Single-photon Spectra Research Articles

Performance of H2GCROC3, the readout ASIC of SiPMs for the back hadronic sections of the CMS High Granularity Calorimeter

H2GCROC is a 130 nm CMOS ASIC designed to read out the SiPMs coupled to the scintillating tiles of the back hadronic sections of CMS HGCAL. Each of its 72 channels comprises a current conveyor, a high-gain preamplifier, a shaper, an ADC for energy measurement, and two discriminators linked to TDCs for capturing time-of-arrival and time-over-threshold information, respectively. This work presents the ASIC architecture and its characterization in the laboratory and test beam environments. The results demonstrate its adaptability in calibration, proving its capability to measure the SiPM single-photon spectrum and MIP's energy with high resolution under the expected radiation conditions during the entire operation of HGCAL.

State carving in a chirally-coupled atom-nanophotonic cavity

Coherent quantum control of multiqubit systems represents one of the challenging tasks in quantum science and quantum technology. Here we theoretically investigate the reflectivity spectrum in an atom-nanophotonic cavity with collective nonreciprocal couplings. In the strong-coupling regime with a high cooperativity, we theoretically predict distinct on-resonance spectral dips owing to destructive interferences of chiral couplings. Due to the well-separated multiple dips in the spectrum, a contrasted reflectivity suggests a new control knob over the desired entangled state preparation in the basis of coupled and uncoupled states from the atoms’ internal hyperfine ground states. We propose to utilize such atom-nanophotonic cavity to quantum engineer the atomic internal states via photon-mediated dipole–dipole interactions in the coupled state and the chirality of decay channels, where the atomic Bell state and W states for arbitrary number of atoms can be tailored and heralded by state carving in the single-photon reflection spectrum. Our results pave the way toward quantum engineering of multiqubit states and offer new opportunities for coherent and scalable multipartite entanglement transport in atoms coupled to nanophotonic devices.

Amplitude Measurements With SiPM and ASIC (Citiroc 1A) Front-End Electronics

The use of Application Specific Integrated Circuits (ASICs) in nuclear physics instrumentation is drastically increasing, thanks to the possibility of incorporating a large number of acquisition channels in compact devices. In this paper, we describe a SiPM-based application with CAEN Front-End Readout System [1] based on Citiroc 1A chip from Weeroc [2]. Besides the use of this chip for well known single photon spectra and event counting, this paper exploits the possibility to acquire energy spectra directly from scintillators, paired with SiPM, through peak-and-hold readout. In particular, good energy resolutions have been achieved even with slow scintillators, like LYSO, CsI(Tl), and BGO, which have 40 ns, 1000 ns, and 300 ns of light decay time, respectively. These values are of the same order of magnitude of the shaping time of the Citiroc 1A chip (maximum value of 87.5 ns) in the case of LYSO, and higher in the case of CsI(Tl) and BGO. Several measurements have been performed using multiple radioactive γ sources and the resulting energy spectra demonstrate a resolution compatible with that found in literature [4] [5] [6] [7], as well as with an alternative acquisition system based on a digitizer that implements an algorithm of Charge Integration in the FPGA [8].

Tunable phononic coupling in excitonic quantum emitters.

Engineering the coupling between fundamental quantum excitations is at the heart of quantum science and technologies. An outstanding case is the creation of quantum light sources in which coupling between single photons and phonons can be controlled and harnessed to enable quantum information transduction. Here we report the deterministic creation of quantum emitters featuring highly tunable coupling between excitons and phonons. The quantum emitters are formed in strain-induced quantum dots created in homobilayer WSe2. The colocalization of quantum-confined interlayer excitons and terahertz interlayer breathing-mode phonons, which directly modulates the exciton energy, leads to a uniquely strong phonon coupling to single-photon emission, with a Huang-Rhys factor reaching up to 6.3. The single-photon spectrum of interlayer exciton emission features a single-photon purity >83% and multiple phonon replicas, each heralding the creation of a phonon Fock state in the quantum emitter. Due to the vertical dipole moment of the interlayer exciton, the phonon-photon interaction is electrically tunable to be higher than the exciton and phonon decoherence rate, and hence promises to reach the strong-coupling regime. Our result demonstrates a solid-state quantum excitonic-optomechanical system at the atomic interface of the WSe2 bilayer that emits flying photonic qubits coupled with stationary phonons, which could be exploited for quantum transduction and interconnection.

