Sakata Itsushi, Sakata Takuya, Mizoguchi Kohji, Tanaka Satoshi, Oohata Goro, Akai Ichiro, Igarashi Yasuhiko, Nagano Yoshihiro, Okada Masato
Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Department of Physical Science, Osaka Prefecture University, Gakuen-cho 1-1, Sakai, 599-8531, Japan.
Sci Rep. 2021 Nov 30;11(1):23169. doi: 10.1038/s41598-021-02413-w.
In a dissipative quantum system, we report the dynamic mode decomposition (DMD) analysis of damped oscillation signals. We used a reflection-type pump-probe method to observe time-domain signals, including the coupled modes of long-lived longitudinal optical phonons and quickly damped plasmons (LOPC) at various pump powers. The Fourier transformed spectra of the observed damped oscillation signals show broad and asymmetric modes, making it difficult to evaluate their frequencies and damping rates. We then used DMD to analyze the damped oscillation signals by precisely determining their frequencies and damping rates. We successfully identified the LOPC modes. The obtained frequencies and damping rates were shown to depend on the pump power, which implies photoexcited carrier density. We compared the pump-power dependence of the frequencies and damping rates of the LOPC modes with the carrier density dependence of the complex eigen-energies of the coupled modes by using the non-Hermitian phenomenological effective Hamiltonian. Good agreement was obtained between the observed and calculated dependences, demonstrating that DMD is an effective alternative to Fourier analysis which often fails to estimate effective damping rates.
在一个耗散量子系统中，我们报告了对阻尼振荡信号的动态模式分解（DMD）分析。我们采用反射型泵浦-探测方法来观测时域信号，包括在不同泵浦功率下长寿命纵向光学声子和快速衰减等离子体激元（LOPC）的耦合模式。所观测到的阻尼振荡信号的傅里叶变换光谱显示出宽且不对称的模式，这使得评估它们的频率和阻尼率变得困难。然后我们使用DMD通过精确确定其频率和阻尼率来分析阻尼振荡信号。我们成功识别出了LOPC模式。结果表明，所获得的频率和阻尼率取决于泵浦功率，这意味着光激发载流子密度。我们通过使用非厄米现象学有效哈密顿量，将LOPC模式的频率和阻尼率对泵浦功率的依赖性与耦合模式复本征能量对载流子密度的依赖性进行了比较。观测到的依赖性与计算得到的依赖性之间取得了良好的一致性，这表明DMD是傅里叶分析的一种有效替代方法，傅里叶分析常常无法估计有效阻尼率。
