Imaging high-dimensional spatial entanglement with a camera

Edgar, M.; Tasca, D. S.; Izdebski, Frauke; Warburton, R. J.; Leach, Jonathan; Agnew, Megan; Buller, Gerald S.; Boyd, Robert W.; Padgett, Miles J.

doi:10.1038/ncomms1988

Cited by 239 publications

(288 citation statements)

References 37 publications

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“…The pump beam diameter was B1 mm (FWHM), which leads to a broad region where the two orthogonally polarized photons (Type II down-conversion) with 810 nm wavelength can be created. In the near-field of the crystal-directly behind it-the photons are correlated in the transverse spatial position 28,29 , that is, if one photon is found to be at a specific transverse spatial location the partner photon will be found ideally at exactly the same location too. This stems from the down-conversion process itself, where the pump photon generates two down-converted photons at some transverse spatial position of the crystal.…”

Section: Methodsmentioning

confidence: 99%

“…After characterization of the reversed MS as an interface between the lateral position and OAM, we demonstrate its use in quantum optical experiments and transform a bipartite path-entangled state to an OAM-entangled state, even for higher-dimensional states. We create pairs of orthogonally polarized, path-entangled photons from position correlation in a spontaneous parametric down-conversion process 2,28,29 (Fig. 4a and Methods).…”

Section: Generation Of Oam Modes With a Ms In Reversementioning

confidence: 99%

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Interface between path and orbital angular momentum entanglement for high-dimensional photonic quantum information

et al. 2014

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Photonics has become a mature field of quantum information science, where integrated optical circuits offer a way to scale the complexity of the set-up as well as the dimensionality of the quantum state. On photonic chips, paths are the natural way to encode information. To distribute those high-dimensional quantum states over large distances, transverse spatial modes, like orbital angular momentum possessing Laguerre Gauss modes, are favourable as flying information carriers. Here we demonstrate a quantum interface between these two vibrant photonic fields. We create three-dimensional path entanglement between two photons in a nonlinear crystal and use a mode sorter as the quantum interface to transfer the entanglement to the orbital angular momentum degree of freedom. Thus our results show a flexible way to create high-dimensional spatial mode entanglement. Moreover, they pave the way to implement broad complex quantum networks where high-dimensionally entangled states could be distributed over distant photonic chips.

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Section: Methodsmentioning

confidence: 99%

Section: Generation Of Oam Modes With a Ms In Reversementioning

confidence: 99%

Interface between path and orbital angular momentum entanglement for high-dimensional photonic quantum information

et al. 2014

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“…The results exhibited a low degree of paradox, far from the theoretical values, though highly significant and in accordance with the full-field requirements 18 . The second experiment 19 exhibited also both near field (position) and far field (momentum) correlations, with a much lower product of the spatial extents. However only one beam of particles was involved, because of type-I phase matching, making the results questionable if intended as a demonstration of an EPR paradox.…”

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confidence: 99%

Einstein-Podolsky-Rosen Paradox in Twin Images

2014

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Spatially entangled twin photons provide both promising resources for modern quantum information protocols, because of the high dimensionality of transverse entanglement 1,2 , and a test of the Einstein-Podolsky-Rosen (EPR) paradox 3 in its original form of position versus impulsion. Usually, photons in temporal coincidence are selected and their positions recorded, resulting in a priori assumptions on their spatio-temporal behavior 4 . Here, we record on two separate electron-multiplying charge coupled devices (EMCCD) cameras twin images of the entire flux of spontaneous down-conversion. This ensures a strict equivalence between the subsystems corresponding to the detection of either position (image or near-field plane) or momentum (Fourier or far-field plane) 5 . We report the highest degree of paradox ever reported and show that this degree corresponds to the number of independent degrees of freedom 6,7 or resolution cells 8 , of the images.In 1935, Einstein, Podolsky and Rosen (EPR) showed that quantum mechanics predicts that entangled particles could have both perfectly correlated positions and momenta, in contradiction with the so-called local realism where two distant particles should be treated as two different systems. Though the original intention of EPR was to show that quantum mechanics is not complete, the standard present view is that entangled particles do experience nonlocal correlations 9,10 . It can be shown that the spatial extent of these correlations corresponds to the size of a spatial unit of information, or mode, offering the possibility of detecting high dimensional entanglement in an image with a sufficient number of resolution cells 2,4 . However, in most experiments the use of single photon detectors and coincidence counting leads to the detection of a very few part of selected photons, generating a sampling loophole in fundamental demonstrations. High sensitivity array detectors have been used outside the single photoncounting regime in order to witness the quantum feature of light, showing the possibility of achieving larger signal-tonoise ratio than in classical imaging 11,12 . However, the EPR paradox is intimately connected to the particle character of light and its detection should involve single photon imaging, possible either with intensified charge coupled devices (ICCD) or, more recently, EMCCDs 13 . ICCDs exhibit a lower noise but have also a lower quantum efficiency than EMCCDs and a more extended spatial impulse response. ICCD are therefore convenient to isolate pairs of entangled photons 14 , as shown in a recent experiment: an ICCD triggered by a single photon detector was used to detect heralded photons in various spatial modes 15 .On the other hand, because of their higher quantum efficiency EMCCDs allow efficient detection of quantum correlations in images, as demonstrated some years ago by measuring sub-shot-noise correlations in far-field images of spontaneous parametric down-conversion (SPDC) 16,17 . More recently, two experiments intended to achieve the demonstra...

