Photon Arrival Times Research Articles

Energy-time entanglement-based dispersive optics quantum key distribution over optical fibers of 20 km

An energy-time entanglement-based dispersive optics quantum key distribution (DO-QKD) is demonstrated experimentally over optical fibers of 20 km. In the experiment, the telecom band energy-time entangled photon pairs are generated through spontaneous four-wave mixing in a silicon waveguide. The arrival time of photons is registered for key generation and security test. High-dimensional encoding in the arrival time of photons is used to increase the information per coincidence of photon pairs. The bin sifting process is optimized by a three-level structure, which significantly reduces the raw quantum bit error rate (QBER) due to timing jitters of detectors and electronics. A raw key generation rate of 151 kbps with a QBER of 4.95% is achieved, in a time bin encoding format with 4 bits per coincidence. This experiment shows that the entanglement-based DO-QKD can be implemented in an efficient and convenient way, which has great potential for quantum secure communication networks in the future.

Iterative Non-Negative Matrix Factorization Filter for Blind Deconvolution in Photon/Ion Counting.

A digital filter based on non-negative matrix factorization (NMF) enables blind deconvolution of temporal information from large data sets, simultaneously recovering both photon arrival times and the instrument impulse response function (IRF). In general, the measured digital signals produced by modern analytical instrumentation are convolved by the corresponding IRFs, which can complicate quantitative analyses. Common examples include photon counting (PC), chromatography, super resolution imaging, fluorescence imaging, and mass spectrometry. Scintillation counting, in particular, provides a signal-to-noise advantage in measurements of low intensity signals, but has a limited dynamic range due to pulse overlap. This limitation can complicate the interpretation of data by masking temporal and amplitude information on the underlying detected signal. Typical methods for deconvolution of the photon events require advanced knowledge of the IRF, which is not generally trivial to obtain. In this work, a sliding window approach was developed to perform NMF one pixel at a time on short segments of large (e.g., 25 million point) data sets. Using random initial guesses for the IRF, the NMF filter simultaneously recovered both the deconvolved photon arrival times and the IRF. Applying the NMF filter to the analysis of triboluminescence (TL) data traces of active pharmaceutical ingredients enabled discrimination between different hypothesized physical origins of the signal.

Constraints on differential Shapiro delay between neutrinos and photons from IceCube-170922A

On 22nd September 2017, the IceCube Collaboration detected a neutrino with energy of about 290 TeV from the direction of the gamma-ray blazar TXS 0506+056, located at a distance of about 1.75 Gpc. During the same time, enhanced gamma-ray flaring was also simultaneously observed from multiple telescopes, giving rise to only the second coincident astrophysical neutrino/photon observation after SN 1987A. We point out that for this event, both neutrinos and photons encountered a Shapiro delay of about 6300 days along the way from the source. From this delay and the relative time difference between the neutrino and photon arrival times, one can constrain violations of Einstein’s Weak Equivalence Principle (WEP) for TeV neutrinos. We constrain such violations of WEP using the Parameterized Post-Newtonian (PPN) parameter gamma , which is given by |gamma _mathrm{{nu }}-gamma _{mathrm{EM}}|<5.5 times 10^{-2}, after assuming time difference of 175 days between neutrino and photon arrival times.

Behavioral Modeling of Photon Arrival Time for Time-of-Flight Measurement Circuit Simulation

This letter proposes a behavioral model to estimate the statistical photon arrival time for time-of-flight (TOF) measurement circuit simulation. A theoretical model is derived to calculate the photon arrival rate by full consideration of a variety of properties of a TOF measurement system, such as laser source, optics, single-photon avalanche diode detector, target distance, and ambient illumination. For the first time, the newly developed model is implemented in behavioral Verilog-A hardware description language and successfully operated on Cadence Spectre simulator for TOF circuit simulation. It is capable of accurately predicting the statistical performance parameters such as photon arrival time and achievable distance, providing a new candidate tool for the ease of design and simulation of various high-performance TOF measurement circuits.

