Holography encodes information using classical light interference with applications ranging from microscopy to data storage. Quantum entanglement enables information processing with capabilities beyond technology based on classical principles. Here we introduce a holographic imaging concept that is conditioned on the coherence, and thus the entanglement, between the qubit terms in a quantum entangled photon state. By harnessing the nonlocal properties of entanglement, we remotely reconstruct an image encoded in the phase of spatial-polarisation hyper-entangled photons. The nonlocal nature of our measurements removes the need for path overlap, resulting in insensitivity to mechanical instabilities, while polarisation encoding provides robustness against random phase disorder. Furthermore, the measurement of correlations removes the sensitivity to the presence of stray light.
High-dimensional entanglement of structured light offers the potential for noise-robust, high-capacity quantum communication protocols. However, the generation, measurement, and transport of high-quality entanglement presents some unique challenges. We demonstrate the generation and measurement of two-photon macro-pixel entanglement with a record dimensionality, quality, and measurement speed. We then discuss an experiment where we unscramble high-dimensional pixel entanglement through a commercial multimode fibre. In contrast with classical techniques, entanglement is also used to measure the transmission matrix of the fibre. Interestingly, we are able to regain entanglement without manipulating the fibre or the photon that entered it.
We utilize a single-photon sensitive electron multiplying CCD camera as a massively parallel coincidence counting apparatus to study spatial entanglement of photon pairs. This allows rapid measurement of transverse spatial entanglement in a fraction of the time required with traditional point-scanning techniques. We apply this technique to quantum experiments on entangled photon pairs: characterization of the evolution of entanglement upon propagation, and measurement of one- and two-photon portions of the state transmitted through non-unitary (lossy) objects, and quantum phase imaging.
When an ultrashort pulse of light propagates in a scattering medium, its spatial and temporal properties get mixed and distorted because of the scattering process. Spatially, the output pattern is the result of the multiple interference between the scattered photons. Temporally, light gets stretched within the medium due to its characteristic confinement time, thus the output pulse is broadened in the time domain. Nonetheless, as the scattering process is linear and deterministic, the spatio-temporal profile of light at the output can be controlled by shaping the input light using a single spatial light modulator (SLM).
We report the first experimental measurement of the Time-Resolved Transmission Matrix of a multiple scattering medium using a coherent time-gated detection system. This operator contains the relationship between the input field, controllable with a SLM, and the output field accessible with a CCD camera for a given arrival time of photons at the output of medium. The delay line of the time-gated detection system sets the arrival time at will within the time of flight distribution of photons of the output pulse.
We exploit this time-resolved matrix to achieve spatio-temporal focusing of the output pulse at any arbitrary space and time position. The pulse is recompressed in time to its original Fourier-limited temporal width and spatially to the diffraction-limited size defined by the speckle grain size. We also generate more sophisticated spatio-temporal profiles such as pump-probe like pulse, thus opening interesting perspectives in coherent control, light-matter interaction and imaging in disordered media.
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