Reduction of the two-photon temporal distinguishability for measurement-device-independent quantum key distribution.

Measurement-device-independent quantum key distribution (MDI-QKD) has been proven to protect legitimate users from attacks against measurement devices. The MDI-QKD requires that the two photons arriving at the instrument be indistinguishable. Precise time control is required to eliminate the distinguishability due to differences in photon arrival times. In the conventional methods, the time difference between photons is measured at a measuring instrument (Charlie), and a control signal is transmitted to the users (Alice and Bob). However, this method requires a long feedback loop, and the control may become unstable for long-distance transmission. This article proposes a method in which the photon arrival time difference is detected and controlled at Charlie. The reference signal for the time control is generated by an optical frequency comb in synchronization with the quantum signal. Therefore, the quantum signal photons can also be synchronized by synchronizing the reference signal pulses. A proof-of-principle experiment confirmed that the time synchronization accuracy required for protocol execution could be obtained. This proposal simplifies the implementation of the MDI-QKD.

Direct measurement of ultrafast temporal wavefunctions.

The large capacity and robustness of information encoding in the temporal mode of photons is important in quantum information processing, in which characterizing temporal quantum states with high usability and time resolution is essential. We propose and demonstrate a direct measurement method of temporal complex wavefunctions for weak light at a single-photon level with subpicosecond time resolution. Our direct measurement is realized by ultrafast metrology of the interference between the light under test and self-generated monochromatic reference light; no external reference light or complicated post-processing algorithms are required. Hence, this method is versatile and potentially widely applicable for temporal state characterization.

Effectiveness of a radiation protective device for anesthesiologists and transesophageal echocardiography operators in structural heart disease interventions.

In structural heart disease (SHD) interventions, the exposure of staff other than the first operator such as anesthesiologists and transesophageal echocardiography (TEE) operators to the radiation can also pose the risks of cancer and cataracts in the long term. This study was conducted to test our new radiation protective device (RPD) for anesthesiologists and TEE operators in SHD interventions. The RPD, which consists of a head side shield and a cradle shield, was mounted on a 0.25 mm Pb-equivalent unleaded radiation protection sheet on a self-made J-shaped acrylic table, and it was placed on the head side and cradle on the operating table. A CT human body phantom was placed on the operating table, and the C-arm was set in five directions: posteroanterior, right anterior oblique 30°, left anterior oblique 30°, caudal 30°, and cranial 30°. The ambient dose equivalent rate at the usual positions of the anesthesiologist and TEE operator were measured under a fluoroscopic sequence with and without the RPD, and the dose reduction rate was obtained. The height of each measurement point was set to 100, 130 or 160 cm. The reduction rates at the positions of the anesthesiologist and the TEE operator were 82.6-86.4% and 77.9-89.5% at the height of 100 cm, 48.5-68.4% and 83.3-91.0% at 130 cm, and 23.6-62.9% and 72.9-86.1% at 160 cm, respectively. The newly developed RPD can thus effectively reduce the radiation exposure of anesthesiologists and TEE operators during SHD interventions.

[Reduction of Operator Exposure Radiation Dose and Evaluation of Image Quality Using Half Scan in CT Fluoroscopy].

In recent years, the number of examinations and treatments using computed tomography fluoroscopy (CTF) has been increasing, and there is concern about an increase in the exposure radiation dose of the operator. Use of half scan CTF can be expected to reduce the exposure radiation dose, but there is no report. The purpose of this study was to evaluate the exposure radiation dose at the operator's position and image quality when using a half scan CTF. The left side facing the gantry was the operator's position, and the ambient dose equivalent at 160 cm, 130 cm, and 100 cm from the floor was measured using an ionization chamber survey meter. The absorbed dose at the forceps holding position of the operator was measured using a fluorescent glass dosimeter with the forceps holding position 15 cm caudal from the scan center. The imaging conditions used a tube voltage of 120 kV and a tube current of 50 mA. Half scan CTF was performed by changing the center angle of the half scan on the console every 45°. As a result, the set angles were 135°and 90°at the operator's position, and 135°at the operator's forceps holding position. In addition, we evaluated the effect of half scan CTF on image quality. CTF images were collected with a cryogenic needle used for cryotherapy punctured in a water-equivalent self-made phantom. The profile curves of the obtained images were drawn and compared using analysis software to evaluate the effects of artifacts. Then, the SD of the CT value of the region of interest with and without the artifact was measured, and the relative artifact index was calculated and evaluated. Using the same image, CT value and SD were tested to evaluate noise. Half scan CTF had no effect on the image quality due to artifacts and noise.