Probing (UN)Folding Transition Paths of Fast-Folding Proteins by Single-Molecule Fluorescence: Exploring the Role of Secondary Structure, Fold Topology and Sequence

Protein folding involves formation of secondary structural elements and their collapse into well-defined 3-dimensional structure. Attempts to study how these processes cooperate to form the native structure and determine folding mechanisms has been focus of research for decades. Addressing these questions require looking at the distributions of behaviors of individual molecules, which has been successfully attained by theory and computer simulations. Experimentally, the problem must be approached by single-molecule spectroscopic methods, which have not had the required time-resolution. We are investigating protein folding at the single-molecule level combining advanced custom-built fluorescence-based SM-FRET techniques optimized for high-count rates and a maximum likelihood analysis (MLA) of photon arrival times that we developed for the detection of (un)folding transition paths of microsecond folding proteins. To investigate the roles of secondary structure, fold topology, and amino acid sequence we are performing these experiments on three fast-folding protein models, all consisting of three secondary structure elements in an antiparallel arrangement: En-HD (three α-helices), and Nedd4-WW3 and FBP11WW2, which fold onto homologous 3-stranded β-sheets but with different amino acid sequence. We are investigating their folding transition paths by 2-color SM-FRET using variants labeled with FRET pairs at the two ends in free diffusion experiments. Because these proteins fold-unfold in microseconds, free diffusion offers the opportunity to catch folding transitions during the diffusive trajectories without immobilization and thus without significantly perturbing folding landscape. Our analysis of these data using MLA of photon trajectories (rather than binning) provides the free energy landscape as a function of the experimental order parameter (FRET-pair distance) and the intramolecular diffusion coefficient. Subsequent reconstruction of the molecular trajectories from the photon trajectories using stochastic methods provide a direct glimpse of barrier crossing events.

Ground verification system of X-ray pulsar navigation with multi-physical properties

Navigation ground verification is an essential part of X-ray pulsar navigation (XPNAV) research. Aiming at the need of real and continuous pulsar signals for navigation algorithm verification, and to avoid the difficulties and high costs of X-ray modulation and detection, we propose an XPNAV ground verification system based on visible light source. In this system, the pulsar signal model at the solar system barycenter and the orbit information are used to establish the real-time photon arrival rate function at a spacecraft, and then the rate function is digitized and converted into voltage signal by the designed hardware system to drive a linear light source. After the processes of light attenuation, signal detection and pulse discrimination are experienced, the real-time photon time of arrivals (TOAs) at a spacecraft can be achieved. These photon TOAs contain characteristics of the pulsar profiles and frequency, the time propagation effect in the solar system, and cosmic X-ray background. The system uses semi-physical devices to modulate and attenuate visible light, and judges whether the spacecraft can observe the navigation pulsar according to the real position, thereby realizing the simulation of X-ray propagation in space. At present, the detection method of pulsar observation with single detector include detection of single pulsar, time division detection of multiple pulsars, and simultaneous detection of multiple pulsars. The system has four channels, each of which has three output modes mentioned above, and can support the verification of multiple navigation modes. This system consists of signal simulator and controller, single photon generator and detector, single photon screening and time tagging, and navigation algorithm verification. This paper presents the testing results of the system characteristics, the authenticity of the simulated photon arrival time series and the navigation verification. Monte Carlo experiments show that the recording accuracy of photon arrival time is 10 ns and the delays of the four channels are (11 ± 2), (15 ± 4), (14 ± 3), and (16 ± 4) &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}${\text{μ}}{\rm{s}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20182232_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20182232_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, respectively. The multi-physical properties of simulated photon arrival time series are introduced in detail, including photon flux, shape of observation profile, pulsar frequency characteristics and Doppler shift. The position and velocity errors of autonomous navigation algorithm test are 13.587 km and 14.277 m·s&lt;sup&gt;–1&lt;/sup&gt;, respectively, with an orbital altitude 26610 km and within 10 h. The ground verification system adopts master-slave control mode, the master computer mainly implements parameter setting and navigation algorithm verification, and the slave computer mainly carry out pulsar signal simulation. The communication based on TCP/IP protocol is applied to realize parameter transmission and real-time control between the master and slave computers in navigation verification process. The results of performance and functional test show that the system is available to accomplish the simulation of photon TOAs of X-ray pulsars at a spacecraft in real time and implement the ground verification of XPNAV.

Multiparametric Time-Correlated Single Photon Counting Luminescence Microscopy.

