Single Photon Research Articles

Dietary Caffeine and Brain Dopaminergic Function in Parkinson Disease.

This study was undertaken to investigate the effects of dietary caffeine intake on striatal dopamine function and clinical symptoms in Parkinson disease in a cross-sectional and longitudinal setting. One hundred sixty-three early Parkinson disease patients and 40 healthy controls were investigated with [123I]FP-CIT single photon emission computed tomography, and striatal dopamine transporter binding was evaluated in association with the level of daily coffee consumption and clinical measures. After a median interval of 6.1 years, 44 patients with various caffeine consumption levels underwent clinical and imaging reexamination including blood caffeine metabolite profiling. Unmedicated early Parkinson disease patients with high coffee consumption had 8.3 to 15.4% lower dopamine transporter binding in all studied striatal regions than low consumers, after accounting for age, sex, and motor symptom severity. Higher caffeine consumption was further associated with a progressive decline in striatal binding over time. No significant effects of caffeine on motor function were observed. Blood analyses demonstrated a positive correlation between caffeine metabolites after recent caffeine intake and dopamine transporter binding in the ipsilateral putamen. Chronic caffeine intake prompts compensatory and cumulative dopamine transporter downregulation, consistent with caffeine's reported risk reduction in Parkinson disease. However, this decline does not manifest in symptom changes. Transiently increased dopamine transporter binding after recent caffeine intake has implications for dopaminergic imaging guidelines. ANN NEUROL 2024.

Creation of memory-memory entanglement in a metropolitan quantum network.

Towards realizing the future quantum internet1,2, a pivotal milestone entails the transition from two-node proof-of-principle experiments conducted in laboratories to comprehensive multi-node set-ups on large scales. Here we report the creation of memory-memory entanglement in a multi-node quantum network over a metropolitan area. We use three independent memory nodes, each of which is equipped with an atomic ensemble quantum memory3 that has telecom conversion, together with a photonic server where detection of a single photon heralds the success of entanglement generation. The memory nodes are maximally separated apart for 12.5 kilometres. We actively stabilize the phase variance owing to fibre links and control lasers. We demonstrate concurrent entanglement generation between any two memory nodes. The memory lifetime is longer than the round-trip communication time. Our work provides a metropolitan-scale testbed for the evaluation and exploration of multi-node quantum network protocols and starts a stage of quantum internet research.

Comparison of three diagnostic strategies for suspicion of pulmonary embolism: planar ventilation-perfusion scan (V/Q), CT pulmonary angiography (CTPA) and single photon emission CT ventilation-perfusion scan (SPECT V/Q): a protocol of a randomised controlled trial

IntroductionPulmonary embolism (PE) is a challenge to diagnose and when missed, exposes patients to potentially fatal recurrent events. Beyond CT pulmonary angiography (CTPA) and planar ventilation/perfusion (V/Q) scan, single photon...

Fermion self-energy and damping rate in a hot magnetized plasma

We derive a general expression for the fermion self-energy in a hot magnetized plasma by using the Landau-level representation. In the one-loop approximation, the Dirac structure of the self-energy is characterized by five different functions that depend on the Landau-level index n and the longitudinal momentum pz. We derive general expressions for all five functions and obtain closed-form expressions for their imaginary parts. The latter receive contributions from three types of on shell processes, which are interpreted in terms of Landau-level transitions, accompanied by a single photon (gluon) emission or absorption. By making use of the imaginary parts of the self-energy functions, we also derive the Landau-level dependent fermion damping rates Γn(pz) and study them numerically in a wide range of model parameters. We also demonstrate that the two-spin degeneracy of the Landau levels is lifted by the one-loop self-energy corrections. While the spin splitting of the damping rates is small, it may be important for some spin and chiral effects. We argue that the general method and the numerical results for the rates can have interesting applications in heavy-ion physics, astrophysics, and cosmology, where strongly magnetized QED or QCD plasmas are ubiquitous. Published by the American Physical Society 2024

On-demand quantum light sources for underwater communications

Quantum communication has been at the forefront of modern research for decades, however it is severely hampered in underwater applications, where the properties of water absorb nearly all useful optical wavelengths and prevent them from propagating more than, in most cases, a few metres. This research reports on-demand quantum light sources, suitable for underwater optical communication. The single photon emitters, which can be engineered using an electron beam, are based on impurities in hexagonal boron nitride. They have a zero phonon line at ∼436 nm, near the minimum value of water absorption and are shown to suffer negligible transmission and purity loss when travelling through water channels. These emitters are also shown to possess exceptional underwater transmission properties compared to emitters at other optical wavelengths and are utilised in a completely secure quantum key distribution experiment with rates of kbits s−1.

