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arXiv 1902.02594cond-mat.stat-mechcond-mat.quant-gas
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陷阱中非相互作用费米子的非平衡动力学

Nonequilibrium dynamics of noninteracting fermions in a trap

David S. Dean, Pierre Le Doussal, Satya N. Majumdar, Gregory Schehr

摘要:

我们考虑了$d=1$中$N$非相互作用费米子的实时动力学。它们从处于势$V_0(x)$的平衡态开始,在俘获势$V(x)$中演化。我们研究了Wigner函数$W(x,p,t)$在相空间$(x,p)$中的时间演化,以及编码所有相关函数的相关核。在$t=0$,大$N$的维格纳函数在费米体积内的相空间中是均匀的,并且在由与艾里函数相关的通用标度函数描述的尺度$e_N$上的费米表面处消失。我们得到精确的解决方案的维格纳函数,密度,和相关的情况下,谐波和平方反比的潜力,为几个$V_0(x)$。在大的$N$限制,附近的密度消失的边缘,我们得到限制内核(Airy或贝塞尔类型),保持平衡的形式,到时间相关的重新缩放。对于非谐波陷阱,费米体积的演化更为复杂。然而,我们表明,中间的时间,费米冲浪仍然是由相同的平衡标度函数,与非平凡的时间和空间依赖的宽度,我们计算分析。我们讨论了谐振子的多时间关联,得到了它们在边缘附近的显式标度形式。最后,我们解决了大的时间限制,放松广义吉布斯包络(GGE)被发现发生在“经典”制度$\hbar \sim 1/N$。使用对角系综,我们计算的Wigner函数的量子情况下(大$N$,固定$\hbar$),并表明,它同意GGE。我们还得到了高阶(非局部)相关的对角系综。

英文摘要:

We consider the real time dynamics of $N$ noninteracting fermions in $d=1$. They evolve in a trapping potential $V(x)$, starting from the equilibrium state in a potential $V_0(x)$. We study the time evolution of the Wigner function $W(x,p,t)$ in the phase space $(x,p)$, and the associated kernel which encodes all correlation functions. At $t=0$ the Wigner function for large $N$ is uniform in phase space inside the Fermi volume, and vanishes at the Fermi surf over a scale $e_N$ being described by a universal scaling function related to the Airy function. We obtain exact solutions for the Wigner function, the density, and the correlations in the case of harmonic and inverse square potentials, for several $V_0(x)$. In the large $N$ limit, near the edges where the density vanishes, we obtain limiting kernels (of the Airy or Bessel types) that retain the form found in equilibrium, up to a time dependent rescaling. For non-harmonic traps the evolution of the Fermi volume is more complex. Nevertheless we show that, for intermediate times, the Fermi surf is still described by the same equilibrium scaling function, with a non-trivial time and space dependent width which we compute analytically. We discuss the multi-time correlations and obtain their explicit scaling forms valid near the edge for the harmonic oscillator. Finally, we address the large time limit where relaxation to the Generalized Gibbs Ensemble (GGE) was found to occur in the "classical" regime $\hbar \sim 1/N$. Using the diagonal ensemble we compute the Wigner function in the quantum case (large $N$, fixed $\hbar$) and show that it agrees with the GGE. We also obtain the higher order (non-local) correlations in the diagonal ensemble.

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