Analysis of the generation of photon pairs in periodically poled lithium niobate

The process of spontaneous parametric down-conversion (SPDC) in nonlinear crystals makes it fairly easy to generate entangled photon states. It has been known for some time that the conversion efficiency can be improved by employing quasi-phase-matching in periodically poled crystals. Using two single-photon detectors, we have analyzed the photon pairs generated by SPDC in a periodically poled lithium niobate crystal pumped by a femtosecond laser. Several parameters could be varied in our setup, allowing us to obtain data in close agreement with both thermal and Poissonian photon-pair distributions.Comment: 4 pages, 4 figures, uses ws-procs10x7.cls; v2: Sign in equation (5) correcte

Joint Temporal Density Measurements for Two-Photon State Characterization

We demonstrate a new technique for characterizing two-photon quantum states based on joint temporal correlation measurements using time resolved single photon detection by femtosecond upconversion. We measure for the first time the joint temporal density of a two-photon entangled state, showing clearly the time anti-correlation of the coincident-frequency entangled photon pair generated by ultrafast spontaneous parametric down-conversion under extended phase-matching conditions. The new technique enables us to manipulate the frequency entanglement by varying the down-conversion pump bandwidth to produce a nearly unentangled two-photon state that is expected to yield a heralded single-photon state with a purity of 0.88. The time-domain correlation technique complements existing frequency-domain measurement methods for a more complete characterization of photonic entanglement in quantum information processing.Comment: 4 pages, 5 figure

0.54 μm resolution two-photon interference with dispersion cancellation for quantum optical coherence tomography.

量子もつれ光を用いた、超高分解能光断層撮影技術を開発-. 京都大学プレスリリース. 2015-12-15.Quantum information technologies harness the intrinsic nature of quantum theory to beat the limitations of the classical methods for information processing and communication. Recently, the application of quantum features to metrology has attracted much attention. Quantum optical coherence tomography (QOCT), which utilizes two-photon interference between entangled photon pairs, is a promising approach to overcome the problem with optical coherence tomography (OCT): As the resolution of OCT becomes higher, degradation of the resolution due to dispersion within the medium becomes more critical. Here we report on the realization of 0.54 μm resolution two-photon interference, which surpasses the current record resolution 0.75 μm of low-coherence interference for OCT. In addition, the resolution for QOCT showed almost no change against the dispersion of a 1 mm thickness of water inserted in the optical path, whereas the resolution for OCT dramatically degrades. For this experiment, a highly-efficient chirped quasi-phase-matched lithium tantalate device was developed using a novel 'nano-electrode-poling' technique. The results presented here represent a breakthrough for the realization of quantum protocols, including QOCT, quantum clock synchronization, and more. Our work will open up possibilities for medical and biological applications

Noncollinear parametric fluorescence by chirped quasi-phase matching for monocycle temporal entanglement

Quantum entanglement of two photons created by spontaneous parametric downconversion (SPDC) can be used to probe quantum optical phenomena during a single cycle of light. Harris [Opt. Express 98, 063602 (2007)] suggested using ultrabroad parametric fluorescence generated from a quasi-phase-matched (QPM) device whose poling period is chirped. In the Harris's original proposal, it is assumed that the photons are collinearly generated and then spatially separated by frequency filtering. Here, we alternatively propose using noncollinearly generated SPDC. In our numerical calculation, to achieve 1.2 cycle temporal correlation for a 532 nm pump laser, only 10%-chirped device is sufficient when noncollinear condition is applied, while a largely chirped (50%) device is required in collinear condition. We also experimentally demonstrate an octave-spanning (790-1610 nm) noncollinear parametric fluorescence from a 10% chirped MgSLT crystal using both a superconducting nanowire single-photon detector and photomultiplier tube as photon detectors. The observed SPDC bandwidth is 194 THz, which is the largest width achieved to date for a chirped QPM device. From this experimental result, our numerical analysis predicts that the bi-photon can be compressed to 1.2 cycles with appropriate phase compensation

Ultrafast phase comparator for phase-locked loop-based optoelectronic clock recovery systems

The authors report on a novel application of a χ2 nonlinear optical device as an ultrafast phase comparator, an essential element that allows an optoelectronic phase-locked loop to perform clock recovery of ultrahigh-speed optical time-division multiplexed (OTDM) signals. Particular interest is devoted to a quasi-phase-matching adhered-ridge-waveguide periodically poled lithium niobate (PPLN) device, which shows a sufficient high temporal resolution to resolve a 640 Gbits OTDM signal.</p

Introduction to the annual S&T poster for everyone, titled "Glass - One S&T poster for Every Household" and its related activities

As an anniversary event of International Year of Glass (IYOG), especially to help advertisement of IYOG in Japan, we devoted ourselves for half a year of making a glass poster, called Ikka-ni Ichimai [the annual S&T (Science and Technology) poster for everyone, in Japanese]. The title of the poster is GLASS - The most universal modern material, and is already distributed, by Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), to all over Japan from elementary to high school, and even university. The distribution is done to promote their interests for science and technology. The final products, the poster, the corresponding webpage, and the movies to explain how to enjoy the poster, are very much welcomed by many people including kids and students who do not major in glass. The poster shows how glass has been evolved by humankind, and how it supported human life to develop. We are quite confident that people can understand, by looking through this poster, how inevitable glass is, in various fields; from culture and art, medicine, science, and technology. Our hopes are to evoke interests of children to glass and material science, which, in a long term, help continuous evolution of glass for the future which supports the humankind. (C)2022 The Ceramic Society of Japan. All rights reserved