Cavity-enhanced photon indistinguishability at room temperature and telecom wavelengths

Indistinguishable single photons in the telecom-bandwidth of optical fibers are indispensable for long-distance quantum communication. Solid-state single photon emitters have achieved excellent performance in key benchmarks, however, the demonstration of indistinguishability at room-temperature remains a major challenge. Here, we report room-temperature photon indistinguishability at telecom wavelengths from individual nanotube defects in a fiber-based microcavity operated in the regime of incoherent good cavity-coupling. The efficiency of the coupled system outperforms spectral or temporal filtering, and the photon indistinguishability is increased by more than two orders of magnitude compared to the free-space limit. Our results highlight a promising strategy to attain optimized non-classical light sources.

Spectroscopy Detection and Imaging System Based on Line Array Single Photon Detectors

Abstract. Single-photon detectors, with their exceptional sensitivity, provide a reliable means for single-photon-level detection, demonstrating significant advantages in detecting weak signals in complex environments compared to traditional detectors. With the continuous advancement in semiconductor manufacturing technology, single-photon detectors based on linear array configurations have emerged and rapidly developed. This study utilizes a linear array single-photon detector in free-running mode combined with a scanning mechanism to design and implement a spectral detection and imaging system. Through the spectral scanning unit, this system successfully achieves precise spectral detection in the 890 nm to 1710 nm range, with a spectral resolution better than 2 nm. Utilizing the imaging scanning unit, the system effectively performs target spectral imaging under single and multiple wavelength conditions at 1064 nm, 1310 nm, and 1520 nm. By optimizing algorithms for data processing, the system can achieve rapid and accurate spectral detection and imaging even under low-light conditions where the average photon count per pixel is less than 3. The results of this study are expected to provide strong technical support for the application of spectral imaging technology in the field of high-speed detection and imaging.

Fluorescence lifetime of plant leaves with sub-nanosecond resolution

Abstract The study aimed to develop a measurement apparatus for in vivo chlorophyll-a (Chl-a) fluorescence decay measurements of plants by means of Time Correlated Single Photon Counting (TCSPC). In this approach, sub-nanosecond laser pulses with a repetition rate of 10 MHz are applied to excite the sample, followed by the analysis of arrival times of the emitted fluorescence photons. Photon statistics are generated by iteratively fitting the sum of 2 exponential functions. The tool was tested on both plastid and in vivo leaf samples of Savoy cabbage (Brassica oleracea var. sabauda) with 3-4 subsequent leaves giving a complete sample coverage starting from the outermost. The Chl-a fluorescence lifetime exhibited a gradual increase in both the isolated plastid suspensions and the in vivo leaf samples towards the innermost leaf layers explained by an increase of natural absence of light (etiolation syndrome). Furthermore, cadmium stress and iron deficiency were investigated on treated sugar beet (Beta vulgaris) samples in vivo using TCSPS measurements. The reduced fluorescence quenching resulted in an increased fluorescence lifetime. Finally, a long-term (10 week) testing of the setup was carried out on Chl-retaining resurrection Haberlea rhodopensis plants protecting themselves by an elevated non-photochemical quenching yielding a decrease of fluorescence lifetime during their desiccation.

Phase I Trial of SPECT-Guided Liver-Directed Radiotherapy for Patients with Low Functional Liver Volume.

