315 research outputs found
Chaotic mode-competition dynamics in a multimode semiconductor laser with optical feedback and injection
Photonic computing is attracting increasing interest to accelerate
information processing in machine learning applications. The mode-competition
dynamics of multimode semiconductor lasers is useful for solving the
multi-armed bandit problem in reinforcement learning for computing
applications. In this study, we numerically evaluate the chaotic
mode-competition dynamics in a multimode semiconductor laser with optical
feedback and injection. We observe the chaotic mode-competition dynamics among
the longitudinal modes and control them by injecting an external optical signal
into one of the longitudinal modes. We define the dominant mode as the mode
with the maximum intensity; the dominant-mode ratio for the injected mode
increases as the optical injection strength increases. We find that the
characteristics of the dominant mode ratio in terms of the optical injection
strength are different among the modes owing to the different optical feedback
phases. We propose a control technique for the characteristics of the dominant
mode ratio by precisely tuning the initial optical frequency detuning between
the optical injection signal and injected mode. We also evaluate the
relationship between the region for the large dominant mode ratio and injection
locking range. The region for the large dominant mode ratio does not correspond
to the injection-locking range. This discrepancy results from the complex
mode-competition dynamics in multimode semiconductor lasers with both optical
feedback and injection. This control technique of chaotic mode-competition
dynamics in multimode lasers is promising for applications in reinforcement
learning and reservoir computing as photonic artificial intelligence.Comment: 17 pages, 12 figures, 1 tabl
Spin relaxation mechanism of strain-induced GaAs quantum dots studied by time-resolved Kerr rotation
We observed electron spin precession under magnetic field in single-layer quantum dots (QDs) by highly sensitive time-resolved Kerr rotation measurement. The spin lifetime is longer than that for the quantum well (QW). This is a result of the additional spatial confinement of electrons in QDs. Below 60 K, the spin lifetime is almost constant, and is 7 times shorter than the carrier lifetime. This suggests that the strong electron-hole exchange interaction dominates over the electron spin lifetime in QDs at low temperature
Longitudinal optical phonons in the excited state of CuBr quantum dots
The size dependence of the longitudinal optical (LO) phonons in the excited state of CuBr quantum dots (QD’s) in glass and NaBr crystals in the intermediate confinement regime was studied by means of persistent spectral hole burning spectroscopy. The phonon-exciton coupled states were clearly observed at a photon energy of about 2.993 eV when the LO phonon energy is close to the energy difference between the ground 1S and excited 1P states of CuBr QD’s in glass. The energies of the LO phonons observed in smaller CuBr QD’s in glass and NaBr crystals were determined to be about 18.6 and 17.6 meV, respectively, which are smaller than that of LO phonons in the bulk CuBr material. The energy softening of the LO phonons was explained in terms of the phonon renormalization
Experimental estimation of sample entropy in a semiconductor laser with optical feedback for random number generation
Estimating the entropy rate of physical random number generators with uncertainty is crucial for information security applications. We evaluate the sample entropy of chaotic temporal waveforms generated experimentally by a semiconductor laser with time-delayed optical feedback. We demonstrate random number generation with uncertainty using a quantitative measurement of the entropy rate
"Per cell" normalization method for mRNA measurement by quantitative PCR and microarrays
BACKGROUND: Transcriptome data from quantitative PCR (Q-PCR) and DNA microarrays are typically obtained from a fixed amount of RNA collected per sample. Therefore, variations in tissue cellularity and RNA yield across samples in an experimental series compromise accurate determination of the absolute level of each mRNA species per cell in any sample. Since mRNAs are copied from genomic DNA, the simplest way to express mRNA level would be as copy number per template DNA, or more practically, as copy number per cell. RESULTS: Here we report a method (designated the "Percellome" method) for normalizing the expression of mRNA values in biological samples. It provides a "per cell" readout in mRNA copy number and is applicable to both quantitative PCR (Q-PCR) and DNA microarray studies. The genomic DNA content of each sample homogenate was measured from a small aliquot to derive the number of cells in the sample. A cocktail of five external spike RNAs admixed in a dose-graded manner (dose-graded spike cocktail; GSC) was prepared and added to each homogenate in proportion to its DNA content. In this way, the spike mRNAs represented absolute copy numbers per cell in the sample. The signals from the five spike mRNAs were used as a dose-response standard curve for each sample, enabling us to convert all the signals measured to copy numbers per cell in an expression profile-independent manner. A series of samples was measured by Q-PCR and Affymetrix GeneChip microarrays using this Percellome method, and the results showed up to 90 % concordance. CONCLUSION: Percellome data can be compared directly among samples and among different studies, and between different platforms, without further normalization. Therefore, "percellome" normalization can serve as a standard method for exchanging and comparing data across different platforms and among different laboratories
Probing polarization states of primordial gravitational waves with CMB anisotropies
We discuss the polarization signature of primordial gravitational waves
imprinted in cosmic microwave background (CMB) anisotropies. The high-energy
physics motivated by superstring theory or M-theory generically yield parity
violating terms, which may produce a circularly polarized gravitational wave
background (GWB) during inflation. In contrast to the standard prediction of
inflation with un-polarized GWB, circularly polarized GWB generates
non-vanishing TB and EB-mode power spectra of CMB anisotropies. We evaluate the
TB and EB-mode power spectra taking into account the secondary effects and
investigate the dependence of cosmological parameters. We then discuss current
constraints on the circularly polarized GWB from large angular scales (l < 16)
of the three year WMAP data. Prospects for future CMB experiments are also
investigated based on a Monte Carlo analysis of parameter estimation, showing
that the circular polarization degree, varepsilon, which is the asymmetry of
the tensor power spectra between right- and left-handed modes normalized by the
total amplitude, can be measured down to |varepsilon| 0.35(r/0.05)^{-0.6}.Comment: 28 pages, 9 figures, Accepted for publication in JCA
Terahertz wireless communication at 560-GHz band using Kerr micro-resonator soliton comb
Terahertz (THz) waves have attracted attention as carrier waves for
next-generation wireless communications (6G). Electronic THz emitters are
widely used in current mobile communications; however, they may face technical
limitations in 6G with upper-frequency limits. We demonstrate wireless
communication in a 560-GHz band by using a photonic THz emitter based on
photomixing of a 560-GHz-spacing soliton microcomb in a uni-travelling carrier
photodiode together with a THz receiver of Schottky barrier diode. The on-off
keying data transfer with 2-Gbit/s achieves a Q-factor of 3.4, thus, satisfying
the limit of forward error correction.Comment: 17 pages, 4 figur
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