Photon Detection Research Articles

Copper Encapsulated Ultra-Thin NbN Films and Damascene Structures on 300 mm Si Wafers

In this report, the development of reactively sputtered ultra-thin niobium nitride (NbN) films and their fabrication into patterned structures using 193 nm optical lithography on 300 mm scale is presented. The target composition of NbN film with Cu encapsulation showed a critical temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_c</i> ) of ∼9.5 K (at a thickness of ∼ 50 nm), with < 7% across-wafer variation in room temperature sheet resistance. Using this film composition, damascene structures of 3-20 nm NbN film thickness and 100 - 3000 nm width, encapsulated by copper, were fabricated on 300 mm Si wafer. These were measured to determine the dependence of the critical current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> ) as a function of film thickness. The variation of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_c</i> of copper encapsulated NbN as a function of Nb to N ratio, and position on the wafer is reported, along with the variation of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_c</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> as a function of linewidth. These results underscore the potential of ultra-thin NbN films deposited over a large area, for a broad range of applications in quantum computing, photon detection and superconducting circuits operating at GHz frequencies.

Coherent Quantum Network of Superconducting Qubits as a Highly Sensitive Detector of Microwave Photons for Searching of Galactic Axions

We propose a novel approach to detect a low power microwave signal with a frequency of the order of several GHz based on a coherent collective response of quantum states occurring in a superconducting qubits network (SQN). An SQN composes of a large number of superconducting qubits embedded in a low-dissipative superconducting resonator. Our theory predicts that an SQN interacting with the off-resonance microwave radiation, demonstrates the collective alternating current Stark effect that can be measured even in the limit of single photon counting. A design of the layout of three terminals SQN detectors containing 10 flux qubits weakly coupled to a low-dissipative R-resonator and T-transmission line was developed. The samples were fabricated by Al-based technology with Nb resonator. The SQN detector was tested in terms of microwave measurements of scattering parameters and two-tone spectroscopy. A substantial shift of the frequency position of the transmission coefficient drop induced by a second tone pump signal was observed, and this effect clearly manifests a nonlinear multiphoton interaction between the second-tone microwave pump signal and an array of qubits.

Electromagnetic Properties of Aluminum-Based Bilayers for Kinetic Inductance Detectors

The complex conductivity of a superconducting thin film is related to the quasiparticle density, which depends on the physical temperature and can also be modified by external pair breaking with photons and phonons. This relationship forms the underlying operating principle of Kinetic Inductance Detectors (KIDs), where the detection threshold is governed by the superconducting energy gap. We investigate the electromagnetic properties of thin-film aluminum that is proximitized with either a normal metal layer of copper or a superconducting layer with a lower $T_C$, such as iridium, in order to extend the operating range of KIDs. Using the Usadel equations along with the Nam expressions for complex conductivity, we calculate the density of states and the complex conductivity of the resulting bilayers to understand the dependence of the pair breaking threshold, surface impedance, and intrinsic quality factor of superconducting bilayers on the relative film thicknesses. The calculations and analyses provide theoretical insights in designing aluminum-based bilayer kinetic inductance detectors for detection of microwave photons and athermal phonons at the frequencies well below the pair breaking threshold of a pure aluminum film.

Soft x-ray photoelectron momentum microscope for multimodal valence band stereography

The photoelectron momentum microscope (PMM) in operation at BL6U, an undulator-based soft x-ray beamline at the UVSOR Synchrotron Facility, offers a new approach for μm-scale momentum-resolved photoelectron spectroscopy (MRPES). A key feature of the PMM is that it can very effectively reduce radiation-induced damage by directly projecting a single photoelectron constant energy contour in reciprocal space with a radius of a few Å−1 or real space with a radius of a few 100 μm onto a two-dimensional detector. This approach was applied to three-dimensional valence band structure E(k) and E(r) measurements (“stereography”) as functions of photon energy (hν), its polarization (e), detection position (r), and temperature (T). In this study, we described some examples of possible measurement techniques using a soft x-ray PMM. We successfully applied this stereography technique to μm-scale MRPES to selectively visualize the single-domain band structure of twinned face-centered-cubic Ir thin films grown on Al2O3(0001) substrates. The photon energy dependence of the photoelectron intensity on the Au(111) surface state was measured in detail within the bulk Fermi surface. By changing the temperature of 1T-TaS2, we clarified the variations in the valence band dispersion associated with chiral charge-density-wave phase transitions. Finally, PMMs for valence band stereography with various electron analyzers were compared, and the advantages of each were discussed.