Traditional constraints specify that 700 cc of liver should be spared a hepatotoxic dose when delivering liver-directed radiotherapy to reduce the risk of inducing liver failure. We investigated the role of single photon emission computed tomography (SPECT) to identify and preferentially avoid functional liver during liver-directed radiation treatment planning in patients with preserved liver function but limited functional liver volume after receiving prior hepatotoxic chemotherapy or surgical resection. This phase I trial with a 3 + 3 design evaluated the safety of liver-directed radiotherapy using escalating functional liver radiation dose constraints in patients with liver metastases. Dose limiting toxicities (DLTs) were assessed 6-8 weeks and 6 months after completing radiotherapy. All twelve patients had colorectal liver metastases and received prior hepatotoxic chemotherapy. Eight patients underwent prior liver resection. Median computed tomography (CT) anatomical non-tumor liver volume was 1,584 cc (range 764-2,699 cc). Median SPECT functional liver volume was 1,117 cc (range 570-1,928cc). Median non-target CT and SPECT liver volumes below the volumetric dose constraint were 997 cc (range 544-1,576 cc) and 684 cc (range 429-1,244 cc), respectively. The prescription dose was 67.5-75 Gy in 15 fractions or 75-100 Gy in 25 fractions. No DLTs were observed during follow-up. One-year in-field control was 57%. One-year overall survival was 73%. Liver-directed radiotherapy can be safely delivered to high doses when incorporating functional SPECT into the radiation treatment planning process which may enable sparing of lower volumes of liver than traditionally accepted in patients with preserved liver function. NCT02626312.

Annealing process and temperature effects on silicon-vacancy and germanium-vacancy centers in CVD grown polycrystalline diamond

The annealing treatment plays a crucial role in tailoring the properties of synthetic diamond materials, especially those doped with various elements in order to form specific color centers like nitrogen-vacancy (NV), silicon-vacancy (Si-V), germanium-vacancy (Ge-V), etc. This study delves into the annealing of 175 μm-thick Ge-doped polycrystalline diamond (PCD) films grown by microwave plasma-assisted chemical vapor deposition (MPCVD). Large-area PCD plate was cut into smaller equivalent 5 × 5 mm2 pieces, which were separately subjected to annealing in microwave plasma in H2 atmosphere, to annealing in vacuum or to annealing under high-pressure high-temperature conditions (HPHT, 5.9 GPa, 2000 °C). The structure, phase composition and photoluminescence (PL) of samples before and after various annealing processes were investigated. All applied types of annealing enhance both the Si-V and Ge-V lines in PL at room temperature. Increasing annealing temperature leads to gradual decrease of full widths at half-maxima (FWHM) of diamond Raman peak (1332.5 cm−1), as well as Si-V (738 nm) and Ge-V (602 nm) PL peaks. In addition, the limitations for each type of annealing are established. The obtained results are crucial for the design of CVD-grown Ge-doped and Si-doped PCD materials that can be used for applications in photonics such as single photon sources, biomarkers, as well as for the fabrication of optical diamond thermometers.

Differentiating Prodromal Dementia with Lewy Bodies from Prodromal Alzheimer's Disease: A Pragmatic Review for Clinicians.

This pragmatic review synthesises the current understanding of prodromal dementia with Lewy bodies (pDLB) and prodromal Alzheimer's disease (pAD), including clinical presentations, neuropsychological profiles, neuropsychiatric symptoms, biomarkers, and indications for disease management. The core clinical features of dementia with Lewy bodies (DLB)-parkinsonism, complex visual hallucinations, cognitive fluctuations, and REM sleep behaviour disorder are common prodromal symptoms. Supportive clinical features of pDLB include severe neuroleptic sensitivity, as well as autonomic and neuropsychiatric symptoms. The neuropsychological profile in mild cognitive impairment attributable to Lewy body pathology (MCI-LB) tends to include impairment in visuospatial skills and executive functioning, distinguishing it from MCI due to AD, which typically presents with impairment in memory. pDLB may present with cognitive impairment, psychiatric symptoms, and/or recurrent episodes of delirium, indicating that it is not necessarily synonymous with MCI-LB. Imaging, fluid and other biomarkers may play a crucial role in differentiating pDLB from pAD. The current MCI-LB criteria recognise low dopamine transporter uptake using positron emission tomography or single photon emission computed tomography (SPECT), loss of REM atonia on polysomnography, and sympathetic cardiac denervation using meta-iodobenzylguanidine SPECT as indicative biomarkers with slowing of dominant frequency on EEG among others as supportive biomarkers. This review also highlights the emergence of fluid and skin-based biomarkers. There is little research evidence for the treatment of pDLB, but pharmacological and non-pharmacological treatments for DLB may be discussed with patients. Non-pharmacological interventions such as diet, exercise, and cognitive stimulation may provide benefit, while evaluation and management of contributing factors like medications and sleep disturbances are vital. There is a need to expand research across diverse patient populations to address existing disparities in clinical trial participation. In conclusion, an early and accurate diagnosis of pDLB or pAD presents an opportunity for tailored interventions, improved healthcare outcomes, and enhanced quality of life for patients and care partners.

