Figure 1

(Color online) Schematic band structure and level configuration of a single QD photodiode in the presence of pulsed polarized light. (a) A polarized laser pulse creates excitations (exciton and biexciton) in the dot, and an applied gate voltage forces the electrons and holes to tunnel out, generating the measured photocurrent signal. (b) Processes and levels involved in this system: $\mid X_{\pm }⟩$ and $\mid B⟩$ are the different exciton-polarization and biexciton states, respectively. Coherent ($\sigma$’s, solid lines) and incoherent ($\Gamma$’s, wavy lines) transitions that occur in the system among the various exciton states $\mid X_{\pm }⟩$, the biexciton $\mid B⟩$, and the ground state $\mid 0⟩$. Curved lines indicate the role of the anisotropic exchange interaction $V$, mixing the $\mid X_{\pm }⟩$ states. Different energies and detunings are indicated on the right axis.Reuse & Permissions

Figure 2

(Color online) Bottom panel: degree of spin polarization of the photocurrent signal as function of pulse area $\Theta$ and polarization angle $\varphi$ of the incoming light. Upper panel: photocurrent polarization for $\varphi =\pi ∕8$ (dashed line on the contour plot), where local maximum contrast is evident. Note the spin reversal of the photocurrent signal for $\Theta \simeq 2\pi$. Right and left insets show light polarization angle and the $0.5\mathrm{ps}$ FWHM Gaussian pulse used, respectively.Reuse & Permissions

Figure 3

(Color online) Photocurrent polarization map vs pulse area $\Theta$ and pulse length for elliptically polarized incoming light with $\varphi =\pi ∕8$, corresponding to the dashed line in Fig. 2. The dashed line here shows the pulse length used in Fig. 2. Inversion of signal is strongly suppressed for longer pulses and the remaining modulation features are due to small anisotropic $e\text{−}h$ exchange interaction $(V=35\mu \mathrm{eV})$.Reuse & Permissions

Figure 4

(Color online) Spin-polarization map vs pulse area and angle; this is the analog of Fig. 2 but for a coherent dot system, using the analytical result, Eq. (13). Notice the same structure of spin-polarization reversals as in Fig. 2, made smoother there by decoherence and relaxation processes and pulse shape effects in the full model.Reuse & Permissions

Figure 5

(Color online) Photocurrent polarization map vs pulse area and anisotropic $e\text{−}h$ exchange interaction $V$ for $1\text{−}\mathrm{ps}$-wide circularly polarized Gaussian pulse ${\sigma }_{+}$ $(\varphi =0)$. Strong exchange interaction $V=1\mathrm{meV}$ (dashed line) results in strong oscillations of polarization as pulse area $\Theta$ increases.Reuse & Permissions

Figure 6

(Color online) Polarization of the photocurrent signal as function of the pulse area for an ensemble of QDs for three different pulse widths and polarization angle $\varphi =\pi ∕8$. The Gaussian size distribution has 20% FWHM.Reuse & Permissions