A new Hong-Ou-Mandel interferometer protocol achieves few-attosecond (nanometer) photon path delay resolution.
Holography is a cornerstone characterisation and imaging technique that can be applied to the full electromagnetic spectrum, from X-rays to radio waves or even particles such as neutrons. The key property in all these holographic approaches is coherence that is required to extract the phase information through interference with a reference beam -without this, holography is not possible. Here we introduce a holographic imaging approach that operates on intrinsically incoherent and unpolarised beams, so that no phase information can be extracted from a classical interference measurement. Instead, the holographic information is encoded in the second order coherence of entangled states of light. Using spatial-polarisation hyper-entangled photons pairs, we remotely reconstruct phase images of complex objects. Information is encoded into the polarisation degree of the entangled state, allowing us to image through dynamic phase disorder and even in the presence of strong classical noise, with enhanced spatial resolution compared to classical coherent holographic systems. Beyond imaging, quantum holography quantifies hyper-entanglement distributed over 10 4 modes via a spatially-resolved Clauser-Horne-Shimony-Holt inequality measurement, with applications in quantum state characterisation.
Imaging through a strongly diffusive medium remains an outstanding challenge in particular in association with applications in biological and medical imaging. Here we propose a method based on a single-photon time-of-flight camera that allows, in combination with computational processing of the spatial and full temporal photon distribution data, to image an object embedded inside a strongly diffusive medium over more than 80 transport mean free paths. The technique is contactless and requires one second acquisition times thus allowing Hz frame rate imaging. The imaging depth corresponds to several cm of human tissue and allows one to perform deep-body imaging, here demonstrated as a proof-of-principle.
Recent results in deeply subwavelength thickness films demonstrated coherent control and logical gate operations with both classical and single photon light sources. However, quantum processing and devices typically involve more than one photon and non-trivial input quantum states. Here we experimentally investigate two-photon N00N state coherent absorption in a multilayer graphene film. Depending on the N00N state input phase, it is possible to selectively choose between single or two photon absorption of the input state in the graphene film. These results demonstrate that coherent absorption in the quantum regime exhibits unique features opening up applications in multiphoton spectroscopy and imaging. Introduction: Coherent absorption is the process by which a partially absorbing material placed in a standing wave pattern can either perfectly transmit or absorb all of the incoming light. This process occurs as a result of the coherent interaction and of the relative phase relation of the two counter-propagating waves. Originally demonstrated in thick slabs of material where the process was likened to a "time-reversed laser" [1, 2]. Coherent absorption was recently extended to deeply subwavelength thickness (2D) materials that have 50% absorption [3,4,6]. Depending on the relative phase of the incident beams, it is possible to totally absorb (or transmit) light, thus providing a method to go beyond the theoretical limit of 50% absorption in a thin film [5], and therefore provide a route to obtain optical gates that rely on absorption [7]. This process relies heavily on the relations between reflection and transmission coefficients, r and t, and absorption rate, α, of the sample [8]. A special case is found for a sub-wavelength material exhibiting precisely 50% absorption, where complete absorption (or transmission) of the energy of the two beams is possible as a result of the relation between reflection and transmission coefficients being forced to r = ±t [5]. This has been shown experimentally with classical continuous wave sources [6], ultrashort pulses [9], and has also been extended to the nonlinear regime to achieve coherent control of nonlinear wave-mixing processes [10]. However, only a few studies have looked at the quantum nature of coherent absorption. Recent experimental work has shown that a single photon also exhibits coherent perfect absorption [11,12], thus implying for example, deterministic absorption of the single photon itself. More intriguing results are expected when non-trivial quantum states interact with a lossy beamsplitter. An N=2 N00N state, (|N, 0 + e iN φ |0, N )/ √ 2 (obtained as
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