next technological revolution, and quantum cryptography, providing a commercial solution for the ultimate security, may well be considered the harbinger of this change. With this proposal, we aim at showing how quantum mechanics can allow to overcome the limits faced in the detection of long wavelength radiation, specifically at terahertz frequencies.Terahertz is a portion of the electromagnetic spectrum that is both extremely hard to access to, and incredibly important from a technological standpoint. It is indeed a key player in security (explosives, drugs, and hazard-free concealed weapons detection), telecommunications (increased data-rate of short distance wireless communication), monitoring and quality control (spectroscopy). Despite its high potential, the lack of efficient sources and detectors prevents a widespread commercial application of terahertz time-domain spectroscopy and imaging. Yet, a number of high-tech companies are investing into terahertz technology and recent market studies hint for a 40%/year increase in the turnover associated to this technology.It is therefore vital to identify now strategies for overcoming the limitations of the current terahertz detectors. This proposal aims at developing such a strategy exploiting the unique properties of quantum, entangled states of light. Entangled photons, separated in space but sharing a common wavefunction, can be generated by commercial nonlinear crystals and boost unusual properties not accessible by classical means. Two of these properties, namely the ability to acquire twice the phase of a classical state upon propagation and the reduced amplitude noise below the classical shot-noise limit, offer a mean for increasing the sensitivity of terahertz time-domain detectors, that operate indeed as a differential phase sensor. Combining such an improvement with recent concepts of super-resolved imaging will also result in an increased resolution of long wavelength mapping.Combining for the first time concepts of quantum optics, recognised as a main pillar for our future technology, and of terahertz photonics, boosting a number of underdeveloped application potential, this proposal is in line with the research strategy set by the UK research councils, and promise to deliver impact on a number of different disciplines, such as biology and material science, as well as on the quality control and security inspection activities.