Squeezed states metrology for THz time-domain spectroscopy.

抽象的。我与Clerici博士讨论的项目的目标是使用量子光学来提高电磁辐射时间分辨测量的灵敏度。具体而言，它旨在开发量子增强的计量工具，以检测弱太赫兹频率（THz）波形。电磁频谱的THz区域对于光谱学（例如危险气体和爆炸物），安全（通过包装材料成像）和制药（质量控制）中的应用具有重要的技术意义。然而，由于灵敏探测器的可用性有限，该光谱区域难以进入。在我的博士项目中，我将研究使用量子光学来改善THz时域光谱技术的技术水平[1]。背景电光采样（EOS）是一种常用的方法，其中短激光脉冲用于测量由二阶非线性晶体中的未知场（电光效应）引起的折射率变化[2]。该技术允许直接在时域中记录THz辐射，并通过获得傅立叶变换来提供辐射光谱。这种技术的灵敏度受到标准量子极限的限制，如果不使用非经典辐射，就不能进一步提高。当使用平均光子数N测量一个量时，在最好的情况下，即如果不存在其他噪声源，我们的测量将受到与灵敏度成比例的误差的影响。经典计量学受到这个极限的限制，称为标准量子极限。增加光子的数量，从而增加探测脉冲强度，提高了测量的灵敏度。在基于EOS的THz检测的情况下，探测强度只能增加到由非线性噪声的开始施加的限制。为了进一步提高灵敏度，可以利用量子关联态来降低误差比例，这是海森堡极限。在我的博士项目中，我的目标是利用光的压缩态实现海森堡极限太赫兹探测。方法论EOS是一种相位测量，其中通过记录探测脉冲上感应的相移，经由二阶非线性晶体中的非线性相互作用，在特定的时间坐标处测量电场。我的博士项目的主要目标将是测试使用双光束的THz EOS的实验方法[3]。这是光的量子态，其特征在于两个光束的光子数具有完美的相关性。它们是压缩光的可能实现之一，并将作为克服太赫兹EOS灵敏度极限的工具进行测试。为了产生和检测双光束，我将扩展我在最后一年工程硕士项目中实施的工作。我将使用Covesion有限公司提供的周期性极化铌酸锂晶体，该晶体设计用于II型相位匹配条件。双光束配置获得的灵敏度的提高，应量化感谢子散粒噪声平衡探测器，我设计，并开始在我的工程硕士最后一年的项目进行验证。一种传统上提高相位测量灵敏度的方法，包括使用激光腔。腔内相位干涉测量（IPI）是标准干涉测量的腔增强版本，其通过用第二个未受干扰的梳拍腔的一个梳来提供对发生在腔的一个梳上的相移的直接访问。具体地，通过记录通过干涉腔梳获得的拍音来执行相位测量。这种技术从未被用于测量太赫兹辐射，我的博士项目的进一步目标将是开发一种基于IPI的太赫兹探测方案。为了实现这一目标，我将遵循克莱里奇博士和联合国组织的监督，我将遵循

Abstract. The project I have discussed with Dr Clerici targets the use of quantum optics to improve the sensitivity of time-resolved measurements of electromagnetic radiation. Specifically, it aims at developing quantum-enhanced metrology tools to detect weak Terahertz-frequency (THz) waveforms. The THz region of the electromagnetic spectrum is technologically important for applications in spectroscopy (for instance hazardous gasses and explosives), security (imaging trough packaging materials) and pharmaceutics (quality control). This spectral region is, however, hard to access due to the limited availability of sensitive detectors. In my PhD project I will investigate techniques to use quantum optics to improve the state of the art of THZ time-domain spectroscopy[1]. Background. Electro-Optical Sampling (EOS) is a commonly employed method where a short laser pulse is used to measure the change in refractive index caused by the unknown field in a second-order nonlinear crystal (electro-optical effect)[2]. This technique allows to record THz radiation directly in the time domain and delivers the radiation spectrum by obtaining the Fourier transform. The sensitivity of this technique is limited by the standard quantum limit and cannot be further improved without the use of non-classical radiation. When measuring a quantity using an average number of photons N, in the best case, i.e. if no other sources of noise are present, our measurement will be affected by an error that is proportional to the sensitivity. Classical metrology is limited by this bound, known as the standard quantum limit. Increasing the number of photons, and hence the probe pulse intensity, improves the sensitivity of the measurement. In the case of EOS-based THz detection, the probe intensity can only be increased up to a limit that is imposed by the onset of nonlinear noise. To further increase the sensitivity, quantum correlated states can be utilised to reduce the error proportionality to,which is the Heisenberg limit. In my PhD project I will aim at attaining a Heisenberg-limited THz detection using squeezed states of light. Methodology. EOS is a phase measurement where the electric field is measured at a specific temporal coordinate by recording the phase shift induced on the probe pulse, via a nonlinear interaction in a second-order nonlinear crystal. A primary goal of my PhD project will be to test an experimental approach inTHz EOS that uses twin-beams[3].These are quantum states of light characterised by two beams with a perfect correlation in their photon number. They are one of the possible realisations of squeezed light and will be tested as a tool to overcome the sensitivity limit of THz EOS. To generate and detect twin-beams, I will expand on the work that I have implemented during my final year MEng project. I will use a periodically poled Lithium Niobate crystal provided by Covesion Ltd. designed to work in a type-II phase matched condition. The improvement in sensitivity acquired with the twin-beam configuration, shall be quantified thanks to the sub-shot-noise balanced detector that I designed and started to characterise during my MEng final year project. A method to classically enhance the sensitivity of phase measurements, comprises of using a laser cavity. Intracavity phase interferometry (IPI) is a cavity enhanced version of standard interferometry that provides direct access to the phase shift occurring on one comb of a cavity by beating it with a second, unperturbed comb. Specifically, the phase measurement is performed by recording the beat note obtained by interfering the cavity combs. This technique has never been used to measure THz radiation, and a further goal of my PhD project will be to develop an IPI-based THz detection scheme. To achieve this goal, I will follow be supervised by Dr Clerici and the UNO group, and I will follow