Quantum interferometric spectroscopy of a biexciton

Fourier transform spectroscopy with classical interferometry corresponds to the measurement of a single-photon intensity spectrum from the viewpoint of the particle nature of light. In contrast, the Fourier transform of two-photon quantum interference patterns provides the intensity spectrum of the two photons as a function of the sum- or difference frequency of the constituent photons. This unique feature of quantum interferometric spectroscopy offers a different type of spectral information from the classical measurement and may prove useful for nonlinear spectroscopy with two-photon emission. Here, we report the experimental demonstration of two-photon quantum interference of biphotons emitted via biexcitons in the semiconductor CuCl. Besides applying Fourier transform to quantum interference patterns, we reconstruct the intensity spectrum of the biexciton luminescence in the two-photon sum- or difference frequency. We discuss the connection between the reconstructed spectra and exciton states in CuCl as well as the capability of quantum interferometry in solid-state spectroscopy.

Two-Photon Excitation Spectra of Various Fluorescent Proteins within a Broad Excitation Range.

Two-photon excitation fluorescence laser-scanning microscopy is the preferred method for studying dynamic processes in living organ models or even in living organisms. Thanks to near-infrared and infrared excitation, it is possible to penetrate deep into the tissue, reaching areas of interest relevant to life sciences and biomedicine. In those imaging experiments, two-photon excitation spectra are needed to select the optimal laser wavelength to excite as many fluorophores as possible simultaneously in the sample under consideration. The more fluorophores that can be excited, and the more cell populations that can be studied, the better access to their arrangement and interaction can be reached in complex systems such as immunological organs. However, for many fluorophores, the two-photon excitation properties are poorly predicted from the single-photon spectra and are not yet available, in the literature or databases. Here, we present the broad excitation range (760 nm to 1300 nm) of photon-flux-normalized two-photon spectra of several fluorescent proteins in their cellular environment. This includes the following fluorescent proteins spanning from the cyan to the infrared part of the spectrum: mCerulean3, mTurquoise2, mT-Sapphire, Clover, mKusabiraOrange2, mOrange2, LSS-mOrange, mRuby2, mBeRFP, mCardinal, iRFP670, NirFP, and iRFP720.

Efficient high-energy photon production in the supercritical QED regime

When dense high-energy lepton bunches collide, the beam particles can experience rest-frame electromagnetic fields which greatly exceed the QED critical one. Here it is demonstrated that beamstrahlung efficiently converts lepton energy to high-energy photons in this so-called supercritical QED regime, as the single-photon emission spectrum exhibits a pronounced peak close to the initial lepton energy. It is also shown that the observation of this high-energy peak in the photon spectrum requires one to mitigate multiple photon emissions during the interaction. Otherwise, the photon recoil induces strong correlations between subsequent emissions which soften the photon spectrum and suppress the peak. The high-energy peak in the photon spectrum constitutes a unique observable of photon emission in the supercritical QED regime and provides decisive advantages for the realization of an efficient multi-TeV laserless gamma-gamma collider based on electron-electron collisions.

Excitonic two-photon absorption in monolayer transition metal dichalcogenides: Impact of screening and trigonal warping

Two-photon spectroscopy is an important tool for detection of states that are dark in single-photon spectra. We calculate two-photon absorption spectra for monolayer transition-metal dichalcogenides including excitonic effects based on a Bethe-Salpeter equation approach. Both spin-orbit coupling and trigonal warping are included. Our results reveal that otherwise dark $p$ states dominate the two-photon response. However, weakly allowed two-photon transitions coinciding with single-photon $s$-state resonances appear due to trigonal warping. The angular momentum character of participating excitons is analyzed and we study the sensitivity to screening by dielectric surroundings and discuss the free-carrier limit. Biexciton contributions to the high-energy two-photon response are estimated using a simplified Wannier approach. Finally, a brief comparison with recent experiments is given.