Thermal radiation effect in near infrared single photon detector

Thermal radiation effect in near infrared single photon detector

Manipulating solid-state spin concentration through charge transport

Solid-state defects are attractive platforms for quantum sensing and simulation, e.g., in exploring many-body physics and quantum hydrodynamics. However, many interesting properties can be revealed only upon changes in the density of defects, which instead is usually fixed in material systems. Increasing the interaction strength by creating denser defect ensembles also brings more decoherence. Ideally one would like to control the spin concentration at will while keeping fixed decoherence effects. Here, we show that by exploiting charge transport, we can take some steps in this direction, while at the same time characterizing charge transport and its capture by defects. By exploiting the cycling process of ionization and recombination of NV centers in diamond, we pump electrons from the valence band to the conduction band. These charges are then transported to modulate the spin concentration by changing the charge state of material defects. By developing a wide-field imaging setup integrated with a fast single photon detector array, we achieve a direct and efficient characterization of the charge redistribution process by measuring the complete spectrum of the spin bath with micrometer-scale spatial resolution. We demonstrate a two-fold concentration increase of the dominant spin defects while keeping the T2 of the NV center relatively unchanged, which also provides a potential experimental demonstration of the suppression of spin flip-flops via hyperfine interactions. Our work paves the way to studying many-body dynamics with temporally and spatially tunable interaction strengths in hybrid charge-spin systems.

Structure-function analysis suggests that the photoreceptor LITE-1 is a light-activated ion channel

Sensation of light is essential for all organisms. The eye-less nematode Caenorhabditis elegans detects UV and blue light to evoke escape behavior. The photosensor LITE-1 absorbs UV photons with an unusually high extinction coefficient, involving essential tryptophans. Here, we modeled the structure and dynamics of LITE-1 using AlphaFold2-multimer and molecular dynamics (MD) simulations and performed mutational and behavioral assays in C.elegans to characterize its function. LITE-1 resembles olfactory and gustatory receptors from insects, recently shown to be tetrameric ion channels. We identified residues required for channel gating, light absorption, and mechanisms of photo-oxidation, involving a likely binding site for the peroxiredoxin PRDX-2. Furthermore, we identified the binding pocket for a putative chromophore. Several residues lining this pocket have previously been established as essential for LITE-1 function. A newly identified critical cysteine pointing into the pocket represents a likely chromophore attachment site. We derived a model for how photon absorption, via a network of tryptophans and other aromatic amino acids, induces an excited state that is transferred to the chromophore. This evokes conformational changes in the protein, possibly leading to a state receptive to oxidation of cysteines and, jointly, to channel gating. Electrophysiological data support the idea that LITE-1 is a photon and H2O2-coincidence detector. Other proteins with similarity to LITE-1, specifically C.elegans GUR-3, likely use a similar mechanism for photon detection. Thus, a common protein fold and assembly, used for chemoreception in insects, possibly by binding of a particular compound, may have evolved into a light-activated ion channel.

The high voltage system of the novel MPGD-based photon detectors of COMPASS RICH-1 and its development towards a scalable High Voltage Power Supply System for MPGDs

