scholarly journals Single-Pixel Imaging with Heralded Single Photons

2021 ◽  
Author(s):  
Steven D Johnson ◽  
Alex McMillan ◽  
Cyril Torre ◽  
Stefan Frick ◽  
John Rarity ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Single Photons ◽  
Probe Light ◽  
Temporal Reference ◽  
Laser Illumination ◽  
Sensing Applications ◽  
Parametric Down Conversion ◽  
Remote Sensing Applications ◽  
Down Conversion ◽  
Single Pixel

Abstract Traditional remote sensing applications are often based on pulsed laser illumination with a narrow linewidth and characteristic repetition rate, which are not conducive to covert operation. Whatever methods are employed for covert sensing, a key requirement is for the probe light to be indistinguishable from background illumination. We present a method to perform single-pixel imaging that suppresses the effect of background light and hence improves the signal-to-noise ratio by using correlated photon-pairs produced via spontaneous parametric down conversion. One of the photons in the pair is used to illuminate the object whilst the other acts as a temporal reference, allowing the signal photons to be distinguished from background noise. This heralding method shows how the noise regime is key to producing higher contrast images.

scholarly journals Experimental scattershot boson sampling

2015 ◽  
Vol 1 (3) ◽  
pp. e1400255 ◽  
Author(s):  
Marco Bentivegna ◽  
Nicolò Spagnolo ◽  
Chiara Vitelli ◽  
Fulvio Flamini ◽  
Niko Viggianiello ◽  
...  
Keyword(s):  
Quantum Computer ◽  
Single Photons ◽  
Experimental Demonstration ◽  
Random Input ◽  
Exponential Increase ◽  
Quantum Device ◽  
Parametric Down Conversion ◽  
Quantum Simulator ◽  
Down Conversion ◽  
Boson Sampling

Boson sampling is a computational task strongly believed to be hard for classical computers, but efficiently solvable by orchestrated bosonic interference in a specialized quantum computer. Current experimental schemes, however, are still insufficient for a convincing demonstration of the advantage of quantum over classical computation. A new variation of this task, scattershot boson sampling, leads to an exponential increase in speed of the quantum device, using a larger number of photon sources based on parametric down-conversion. This is achieved by having multiple heralded single photons being sent, shot by shot, into different random input ports of the interferometer. We report the first scattershot boson sampling experiments, where six different photon-pair sources are coupled to integrated photonic circuits. We use recently proposed statistical tools to analyze our experimental data, providing strong evidence that our photonic quantum simulator works as expected. This approach represents an important leap toward a convincing experimental demonstration of the quantum computational supremacy.

scholarly journals Spontaneous parametric down-conversion in chirped, aperiodically-poled crystals

2015 ◽  
Vol 13 (05) ◽  
pp. 1550032 ◽  
Author(s):  
X. Sánchez-Lozano ◽  
J. L. Lucio M.
Keyword(s):  
Single Photon ◽  
Nonlinear Crystal ◽  
Spectral Amplitude ◽  
Single Photons ◽  
Ppln Crystal ◽  
Temporal Properties ◽  
Photon Pairs ◽  
Spectral Components ◽  
Parametric Down Conversion ◽  
Down Conversion

We present a theoretical analysis of the process of spontaneous parametric down conversion (SPDC) in a nonlinear crystal characterized by a linearly-chirped χ(2) grating along the direction of propagation. Our analysis leads to an expression for the joint spectral amplitude, based on which we can derive various spectral–temporal properties of the photon pairs and of the heralded single photons obtained from the photon pairs, including: The single-photon spectrum (SPS), the chronocyclic Wigner function (CWF) and the Schmidt number. The simulations that we present are for the specific case of a collinear SPDC source based on a PPLN crystal with the signal and idler photons emitted close to the telecom window. We discuss the mechanism for spectral broadening due to the presence of a linearly chirped χ(2) grating, showing that not only the width but also to some extent the shape of the SPDC spectrum may be controlled. Also, we discuss how the fact that the different spectral components are emitted on different planes in the crystal leads to single-photon chirp.