State preparation robust to modulation signal degradation by use of a dual parallel modulator for high-speed BB84 quantum key distribution systems.

Security certification of quantum key distribution systems with a practical device is essential for their social deployment. Considering the transmitter, we investigate quantum state generation affected by degraded electrical signals from practical bandwidth-limited devices on high-speed phase-encoding BB84 quantum key distribution systems. The state preparation flaw caused by this degradation undesirably enhances the distinguishability between the two bases for the BB84 protocol and decreases the key generation rate. We propose the state preparation with a dual parallel modulator for increasing the robustness to signal degradation. To verify the effectiveness of the dual parallel modulator, we characterize the generated states using state tomography and estimate the key generation rate based on the Gottesman-Lo-Lütkenhaus-Preskill theory with fidelity derived from the estimated density matrices. Simulation results show that the key generation rate remains unaffected by modulation voltage shifts up to 20%.

Wavefront superposition method for accurate and efficient mode conversion.

A wavefront superposition (WS) method is proposed for accurate and efficient mode conversion in mode-division multiplexing transmission. The WS method converts an input beam to the WS state, which is composed of the conversion target and radiation modes of a few-mode fiber. The appropriate weighting for the modal component of the WS state enables more efficient conversion than the conventional method in which the output beam consists only of the conversion target. Further, since the components of the radiation modes in the output are eliminated by the mode-filtering property of the few-mode fiber, no modal crosstalk occurs in the WS method. We examine the conversion performance of the WS method by a numerical simulation for the mode-multiplexing numbers 3, 6, 10, and 15. The WS method shows a 2.4 dB higher efficiency than the conventional method, while maintaining an extremely low modal crosstalk (less than -80 dB), even when the number of multiplexed modes is 15.

Virtual phase conjugation based optical tomography for single-shot three-dimensional imaging.

We propose a virtual phase conjugation (VPC) based optical tomography (VPC-OT) for realizing single-shot optical tomographic imaging systems. Using a computer-based numerical beam propagation, the VPC combines pre-modulation and post-demodulation of the probe beam's wavefront, which provides an optical sectioning capability for resolving the depth coordinates. In VPC-OT, the physical optical microscope system and VPC are coupled using digital holography. Therefore, in contrast to conventional optical tomographic imaging (OTI) systems, this method does not require additional elements such as low-coherence light sources or confocal pinholes. It is challenging to obtain single-shot three-dimensional (3D) tomographic images using a conventional OTI system; however, this can be achieved using VPC-OT, which employs both digital holography and computer based numerical beam propagation. In addition, taking into account that VPC-OT is based on a complex amplitude detection using digital holography, this method allows us to simultaneously obtain quantitative phase contrast images. Using an objective lens with a numerical aperture (NA) of 0.8, we demonstrate a single-shot 3D imaging of frog blood cells with a depth resolution of 0.94 µm.

Volume holographic spatial mode demultiplexer with a dual-wavelength method.

Volume holographic demultiplexers (VHDMs) provide spatial mode demultiplexing using simple optical systems. However, applying VHDM to practical optical communication systems is difficult, as typical holographic media have no sensitivity in the infrared region, which includes optical transmission bands. In this paper, we propose a VHDM scheme combined with a dual-wavelength method (DWM). Using the DWM, VHDMs are able to perform mode demultiplexing in the optical transmission bands. We experimentally demonstrated the basic operation of our proposal using experiments performed at an 850-nm wavelength. In addition, we performed numerical simulations to investigate the application of VHDM to the C-band.

