Quantum coherence in noise power spectrum in two quantum dots

Abstract

We present studies of quantum interference in a noise power spectrum in the system of two quantum dots (2QD) in a T-geometry. Performing the spectral decomposition we are able to separate local currents and distinguish between the intra- and inter-level current correlation contributions to the noise power spectrum. In particular, we analyzed the large bias regime and show that for a weak coupling of 2QD with the electrodes the noise power spectrum has dips at frequencies characteristic to inter-level excitations. For a strong coupling the electron transport changes its nature and the dynamics of the current correlations is different: there are two coherently coupled relaxators with different relaxation frequencies. These two regimes of current dynamics are separated by a quantum critical point, in which the noise power spectrum shows a specific frequency dependence. In the linear response limit the noise power spectrum is related to the admittance, which shows characteristics different, due to quantum interference, for the weak and strong coupling case.

Figures (2)

• Figure 1: Frequency dependence of the current correlation $S_{LL} (\omega)$ in the large voltage bias regime for different couplings, $\gamma_L=\gamma_R=\gamma=0.1$, $0.5$ and $1.0$ (the red, blue and black curve, respectively). The dot levels are taken: $\epsilon_1=\epsilon_2=0$ and the inter-dot hopping parameter $t_{12}=-1$, which is taken as unity. The plots are normalized to $2eI$, with the current $I=(2e/\hbar)2\gamma_L\gamma_R/\gamma_N$. The inset shows the considered 2QD system.
• Figure 2: Real part of the admittance $\mathcal{G}_{LR}$ (in units of $2e^2/h$) and the density of the current cross-correlation function $\mathscr{S}_{LR}^{\text{eq}}$ plotted vs the Fermi energy $E_F$ and the single electron energy $E$ for different $\hbar\omega=$ 0, 1, 2, 4, as well as for the weak and strong coupling to the electrodes, $\gamma=0.5$ and $\gamma=1.5$, respectively. Temperature is taken $T=0$ and the other parameters are the same as in Fig.1.