A novel high dynamic-range SiPM for scintillator-based hadronic calorimetry

The Analog Hadronic Calorimeter (AHCAL) is one option of highly granular calorimeters optimised with the Particle Flow Algorithm (PFA) and considered for experiments at future lepton colliders. It consists of dense steel plates as absorber interleaved with plastic scintillator tiles, individually read out by Silicon Photomultipliers (SiPMs). A novel SiPM developed by the Novel Device Laboratory (NDL) with an active area of 1 mm2 and a pixel pitch of 12.5 micron[NDL-SiPM-12.5] has been mainly investigated. The characterisation studies include single photon calibration, dynamic range and performance of crosstalk as well as Minimum Ionising Particle (MIP) detection efficiency of a detector unit. Combined tests with a dedicated ASIC (SPIROC2E) for multi-channel SiPMs show that single photon spectra can be obtained, given the relatively small SiPM gain (∼2 × 105). The linearity of the SiPMs in response to incident photons of less than 10,000 (500 MIPs) is within 5% from measurements. Meanwhile, the dark count rate (DCR) is around 2×10-3 Hz at a threshold 0.5 MIP (10 p.e.) and the MIP detection efficiency of a detector unit can be near 95% from the MIP spectrum. These studies indicate the NDL-SiPM-12.5 can be a photosensor candidate for the future scintillator-based hadronic calorimeters.

Spectral characterization of SPDC-based single-photon sources for quantum key distribution

In our laboratory, we employ two biphoton sources for quantum key distribution. The first is based on cw parametric down-conversion of photons at 404 nm in PPKTP waveguide chips, while the second is based on the pulsed parametric down-conversion of 775 nm photons in PPLN waveguides. The spectral characterization is important for the determination of certain side-channel attacks. A Hong-Ou-Mandel experiment employing the first photon source revealed a complex structure of the common Hong-Ou-Mandel dip. By measuring the spectra of the single photons at 808 nm, we were able to associate these structures to the superposition of different transverse modes of the pump photons in our waveguide chips. The pulsed source was characterized by means of single-photon spectra measured by a sensitive spectrum analyzer as well as dispersion-based measurements. Finally, we also describe Hong-Ou-Mandel experiments using the photons from the second source.

Effect of dipole–dipole interactions on the one-photon and two-photon photoluminescence in an ensemble of quantum dots doped in a polymer matrix

We have developed a theory for the one-photon and two-photon fluorescence of a nanohybrid composite comprised of an ensemble of quantum dots encased in a matrix of polymer. The quantum dots are comprised of four-level quantum emitters encased within a coating of dielectric material. The fluorescence of the quantum dot system is calculated using the master equation method where dipole–dipole interaction (DDI) coupling is present. The application of a probe field to the nanohybrid composite material in conjunction with the DDI between the quantum dots generates an enhancement of both the single-photon and double-photon fluorescence, and in certain conditions causes spectrum splitting. With a strong DDI field, the two-photon emission spectrum experiences slight quenching and shifts from one peak to two peaks. The dressed states are a result of strong coupling effects between the DDI field and the quantum dots. We generated an analytical expression for the fluorescence spectrum and intensity, and quantitatively compared it to experimental data in which ZnSe quantum dots were embedded within a P3HT polymer film, with our theory strongly correlating with the experiment. We also quantitatively compared our theory with experimental data that demonstrated the single-photon emission spectrum of colloidal quantum dots comprised of a CdZnS/ZnS gradient structure in varying probe field strengths. We found that our theory predicted the spectrum peak splitting that the experiment produced.

