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Modern imaging technologies are widely based on classical principles of light or electromagnetic wave propagation. They can be remarkably sophisticated, with recent successes ranging from single-molecule microscopy to imaging far-distant galaxies. However, new imaging technologies based on quantum principles are gradually emerging. They can either surpass classical approaches or provide novel imaging capabilities that would not otherwise be possible. Here we provide an overview of the most recently developed quantum imaging systems, highlighting the nonclassical properties of sources, such as bright squeezed light, entangled photons and single-photon emitters that enable their functionality. We outline potential upcoming trends and the associated challenges, all driven by a central enquiry, which is to understand whether quantum light can make visible the invisible.

We present the experimental implementation of simultaneous spatial multimode demultiplexing as a distance measurement tool. We use this technique to estimate the distance between two incoherent beams in both directions of the transverse plane, and find a perfect accordance with theoretical predictions, given a proper calibration of the demultiplexer. We show that, even though sensitivity is limited by the cross-talk between channels, we can perform measurements in two dimensions much beyond the Rayleigh limit over a large dynamic range.

Advanced quantum technologies require scalable and controllable quantum resources1,2. Gaussian states of multimode light, such as squeezed states and cluster states, are scalable quantum systems3–5, which can be generated on demand. However, non-Gaussian features are indispensable in many quantum protocols, especially to reach a quantum computational advantage6. Embodying non-Gaussianity in a multimode quantum state remains a challenge as non-Gaussian operations generally cannot maintain coherence among multiple modes. Here, we generate non-Gaussian quantum states of a multimode light field by removing a single photon in a mode-selective manner from a Gaussian state7. To highlight the potential for continuous-variable quantum technologies, we first demonstrated the capability to generate negativity of the Wigner function in a controlled mode. Subsequently, we explored the interplay between non-Gaussianity and quantum entanglement and verify a theoretical prediction8about the propagation of non-Gaussianity along the nodes of photon-subtracted cluster states. Our results demonstrate large-scale non-Gaussianity with great flexibility along with an ensured compatibility with quantum information protocols. This range of features makes our approach ideal to explore the physics of non-Gaussian entanglement9,10and to develop quantum protocols, which range across quantum computing11,12, entanglement distillation13and quantum simulations14.

Du fait de ses potentielles applications, la mise en forme spatiale de la lumière est une des problématiques d’optique les plus actives. Ses succès sont déjà multiples, que ce soit en astronomie ou imagerie biologique, via l’optique adaptative, ou encore pour la focalisation à travers des milieux diffusants. L’optique quantique aussi y a puisé de l’inspiration, pour permettre en particulier d’ordonner spatialement les fluctuations quantiques et réaliser des expériences de métrologie quantique. De manière remarquable, les procédés développés pour ces études fondamentales ont des applications en télécommunications par fibre optique et ont permis de fonder la société CAILabs.

We study noise propagation dynamics in a femtosecond oscillator by injecting external noise on the pump intensity. We utilize a spectrally resolved homodyne detection technique that enables simultaneous measurement of amplitude and phase quadrature noises of different spectral bands of the oscillator. We perform a modal analysis of the oscillator noise in which each mode corresponds to a particular temporal/spectral shape of the pulsed light. We compare this modal approach with the conventional noise detection methods and find the superiority of our method, in particular unveiling a complete physical picture of noise distribution in the femtosecond oscillator.

In this work, we investigate three different compact fibered systems generating vacuum squeezing that involve optical cavities limited by the end surface of a fiber and by a curved mirror and containing a thin parametric crystal. These systems have the advantage to couple squeezed states directly to a fiber, allowing the user to benefit from the flexibility of fibers in the use of squeezing. Three types of fibers are investigated: standard single-mode fibers, photonic-crystal large-mode-area single-mode fibers, and short multimode fibers taped to a single-mode fiber. The observed squeezing is modest (−0.56  dB, −0.9  dB, −1  dB), but these experiments open the way for miniaturized squeezing devices that could be a very interesting advantage in scaling up quantum systems for quantum processing, opening new perspectives in the domain of integrated quantum optics.