The COMPASS RICH-1 detector has undergone a major upgrade in 2016 with the installation of four novel MPGD-based photon detectors. They consist of large-size hybrid MPGDs with multi-layer architecture composed of two layers of Thick-GEMs and bulk resistive MicroMegas. A dedicated high voltage power supply system, based on CAEN HV modules, has been built and put in operation: it controls more than 100 HV channels. The system is required to protect the detectors against errors by the operator, monitor voltages and currents at a 1 Hz rate and automatically react to detector misbehavior. It includes also a HV compensation system against environmental pressure and temperature variation to grant the detector stability. The operation of a MPGD based single photon detector poses challenging requirements to the high voltage power supply systems employed in terms of high-resolution diagnostic features and dynamic voltage control. Systems satisfying all the needed features are not commercially available; for this reason a novel single channel high voltage system matching the MPGD needs has been designed and realized. In this article the COMPASS RICH-1 MPGD HV system implementation is described as well as its performance in terms of stability of the novel MPGD-based photon detectors during the physics data taking at COMPASS. The design, implementation and performance of a novel HV power supply system based on DC to DC converters and controlled by a FPGA device is presented. The capabilities of the first prototype of the new single HV channel power supply are illustrated when operated with a MPGD based single photon detector during a test beam exercise. The preliminary result of the multi channel system are briefly discussed.

Demonstration of thermal limit mean transverse energy from cesium antimonide photocathodes

The mean transverse energy (MTE) of electrons emitted from cathodes is a critical parameter that determines the brightness of electron beams for applications, such as x-ray free electron lasers, particle colliders, and ultrafast electron scattering experiments. Achieving a MTE close to the thermal limit is a key step toward realizing the full potential of electron sources in these applications. Cesium antimonide (Cs3Sb) is a technologically important material with a long history of use in photon detection and electron sources. The smallest MTE of electrons photoemitted from Cs3Sb has always been appreciably greater than the thermal limit and was attributed to surface non-uniformities. In this work, we present comprehensive measurements of the photoemission electron energy spectra (PEES), quantum efficiency, and MTE from Cs3Sb in a wide photoexcitation energy range from 1.5 to 2.3 eV. Our PEES measurements demonstrate a notably low photoemission threshold of around 1.5 eV, which is in contrast with the previously perceived threshold of 1.8–2.0 eV. Moreover, we show that the MTE at this threshold of 1.5 eV nearly converges to the thermal limit at 300 K. At 1.8 eV, the MTE measured is 40 meV, which is comparable to the previously reported value. We conclude that this MTE value at 1.8 eV photon energy is not due to surface roughness effects as previously believed, but is a direct consequence of the excess energy.

Analysis of single photon detectors in differential phase shift quantum key distribution

Analysis of single photon detectors in differential phase shift quantum key distribution

Mixed simulation and verification of photon detection probability for single photon avalanche diode

Owing to the complex and expensive process of complementary metal oxide semiconductor (CMOS), it is time-consuming and laborious to improve the photon detection probability (PDP) of Single photon avalanche diodes (SPAD) by tape-out. Therefore, we need to optimize PDP according to simulations. In this paper, we proposed a mixed simulation method to simulate PDP curve. The method includes numerical simulation in Matlab and technology computer-aided design (TCAD) simulation in Silvaco. The former is used for electrical parameters simulations. Optical parameters are simulated by TCAD simulation. The above parameters are substituted into the PDP model to obtain the functional relationship between photon detection probability and wavelength. In the simulation and measurement curves, the peak positions are 560 nm and 520 nm, respectively. The corresponding amplitudes are 31.6% and 31.9%. In other words, final results show that the peak positions in the PDP curves of the simulation and measurement differ by only 40 nm. And the peak difference is only 0.3%. Consequently, the validity of the PDP model is verified.

Topotactic fabrication of transition metal dichalcogenide superconducting nanocircuits

Superconducting nanocircuits, which are usually fabricated from superconductor films, are the core of superconducting electronic devices. While emerging transition-metal dichalcogenide superconductors (TMDSCs) with exotic properties show promise for exploiting new superconducting mechanisms and applications, their environmental instability leads to a substantial challenge for the nondestructive preparation of TMDSC nanocircuits. Here, we report a universal strategy to fabricate TMDSC nanopatterns via a topotactic conversion method using prepatterned metals as precursors. Typically, robust NbSe2 meandering nanowires can be controllably manufactured on a wafer scale, by which a superconducting nanowire circuit is principally demonstrated toward potential single photon detection. Moreover, versatile superconducting nanocircuits, e.g., periodical circle/triangle hole arrays and spiral nanowires, can be prepared with selected TMD materials (NbS2, TiSe2, or MoTe2). This work provides a generic approach for fabricating nondestructive TMDSC nanocircuits with precise control, which paves the way for the application of TMDSCs in future electronics.