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“…When the emergent photons equally share the energy of the input, the process is known as degenerate down-conversion (DDC); an alternative perspective is to regard the conversion as an exact time reversal of second-harmonic generation [1,2]. Much work has been carried out on correlated photon pairs, including their generation [3][4][5], manipulation [6][7][8][9], and application [10][11][12]. The entanglement of the quantum states in each pair has important applications in quantum computing and communication [13], and potential utilization clinically [14].…”

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confidence: 99%

Nonlocalized Generation of Correlated Photon Pairs in Degenerate Down-Conversion

2017

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The achievement of optimum conversion efficiency in conventional spontaneous parametric downconversion requires consideration of quantum processes that entail multisite electrodynamic coupling, actively taking place within the conversion material. The physical mechanism, which operates through virtual photon propagation, provides for photon pairs to be emitted from spatially separated sites of photon interaction; occasionally pairs are produced in which each photon emerges from a different point in space. The extent of such nonlocalized generation is influenced by individual variations in both distance and phase correlation. Mathematical analysis of the global contributions from this mechanism provides a quantitative measure for a degree of positional uncertainty in the origin of down-converted emission. DOI: 10.1103/PhysRevLett.118.133602 Spontaneous parametric down-conversion (SPDC) is a process in which light passing through an optically nonlinear medium can generate double-wavelength output. At a fundamental level, the process entails the conversion of pump photons into conascent, phase-matched pairs, executed by material interactions that entail the secondorder nonlinear optical susceptibility: a third-order electric dipole response. Each generated pair of photons has a combined energy and momentum equal to that of the corresponding annihilated photon, and they also exhibit correlated polarization. When the emergent photons equally share the energy of the input, the process is known as degenerate down-conversion (DDC); an alternative perspective is to regard the conversion as an exact time reversal of second-harmonic generation [1,2]. Much work has been carried out on correlated photon pairs, including their generation [3][4][5], manipulation [6][7][8][9], and application [10][11][12]. The entanglement of the quantum states in each pair has important applications in quantum computing and communication [13], and potential utilization clinically [14].In this Letter we develop an expanded theory of SPDC, highlighting and quantifying an important contribution from nonlocalized couplings. While SPDC is one of the main sources of entangled photon pairs [15], an exact location for the creation of each output photon cannot of course be inferred by direct observation-although pump photon annihilation and down-converted photon emission are generally assumed to be colocated. Of course, the diffuse nature of atomic and molecular orbitals precludes exact identification of the location for any photon creation event; equally, even the emission of two correlated photons cannot be considered as precisely colocated in origin. However, the spatial extent of the region from within which a pair of down-converted photons may emerge is considerably larger than may usually be supposed.In fact, there is a possibility that for each input photon the process may entail correlated photon interactions at two separate locations, creating one down-converted photon at each as indicated in Fig. 1. Accounting for such delocalized interact...

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Imaging high-dimensional spatial entanglement with a camera

Cited by 239 publications

References 37 publications

Interface between path and orbital angular momentum entanglement for high-dimensional photonic quantum information

Interface between path and orbital angular momentum entanglement for high-dimensional photonic quantum information

Einstein-Podolsky-Rosen Paradox in Twin Images

Nonlocalized Generation of Correlated Photon Pairs in Degenerate Down-Conversion

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