Boson Sampling with efficient scaling and efficient verification

A universal quantum computer of moderate scale is not available yet, however intermediate models of quantum computation would still permit demonstrations of a quantum computational advantage over classical computing and could challenge the Extended Church-Turing Thesis. One of these models based on single photons interacting via linear optics is called Boson Sampling. Proof-of-principle Boson Sampling has been demonstrated, but the number of photons used for these demonstrations is below the level required to claim quantum computational advantage. To make progress with this problem, here we conclude that the most practically achievable pathway to scale Boson Sampling experiments with current technologies is by combining continuous-variables quantum information and temporal encoding. We propose the use of switchable dual-homodyne and single-photon detections, the temporal loop technique and scattershot based Boson Sampling. This proposal gives details as to what the required assumptions are and a pathway for a quantum optical demonstration of quantum computational advantage. Furthermore, this particular combination of techniques permits a single efficient implementation of Boson Sampling and efficient verification in a single experimental setup

Quantum metrology timing limits of the Hong-Ou-Mandel interferometer and of general two-photon measurements

We examine the precision limits of Hong-Ou-Mandel (HOM) timing measurements, as well as precision limits applying to generalized two-photon measurements. As a special case, we consider the use of two-photon measurements using photons with variable bandwidths and frequency correlations. When the photon bandwidths are not equal, maximizing the measurement precision involves a trade-off between high interference visibility and strong frequency anticorrelations, with the optimal precision occuring when the photons share non-maximal frequency anticorrelations. We show that a generalized measurement has precision limits that are qualitatively similar to those of the HOM measurement whenever the generalized measurement is insensitive to the net delay of both photons. By examining the performance of states with more general frequency distributions, our analysis allows for engineering of the joint spectral amplitude for use in realistic situations, in which both photons may not have ideal spectral properties.Comment: 12 pages, 6 figures; resubmissio

Spectral characterization of a SPDC source with a fast broadband spectrometer

Knowing the properties of the single photons produced in a Spontaneous Parametric Down-Conversion (SPDC) source can be crucial for specific applications and uses. In particular, the spectral properties are of key relevance. Here, we investigate a commercial SPDC source using our fast broadband spectrometer. Our analysis is a valid method for other SPDC sources, as well as other single-photon generation techniques, thus providing a good example of how to use this spectrometer design. We calibrate the spectrometer using known lines of the argon emission spectrum. We show that the two down-converted photons from the SPDC source have different spectral properties depending on the pump power, and in which condition we measured spectrally similar down-converted photons. Lastly, we were able to reconstruct and investigate the spectral information for the pump photon

Reduction of computational times using the equivalent rectangle concept in the physics-based surface - subsurface models

The interaction between surface and subsurface domains in a basin can be studied using a physics-based model; however, the calibration and validation processes require a high computational effort due to their complex geometry. The authors propose an alternative to reduce the computational times during the calibration model by simplifying the geometry of the watershed that applies the equivalent rectangle concept. A quasi-3D equivalent rectangle is used to define the specific soil parameters of the Lerma river basin through sensitivity analysis that will later be applied in the calibration. The simplified model can highly accurately identify the parameter range for the initial values of the calibration process as well as if the reduction in running times is significant. Thus, the rectangle equivalent concept offers an alternative to speed-up the calibration of a 3-D fully-coupled surface sub-surface model.La interacción entre la superficie y subsuperficie de una cuenca se puede estudiar utilizando modelos físicos, pero debido a su compleja geometría los procesos de calibración y validación requieren altos tiempos computacionales. Para ello, se propone una alternativa que permita reducir los tiempos de calibración del modelo, mediante la simplificación de la geometría de la cuenca y empleando el concepto del rectángulo equivalente. El rectángulo equivalente es usado para definir los parámetros del suelo de la cuenca del río Lerma, a través de un análisis de sensibilidad, que posteriormente son empleados dentro de la calibración. El modelo simplificado identifica con una gran precisión los rangos y valores iniciales de los parámetros utilizados para los procesos de calibración y además reduce significativamente los tiempos computacionales. Por lo tanto, el concepto de rectángulo equivalente ofrece una alternativa para acelerar la calibración de modelos acoplados superficie-subsuperficie

Specifying Value in GRL for Guiding BPMN Activities Prioritization

In a value-based requirements engineering approach, the stakeholders’ value propositions must be considered ahead in order to prioritize which requirements will be developed first to drive the software development activities. Early requirements approaches like the Goal- Oriented Requirements Language (GRL) focuses on modeling goals, tasks, contributions, and dependencies in order to satisfy the stakeholders’ needs, but do not provide a mechanism to specify value according to stakeholders’ value propositions. Moreover, in software development, after specifying value propositions, there is a need to align goal elements into business process elements in order to prioritize which business process activity is going to be developed next. Thus, we propose a new approach (value@GRL) to improve GRL and prioritize Business Process Model and Notation (BPMN) activities. Value@GRL provides guidelines for specifying value in GRL models according to the stakeholders’ needs and prioritization mechanisms to define BPMN activities\u27 order in an incremental software development

Towards Quantum Telescopes: Demonstration of a Two-Photon Interferometer for Quantum-Assisted Astronomy

Classical optical interferometery requires maintaining live, phase-stable links between telescope stations. This requirement greatly adds to the cost of extending to long baseline separations, and limits on baselines will in turn limit the achievable angular resolution. Here we describe a novel type of two-photon interferometer for astrometry, which uses photons from two separate sky sources and does not require an optical link between stations. Such techniques may make large increases in interferometric baselines practical, even by orders of magnitude, with corresponding improvement in astrometric precision benefiting numerous fields in astrophysics. We tested a benchtop analogue version of the two-source interferometer and unambiguously observe correlated behavior in detections of photon pairs from two thermal light sources, in agreement with theoretical predictions. This work opens new possibilities in future astronomical measurements

Fast spectrometer near the Heisenberg limit with direct measurement of time and frequency for multiple single photons

We present a single-photon-sensitive spectrometer, based on a linear array of 512 single-photon avalanche diodes, with 0.04 nm spectral and 40 ps temporal resolutions. We employ a fast data-driven operation that allows direct measurement of time and frequency for simultaneous single photons. Combining excellent temporal and spectral resolution, our result is only a factor of ten above the Heisenberg Uncertainty Principle limit of hbar/2 for energy and time, despite the simplicity of our experimental setup. This work opens numerous applications in quantum photonics, especially when both spectral and temporal properties of single photons are exploited