Geiger-Mode Operation 4H-SiC Recessed-Window Avalanche Photodiodes Fabricated by N Ion Implantation

In this work, a 4H-SiC n-i-p avalanche photodiode (APD) with n-layer formed by N ion implantation is demonstrated, in which recessed-window structure is used as termination for reducing electrical field crowding effect around the device edge. The APD with 20 μm diameter active region exhibits low dark current of ~5 pA, high gain of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> , zero-bias peak quantum efficiency of 53.8 % at 265 nm. Two-dimensional avalanche photocurrent mapping indicates that uniform gain is realized across the device central region while edge-located premature breakdown is effectively suppressed. Since there is no shading effect of top contact metal, close to 100% percent of fill factor is achieved in the multiplication region. The APD can operate in Geiger mode by using a passive quenching circuit. A room temperature single photon detection capability is obtained at 280 nm, when the dark count rate is ~ 28.8 Hz/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Wide dynamic range signal detection for underwater optical wireless communication using a PMT detector.

In the underwater optical wireless communication (UOWC) scenario, a photomultiplier tube (PMT) with higher sensitivity, lower noise, and a larger receiver area is employed as the photon detector to further extend the transmission distance. Due to the complex underwater environment, the high directionality of the light beam, and the vibration of a transceiver, the incident optical power usually spans a very wide dynamic range, and the PMT may operate in any one of the three regimes: pulse, transition, and waveform. While it is difficult to obtain the analytical characterization of the output electric signals across these regimes, this paper resorts to experimental measurements of the upsampled discrete samples within a training symbol duration. Among different statistical distribution fitting options, generalized extreme value (GEV) distribution is found to show excellent performance in fitting the probability density function (PDF) of either multiple samples or the superimposition of all samples within a symbol duration. Then joint sample distribution (JSD) based and superimposed sample distribution (SSD) based symbol detection methods are proposed by adopting the GEV distribution and log-likelihood ratio (LLR) testing criterion. The proposed methods are experimentally evaluated under different received signal optical powers, data rates, and sampling rates. They are shown to outperform the Poisson and Gaussian based maximum likelihood detection methods which are employed for the pulse regime and waveform regime respectively. Furthermore, the effectiveness of the proposed methods in alleviating strong ambient radiation is experimentally verified.

Performance evaluation of the 8-inch MCP-PMT for Jinping Neutrino Experiment

Jinping Neutrino Experiment plans to deploy a new type of 8-inch MCP-PMT with high photon detection efficiency for MeV-scale neutrino measurements. This work studies the performance of the MCP-PMTs, including the photon detection efficiency, the charge resolution of the single photoelectron, the transition time spread, single photoelectron response, rates of dark counts and after pulses. We find a long tail in the charge distribution, and combined with the high photon detection efficiency, the overall energy resolution sees substantial improvements. Those results will be provided as the inputs to detector simulation and design. Our results show that the new PMT satisfies all the requirements of the Jinping Neutrino Experiment.

Characterizing Low-Energy Charged Particles in the Magnetosphere with the LEM CubeSat Spectrometer Project: Detector Concept and Hardware Characterisation

An accurate flux measurement of low-energy charged particles trapped in the magnetosphere is necessary for space weather characterization and to study the coupling between the lithosphere and magnetosphere, which allows for the investigation of the correlations between seismic events and particle precipitation from Van Allen belts. In this work, the project of a CubeSat space spectrometer, the low-energy module (LEM), is shown. The detector will be able to perform an event-based measurement of the energy, arrival direction, and composition of low-energy charged particles down to 0.1 MeV. Moreover, thanks to a CdZnTe mini-calorimeter, the LEM spectrometer also allows for photon detection in the sub-MeV range, joining the quest for the investigation of the nature of gamma-ray bursts (GRBs) and terrestrial gamma-ray flashes (TGFs). The particle identification of the LEM relies on the ΔE−E technique performed by thin silicon detectors. This multipurpose spectrometer will fit within a 10 × 10 × 10 cm3 CubeSat frame, and it will be constructed as a joint project between the University of Trento, FBK, and INFN-TIFPA. To fulfil the size and mass requirements, an innovative approach, based on active particle collimation, was designed for the LEM; this avoids the heavy/bulky passive collimators of previous space detectors. In this paper, we will present the LEM geometry, its detection concept, the results from the developed GEANT4 simulation, and some characterisations of a candidate silicon detector for the instrument payload.