Controlling Exciton-Phonon Interactions via Electromagnetically Induced Transparency.

Highly excited Rydberg states of excitons in Cu_{2}O semiconductors provide a promising approach to explore and control strong particle interactions in a solid-state environment. A major obstacle has been the substantial absorption background that stems from exciton-phonon coupling and lies under the Rydberg excitation spectrum, weakening the effects of exciton interactions. Here, we demonstrate that two-photon excitation of Rydberg excitons under conditions of electromagnetically induced transparency (EIT) can be used to control this background. Based on a microscopic theory that describes the known single-photon absorption spectrum, we analyze the conditions under which two-photon EIT permits separating the optical Rydberg excitation from the phonon-induced absorption background, and even suppressing it entir7ely. Our findings thereby pave the way for the exploitation of Rydberg blockade with Cu_{2}O excitons in nonlinear optics and other applications.

Analysis of the performance of photon detection methods using silicon photomultiplier in the application with high throughput requirements

Abstract An analysis and comparison of the performance of photon detection methods using a silicon photomultiplier (SiPM) in applications which require fast timings is presented. The front-end circuit enables measurement of the amplitude, charge, width of the pulse from the SiPM (time over threshold) and counting of events. The system was tested by generating light of different intensities where signals tend to pile-up. The signals generated by various numbers of photons are well separated on the single photon spectra. All methods have strong linearity parameters. The amplitude and charge methods are more accurate, have higher r-squared values, lower prediction intervals and higher sensitivity. On the other hand they require a more complicated readout system. The event’s counting and ToT methods have weaker parameters; however the advantage is simpler readout.

Lightning black holes as unidentified TeV sources

Imaging Atmospheric Cherenkov Telescopes have revealed more than 100 TeV sources along the Galactic Plane, around 45% of them remain unidentified. However, radio observations revealed that dense molecular clumps are associated with 67% of 18 unidentified TeV sources. In this paper, we propose that an electron-positron magnetospheric accelerator emits detectable TeV gamma-rays when a rapidly rotating black hole enters a gaseous cloud. Since the general-relativistic effect plays an essential role in this magnetospheric lepton accelerator scenario, the emissions take place in the direct vicinity of the event horizon, resulting in a point-like gamma-ray image. We demonstrate that their gamma-ray spectra have two peaks around 0.1 GeV and 0.1 TeV and that the accelerators become most luminous when the mass accretion rate becomes about 0.01% of the Eddington accretion rate. We compare the results with alternative scenarios such as the cosmic-ray hadron scenario, which predicts an extended morphology of the gamma-ray image with a single power-law photon spectrum from GeV to 100 TeV.

Generation and Coherent Control of Pulsed Quantum Frequency Combs.

We present a method for the generation and coherent manipulation of pulsed quantum frequency combs. Until now, methods of preparing high-dimensional states on-chip in a practical way have remained elusive due to the increasing complexity of the quantum circuitry needed to prepare and process such states. Here, we outline how high-dimensional, frequency-bin entangled, two-photon states can be generated at a stable, high generation rate by using a nested-cavity, actively mode-locked excitation of a nonlinear micro-cavity. This technique is used to produce pulsed quantum frequency combs. Moreover, we present how the quantum states can be coherently manipulated using standard telecommunications components such as programmable filters and electro-optic modulators. In particular, we show in detail how to accomplish state characterization measurements such as density matrix reconstruction, coincidence detection, and single photon spectrum determination. The presented methods form an accessible, reconfigurable, and scalable foundation for complex high-dimensional state preparation and manipulation protocols in the frequency domain.

Controlling single-photon transport in an optical waveguide coupled to an optomechanical cavity with a Λ-type three-level atom

We theoretically study the single-photon transport along a one-dimensional optical waveguide coupled to an optomechanical cavity containing a Λ-type three-level atom. Our numerical results show that the transmission spectra of the incident photon can be well controlled by such a hybrid atom-optomechanical system. The effects of the optomechanical coupling strength, the classical laser beam applied to the atom, atom-cavity detuning, and atomic dissipation on the single-photon transport properties are analyzed. It is of particular interest that an analogous double electromagnetically induced transparency emerges in the single-photon transmission spectra.

