Optical Bistability under Nonresonant Excitation in Spinor Polariton Condensates

We realize bistability in the spinor of polariton condensates under nonresonant optical excitation and in the absence of biasing external fields. Numerical modeling of the system using the Ginzburg-Landau equation with an internal Josephson coupling between the two spin components of the condensate qualitatively describes the experimental observations. We demonstrate that polariton spin bistability strongly depends on the condensate’s overlap with the exciton reservoir by tuning the excitation geometry and sample temperature. We obtain noncollapsing bistability hysteresis loops for a record range of sweep times, [$10\mu \mathrm{s}$, 1 s], offering a promising route to spin switches and spin memory elements.

Figure 1

Schematic of the optical excitation scheme. The red ring on the surface of the microcavity is an intensity map of the pump beam; the black mesh annular barrier represents the confining potential due to the exciton reservoir. A section of the barrier is removed to show the trapped condensate shown as the rainbow-colored Gaussian mode in the center of the confining potential. The red and the blue spheres show the spin-up and spin-down states forming the condensate, respectively. The arrow shows a current of polaritons between the two spin states.

Figure 2

Schematic of the experimental setup. SLM, spatial light modulator; AOM, acousto-optical modulator; PBS, polarizing beam splitter; DBS, dichroic beam splitter; Obj, microscope objective lens; $L$, plano-convex lens; $\lambda /4$, quarter wave plate; $\lambda /2$, half wave plate; and PD (1,2,3) photodiodes measuring the spin components of the photoluminescence and the corresponding laser intensity. (a) Measured third Stokes component $S_Z$, representing the degree of circular polarization (DCP) versus pump power displaying the characteristic hysteresis loop of bistability for an annulus of $\sim 16.1\mu \mathrm{m}$ diameter and 1.67 ms sweep time at a detuning of $-7.6\mathrm{meV}$. (b) Hysteresis loop in $S_Z$ versus pump power resulting from the numerical simulations.

Figure 3

(a) The dependence of the hysteresis area (symbols) on the diameter of the annular pump at $\sim 6\mathrm{K}$. The dotted red line shows the estimated overlap between the condensate and exciton reservoir, $\mathrm{\Omega }$, versus the annular pump diameter. The vertical dash-dotted line separates the regimes wherein only the ground state ${\psi }_{00}$, or both ${\psi }_{00}$ and the first excited state ${\psi }_{01}$, coexists. (b) Temperature dependence of the hysteresis area for an $\sim 15.4\mu \mathrm{m}$ diameter annular pump. The data in (a) and (b) are recorded with a 1 ms sweep time. (c) Hysteresis area as a function of sweep time $T_P$ for an $\sim 13.1\mu \mathrm{m}$ diameter annular pump recorded at $\sim 6\mathrm{K}$. The black (red) lines are power-law fits. In all of the above data points, solid circles are recorded at a detuning of $-11.2\mathrm{meV}$, while solid diamonds at $-7.6\mathrm{meV}$.