Du fait de ses potentielles applications, la mise en forme spatiale de la lumière est une des problématiques d’optique les plus actives. Ses succès sont déjà multiples, que ce soit en astronomie ou imagerie biologique, via l’optique adaptative, ou encore pour la focalisation à travers des milieux diffusants. L’optique quantique aussi y a puisé de l’inspiration, pour permettre en particulier d’ordonner spatialement les fluctuations quantiques et réaliser des expériences de métrologie quantique. De manière remarquable, les procédés développés pour ces études fondamentales ont des applications en télécommunications par fibre optique et ont permis de fonder la société CAILabs.

We investigate quantum properties of light in optical parametric oscillators (OPOs) based on four-wave mixing gain in media with third-order nonlinearities. In spite of other competing χ^(3) effects such as phase modulation, bipartite and tripartite entanglement is predicted above threshold. These findings are relevant for recent implementations of complementary metal-oxide-semiconductor (CMOS)-compatible on-chip OPOs.

We report an upconversion experiment using an orientation-patterned gallium arsenide (OP-GaAs) crystal to detect small mid-infrared signals on an InGaAs avalanche photodiode. A conversion efficiency up to 20% with a nonpolarized pulsed fiber pump is demonstrated. Our uncooled setup is favorably compared in terms of noise equivalent power, dynamic range, and response time to cryogenically cooled HgCdTe detectors. Its dependence on the polarization of both the pump and signal beams is also investigated.

It is shown that the sensitivity of a highly sensitive homodyne timing measurement scheme with femtosecond (fs) lasers [Phys. Rev. Lett.101, 123601 (2008).] is limited by carrier-envelope-phase (CEO) noise. We describe the use of a broadband passive cavity to analyze the phase noise of a Ti:Sapphire oscillator relative to the standard quantum limit. This cavity also filters the lowest levels of classical noise at sidebands above 100 kHz detection frequency. Leading to quantum-limited CEO-phase noise at millisecond time scales, it can improve the sensitivity of the homodyne pulse timing measurement by 10 dB.

Free space propagation and conventional optical systems such as lenses and mirrors all perform spatial unitary transforms. However, the subset of transforms available through these conventional systems is limited in scope. We present here a unitary programmable mode converter (UPMC) capable of performing any spatial unitary transform of the light field. It is based on a succession of reflections on programmable deformable mirrors and free space propagation. We first show theoretically that a UPMC without limitations on resources can perform perfectly any transform. We then build an experimental implementation of the UPMC and show that, even when limited to three reflections on an array of 12 pixels, the UPMC is capable of performing single mode tranforms with an efficiency greater than 80% for the first four modes of the transverse electromagnetic basis.

Based on a standard binomial model of sub-Poissonian photocounting statistics, we analyze the discrimination performance between the two possibilities that light has been potentially absorbed or not. For that purpose, we study with numerical simulations the behavior of different information-theory-based measures of the contrast and show that the Chernoff measure allows one to obtain a useful contrast characterization that has simple physical interpretation and that helps in analyzing the benefit of using sub-Poissonian light to improve detection tasks.

We consider the problem of measurement of optical transverse profile parameters and their conjugate variable. Using multimode analysis, we introduce the concept of detection noise modes. For Gaussian beams, displacement and tilt are a pair of transverse-profile conjugate variables. We experimentally demonstrate the optimal encoding and detection of these variables with a spatial homodyning scheme. Using higher-order spatial mode squeezing, we show the sub-shot-noise measurements for the displacement and tilt of a Gaussian beam.

We describe a spontaneous symmetry-breaking phenomenon between the intensities of the ordinary and extraordinary components of the fundamental field in intracavity type II harmonic generation. It is based on a triply resonant cavity containing a type II ?^2 crystal pumped at fundamental frequency ?_0. The pump beam generates a second-harmonic mode at frequency 2?_0 that acts as a pump for frequency-degenerate type II parametric downconversion. Under operating conditions symmetric with respect to the ordinary and extraordinary components of the fundamental wave, we show a breaking of the symmetry of the intensities of these two waves.