Photon-flux determination by the Poisson-fitting technique with quenching corrections

Single- and multi-photon spectra of pulsed γ-ray beams produced at 17, 34, and 40 MeV in the laser Compton scattering were measured with an 8” × 12” NaI(Tl) detector. By using the experimental single-photon spectra as the probability function of generating random numbers, response functions of the NaI(Tl) detector to j-fold photons (j = 2, 3, 4 ...) were constructed. The least-square fits to the experimental multi-photon spectra by the Poisson distribution consisting of the response functions were made. The multi-photon spectra measured at 17 and 34 MeV follow the Poisson distribution. A quenching phenomenon of multi-photon spectra was observed for 40 MeV γ-rays as a result of the saturation at the photomultiplier tube of the NaI(Tl) detector. The original Poisson distributions were restored from the quenched spectra using a saturation curve in the form of y=a⋅xη with η=e−bx. We discuss the accuracy of photon-flux determination.

Controllable single-photon transport in an optical waveguide coupled to an optomechanical cavity with a V-type three-level atom

We theoretically study the single-photon transport along a one-dimensional optical waveguide coupled to an optomechanical cavity containing a Lambda-type three-level atom. Our numerical results show that the transmission spectra of the incident photon can be well controlled by such a hybrid atom-optomechanical system. The effects of the optomechanical coupling strength, the classical laser beam applied to the atom, atom-cavity detuning, and atomic dissipation on the single-photon transport properties are analyzed. It is of particular interest that an analogous double electromagnetically induced transparency emerges in the single-photon transmission spectra.

Conformation of protonated glutamic acid at room and cryogenic temperatures.

Recognition properties of biologically relevant molecules depend on their conformation. Herein, the conformation of protonated glutamic acid (H+Glu) isolated in quadruple ion traps is characterized by vibrational spectroscopy at room and cryogenic temperatures and dispersion-corrected density functional theory calculations at the B3LYP-D3/aug-cc-pVTZ level. The infrared multiple photon dissociation (IRMPD) spectrum recorded in the fingerprint range at room temperature using an IR free electron laser is attributed to the two most stable and nearly isoenergetic conformations (1-cc and 2-cc) with roughly equal population (ΔG298 = 0.0 kJ mol-1). Both have bridging C[double bond, length as m-dash]O(HNH)+O[double bond, length as m-dash]C ionic H-bonds of rather different strengths but cannot be distinguished by their similar IRMPD spectra. In contrast, the higher-resolution single-photon IRPD spectrum of H2-tagged H+Glu recorded in the conformation-sensitive X-H stretch range in a trap held at 10 K distinguishes both conformers. At low temperature, 1-cc is roughly twice more abundant than 2-cc, in line with its slightly lower calculated energy (ΔE0 = 0.5 kJ mol-1). This example illustrates the importance of cryogenic cooling, single-photon absorption conditions, and the consideration of the X-H stretch range for the identification of biomolecular conformations involving hydrogen bonds.

Controllable single-photon transport in a one-dimensional coupled-resonator waveguide coupled to two nanocavities interacting with atoms

We investigate controllable single-photon transport in a one-dimensional coupled-resonator waveguide coupled to two nanocavities interacting with atoms. The reflection and transmission coefficients for a single photon propagating in such a system are deduced by using the discrete coordinates approach. The resonator–nanocavity coupling strength, atom–nanocavity coupling coefficient, and the detuning between the incident photon and the atom, respectively, which affect the transport properties of the single photon, are analyzed. It is found that some useful information, such as the atom–nanocavity coupling strength, can be extracted from the single-photon transmission spectrum under proper parameter settings. We also study how the coupling between two nanocavities affects the single-photon transmission property.