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  1. Consolidation of ultrafast optics in electron spectroscopies based on free electron energy exchange with matter has matured significantly over the past two decades, offering an attractive toolbox for the exploration of elementary events with unprecedented spatial and temporal resolution. Here, we propose a technique for monitoring electronic and nuclear molecular dynamics that is based on self-heterodyne coherent beating of a broadband pulse rather than incoherent population transport by a narrowband pulse. This exploits the strong exchange of coherence between the free electron and the sample. An optical pulse initiates matter dynamics, which is followed by inelastic scattering of a delayed high-energy broadband single-electron beam. The interacting and noninteracting beams then interfere to produce a heterodyne-detected signal, which reveals snapshots of the sample charge density by scanning a variable delay T . The spectral interference of the electron probe introduces high-contrast phase information, which makes it possible to record the electronic coherence in the sample. Quantum dynamical simulations of the ultrafast nonradiative conical intersection passage in uracil reveal a strong electronic beating signal imprinted onto the zero-loss peak of the electronic probe in a background-free manner.
    Free, publicly-accessible full text available May 31, 2023
  2. Abstract Optical interferometry has been a long-standing setup for characterization of quantum states of light. Both linear and the nonlinear interferences can provide information regarding the light statistics and underlying detail of the light-matter interactions. Here we demonstrate how interferometric detection of nonlinear spectroscopic signals may be used to improve the measurement accuracy of matter susceptibilities. Light-matter interactions change the photon statistics of quantum light, which are encoded in the field correlation functions. Application is made to the Hong-Ou-Mandel two-photon interferometer that reveals entanglement-enhanced resolution that can be achieved with existing optical technology.
  3. Correlated photons inspire abundance of metrology-related platforms, which benefit from quantum (anti-) correlations and outperform their classical counterparts. While these mainly focus on entanglement, the role of photon exchange phase and degree of distinguishability has not been widely used in quantum applications. Using an interferometric setup, we theoretically show that, when a two-photon wave function is coupled to matter, it is encoded with “which pathway?” information even at low-degree of entanglement. An interferometric protocol, which enables phase-sensitive discrimination between microscopic interaction histories (pathways), is developed. We find that quantum light interferometry facilitates utterly different set of time delay variables, which are unbound by uncertainty to the inverse bandwidth of the wave packet. We illustrate our findings on an exciton model system and demonstrate how to probe intraband dephasing in the time domain without temporally resolved detection. The unusual scaling of multiphoton coincidence signals with the applied pump intensity is discussed.
  4. We develop closed expressions for a time-resolved photon counting signal induced by an entangled photon pair in an interferometric spectroscopy setup. Superoperator expressions in Liouville-space are derived that can account for relaxation and dephasing induced by coupling to a bath. Interferometric setups mix matter and light variables non-trivially, which complicates their interpretation. We provide an intuitive modular framework for this setup that simplifies its description. Based on the separation between the detection stage and the light–matter interaction processes, we show that the pair entanglement time and the interferometric time-variables control the observed physics time scale. Only a few processes contribute in the limiting case of small entanglement time with respect to the sample response, and specific contributions can be singled out.

  5. We propose a quantum diffraction imaging technique whereby one photon of an entangled pair is diffracted off a sample and detected in coincidence with its twin. The image is obtained by scanning the photon that did not interact with matter. We show that when a dynamical quantum system interacts with an external field, the phase information is imprinted in the state of the field in a detectable way. The contribution to the signal from photons that interact with the sample scales as ∝ I p 1 / 2 , where I p is the source intensity, compared with ∝ I p of classical diffraction. This makes imaging with weak fields possible, providing high signal-to-noise ratio, avoiding damage to delicate samples. A Schmidt decomposition of the state of the field can be used for image enhancement by reweighting the Schmidt modes contributions.