Classic time-correlated single photon counting (TCSPC) technique involves detection of single photons of a periodic optical signal, registration of the photon arrival time in respect to the reference pulse, and construction of photon distribution with regard to the detection times. This technique achieves extremely high time resolution and near-ideal detection efficiency. Modern TCSPC is multi-dimensional, i.e., in addition to the photon arrival time relative to the excitation pulse, spatial coordinates within the image area, wavelength, time from the start of the experiment, and many other parameters are determined for each photon. Hence, the multi-dimensional TCSPC allows generation of photon distributions over these parameters. This review describes both classic and multi-dimensional types of TCSPC microscopy and their application for fluorescence lifetime imaging in different areas of biological studies.

A Robust Quantum Random Number Generator Based on an Integrated Emitter-Photodetector Structure

We present a new compact photonic quantum random number generator based on an emitter (source of entropy) and a single-photon detector integrated in the same silicon chip. Not only they are integrated one close to the other, but also they are fabricated with the same fabrication process. The emitter is a small silicon photomultiplier, composed of passively-quenched single photon avalanche diodes (SPADs), having the same layout of the single SPAD used as the detector. The emitter is a reverse-biased silicon p-n junction, generating photons mainly due to impact ionization during the avalanche breakdown process. The detector is shielded from ambient light by a top metal layer: only photons from the emitter are detected, making this integrated approach more robust. The random bits are extracted with a robust methodology based on the measurement of photon arrival times, using discrete time bins, in a time frame cyclically repeated in time. No postprocessing is required for the raw data to pass the statistical tests.

Model, Validation, and Characterization of a Robust Quantum Random Number Generator Based on Photon Arrival Time Comparison

A Quantum Random Number Generator (QRNG) based on the detection of the arrival time of photons is presented. A stochastic model of the QRNG prototype is derived, showing its consistency with output data sets, in order to estimate the entropy produced by the device. Experimental data, in accord with the model, demonstrates the robustness of the approach versus possible variations of external parameters such as temperature or intensity of the light.

A SPAD-based random number generator pixel based on the arrival time of photons

A quantum random generator based on photon detection is here presented. The system consists of a photon source, typically a commercial LED, coupled with a detector with single photon detection capability. The detector is composed of a Single-Photon Avalanche Diode (SPAD) and a time stamp circuit, which samples the arrival time of impinging photons within a predefined temporal window. The proposed implementation optimizes the area, allowing embedding all circuitry into a single pixel, and increases the efficiency of random bit extraction. Moreover, the adopted fast pre-charge mode of the SPAD quenching circuit reduces the afterpulsing probability, and hence possible undesirable correlation in the resulting random bit sequence. Thanks to the implemented random bit extraction, experimental results show that the pixel has a flat behavior for a significant range of light intensity, which makes the pixel robust against variations of external PVT parameters. The maximum achievable bit rate has been measured equal to 1 Mbps, while random sequences are shown to pass NIST tests without any post-processing.

Single-photon 3D imaging with deep sensor fusion

Sensors which capture 3D scene information provide useful data for tasks in vehicle navigation, gesture recognition, human pose estimation, and geometric reconstruction. Active illumination time-of-flight sensors in particular have become widely used to estimate a 3D representation of a scene. However, the maximum range, density of acquired spatial samples, and overall acquisition time of these sensors is fundamentally limited by the minimum signal required to estimate depth reliably. In this paper, we propose a data-driven method for photon-efficient 3D imaging which leverages sensor fusion and computational reconstruction to rapidly and robustly estimate a dense depth map from low photon counts. Our sensor fusion approach uses measurements of single photon arrival times from a low-resolution single-photon detector array and an intensity image from a conventional high-resolution camera. Using a multi-scale deep convolutional network, we jointly process the raw measurements from both sensors and output a high-resolution depth map. To demonstrate the efficacy of our approach, we implement a hardware prototype and show results using captured data. At low signal-to-background levels, our depth reconstruction algorithm with sensor fusion outperforms other methods for depth estimation from noisy measurements of photon arrival times.

