Quantum interference in double photon emission

We study Fano-like interference in double photon absorption, describing quantum beats in the second-order correlation function for both a free Λ-V system and a driven four-level scheme which approximately reproduces the first one in the dressed state picture. Because of interference, both amplitude and frequency of the beat oscillations are modified and (in some case) suppressed. In the case of the driven system, a partial coherent control of these features can be obtained, even in the presence of spontaneous emission for the driven transition.     

A coated pixel device TimePix with micron spatial resolution for UCN detection

A position sensitive detector for ultra-cold neutrons (UCNs) has been developed. Here we present the first experimental results and compare them with Monte-Carlo simulations. The silicon pixel device “TimePix” with a spatial resolution below 1 μm for strongly ionizing particles has been coated with a conversion layer of ⁶LiF for the detection of UCN. A spatial resolution of 5.3 μm has been measured for UCN. An optimized setup with 10B as conversion layer can achieve a spatial resolution below 3 μm.     

Quantum dot photon statistics measured by three-dimensional particle tracking

We present an instrument for performing correlation spectroscopy on single fluorescent particles while tracking their Brownian motion in three dimensions using real-time feedback. By tracking CdSe/ZnS quantum dots in water (diffusion coefficient approximately 20 microm2/s), we make the first measurements of photon antibunching (at approximately 10 ns) on single fluorophores free in solution and find fluorescence lifetime heterogeneity within a quantum dot sample. In addition, we show that 2-mercaptoethanol suppresses short time-scale intermittency (1 ms to 1 s) in quantum dot fluorescence by reducing time spent in the off-state.     

Conservative classical and quantum resolution limits for incoherent imaging

Abstract

I propose classical and quantum limits to the statistical resolution of two incoherent optical point sources from the perspective of minimax parameter estimation. Unlike earlier results based on the Cramér-Rao bound (CRB), the limits proposed here, based on the worst-case error criterion and a Bayesian version of the CRB, are valid for any biased or unbiased estimator and obey photon-number scalings that are consistent with the behaviours of actual estimators. These results prove that, from the minimax perspective, the spatial-mode demultiplexing measurement scheme recently proposed by Tsang, Nair, and Lu [Phys. Rev. X 2016, 6 031033.] remains superior to direct imaging for sufficiently high photon numbers.     

Quantum nondemolition measurement of the photon number in a Josephson-junction cavity

This paper proposes a quantum nondemolition measurement of the photon number in a Josephson-junction cavity. Under a current-biased Josephson junction with small capacitance, the Josephson phase fluctuates quantum-mechanically around its classical value due to the charging effect, and it couples to the photons in the junction cavity nonlinearly, which is necessary for the quantum nondemolition measurement. We show that the photon number in the junction cavity can be nondestructively measured by detecting the fluctuation of Josephson supercurrent through the junction.     

A Fourier approach to the natural pixel discretization of brain single‐photon emission computed tomography

We apply the natural pixel (NP) approach to the single‐photon emission computed tomography (SPECT) problem. The NP approach allows us to split the tomographic problem into two subproblems. The first is a linear inverse problem. The data are the measured projections and the linear operator is described by a Gram matrix, and provides a set of coefficients. The second consists of computing the solution of the tomographic problem as a linear combination of the elements of the NP basis with respect to the coefficients obtained by solving the first problem, and it provides a solution for any given grid of points. The spatially varying geometric response of the system is taken into account by properly choosing the elements of the basis. The rotational invariance shown by the elements of the considered basis induces a block circulant structure in the Gram matrix. This structure can be used to reduce the computational efforts needed for solving the inverse problem. In particular, we diagonalize (blockwise) the Gram matrix by applying the discrete Fourier transform and we solve the inverse problem in the frequency domain associated with the rotation angles. We develop numerical validation with synthetic data in order to test the performance of the NP approach and to assess the reliability of the results. A reconstruction of a two‐dimensional image requires 45–94 s, which is an acceptable time for clinical purposes. Finally, we apply the method to acquired clinical data that consist of a three‐dimensional brain scan. © 2002 John Wiley & Sons, Inc. Int J Imaging Syst Technol 12, 1–8, 2002     

The spectral resolution of high temperature GaAs photon counting soft X-ray photodiodes

Circular mesa GaAs p⁺-i-n⁺ diodes for photon counting soft X-ray spectroscopy have been fabricated and characterised over a temperature range of +80 to -30 °C. The spectroscopic performance of the diodes, as measured by the FWHM of the Mn K_α X-ray line from an ⁵⁵Fe radioisotope, is reported. In addition, we compare the GaAs diodes with previously fabricated and characterised Al_0.8Ga_0.2As p⁺-i-n⁺ diodes of similar geometry.     

