We report on the experimental implementation of a polarimeter based on a scheme known to be optimal for obtaining the polarization vector of ensembles of spin-1 2 quantum systems, and the alignment procedure for this polarimeter. We also show how to use this polarimeter to estimate the polarization state for identically prepared ensembles of single photons and photon pairs and extend the method to obtain the density matrix for generic multi-photon states. State reconstruction and performance of the polarimeter is illustrated by actual measurements on identically prepared ensembles of single photons and polarization entangled photon pairs.

BackgroundEstablishing the cancer type and site of origin is important in determining the most appropriate course of treatment for cancer patients. Patients with cancer of unknown primary, where the site of origin cannot be established from an examination of the metastatic cancer cells, typically have poor survival. Here, we evaluate the potential and limitations of utilising gene alteration data from tumour DNA to identify cancer types.MethodsUsing sequenced tumour DNA downloaded via the cBioPortal for Cancer Genomics, we collected the presence or absence of calls for gene alterations for 6640 tumour samples spanning 28 cancer types, as predictive features. We employed three machine-learning techniques, namely linear support vector machines with recursive feature selection, L 1-regularised logistic regression and random forest, to select a small subset of gene alterations that are most informative for cancer-type prediction. We then evaluated the predictive performance of the models in a comparative manner.ResultsWe found the linear support vector machine to be the most predictive model of cancer type from gene alterations. Using only 100 somatic point-mutated genes for prediction, we achieved an overall accuracy of 49.4±0.4 % (95 % confidence interval). We observed a marked increase in the accuracy when copy number alterations are included as predictors. With a combination of somatic point mutations and copy number alterations, a mere 50 genes are enough to yield an overall accuracy of 77.7±0.3 %.ConclusionsA general cancer diagnostic tool that utilises either only somatic point mutations or only copy number alterations is not sufficient for distinguishing a broad range of cancer types. The combination of both gene alteration types can dramatically improve the performance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13073-017-0493-2) contains supplementary material, which is available to authorized users.

We present experimental results on a method to perform polarimetry on ensembles of single photons. Our setup is based on a measurement method known to be optimal for estimating the state of two level systems. The setup has no moving parts and is sensitive to weak sources (emitting single photons) of light as it relies on photon counting and has potential applications in both classical polarization measurements and quantum communication scenarios. In our implementation, we are able to reconstruct the Stokes parameters of pure polarization states with an average fidelity of 99.9%.Polarization measurement (also called polarimetry) is fundamental for many optical measurement techniques. In classical optics, applications include stress measurement, magnetic field sensing and optical thin film characterization [1]. More recently, polarization measurement of single photons prepared in particular ways has allowed experimental tests of non-locality and enabled applications in the field of quantum communication and information processing.The purpose of this paper is to report on an implementation of an optimal polarimeter without moving parts suitable for accurate polarization measurement at faint light (single photon) levels. Polarimetry is usually performed using a combination of rotating wave plates and a linear polarizer. Implementations without moving parts to ensure speed and reliability have been reported before [2,3] and exhaustive research has been performed on optimizing them [4,5,6,7,8]. Both types of polarimeters are applicable to complete state estimation techniques (also called state tomography) which are of interest in quantum information.Optimal polarimeters have been studied recently in the context of quantum key distribution [10,12] where the concern is to obtain the best possible estimate on the polarization state of a limited collection of photons. While tomographic techniques are fairly common in quantum optics and related areas [11], it should be noted that classical optics has used such techniques ever since Stokes showed how to determine

We report on the implementation of a photon counting polarimeter based on a scheme known to be optimal for obtaining the polarization vector of ensembles of spin-1 2 quantum systems. We show how to use this polarimeter to estimate the complete polarization state for generic multi-photon states. State reconstruction using the polarimeter is illustrated by actual measurements on prepared ensembles of one-and two-photon systems. The rate at which the estimated polarization state converges to an asymptote state is also measured and presented.