Self-calibrating Optical Low-Coherence Reflectometry with Energy-Time Entangled Photons for Absolute Distance Measurements

Optical low-coherence reflectometry is capable of unambiguously measuring positions of stacked, partially reflective layers in a sample object. It relies on the low coherence of the light source and the absolute distances are obtained from the position reading of a mechanical motor stage. We show how to exploit the simultaneous high and low coherence properties of energy-time entangled photon pairs to directly calibrates the position scale of an OLCR scan with a reference laser wavelength. In experiment, a precision of 1.6\,nm and good linearity is demonstrated.Comment: 5 pages, 6 figure

Super-Resolution Quantum Imaging at the Heisenberg Limit

Quantum imaging exploits the spatial correlations between photons to image object features with a higher resolution than a corresponding classical light source could achieve. Using a quantum correlated $N$-photon state, the method of optical centroid measurement (OCM) was shown to exhibit a resolution enhancement by improving the classical Rayleigh limit by a factor of $1/N$. In this work, the theory of OCM is formulated within the framework of an imaging formalism and is implemented in an exemplary experiment by means of a conventional entangled photon pair source. The expected resolution enhancement of a factor of two is demonstrated. The here presented experiment allows for single-shot operation without scanning or iteration to reproduce the object in the image plane. Thereby, photon detection is performed with a newly developed integrated time-resolving detector array. Multi-photon interference effects responsible for the observed resolution enhancement are discussed and possible alternative implementation possibilities for higher photon number are proposed

Characterization of space-momentum entangled photon with a time resolving CMOS SPAD array

Single photon avalanche diode arrays can provide both the spatial and temporal information of each detected photon. We present here the characterization of entangled light with a sensor specifically designed for quantum imaging applications. The sensors is time-tagging each detection events at the pixel level with sub-nanosecond accuracy, within frames of 50 ns. The spatial correlations between any number of detections in a defined temporal window can thus be directly extracted from the data. We show the ability of the sensor to characterize space-momentum entangled photon pairs emitted by spontaneous parametric downconversion. Their entanglement is demonstrated by violating an EPR-type inequality.Comment: 15 pages, 12 figure

Self-calibrating optical low-coherence reflectometry with energy-time entangled photons for absolute distance measurements

Optical low-coherence reflectometry is capable of unambiguously measuring positions of stacked, partially reflective layers in a sample object. It relies on the low coherence of the light source and the absolute distances are obtained from the position reading of a mechanical motor stage. We show how to exploit the simultaneous high and low coherence properties of energy-time entangled photon pairs to directly calibrates the position scale of an OLCR scan with a reference laser wavelength. In experiment, a precision of 1.6\,nm and good linearity is demonstrated

Estimation of the rate of entangled-photon-pair interaction with metallic nanoparticles based on classical-light second-harmonic generation measurements

Entangled-photon-pair interaction (EPPI) with matter is a key element in many suggested quantum-light applications and an enhancement of this interaction is of great importance. In this paper, we suggest and investigate the use of metallic nanoparticles (MNPs), with their exceptional capability of light–matter coupling at their localized surface plasmon resonance, for a potential enhancement of EPPI. We specifically investigate second-harmonic generation and theoretically estimate the rate of EPPI with MNPs using measurements with classical-light. We perform a simple measurement based on approximating the optical-setup factor G, of hyper-Rayleigh scattering. Experimental results, obtained for solutions of silver NPs (SNPs) with different densities, show a hyperpolarizability of about The results indicate that the use of SNPs can indeed be advantageous for EPPI, with an estimated three orders-of magnitude enhancement of the hyperpolarizability, relative to the best organic molecules. However, we show that further optimization of the SNPs should be carried out to enlarge their EPPI cross-section even more

Coincidence detection of spatially correlated photon pairs with a monolithic time-resolving detector array

We demonstrate coincidence measurements of spatially entangled photons by means of a multi-pixel based detection array. The sensor, originally developed for positron emission tomography applications, is a fully digital 8×16 silicon photomultiplier array allowing not only photon counting but also per-pixel time stamping of the arrived photons with an effective resolution of 265 ps. Together with a frame rate of 500 kfps, this property exceeds the capabilities of conventional charge-coupled device cameras which have become of growing interest for the detection of transversely correlated photon pairs. The sensor is used to measure a second-order correlation function for various non-collinear configurations of entangled photons generated by spontaneous parametric down-conversion. The experimental results are compared to theory

Coincidence detection of spatially correlated photon pairs with a novel type of monolithic time-resolving detector array

We demonstrate a novel type of multi-pixel detector array which enables per-pixel time stamping with sub-nanosecond timing resolution and a high frame rate by measuring second-order correlation functions of transverse momentum entangled photons