Simulation of the optical system in the GroundBIRD telescope.

GroundBIRD is a ground-based telescope for measuring the polarization of cosmic microwave background radiation, and it is soon to be operational at the Teide Observatory. The GroundBIRD telescope employs Mizuguchi-Dragone dual reflectors and 161 kinetic inductance detectors coupled with single polarization antennas as photon detectors. We present the results of our optical simulation on the pointing direction, stray light response, and influence of the blackbody radiation from the baffle. We also find that the power of the baffle radiation incident on the detectors is reduced by 99.95% when corrugated feed horns are coupled to the detectors.

Dark matter searches and energy accumulation and release in materials

Efforts to identify dark matter by detecting nuclear recoils produced by dark matter particles reveal low-energy backgrounds of unknown origin in different types of detectors. In many cases, energy accumulation and delayed burst-like releases of stored energy could provide an explanation. These dynamics follow Prigogine’s ideas on systems with energy flow and the general Self-Organized Criticality scenario. We compare these models with properties of excess backgrounds in cryogenic solid-state detectors, relaxation processes in glasses and crystals, our observations of delayed luminescence in NaI(Tl), and make predictions for more phenomena present in these systems and in superconducting photon detectors and qubits. Experiments to create accurate phenomenological models are needed.

Fast Wide‐Field Quantum Sensor Based on Solid‐State Spins Integrated with a SPAD Array

AbstractAchieving fast, sensitive, and parallel measurement of a large number of quantum particles is an essential task in building large‐scale quantum platforms for different quantum information processing applications such as sensing, computation, simulation, and communication. Current quantum platforms in experimental atomic and optical physics based on CMOS sensors and charged coupled device cameras are limited by either low sensitivity or slow operational speed. Here an array of single‐photon avalanche diodes is integrated with solid‐state spin defects in diamond to build a fast wide‐field quantum sensor, achieving a frame rate up to 100 kHz. The design of the experimental setup to perform spatially resolved imaging of quantum systems is presented. A few exemplary applications, including sensing DC and AC magnetic fields, temperature, strain, local spin density, and charge dynamics, are experimentally demonstrated using a nitrogen‐vacancy ensemble diamond sample. The developed photon detection array is broadly applicable to other platforms such as atom arrays trapped in optical tweezers, optical lattices, donors in silicon, and rare earth ions in solids.

Flexible gamma photon detector based on plastic scintillation optical fibers

Detecting small-volume tumoral tissues is a central goal within the nuclear imaging disciplines. Early detection of such small tumors may contribute to the suitable treatment of diverse cancers or the identification of metastatic nodules. Furthermore, the application of feasible radionuclides could contribute to the identification of such tumoral tissues. However, characterizing such radiation sources requires detectors that must adapt their forms to obtain a precise identification of the tumor location. This study's primary outcome was a suitable flexible gamma-ray detector capable of measuring the radiation emitted from small-volumetrics. The detector implements scintillating plastic fibers integrated into an avalanche photodiode (APD), which constitute the main elements of the proposed detection system. The proposed system was characterized in terms of the electrical response, as well as the detection characteristics of the radionuclide source. The optical efficiency of the plastic optical fibers and the photons detection settings of the APD served to develop a prototype of a gamma-probe system. This detection device can be specifically oriented to provide a trustable gamma detector of small-volume radiation sources with the corresponding corrections for the scattering and the compensation for attenuation and background factors. The system design included the corresponding electrical conditioning circuit and the signal processing software. This software detected and discriminated the voltage level to characterize the photon energy. A preclinical study represented the distance and angular sensibilities of the proposed detector to the 99m Tc-RGD (pegylated arginine-glycine-aspartic acid) radiopharmaceutical in a murine model.