Reduction Method of Operator and Medical Staff Radiation Exposure in Balloon Pulmonary Angioplasty for Chronic Thromboembolic Pulmonary Hypertension.

The purpose of this study is to investigate a reduction method of radiation exposure for operator and medical staff in balloon pulmonary angioplasty (BPA) for chronic thromboembolic pulmonary hypertension (CTEPH). We devised a new radiation protection, which is U-shaped acrylic supporting table with 0.35 mmPb unleaded radiation protection sheet. A human phantom was put on the bed of cardiac angiography system [C-arm angulation: posteroanterior (PA), L-arm angulation: left anterior oblique (LAO) 60°]. The ambient equivalent dose rate was measured under fluoroscopy with and without three radiation protections: U-shaped acrylic supporting table with 0.35 mmPb unleaded radiation protection sheet, radiation protection for the lower body, and radiation protection for the upper body. With the three radiation protections, the ambient equivalent dose rate was decreased more than 99% at the height of 100 cm above the floor at the operator position (PA: from 186.2 µSv/h to 0.5 µSv/h, LAO 60°: from 350.4 µSv/h to 1.6 µSv/h). Ambient equivalent dose rate at the other points are also decreased effectively. The devised dose reduction method can reduce operator and medical staff radiation exposure effectively and be set up without interference for BPA procedure.

Effective luminance deterioration of medical liquid crystal displays in clinical use.

The objective of this work was to evaluate the maximum luminance (L max) level of medical liquid crystal displays (LCDs) as a function of backlight hours (BLH) annually. The L max values for 249 2-megapixel color LCDs (RadiForce RX210, EIZO Corporation) were measured in February 2014, 2015, and 2016. Four near-range luminance meters and the built-in type luminance meters, each with an LCD, were used for the measurements. The average and standard deviation (SD) of BLH measured in 2014 was 15,371 ± 8219 h. Four, twenty, and thirty-nine LCDs failed in the constancy tests performed in February 2014, 2015, and 2016, respectively, i.e., they were unable to output 170 cd/m2. The SD of L max increased each year and as BLH became longer. In conclusion, evaluation of L max as a function of BLH during constancy testing will help predict the decrease in L max of a clinically used medical color LCD.

Intensity fluctuation of a gain-switched semiconductor laser for quantum key distribution systems.

Security certification of quantum key distribution (QKD) systems under practical conditions is necessary for social deployment. This article focused on the transmitter, and, in particular, investigated the intensity fluctuation of the optical pulses emitted by a gain-switched semiconductor laser used in QKD systems implementing decoy-BB84 protocol. A large intensity fluctuation was observed for low excitation, showing strong negative correlation between the adjacent pulses, which would affect the final key rate. The fluctuation decreased and the correlation disappeared as excitation increased. Simulation with rate equations successfully reproduced the experimental results and revealed that the large fluctuation originates from an intrinsic instability of gain-switched lasers driven periodically at a rate comparable to the inverse of carrier lifetime, as in GHz-clock QKD systems. Methods for further reduction of the intensity fluctuation were also discussed.

Reference-free holographic diversity interferometry via iterative measurements for high accuracy phase detection.

