Imaging through noise with quantum illumination

Abstract

The contrast of an image can be degraded by the presence of background light and sensor noise.To overcome this degradation, quantum illumination protocols have been theorised (Science 321 (2008), Physics Review Letters 101 (2008)) that exploit the spatial correlations between photonpairs. Here we demonstrate the first full-field imaging system using quantum illumination, by an enhanced detection protocol. With our current technology we achieve a rejection of background and stray light of order 5 and also report an image contrast improvement up to a factor of 5.5, which is resilient to both environmental noise and transmission losses. The quantum illumination protocol differs from usual quantum schemes in that the advantage is maintained even in the presence of noise and loss. Our approach may enable laboratory-based quantum imaging to be applied to real-world applications where the suppression of background light and noise is important, such as imaging under low-photon flux and quantum LIDAR.Conventional illumination uses a spatially and temporally random sequence of photons to illuminate an object, whereas quantum illumination can use spatial correlations between pairs of photons to achieve performance enhancements in the presence of noise and/or losses. This enhancement is made possible by using detection techniques that preferentially select photon-pair events over isolated background events.The quantum illumination protocol was introduced by Lloyd [1], and generalized to Gaussian states by Tan et al. [2], where they proposed a practical version of the protocol. Quantum illumination has applications in the context of quantum information protocol such as secure communication [3,4] where it secures communication against passive eavesdropping techniques that take advantage of noise and losses. The protocol has also been proposed to be useful for detecting the presence of a target object embedded within a noisy background, despite environmental perturbations and losses destroying the initial entanglement [5,6,7].In 2013, Lopaeva et al. performed an experimental demonstration of the quantum illumination principle, to determine the presence or absence of a semi-transparent object, by exploiting intensity correlations of a quantum origin in the presence of thermal light [8]. Additionally, a quantum illumination protocol has been experimentally demonstrated in the microwave domain [9] and a further demonstration in which joint detection of the signal and idler is not required [10]. However, these previous demonstrations were restricted 1 to simply detecting the presence or absence of a target, rather than performing any form of spatially resolved imaging. The acquisition of an image using quantum illumination has recently been reported [11], but that demonstration was performed using a mono-mode source of correlations and by raster-scanning the object within this single-mode beam. The aforementioned demonstration may be seen as a qualitative assessment of the method but a full field imaging implementation of the qua...

Imaging and certifying high-dimensional entanglement with a single-photon avalanche diode camera

“…We have used a SPAD camera to characterise and quantify highdimensional entanglement between photon pairs. By measuring position and momentum correlations using 10 7 intensity images, we showed a violation of an EPR criterion by 227 sigmas for an acquisition time of 140 s. While EPR violation has been demonstrated by acquiring very few frames with a highly sensitive EMCCD camera 46 , quantum imaging approaches based on correlation measurements between spatially entangled photon pairs require the measurement of a large number of frames 26,28,29,31,47,48 , typically on the order of 10 6 -10 7 . This is to ensure high enough SNR on the conditional projections to reconstruct the image by exploiting photon-pair correlations.…”

“…The governing law for this process is momentum conservation that ensures correlations between the photons in the pair 19,20 . These correlations can be exploited for ghost imaging [21][22][23] , imaging Bell-type non-local behaviour 24 , imaging at enhanced spatial resolution 25,26 , quantum-enhanced target detection 27 and to distil an image encoded in quantum states in the presence of classical background radiation 28,29 . We note that recently, Ianzano et al 30 have demonstrated the measurement of polarisation entanglement using a camera, owing to its high-temporal resolution (1.5 ns).…”

How many photons does it take to form an image?

“…The literature reports many different types of imaging systems based on low numbers of photons ranging from: the use of entangled photon sources to give sub-shot noise images 1 and sensing 2,3 , imaging and manipulation of correlations and entanglement [4][5][6][7][8][9][10][11][12] , single-photon 3D imaging 13 , imaging with fewer than one detected photon per pixel 14 , indirect 3D imaging based on first-photon arrival 15 and object tracking outwith the direct line of sight 16 . However, in this short perspective we wish to discuss the more basic principle: given near perfect technology how many detected photons are required to infer an image?…”

“…Note that in this context so called quantum illumination protocols 48,49 can be implemented to get rid of some of the camera single photon counting noise, together with potential external sources of noise that could pollute the image and prevent a low photon acquisition from being performed 8,9 . We can use entangled photon pairs that exhibit spatial correlations to perform imaging in the presence of a spoofed scene that is illuminated by a thermal source.…”

“…Simplified experimental setup of the implementation of the quantum illumination protocol in the context of imaging 9 . By exploiting the spatial correlations between the entangled photon-pairs the image of the object illuminated by quantum light (the bird) may be recovered in the presence of both detector noise and a false image illuminated here by thermal light (the cage).…”