Coincidence landscapes for polarized bosons

Passive optical interferometry with single photons injected into some input ports and vacuum into others is enriched by admitting polarization, thereby replacing the scalar electromagnetic description by a vector theory, with the recent triad phase being a celebrated example of this richness. On the other hand, incorporating polarization into interferometry is known to be equivalent to scalar theory if the number of channels is doubled. We show that passive multiphoton $m$-channel interferometry described by $\mathrm{SU}(m)$ transformations is replaced by $\mathrm{SU}(2m)$ interferometry if polarization is included and thus that the multiphoton coincidence landscape, whose domain corresponds to various relative delays between photon arrival times, is fully explained by the now-standard approach of using immanants to compute coincidence sampling probabilities. Consequently, we show that the triad phase is manifested simply as SU(6) interferometry with three input photons, with one photon in each of three different input ports. Our analysis incorporates passive polarization multichannel interferometry into the existing scalar-field approach to computing multiphoton coincidence probabilities in interferometry and demystifies the triad phase.

Topological track reconstruction in unsegmented, large-volume liquid scintillator detectors

Unsegmented, large-volume liquid scintillator (LS) neutrino detectors have proven to be a key technology for low-energy neutrino physics. The efficient rejection of radionuclide background induced by cosmic muon interactions is of paramount importance for their success in high-precision MeV neutrino measurements. We present a novel technique to reconstruct GeV particle tracks in LS, whose main property, the resolution of topological features and changes in the differential energy loss dE/dx, allows for improved rejection strategies. Different to common track reconstruction approaches, our method does not rely on concrete track / topology hypotheses. Instead, based on a reference point in space and time, the observed distribution of photon arrival times at the photosensors and the detector's characteristics in terms of photon production, propagation and detection (optical model), it reconstructs the voxelized distribution of optical photon emissions. Techniques from three-dimensional data analysis can then be applied to extract parameters describing the topology, e.g., the direction of a track. We performed a first performance evaluation of our method using single muon events with up to 10 GeV from a Geant4 simulation of the LENA detector. The current results indicate that our approach is competitive with existing reconstruction methods— although its full potential has not yet been exploited. We also remark on other detector technologies in astroparticle physics as well as applications in medical imaging that could benefit from the fundamental ideas of our method.

Driving-induced population trapping and linewidth narrowing via the quantum Zeno effect

We investigate the suppression of spontaneous emission from a driven three-level system embedded in an optical cavity via a manifestation of the quantum Zeno effect. Strong resonant coupling of the lower two levels to an external optical field results in a decrease of the exponential decay rate of the third upper level. We show that this effect has observable consequences in the form of emission spectra with subnatural linewidths, which should be measurable using, for example, quantum dot--cavity systems in currently obtainable parameter regimes. These results constitute a novel method to control an inherently irreversible and dissipative process, and may be useful in applications requiring the control of single photon arrival times and wavepacket extent.

Compact Quantum Random Number Generator with Silicon Nanocrystals Light Emitting Device Coupled to a Silicon Photomultiplier

A small-sized photonic quantum random number generator, easy to be implemented in small electronic devices for secure data encryption and other applications, is highly demanding nowadays. Here, we propose a compact configuration with Silicon nanocrystals large area light emitting device (LED) coupled to a Silicon photomultiplier to generate random numbers. The random number generation methodology is based on the photon arrival time and is robust against the non-idealities of the detector and the source of quantum entropy. The raw data show high quality of randomness and pass all the statistical tests in national institute of standards and technology tests (NIST) suite without a post-processing algorithm. The highest bit rate is 0.5 Mbps with the efficiency of 4 bits per detected photon.

Fluorescence Correlation Spectroscopy with Photobleaching Correction in Slowly Diffusing Systems.

Fluorescence correlation spectroscopy (FCS) is a powerful tool to quantitatively study the diffusion of fluorescently labeled molecules. It allows in principle important questions of macromolecular transport and supramolecular aggregation in living cells to be addressed. However, the crowded environment inside the cells slows diffusion and limits the reservoir of labeled molecules, causing artifacts that arise especially from photobleaching and limit the utility of FCS in these applications. We present a method to compute the time correlation function from weighted photon arrival times, which compensates computationally during the data analysis for the effect of photobleaching. We demonstrate the performance of this method using numerical simulations and experimental data from model solutions. Using this technique, we obtain correlation functions in which the effect of photobleaching has been removed and in turn recover quantitatively accurate mean-square displacements of the fluorophores, especially when deviations from an ideal Gaussian excitation volume are accounted for by using a reference calibration correlation function. This allows quantitative FCS studies of transport processes in challenging environments with substantial photobleaching like in living cells in the future.