To obtain a phase distribution without the use of an optical path besides an object beam, a reference-free holographic diversity interferometry (RF-HDI) has been proposed. Although the RF-HDI can generate an internal reference beam from the object beam, the method has a problem of measurement accuracy due to insufficient power of the internal reference beam. To solve the problem, we newly propose a RF-HDI via iterative measurements. Our method improves the measurement accuracy by utilizing iterative measurements and feedback of each obtained phase image to the measurement system. In the experiment, the phase image, which has a random pattern, can be measured as an object beam with a higher accuracy than in the conventional RF-HDI. To support this result, we also evaluated the wavefront accuracy and optical power efficiency of an internal reference beam in this method. As a result, we verified that our method enables us to generate an internal reference beam that has the wavefront of a near single plane wave and a higher power efficiency than the conventional RF-HDI. In addition, our method can be applied to measurement for the modal content in an optical fiber, atmosphere turbulence, etc., where it is difficult to prepare an external reference beam with a high coherency.

Virtual interferogram-generation algorithm for robust complex amplitude measurement using two interferograms.

We propose a virtual interferogram-generation algorithm using two interferograms. This algorithm can measure a complex amplitude of a signal beam with high accuracy even when its intensity is greater than the intensity of a reference beam. Unlike the conventional algorithm that uses two interferograms, our algorithm can compute measurements when the phase shift of interferograms in not equal to π/2. Our method generates two phase-shifted holograms in a computer by capturing the intensities of two signal beams, two reference beams, and two interferograms. The complex amplitude of a signal beam is calculated by four interference patterns, two holograms, and two interferograms. The proposed algorithm can drastically suppress the calculation error caused by the smaller value between the intensity of the reference beam and can choose the most suitable phase shift.

Classical realization of dispersion-canceled, artifact-free, and background-free optical coherence tomography.

Quantum-optical coherence tomography (Q-OCT) provides a dispersion-canceled axial-imaging method, but its practical use is limited by the weakness of the light source and by artifacts in the images. A recent study using chirped-pulse interferometry (CPI) has demonstrated dispersion-canceled and artifact-free OCT with a classical system; however, unwanted background signals still remain after removing the artifacts. Here, we propose a classical optical method that realizes dispersion-canceled, artifact-free, and background-free OCT. We employ a time-reversed system for Q-OCT with transform-limited input laser pulses to achieve dispersion-canceled OCT with a classical system. We have also introduced a subtraction method to remove artifacts and background signals. With these methods, we experimentally demonstrated dispersion-canceled, artifact-free, and background-free axial imaging of a coverglass and cross-sectional imaging of the surface of a coin.

[Stress reactions among bus drivers: towards the development of an educational resource for better management of emotions].

Interview and questionnaire surveys were conducted with bus drivers in Japan, with the goal of developing an educational program for better control of emotions among bus drivers. The interviews aimed at identifying stressors and ways in which stress negatively influenced bus services. The questionnaire survey. which was being developed as a self-diagnosis tool, further provided bus drivers with the opportunity to understand their own emotional tendencies. Factor analysis identified six factors underlying work-related stress: anger at unsafe behaviours of nearby road users, irritation caused by complaints from passengers, time pressures, anxiety about traffic accidents, impatience with slow passengers, and resentment of bad-mannered passengers. The influence of stress on the drivers comprised four factors: cognitive failure, sullen behaviour, abrupt acceleration/deceleration, and aggressive driving. Moreover, drivers with lower stress were relatively older and more experienced. Based on these results, educational materials were proposed with the aim of enhancing bus drivers' understanding of their emotional processes and coping skills.

[Inspection of dose reduction in patients during percutaneous coronary intervention and catheter ablation procedures].

With an increasing number of interventional radiology (IVR) procedures, it is a critical issue to control and reduce the radiation dose for patients by radiological technologists. In our study, we analyzed the usefulness of a provision for radiation reduction on catheter ablation and percutaneous coronary intervention (PCI) procedures based on the data from radiation information system (RIS). With regard to catheter ablation, 50% reduction was enabled with decreasing fluoroscopic and radiographic conditions regardless of each technique. Radiation reduction enabled a decrease in the fluoroscopic dose during PCI procedure. However, note that excessive radiation reduction does not show positive results of the radiation dose reduction. Moreover it leads to an increase in fluoroscopic time.

Permeation characteristics of electrolytes and neutral solutes through titania nanofiltration membranes at high temperatures.