Generating quantum correlated photon pairs in a hybrid silicon–BTO platform

Here, we show photon pair generation from ring resonator and waveguide structures in a hybrid silicon–BTO on an insulator platform with a pulsed pump. Our analysis of single photon and coincidence generation rates show that spontaneous four-wave mixing is comparable to that expected from SOI devices with similar characteristics and find γeff of (14.7 ± 1.3) and (2.0 ± 0.3) MHz/mW2 for ring resonator and waveguide structures, respectively.

2D signal estimation for sparse distributed target photon counting data

In this study, we explore the utilization of penalized likelihood estimation for the analysis of sparse photon counting data obtained from distributed target lidar systems. Specifically, we adapt the Poisson Total Variation processing technique to cater to this application. By assuming a Poisson noise model for the photon count observations, our approach yields denoised estimates of backscatter photon flux and related parameters. This facilitates the processing of raw photon counting signals with exceptionally high temporal and range resolutions (demonstrated here to 50 Hz and 75 cm resolutions), including data acquired through time-correlated single photon counting, without significant sacrifice of resolution. Through examination involving both simulated and real-world 2D atmospheric data, our method consistently demonstrates superior accuracy in signal recovery compared to the conventional histogram-based approach commonly employed in distributed target lidar applications.

Experimental measurement of local noise power spectrum (NPS) in photon counting detector-CT (PCD-CT) using a single data acquisition.

Accurate noise power spectra (NPS) measurement in clinical X-ray CT exams is challenging due to the need for repeated scans, which expose patients to high radiation risks. A reliable method for single CT acquisition NPS estimation is thus highly desirable. To develop a method for estimating local NPS from a single photon counting detector-CT (PCD-CT)acquisition. A novel nearly statistical bias-free estimator was constructed from the raw counts data of PCD-CT scan to estimate the variance of sinogram projection data. An analytical algorithm is employed to reconstruct point-wise covariance between any two image pixel/voxel locations and . A Fourier transform is applied to obtain the desired point-wise NPS for any chosen location . The method was validated using experimental data acquired from a benchtop PCD-CT system with various physical phantoms, and the results were compared with the conventional local NPS measurement method using repeated scans and statistical ensembleaveraging. The experimental results demonstrate that (1) the proposed method can achieve pointwise/local NPS measurement for a region of interest (ROI) located at any chosen position, accurately characterizing the NPS with spatial structures resulting from image content heterogeneity; (2) the local NPS measured using the proposed method show a higher precision in the measured NPS compared to the conventional measurement method; (3) spatial averaging of the local NPS yields the conventional NPS for a given localROI. A new method was developed to enable local NPS from a single PCD-CTacquisition.

All-fiber multifunction differential absorption CO2 lidar integrating single-photon and coherent detection

All-fiber multifunction differential absorption CO2 lidar integrating single-photon and coherent detection

Photon Upconversion Cooperates with Downshifting in Chiral Systems: Modulation, Amplification, and Applications of Circularly Polarized Luminescence.

