Photon-number distributions of twin beams generated in spontaneous parametric down-conversion and measured by an intensified CCD camera

The measurement of photon-number statistics of fields composed of photon pairs, generated in spontaneous parametric down-conversion and detected by an intensified CCD camera is described. Final quantum detection efficiencies, electronic noises, finite numbers of detector pixels, transverse intensity spatial profiles of the detected beams as well as losses of single photons from a pair are taken into account in a developed general theory of photon-number detection. The measured data provided by an iCCD camera with single-photon detection sensitivity are analyzed along the developed theory. Joint signal-idler photon-number distributions are recovered using the reconstruction method based on the principle of maximum likelihood. The range of applicability of the method is discussed. The reconstructed joint signal-idler photon-number distribution is compared with that obtained by a method that uses superposition of signal and noise and minimizes photoelectron entropy. Statistics of the reconstructed fields are identified to be multi-mode Gaussian. Elements of the measured as well as the reconstructed joint signal-idler photon-number distributions violate classical inequalities. Sub-shot-noise correlations in the difference of the signal and idler photon numbers as well as partial suppression of odd elements in the distribution of the sum of signal and idler photon numbers are observed.Comment: 14 pages, 14 figure

Non-trivial surface states of samarium hexaboride at the (111) surface

The peculiar metallic electronic states observed in the Kondo insulator, samarium hexaboride (SmB$_6$), has stimulated considerable attention among those studying non-trivial electronic phenomena. However, experimental studies of these states have led to controversial conclusions mainly to the difficulty and inhomogeneity of the SmB$_6$ crystal surface. Here, we show the detailed electronic structure of SmB$_6$ with angle-resolved photoelectron spectroscopy measurements of the three-fold (111) surface where only two inequivalent time-reversal-invariant momenta (TRIM) exist. We observe the metallic two-dimensional state was dispersed across the bulk Kondo gap. Its helical in-plane spin polarisation around the surface TRIM suggests that SmB$_6$ is topologically non-trivial, according to the topological classification theory for weakly correlated systems. Based on these results, we propose a simple picture of the controversial topological classification of SmB$_6$.Comment: 34 pages, 4 figures for main text; 9 figures for supplementary materia

Detector-Agnostic Phase-Space Distributions

The representation of quantum states via phase-space functions constitutes an intuitive technique to characterize light. However, the reconstruction of such distributions is challenging as it demands specific types of detectors and detailed models thereof to account for their particular properties and imperfections. To overcome these obstacles, we derive and implement a measurement scheme that enables a reconstruction of phase-space distributions for arbitrary states whose functionality does not depend on the knowledge of the detectors, thus defining the notion of detector-agnostic phase-space distributions. Our theory presents a generalization of well-known phase-space quasiprobability distributions, such as the Wigner function. We implement our measurement protocol, using state-of-the-art transition-edge sensors without performing a detector characterization. Based on our approach, we reveal the characteristic features of heralded single- and two-photon states in phase space and certify their nonclassicality with high statistical significance

Measurement of the position resolution of the Gas Pixel Detector

The Gas Pixel Detector was designed and built as a focal plane instrument for X-ray polarimetry of celestial sources, the last unexplored subtopics of X-ray astronomy. It promises to perform detailed and sensitive measurements resolving extended sources and detecting polarization in faint sources in crowded fields at the focus of telescopes of good angular resolution. Its polarimetric and spectral capability were already studied in earlier works. Here we investigate for the first time, with both laboratory measurements and Monte Carlo simulations, its imaging properties to confirm its unique capability to carry out imaging spectral-polarimetry in future X-ray missions.Comment: Submitted to Nuclear Instruments and Methods in Physics Research Section A; 15 figures, 3 table

Generation and characterization of spatially structured few-photon states of light