Nanoporous titania membranes with controlled pore sizes ranging from 0.7 to 2.5 nm, which had molecular weight cutoffs (MWCO) ranging from 500 to 2000, were successfully prepared by sol-gel processing, and the transport characteristics were evaluated across a temperature range of 30-80 degrees C. With increasing temperature, the permeate flux increased 2- to 3-fold, depending on the pore size. The water permeation mechanism was found to be different from viscous flow and was explained by the state of the water (free water/bound water/nonfreezing water) inside confined pores. The rejection of neutral solutes such as raffinose, the separation mechanism of which is molecular sieving (steric hindrance), decreased with temperature whereas that of electrolytes (MgCl(2) and NaCl), the separation mechanism of which is the charge effect (Donnan exclusion), was approximately constant. The temperature dependence of neutral and electrolyte solutes was analyzed using the Spiegler-Kedem equation by combining the Arrhenius equations for diffusivity and viscosity, which we obtained DeltaE(m), the activation energy of diffusion, after eliminating the effect of viscosity. For large DeltaE(m), which corresponds to the rejection of neutral solutes on the basis of molecular sieving, rejection decreased with temperature but remained unchanged for small DeltaE(m), which corresponds to the rejection of electrolytes based on the charge effect.

Digital cine angiography permits radiation dose reduction without reduction in image quality.

PURPOSE: To investigate how much the radiation dose in digital cine angiography (DCA) systems can be reduced while maintaining an image quality equivalent to that of conventional cine angiography (CCA). MATERIALS AND METHODS: Simulated vessel phantoms were subjected to DCA and CCA. In DCA, the input dose value to the image intensifier built in the system was 0.10, 0.12, 0.14, 0.17, 0.2, and 0.24 microGy. The detectability for simulated vessel phantoms was visually evaluated by five observers. The radiation dose was measured using radiofluorescent glass-rod dosimeters. Doses of digital cine imaging were measured as relative values with the dose of CCA considered as 1.0. RESULTS: The relative DCA/CCA values in DCA, measured by radiofluorescent glass-rod dosimeters, ranged from 0.414 to 0.901 for simulated vessel phantoms CONCLUSION: DCA allows a reduction by 59% of the radiation dose compared with CCA without reduction of image quality.

[Optimization of the chest exposure condition with a contrast-detail phantom: evaluation of the flat-panel versus computed radiography systems].

In this study, we evaluated the performance of a digital chest imaging system using a contrast-detail (C-D) phantom. In the initial step, 76 sample images of the C-D phantom were produced by changing the doses from 0.5, 0.75, 1.0, 1.25, 1.5, to 2.0 times the dose for a screen-film (S/F) system. The sample images were analyzed by five radiological technologists and two medical physicists, and the image quality figure (IQF) was determined. The quality of each image was examined, and appropriate doses were determined from the calculated IQF to obtain the same image quality for other digital chest imaging systems. The method of determining IQF from C-D phantom analysis was very useful for comparing image quality and determining radiographic techniques.

[Low contrast detectability of a new CR system with two-sided reading].

A new imaging plate (IP) with a transparent support and reading system that can detect emissions from both sides of the IP has been developed and has already been introduced in some facilities. In this study, low contrast threshold detectability was investigated experimentally for a CR system with a two-sided reading system (new CR) and for a conventional CR system. Images of a Contrast-Detail phantom were obtained with the new and conventional CR systems at dose levels corresponding to 26%, 49%, 82%, 103%, and 164% of the dose used for the screen-film system. Using an observer performance study of Contrast-Detail phantom images, the threshold contrast of disk-shaped objects ranging from 0.3 mm to 4.0 mm in diameter was determined. We also calculated image quality figure (IQF) from the results of observation. The new CR system showed significantly better contrast detectability than the conventional CR system. The use of a new CR system provided a reduction of approximately 25% in radiographic dose while providing comparable IQF.