Circularly polarized luminescence (CPL)-active materials are increasingly recognized for their potential applications such as 3D imaging, data storage, and optoelectronic devices. Typically, CPL materials have required high-energy (HE) photons for excitation to emit low-energy (LE) circularly polarized light, a process known as downshifting CPL (DSCPL). However, the emergence of upconverted CPL (UCCPL), where the absorption of multi LE photons results in the emission of a single HE photon with circular polarization, has recently attracted considerable attention. This minireview highlights the intricate relationship between upconversion and CPL phenomena. During upconversion, the dissymmetry factor (glum) value can be improved in certain systems. Additionally, the integration of both LE and HE photons in upconversion-downshifting-synergistic systems offers avenues for dual-excitation or dual-emission CPL functionalities. More in detail, the emerging UCCPL based on various photon upconversion mechanisms and their synergy with DSCPL are introduced. Additionally, several examples that demonstrate the applications of UCCPL are presented to highlight the future opportunities.

Photon Upconversion Cooperates with Downshifting in Chiral Systems: Modulation, Amplification, and Applications of Circularly Polarized Luminescence

Circularly polarized luminescence (CPL)‐active materials are increasingly recognized for their potential applications such as 3D imaging, data storage, and optoelectronic devices. Typically, CPL materials have required high‐energy (HE) photons for excitation to emit low‐energy (LE) circularly polarized light, a process known as downshifting CPL (DSCPL). However, the emergence of upconverted CPL (UCCPL), where the absorption of multi LE photons results in the emission of a single HE photon with circular polarization, has recently attracted considerable attention. This minireview highlights the intricate relationship between upconversion and CPL phenomena. During upconversion, the dissymmetry factor (glum) value can be improved in certain systems. Additionally, the integration of both LE and HE photons in upconversion‐downshifting‐synergistic systems offers avenues for dual‐excitation or dual‐emission CPL functionalities. More in detail, the emerging UCCPL based on various photon upconversion mechanisms and their senergy with DSCPL are introduced. Additionally, several examples that demonstrate the applications of UCCPL are presented to highlight the future opportunities.

Generation of single photon emitters at a SiO2/SiC interface by high-temperature oxidation and reoxidation at lower temperatures

We report on an approach to produce single photon emitters at the SiO2/SiC interface. We form a high-quality SiO2/SiC interface by high-temperature oxidation and subsequently perform oxidation at lower temperatures (200 °C–1000 °C) to generate the emitters. After reoxidation at 800 °C, we confirmed the formation of emitters with a bright luminescence (>50 kcps). Through Hambury-Brown and Twiss measurements, single photon characteristics were confirmed. Thus, the proposed approach is effective in generating highly bright single photon emitters at the SiO2/SiC interface.

Superconducting Qubit Network as a Single Microwave Photon Detector for Galactic Axion Search

Superconducting Qubit Network as a Single Microwave Photon Detector for Galactic Axion Search

Boosting UV responsivity of silicon photodetectors through efficient quantum-cutting with La3+, Yb3+ co-doped perovskite quantum dots

Quantum cutting involves the absorption of a single high-energy photon, followed by the release of its energy through the emission of two or more lower-energy photons. This approach holds promise as a method to improve the ultraviolet (UV) performance of silicon photodetectors (Si PDs). In this study, we successfully fabricated La3+, Yb3+ co-doped CsPbClBr2 perovskite quantum dots (PQDs) using a modified hot-injection method, achieving a remarkable photoluminescent quantum yields (PLQYs) of 181 %. Subsequently, we spin-coated a film of La3+, Yb3+ co-doped CsPbClBr2 PeQDs, serving as a light conversion material, onto the front surface of Si PDs. The resulting configuration exhibited enhanced responsivity (0.131 A/W) and external quantum efficiency (55.6 %), long-term stability at 360 nm, and expanded responsiveness into the deep UV region (200 nm). Simultaneously, the responsivity and external quantum efficiency in the visible and near-infrared regions exhibited minimal reduction. This significant performance can be attributed to two key factors: (1) The higher efficient quantum cutting PLQYs (181 %) of La3+, Yb3+ co-doped CsPbClBr2 PeQDs and (2) the presence of fewer traps and a larger tolerance factor resulting from La3+ and Yb3+ co-doping.