Probabilistic model of multiple light scattering based on rigorous computation of the first and the second moments of photon coordinates

We consider a concise method based on recurrent relations that permit rigorous computing of the first and the second moments of the components of the vector locating a randomly walking photon in an infinite homogeneous light-scattering medium. On assumption that the components obey a three-dimensional Gaussian distribution a probability density for the photon locations at the Nth scattering event can readily be written down and the light-intensity distribution in the medium may be calculated. The results from theoretical analyses are compared with the solution of a light-diffusion equation and with results of Monte Carlo simulations and show a better fit with simulated data than the diffusion approximation.     

Quantum limits for minimum-uncertainty (MU) angular momentum polarization squeezed states

It is shown that there are certain quantum limits to angular momentum minimum-uncertainty (MU) obtained by polarization squeezing Hamiltonians, beyond which the MU cannot be realized. The analysis is made for two cases: (a) when a strong coherent state is in one mode and a squeezed vacuum is in the other mode. (b) For the interference between two optical modes which are amplitude squeezed, with equal squeezing and intensities’ magnitudes.     

Estimation of radiation-source coordinates from satellite-observation data

An algorithm is developed for precision evaluation of optical-radiation-source coordinates from satellite-observation data. The results of a numerical experiment confirm its effectiveness and possibility of use in space metrology. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 3–8, July, 2000.     

Imaging in turbid media by photon density waves: spatial resolution and scaling relations

Spatial resolution of transillumination imaging through highly scattering media normalized to sample thickness d depends on only the normalized wavelength ?/d of photon density waves and normalized penetration depth delta/d. This was concluded theoretically and verified experimentally by the derivation of edge-spread functions from measured time-resolved transmittance and its Fourier transform by the use of dilute milk at various concentrations as scatterer in cuvettes of d = 2 cm and d = 4 cm. In the frequency domain and the time domain, spatial resolution was found experimentally to be given by approximately 0.3 d obtained at ? approximately d or when only the first arriving 1% of all photons detected were taken into account.     

Derivation of plasmonic resonances in the Fourier modal method with adaptive spatial resolution and matched coordinates

A very stable approach for finding optical resonances is to solve an eigenvalue equation that evolves from the linearization of the inverse scattering matrix. In this paper, we show how to use this approach in the Fourier modal method so that advanced coordinate transformation methods such as adaptive spatial resolution and matched coordinates can be included. Furthermore, we present a way that accelerates the computation of the inverse scattering matrix tremendously and allows the derivation of the resonant field distribution inside the structure efficiently.     

Quantum dynamics and nonclassical photon statistics of coherently driven Raman transition in bimodal cavity

We study a classically driven two-level system in a harmonic trap and a lossy two-mode cavity, with the first mode being resonant to the driving field and an electronic transition, and the second mode being off-resonant, forming a vibrational-assisted Raman transition. Using an exact numerical method, we compute the steady state as well as the time evolution of the photon statistics. We further investigate the photon correlations of both the cavity modes and identify the laser parameters and coupling strength that give the nonclassical sub-Poissonian property. The work is useful for coherent control of photon statistics and photon correlations in the trapped two-level system.     

Multilayered Josephson transmission line based photon counting detector with ultra-high temporal and high spatial resolution

A superconducting Josephson transmission line (JTL) fabricated with multilayered tunnel junctions with thin (100 Å) superconducting layers may be used as an ionizing radiation detector. The suppression of the superconducting energy gap in the layers of such a JTL, due to the local deposition of energy by incident radiation, will initiate the propagation of one or more fluxons in the device. These fluxons represent digital information in the form processable by single flux quantum (SFQ) superconducting digital circuitry. Designs for JTL based detectors with temporal resolutions on the order of picoseconds and spatial resolution on the order of microns, along with numerical simulation results, are presented.     

微桥对 UFPA探测单元的影响

通过So1—Gel方法和半导体工艺，制备出基于Ba0.8Sr0.2TiO3(BST)薄膜的非致冷红外焦平面阵列(UFPA)探测单元。用ANSYS有限元分析软件，对探测单元进行了热分析。分析结果表明：微桥的大小可以极大的影响薄膜受到辐射后的温度以及薄膜温度的均匀性。对微桥和硅衬底上的BST薄膜进行了结构和性能上的对比。发现微桥上面的BST薄膜其介电常数有所下降，漏电流增加。而且为了得到致密无裂纹的BST薄膜，必须减少它的厚度。对所制备的UFPA探测单元进行了红外测试，得到1．6mV左右的信号输出，可以满足下一步信号处理的需要。