Control and Ultrafast Dynamics of a Two-Fluid Polariton Switch

We investigate the cross interactions in a two-component polariton quantum fluid coherently driven by two independent pumping lasers tuned at different energies and momenta. We show that both the hysteresis cycles and the on-off threshold of one polariton signal can be entirely controlled by a second polariton fluid. Furthermore, we study the ultrafast switching dynamics of a driven polariton state, demonstrating the ability to control the polariton population with an external laser pulse, in less than a few picoseconds.

Figure 1

Upper panel: experimental polariton dispersion relation with superimposed two laser pumps at the corresponding energy ($E_1=1.482\mathrm{eV}$ and $E_2=1.4826\mathrm{eV}$) and momenta ($k_1=0.2\mu {\mathrm{m}}^{-1}$ and $k_2=0.4\mu {\mathrm{m}}^{-1}$) used to excite two different polariton states. Lower panels: theoretically evaluated phase diagram showing the off and on states of state S1 (left panel) and state S2 (right panel) as a function of the rescaled pump intensities $f_{1,2^{\prime }}=\sqrt{g_X}{f}_{1,2}[\mathrm{me}{\mathrm{V}}^{3/2}]$. In the yellow region the states S1 and S2 can only be weakly populated (off), while in the red one they can only be strongly populated (on). In the green region both on and off solutions coexist (bistable region). The black thick vertical and horizontal lines correspond to the cases studied in Fig. 2, where one pump is kept constant while the other scans different intensity values.

Figure 2

Experimental (1e, 2e, 3e, and 4e) and theoretical (1t, 2t, 3t, and 4t) normalized emission intensities from the two states S1 (black) and S2 (red) obtained by either changing the pump power P1 for fixed pump power P2 (left column), or changing pump power P2 for a fixed pump power P1 (right column). Arrows and symbols correspond to the power change variation: increasing power, solid symbol; decreasing power, open symbols. Note that for the theoretical emission intensity we consider $|\Psi ^{SS}{}_{1C}{|}^2$ and $|\Psi ^{SS}{}_{2C}{|}^2$, respectively, which are proportional to the experimental emission intensities when the Hopfield factors are taken into account.

Figure 3

Time-resolved photoluminescence intensity of state S1 excited by a cw (P1) and a fs pulsed (P2) laser under the conditions shown in the inset of Fig. 2a): $k_1=0.35\mu {\mathrm{m}}^{-1}$ and $E_1=1.494\mathrm{eV}$, $k_2=0.73\mu {\mathrm{m}}^{-1}$ and $E_2=1.491\mathrm{eV}$. The spectra shown are obtained under four different excitation conditions: (a) the state is pumped only by the cw laser P1 at a very low pump power of 3.3 mW. Under this condition state S1 is on an off state; (b) state S1, same as in (a) but a fs pulsed laser exciting the system with a low power $\mathrm{P}2=6\mathrm{mW}$ switches on the S1 state; (c), (d) state S1, in an on state (continuously pumped by P1 at 30 mW), is switched off by the pulsed laser. The insets in (b) and (d) show the influence of a fs pulsed laser (P2) pumping the system resonantly. The continuous pump P1 is schematized by the red dots.