ANGULAR DISPERSION IN SPONTANEOUS PARAMETRIC DOWN CONVERSION: A TOOL TO GENERATE NARROW TEMPORAL BIPHOTONS AND PURE HERALDED SINGLE PHOTONS

2009 ◽  
Vol 07 (supp01) ◽  
pp. 9-15
Author(s):  
ALEJANDRA VALENCIA ◽  
MARTIN HENDRYCH ◽  
XIAOJUAN SHI ◽  
JUAN P. TORRES
Keyword(s):  
Fourier Transform ◽  
Pump Beam ◽  
Single Photons ◽  
Angular Dispersion ◽  
Joint Spectrum ◽  
Full Control ◽  
Parametric Down Conversion ◽  
Down Conversion

In this paper, we describe how introducing angular dispersion into the pump beam and the downconverted photons in spontaneous parametric downconversion allows us to manipulate the joint spectrum of the paired photons. In particular, when collinear geometries are used, we demonstrate an increase of the photons' bandwidth and discuss the implications of this method for the generation of narrow temporal Fourier transform limited biphotons. Additionally, we describe the situation in which angular dispersion is combined with noncollinear geometries. In this case, a full control of the joint spectrum is achieved and heralded pure single photons with controllable bandwidth can be obtained.

scholarly journals Spectral characterization of SPDC-based single-photon sources for quantum key distribution

2021 ◽  
Author(s):  
Sabine Euler ◽  
Erik Fitzke ◽  
Oleg Nikiforov ◽  
Daniel Hofmann ◽  
Till Dolejsky ◽  
...  
Keyword(s):  
Quantum Key Distribution ◽  
Single Photon ◽  
Complex Structure ◽  
Key Distribution ◽  
Spectral Characterization ◽  
Single Photons ◽  
Transverse Modes ◽  
Parametric Down Conversion ◽  
Photon Spectra ◽  
Down Conversion

AbstractIn our laboratory, we employ two biphoton sources for quantum key distribution. The first is based on cw parametric down-conversion of photons at 404 nm in PPKTP waveguide chips, while the second is based on the pulsed parametric down-conversion of 775 nm photons in PPLN waveguides. The spectral characterization is important for the determination of certain side-channel attacks. A Hong-Ou-Mandel experiment employing the first photon source revealed a complex structure of the common Hong-Ou-Mandel dip. By measuring the spectra of the single photons at 808 nm, we were able to associate these structures to the superposition of different transverse modes of the pump photons in our waveguide chips. The pulsed source was characterized by means of single-photon spectra measured by a sensitive spectrum analyzer as well as dispersion-based measurements. Finally, we also describe Hong-Ou-Mandel experiments using the photons from the second source.

scholarly journals Sensitivity of Optimal Estimation Satellite Retrievals to Misspecification of the Prior Mean and Covariance, with Application to OCO-2 Retrievals

2019 ◽  
Vol 11 (23) ◽  
pp. 2770 ◽  
Author(s):  
Hai Nguyen ◽  
Noel Cressie ◽  
Jonathan Hobbs
Keyword(s):  
Remote Sensing ◽  
Probability Distribution ◽  
Signal To Noise Ratio ◽  
Optimal Estimation ◽  
The State ◽  
Sensing Applications ◽  
Trade Offs ◽  
Subject Matter Expertise ◽  
Remote Sensing Applications ◽  
Retrieval Bias

Optimal Estimation (OE) is a popular algorithm for remote sensing retrievals, partly due to its explicit parameterization of the sources of error and the ability to propagate them into estimates of retrieval uncertainty. These properties require specification of the prior distribution of the state vector. In many remote sensing applications, the true priors are multivariate and hard to characterize properly. Instead, priors are often constructed based on subject-matter expertise, existing empirical knowledge, and a need for computational expediency, resulting in a “working prior.” This paper explores the retrieval bias and the inaccuracy in retrieval uncertainty caused by explicitly separating the true prior (the probability distribution of the underlying state) from the working prior (the probability distribution used within the OE algorithm), with an application to Orbiting Carbon Observatory-2 (OCO-2) retrievals. We find that, in general, misspecifying the mean in the working prior will lead to biased retrievals, and misspecifying the covariance in the working prior will lead to inaccurate estimates of the retrieval uncertainty, though their effects vary depending on the state-space signal-to-noise ratio of the observing instrument. Our results point towards some attractive properties of a class of uninformative priors that is implicit for least-squares retrievals. Furthermore, our derivations provide a theoretical basis, and an understanding of the trade-offs involved, for the practice of inflating a working-prior covariance in order to reduce the prior’s impact on a retrieval (e.g., for OCO-2 retrievals). Finally, our results also lead to practical recommendations for specifying the prior mean and the prior covariance in OE.

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