The present doctoral dissertation discusses the results of research on the characterization of spatial structure and statistical properties of few-photon states of light generated i.a. with the use of a new source based on multimode atomic memory. The dissertation comprises nine chapters grouped into the following parts: a literature and theoretical introduction, and three main parts providing the experimental results. Part I discusses the characteristics of a scientific complementary metal-oxide semiconductor camera equipped with an image intensifier (I-sCMOS) constructed by our group. We provide theoretical models of saturation of photon-number-resolving detectors which relate qualitatively to our camera. We perform experimental tomography of the I-sCMOS camera and use its results for high-fidelity reconstruction of the original statistics of the impinging light. In Part II we present an atomic memory setup in warm rubidium vapors where the write-in and readout occur due to collective Raman scattering. The memory is able to store information about the spatial structure of light. We describe the experimental setup thoroughly, with particular attention to the filtering system. We characterize multimode Raman scattering and investigate the storage performance of the memory which is limited by diffusional decoherence. We demonstrate spatial correlations between delayed Stokes and anti-Stokes photons. Using the I-sCMOS camera together with an advanced filtering system we observe spatial correlations down to single atomic excitations per memory mode. In Part III we discuss the use of the I-sCMOS camera to observe the Hong-Ou-Mandel two-photon interference with spatial resolution. We study the influence of finite spatial distinguishability of photons on the interference results, which leads us to measurements of the local spatial structure of a single photon. We observe and examine closely the following relatively unexplored phenomena. In Part I we investigate seemingly nonclassical effects in measurements of photon counts statistics on the camera. In Part II we are the first ones to show multimode Raman scattering in atomic memories. Finally, in Part III we describe the first observation of the Hong-Ou-Mandel effect with spatial resolution which is studied further in terms of finite spatial distinguishability of the interfering photons. In this thesis, we present the following novel experimental methodology. We use a new-type of I-sCMOS camera. We implement and perform the reconstruction of photon statistics based on tomographic characterization of the detector. We also build an efficient filtering system for photons generated in atomic memory. Moreover, we create an accurate method of measuring diffusion coefficients in atomic memory. We present our own methods of spatial characterization of the properties of light. Eventually, we introduce an entirely novel method: holographic measurement of the phase structure of a single photon using i.a. a specially developed phase reconstruction algorithm. The presented results fall within the scope of contemporary research in quantum optics and have a number of possible applications, as discussed in the final remarks section.Niniejsza praca doktorska prezentuje wyniki badań poświęconych charakteryzacji struktury przestrzennej i właściwości statystyk kilkufotonowych stanów światła generowanych m.in. z użyciem nowego źródła opartego na wielomodowej pamięci atomowej. Praca składająca się z 9 rozdziałów podzielona jest na wstęp literaturowy i teoretyczny oraz trzy części zawierające merytoryczne wyniki badań. Kolejno w części I prezentujemy i charakteryzujemy skonstruowany układ kamery sCMOS ze wzmacniaczem obrazu (I-sCMOS). Przedstawiamy teoretyczne modele nasycania detektorów rozróżniających liczbę fotonów, które jakościowo odnoszą się do kamery. Przeprowadzamy eksperymentalną tomografię kamery I-sCMOS a jej wyniki wykorzystujemy do wiernej rekonstrukcji pierwotnych statystyk światła padającego na kamerę. W części II prezentujemy układ pamięci atomowej w ciepłych parach rubidu, do której zapis i odczyt odbywa się w wyniku kolektywnego rozpraszania Ramana. Pamięć jest w stanie przechować informacje na temat przestrzennej struktury światła. Dokładnie opisujemy układ doświadczalny, w szczególności pod kątem układu filtrowania. Charakteryzujemy wielomodowe rozpraszanie Ramana oraz badamy zdolność przechowywania pamięci ograniczoną dekoherencją dyfuzyjną. Demonstrujemy korelacje przestrzenne pomiędzy opóźnionymi w czasie fotonami Stokesa i anty-Stokesa. Używając kamery I-sCMOS i zaawansowanego systemu filtrowania obserwujemy korelacje przestrzenne aż do reżimu pojedynczych wzbudzeń atomowych na mod pamięci. W części III wykorzystujemy kamerę I-sCMOS do badania zjawiska interferencji dwufotonowej Hong-Ou-Mandela obserwowanego z rozdzielczością przestrzenną. Studiujemy wpływ skończonej widzialności przestrzennej na wynik interferencji, która służy nam do pomiaru lokalnej struktury przestrzennej pojedynczego fotonu. Zaobserwowaliśmy i zbadaliśmy następujące słabo zbadane zjawiska. W części I badamy pozorne efekty nieklasyczne w statystykach zliczeń fotonów zmierzonych za pomocą kamery. W części II po raz pierwszy pokazujemy wielomodowe rozpraszanie Ramana w pamięciach atomowych. Natomiast w części III prezentujemy pierwszą obserwację efektu Hong-Ou-Mandela z rozdzielczością przestrzenną, którą następnie badamy pod kątem wpływu skończonej rozróżnialności przestrzennej interferujących fotonów. Na potrzeby tej pracy zostały stworzone i opracowane następujące, nowe metodologie badawcze. Stosujemy nowego typu kamerę I-sCMOS, opracowujemy rekonstrukcje statystyk fotonów na podstawie tomograficznej charakteryzacji detektora. Konstruujemy skuteczny układ filtrowania fotonów w pamięci atomowej. Tworzymy nową dokładną metodę pomiaru współczynników dyfuzji w pamięci atomowej. Prezentujemy także własne metody charakteryzacji przestrzennej statystycznych właściwości światła. W końcu, pokazujemy zupełnie nowatorską metodę holograficznego pomiaru struktury fazy pojedynczego fotonu, wykorzystującą m.in. specjalnie stworzony algorytm rekonstrukcji fazy. Zaprezentowane wyniki wpisują się w kontekst współczesnych badań w optyce kwantowej, a także posiadają szereg potencjalnych zastosowań, przedyskutowanych w podsumowaniu pracy

Development of x-ray holography methods for structure determination : Application of high speed detectors and novel numerical methods

Holographic methods show much promise to enable direct determination of atomic structure with minimal assumptions and approximations. The approach can, in principle, provide three dimensional information on atomic positions. However, significant developments in experimental techniques, instrumentation and in data collection and analysis are needed. A review of the holography method is given with a focus on X-ray fluorescence holography. Methods for analysis of X-ray holographic data are also reviewed. An overview of the detectors relevant to X-ray measurements is also presented. An experimental apparatus for rapid acquisition of X-ray holographs using novel X-ray detectors has been developed. The integration of high speed detectors and the utilization of rapid sampling methods to produce high quality holograms form the core of this work. A new method for direct extraction of the electron charge density based on expansion of the hologram with respect to a spherical harmonic basis is developed. This approach attacks the problem of obtaining the electron density from the hologram by the introduction of periodic constraints (fixed unit cells) while maintaining flexibility by making no assumptions about the positions of atoms within the unit cells. Problems with local or long range distortions can be solved by utilizing cells of the appropriate size. The method makes no other assumptions. Model charge densities derived from this approach are shown to match quite well with the input model crystal structures with no need for heavy filtering typical of the Barton Transform. The algorithm can be fully automated and hence falls into the class of Direct Methods . This new approach may move the method of X-ray holography from the developmental stage to a powerful and routine tool for the solution of single crystal structures relevant to inorganic materials and organic systems

Research in the development effort of an improved multiplier phototube final report

Single electron counting characteristics of multiplier phototubes - Pulse height distribution of windowless multiplie