New distance measures for classifying X-ray astronomy data into stellar classes

The classification of the X-ray sources into classes (such as extragalactic sources, background stars, ...) is an essential task in astronomy. Typically, one of the classes corresponds to extragalactic radiation, whose photon emission behaviour is well characterized by a homogeneous Poisson process. We propose to use normalized versions of the Wasserstein and Zolotarev distances to quantify the deviation of the distribution of photon interarrival times from the exponential class. Our main motivation is the analysis of a massive dataset from X-ray astronomy obtained by the Chandra Orion Ultradeep Project (COUP). This project yielded a large catalog of 1616 X-ray cosmic sources in the Orion Nebula region, with their series of photon arrival times and associated energies. We consider the plug-in estimators of these metrics, determine their asymptotic distributions, and illustrate their finite-sample performance with a Monte Carlo study. We estimate these metrics for each COUP source from three different classes. We conclude that our proposal provides a striking amount of information on the nature of the photon emitting sources. Further, these variables have the ability to identify X-ray sources wrongly catalogued before. As an appealing conclusion, we show that some sources, previously classified as extragalactic emissions, have a much higher probability of being young stars in Orion Nebula.

A true random number generator based on the photon arrival time registered in a coincidence window between two single-photon counting modules

True random number generators are essential components for communications to be confidentially secured. In this paper a new method is proposed to generate random sequences of numbers based on the difference of the arrival times of photons detected in a coincidence window between two single-photon counting modules.

Detector random time delay compensation method for X-ray pulsar observation

For recent few decades, the observation for X-ray emission of pulsar is very popular. Among the multiple experiments, to construct the signal profile of X-ray pulsar is a significant one. During the observation, the X-ray signal photons of pulsars need to be collected by sensors in space. At present, the applied silicon-based X-ray sensors include Silicon Drift Detector (SDD), Swept Charge Device (SCD) and so on. Owing to the X-ray photons reach different places on the sensor at a time, the photon arrival time these detectors record always includes random time delay. This kind of delay will decrease the accuracy of detected signal profile. Therefore, studying how to compensate this delay is very necessary. In this paper, the principle how sensor time delay affects the signal profile is presented. Furthermore, based on the deconvolution calculation, a time delay compensation method is proposed. According to simulation and the hardware-in-loop experiments, it can be proven that the method can eliminate the effects of profile time delay and profile distortion. The method can support astro observation in space and X-ray pulsar-based navigation.

A Millisecond Pulsar Discovery in a Survey of Unidentified Fermi γ-Ray Sources with LOFAR

Abstract Using LOFAR, we have performed a very-low-frequency (115−155 MHz) radio survey for millisecond pulsars (MSPs). The survey targeted 52 unidentified Fermi γ-ray sources. Employing a combination of coherent and incoherent dedispersion, we have mitigated the dispersive effects of the interstellar medium while maintaining sensitivity to fast-spinning pulsars. Toward 3FGL J1553.1+5437 we have found PSR J1552+5437, the first MSP to be discovered (through its pulsations) at a radio frequency &lt;200 MHz. PSR J1552+5437 is an isolated MSP with a 2.43 ms spin period and a dispersion measure of 22.9 pc cm−3. The pulsar has a very steep radio spectral index ( 2.8 ± 0.4). We obtain a phase-connected timing solution combining the 0.74 years of radio observations with γ-ray photon arrival times covering 7.5 years of Fermi observations. We find that the radio and γ-ray pulse profiles of PSR J1552+5437 appear to be nearly aligned. The very steep spectrum of PSR J1552+5437, along with other recent discoveries, hints at a population of radio MSPs that have been missed in surveys using higher observing frequencies. Detecting such steep spectrum sources is important for mapping the population of MSPs down to the shortest spin periods, understanding their emission in comparison to slow pulsars, and quantifying the prospects for future surveys with low-frequency radio telescopes like SKA-Low and its precursors.