76 research outputs found
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
Ultrabright narrow-band telecom two-photon source for long-distance quantum communication
We demonstrate an ultrabright narrow-band two-photon source at the 1.5 -\mu m
telecom wavelength for long-distance quantum communication. By utilizing a
bow-tie cavity, we obtain a cavity enhancement factor of . Our
measurement of the second-order correlation function reveals
that the linewidth of MHz has been hitherto unachieved in the 1.5 -\mu m
telecom band. This two-photon source is useful for obtaining a high absorption
probability close to unity by quantum memories set inside quantum repeater
nodes. Furthermore, to the best of our knowledge, the observed spectral
brightness of pairs/(sMHzmW) is also the
highest reported over all wavelengths.Comment: 11 pages, 4 figures, 2 table
On the efficiency of quantum lithography
Quantum lithography promises, in principle, unlimited feature resolution,
independent of wavelength. However, in the literature at least two different
theoretical descriptions of quantum lithography exist. They differ in to which
extent they predict that the photons retain spatial correlation from generation
to the absorption, and while both predict the same feature size, they differ
vastly in predicting how efficiently a quantum lithographic pattern can be
exposed.
Until recently, essentially all experiments reported have been performed in
such a way that it is difficult to distinguish between the two theoretical
explanations. However, last year an experiment was performed which gives
different outcomes for the two theories. We comment on the experiment and show
that the model that fits the data unfortunately indicates that the trade-off
between resolution and efficiency in quantum lithography is very unfavourable.Comment: 19 pages, extended version including a thorough mathematical
derivatio
Quantum receiver beyond the standard quantum limit of coherent optical communication
The most efficient modern optical communication is known as coherent
communication and its standard quantum limit (SQL) is almost reachable with
current technology. Though it has been predicted for a long time that this SQL
could be overcome via quantum mechanically optimized receivers, such a
performance has not been experimentally realized so far. Here we demonstrate
the first unconditional evidence surpassing the SQL of coherent optical
communication. We implement a quantum receiver with a simple linear optics
configuration and achieve more than 90% of the total detection efficiency of
the system. Such an efficient quantum receiver will provide a new way of
extending the distance of amplification-free channels, as well as of realizing
quantum information protocols based on coherent states and the loophole-free
test of quantum mechanics.Comment: 5 pages, 3 figure
On the distribution of 1550-nm photon pairs efficiently generated using a periodically poled lithium niobate waveguide
We report on the generation of photon pairs in the 1550-nm band suitable for
long-distance fiber-optic quantum key distribution. The photon pairs were
generated in a periodically poled lithium niobate waveguide with a high
conversion-efficiency. Using a pulsed semiconductor laser with a pulse rate of
800 kHz and a maximum average pump power of 50 muW, we obtained a coincidence
rate of 600 s^-1. Our measurements are in agreement with a Poissonian
photon-pair distribution, as is expected from a comparison of the coherence
time of the pump and of the detected photons. An average of 0.9 photon pairs
per pulse was obtained.Comment: 12 pages, 3 figure
Quantum limits on phase-shift detection using multimode interferometers
Fundamental phase-shift detection properties of optical multimode
interferometers are analyzed. Limits on perfectly distinguishable phase shifts
are derived for general quantum states of a given average energy. In contrast
to earlier work, the limits are found to be independent of the number of
interfering modes. However, the reported bounds are consistent with the
Heisenberg limit. A short discussion on the concept of well-defined relative
phase is also included.Comment: 6 pages, 3 figures, REVTeX, uses epsf.st
SARS-CoV-2 spike receptor-binding domain is internalized and promotes protein ISGylation in human induced pluripotent stem cell-derived cardiomyocytes
Although an increased risk of myocarditis has been observed after vaccination with mRNA encoding severe acute respiratory syndrome coronavirus 2 spike protein, its underlying mechanism has not been elucidated. This study investigated the direct effects of spike receptor-binding domain (S-RBD) on human cardiomyocytes differentiated from induced pluripotent stem cells (iPSC-CMs). Immunostaining experiments using ACE2 wild-type (WT) and knockout (KO) iPSC-CMs treated with purified S-RBD demonstrated that S-RBD was bound to ACE2 and internalized into the subcellular space in the iPSC-CMs, depending on ACE2. Immunostaining combined with live cell imaging using a recombinant S-RBD fused to the superfolder GFP (S-RBD-sfGFP) demonstrated that S-RBD was bound to the cell membrane, co-localized with RAB5A, and then delivered from the endosomes to the lysosomes in iPSC-CMs. Quantitative PCR array analysis followed by single cell RNA sequence analysis clarified that S-RBD-sfGFP treatment significantly upregulated the NF-kβ pathway-related gene (CXCL1) in the differentiated non-cardiomyocytes, while upregulated interferon (IFN)-responsive genes (IFI6, ISG15, and IFITM3) in the matured cardiomyocytes. S-RBD-sfGFP treatment promoted protein ISGylation, an ISG15-mediated post-translational modification in ACE2-WT-iPSC-CMs, which was suppressed in ACE2-KO-iPSC-CMs. Our experimental study demonstrates that S-RBD is internalized through the endolysosomal pathway, which upregulates IFN-responsive genes and promotes ISGylation in the iPSC-CMs.Okuno S., Higo S., Kondo T., et al. SARS-CoV-2 spike receptor-binding domain is internalized and promotes protein ISGylation in human induced pluripotent stem cell-derived cardiomyocytes. Scientific Reports 13, 21397 (2023); https://doi.org/10.1038/s41598-023-48084-7
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