Manipulating the character and shape of ultrashort quantum light states
Dr Marco Bellini, National Institute of Optics (CNR-INO), Italy
A fully controlled state and mode engineering of nonclassical light is one of the major challenges in the path of future quantum technologies.
In recent years, quantum state engineering has quickly evolved, with new tools and techniques, such as photon addition and subtraction, which have demonstrated their extreme versatility for performing operations normally unavailable in the realm of Gaussian quantum optics. While photon subtraction can enhance nonclassicality and entanglement in a quantum light state, photon addition has the unique capability of creating nonclassicality and entanglement from scratch, whatever the input. However, engineering quantum states in a single, well-defined, mode is rarely enough. In real experiments, states are often prepared in modes that do not coincide with those used for their processing and detection, or for the optimal coupling to matter systems. Gaining access to the rich mode structure of quantum light would also greatly increase the capacity of communicating, manipulating, and storing quantum information. For all these tasks, and for those related to possible spectroscopic applications of nonclassical light, it is of fundamental importance to gain a full control over the modes that host the quantum states. In this talk, I will briefly present some of our recent experimental results towards the controlled generation, manipulation, and detection of the quantum state and mode structure of ultrashort light wavepackets.
Exploiting quantum correlations for spectroscopy, imaging and remote sensing
Professor John Rarity FRS, University of Bristol, UK
In this talk I will review recent work on sensing technologies focussing on pair photon correlations applied to rangefinding and remote sensing. These experiments primarily exploit the time (energy) correlations between photons  and were recently popularised as quantum illumination . I will review recent experimental results showing the possibility of 3D imaging and covert rangefinding using parametric pair photon sources. I will also review work towards practical photon limited gas sensing using near infra-red wavelengths  and extensions to longer wavelengths using non-linear interferometry  in bulk and chip scale experiments [5, 6].
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Infrared metrology with visible light
Dr Leonid Krivitskiy, Agency for Science, Technology and Research (A*STAR), Singapore
Infrared (IR) optical range is important for material characterization and sensing. Also, imaging in the IR range yields superior image contrast due to a significant reduction of scattering losses. Thus IR metrology is widely used in petrochemical, pharma, biomedical, homeland security, and other areas.
Even though there are well-developed conventional methods for IR metrology, the remaining challenges are associated with high cost, low efficiency and regulatory requirements for IR light sources and detectors. To mitigate these issues the team is developing new quantum-enabled techniques which allow them to retrieve properties of materials in the IR range from the measurements of visible range photons. The approach is based on the nonlinear interference of frequency correlated photons produced via spontaneous parametric down conversion (SPDC) [1, 2]. Within this process, one of the photons is generated in the visible range, and its correlated counterpart in the IR range is used to probe the properties of the medium. The visibility and phase of the observed fringes depend on the properties of the IR photon, which interacts with the sample. This allows the team to infer the properties of the sample in the IR range from the measurements of visible range photons. In a series of experiments, they demonstrate the IR spectroscopy [1-3], tunable optical coherence tomography (OCT) , and polarimetry . In all these demonstrations the IR properties (absorption spectra, refractive index, 3D images, and polarization) are inferred from the measurements of the interference pattern in the visible range thus making IR measurements more affordable.
 D. Kalashnikov, A. Paterova, S. Kulik, L. Krivitsky, Nature Photonics 10, 98 (2016).
 A. Paterova, S. Lung, D. Kalashnikov, L. Krivitsky, Scientific reports 7, 42608 (2017).
 A. Paterova, H. Yang, Ch. An, D. Kalashnikov, L. Krivitsky, New Journal of Physics 20, 043015 (2018).
 A. Paterova, H. Yang, Ch. An, D. Kalashnikov, L. Krivitsky, Quantum Science & Technology 3, 025008 (2018).
 A. Paterova, H. Yang, C. An, D. Kalashnikov, L. Krivitsky, Opt. Express 27, 2589-2603 (2019).
Single photon spectroscopy of atoms and solids
Dr Alex S Clark, Imperial College London, UK
The absorption and reflection of light allows us to determine the properties of the world around us. Alex S Clark will present two recent experiments using single photons to perform absorption spectroscopy. The first uses photons generated by four-wave mixing in optical fiber. Two pump photons (~750nm) are annihilated to simultaneously generate time-correlated pairs of photons at widely spaced wavelengths (~650nm signal and ~900nm idler). The researchers tune the pump wavelength to scan idler photons across the absorption band-edge of gallium arsenide placed in the idler beam path. The transmission of the idler photons alone does not reveal the absorption due to overlapping Raman noise, but when correlated with detected signal photons, the absorption is revealed, a form of ‘ghost-spectroscopy’. The second experiment uses a bright pump laser to saturate rubidium atoms in a vapour cell, while a counter-propagating and cross-polarized single photon level probe reveals narrow transmission peaks corresponding to the hyperfine excited state energy levels of the atoms. The pump and probe are independently tunable, meaning atoms moving in all directions can be addressed by compensating the counter-propagating optical frequencies for the relevant Doppler shifts. This experiment forms a basis for building an atomic quantum memory.