Paul-Antoine Moreau

Einstein-Podolsky-Rosen paradox in twin images.

Spatially entangled twin photons provide both promising resources for modern quantum information protocols, because of the high dimensionality of transverse entanglement, and a test of the Einstein-Podolsky-Rosen paradox 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 spatiotemporal behavior. In this Letter, we record, on two separate electron-multiplying charge coupled devices 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). We report the highest degree of paradox ever reported and show that this degree corresponds to the number of independent degrees of freedom, or resolution cells, of the images.

Realization of the purely spatial Einstein-Podolsky-Rosen paradox in full-field images of spontaneous parametric down conversion.

6174,Route de Gray 25030 Besanc¸on Cedex, FRANCE(Dated: July 20, 2012)We demonstrate Einstein-Podolsky-Rosen (EPR) entanglement by detecting purely spatial quan-tum correla-tions in the near and far fields of spontaneous parametric down-conversion generatedin a type-2 beta barium borate crystal. Full-field imaging is performed in the photon-countingregime with an electron-multiplying CCD camera. The data are used without any postselection,and we obtain a violation of Heisenberg inequalities with inferred quantities taking into accountall the biphoton pairs in both the near and far fields by integration on the entire two-dimensionaltransverse planes. This ensures a rigorous demonstration of the EPR paradox in its original position-momentum form.

Demonstrating an absolute quantum advantage in direct absorption measurement

Engineering apparatus that harness quantum theory promises to offer practical advantages over current technology. A fundamentally more powerful prospect is that such quantum technologies could out-perform any future iteration of their classical counterparts, no matter how well the attributes of those classical strategies can be improved. Here, for optical direct absorption measurement, we experimentally demonstrate such an instance of an absolute advantage per photon probe that is exposed to the absorbative sample. We use correlated intensity measurements of spontaneous parametric downconversion using a commercially available air-cooled CCD, a new estimator for data analysis and a high heralding efficiency photon-pair source. We show this enables improvement in the precision of measurement, per photon probe, beyond what is achievable with an ideal coherent state (a perfect laser) detected with 100% efficient and noiseless detection. We see this absolute improvement for up to 50% absorption, with a maximum observed factor of improvement of 1.46. This equates to around 32% reduction in the total number of photons traversing an optical sample, compared to any future direct optical absorption measurement using classical light.

Sub-Shot-Noise Transmission Measurement Enabled by Active Feed-Forward of Heralded Single Photons

J. Sabines-Chesterking,1 R. Whittaker,1 S. K. Joshi,2 P. M. Birchall,1 P. A. Moreau,1 A. McMillan,1 H. V. Cable,1 J. L. O’Brien,1 J. G. Rarity,1 and J. C. F. Matthews1 Quantum Engineering Technology Labs, H. H. Wills Physics Laboratory and Department of Electrical & Electronic Engineering, University of Bristol, BS8 1FD, UK. Institute for Quantum Optics and Quantum Information (IQOQI) Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria (Dated: November 24, 2016)

Temporal ghost imaging with twin photons

We use twin photons generated by spontaneous parametric down conversion to perform temporal ghost imaging of a single time signal. The retrieval of a binary signal containing eight bits is performed with an error rate below 1%.

Resolution limits of quantum ghost imaging

Quantum ghost imaging uses photon pairs produced from parametric downconversion to enable an alternative method of image acquisition. Information from either one of the photons does not yield an image, but an image can be obtained by harnessing the correlations between them. Here we present an examination of the resolution limits of such ghost imaging systems. In both conventional imaging and quantum ghost imaging the resolution of the image is limited by the point-spread function of the optics associated with the spatially resolving detector. However, whereas in conventional imaging systems the resolution is limited only by this point spread function, in ghost imaging we show that the resolution can be further degraded by reducing the strength of the spatial correlations inherent in the downconversion process.

Resolution-enhanced imaging with quantum correlations

The resolution of optical systems is limited by diffraction. We exploit the spatial properties of correlated photon-pairs to reconstruct a super-resolved image made of bisectant pixel-coordinates, achieving 40% of the theoretical V2 optical resolution enhancement.

Experimental Limits of Ghost Diffraction: Popper’s Thought Experiment

Quantum ghost diffraction harnesses quantum correlations to record diffraction or interference features using photons that have never interacted with the diffractive element. By designing an optical system in which the diffraction pattern can be produced by double slits of variable width either through a conventional diffraction scheme or a ghost diffraction scheme, we can explore the transition between the case where ghost diffraction behaves as conventional diffraction and the case where it does not. For conventional diffraction the angular extent increases as the scale of the diffracting object is reduced. By contrast, we show that no matter how small the scale of the diffracting object, the angular extent of the ghost diffraction is limited (by the transverse extent of the spatial correlations between beams). Our study is an experimental realisation of Popper’s thought experiment on the validity of the Copenhagen interpretation of quantum mechanics. We discuss the implication of our results in this context and explain that it is compatible with, but not proof of, the Copenhagen interpretation.

Sub-shot-noise shadow sensing with quantum correlations

The quantised nature of the electromagnetic field sets the classical limit to the sensitivity of position measurements. However, techniques based on the properties of quantum states can be exploited to accurately measure the relative displacement of a physical object beyond this classical limit. In this work, we use a simple scheme based on the split-detection of quantum correlations to measure the position of a shadow at the single-photon light level, with a precision that exceeds the shot-noise limit. This result is obtained by analysing the correlated signals of bi-photon pairs, created in parametric downconversion and detected by an electron multiplying CCD (EMCCD) camera employed as a split-detector. By comparing the measured statistics of spatially anticorrelated and uncorrelated photons we were able to observe a significant noise reduction corresponding to an improvement in position sensitivity of up to 17% (0.8dB). Our straightforward approach to sub-shot-noise position measurement is compatible with conventional shadow-sensing techniques based on the split-detection of light-fields, and yields an improvement that scales favourably with the detectors quantum efficiency.