Coherent manipulation of spin ensembles is a key issue in the development of spintronics. In particular, multivalued spin switching may lead to new schemes of logic gating and memories. This phenomenon has been studied with atom vapours 30 years ago, but is still awaited in the solid state. Here, we demonstrate spin multistability with microcavity polaritons in a trap. Owing to the spinor nature of these light-matter quasiparticles and to the anisotropy of their interactions, we can optically control the spin state of a single confined level by tuning the excitation power, frequency and polarization. First, we realize high-efficiency power-dependent polarization switching. Then, at constant excitation power, we evidence polarization hysteresis and determine the conditions for realizing multivalued spin switching. Finally, we demonstrate an unexpected regime, where our system behaves as a high-contrast spin trigger. These results open new pathways to the development of advanced spintronics devices and to the realization of multivalued logic circuits.

Multistability of a coherent spin ensemble in a semiconductor microcavity

Control of the switch between optical multistability and bistability in three-level V-type atoms

Effect of spontaneously generated coherence on optical bistability in three-level Λ-type atomic system

We have experimentally observed optical multistability (OM) in an optical ring cavity containing three-level $\ensuremath{\Lambda}$-type Doppler-broadened rubidium atoms. The shape of the OM curve can be significantly modified by changing the power of the control laser field. An all-optical multistate switching or coding element is realized and flexibly controlled by adding a pulse sequence to the input (probe) intensity.

Realization of all-optical multistate switching in an atomic coherent medium.

Non-linear interactions in coherent gases are not only at the origin of bright and dark solitons and superfluids; they also give rise to phenomena such as multistability, which hold great promise for the development of advanced photonic and spintronic devices. In particular, spinor multistability in strongly coupled semiconductor microcavities shows that the spin of hundreds of exciton-polaritons can be coherently controlled, opening the route to spin-optronic devices such as ultrafast spin memories, gates or even neuronal communication schemes. Here we demonstrate that switching between the stable spin states of a driven polariton gas can be controlled by ultrafast optical pulses. Although such a long-lived spin memory necessarily relies on strong and anisotropic spinor interactions within the coherent polariton gas, we also highlight the crucial role of non-linear losses and formation of a non-radiative particle reservoir for ultrafast spin switching.

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Ultrafast tristable spin memory of a coherent polariton gas

Optical tristability via optical pumping has been observed in the transmission of a Fabry-Perot interferometer containing Na vapor irradiated by light from a cw dye laser on the high-frequency wing of the ${D}_{1}$ line. For linearly polarized incident light, three stable states appear in the polarization of the transmitted light: ${\ensuremath{\sigma}}_{+}$ dominant, ${\ensuremath{\sigma}}_{\ensuremath{-}}$ dominant, and linear polarization.

Observation of Optical Tristability in Sodium Vapors

Multistability in a sodium filled Fabry-Perot: D1 line, hyperfine and Zeeman pumping

We report on the static and dynamic behavior of the intensity and polarization of the light transmitted by a Fabry–Perot cavity filled with sodium vapor without a buffer gas. The light beam is resonant with the D1 transition, and the behavior can be traced back to the simultaneous presence of Zeeman pumping and hyperfine pumping in the sodium ground state, combined with velocity-selective hole-burning effects. Together with optical bistability, tristability, and pitchfork bifurcation, the system displays intrinsic oscillations in the absence of a magnetic field. We discuss the features of these phenomena, particularly the appearance of Hopf bifurcations, and the ways they are affected by the experimental control parameters. We also report evidence of period doubling and of more-complex dynamics in the presence of a magnetic field.

Intrinsic oscillations in the polarization of light transmitted by a sodium-filled Fabry–Perot resonator

A Fabry-Perot cavity (FP) filled with sodium vapor has demonstrated to show a large variety of behaviors in its transmission when the input laser frequency is tuned across the D1 resonance. Many authors examined theoretically the dynamical behavior of optical resonators filled with a nonlinear medium at different levels of complexity, extending the first analysis of OT in a Λ three-level system with the inclusion of saturation of the upper state [1], or considering the role of induced ground-state coherence [2]; these models showed instabilities in the form of self-pulsing. Period doubling and chaos were also found in a four-level model [3] based on a J=1/2 to J’=1/2 transition. As a complementary approach, the coupling among four waves distinct in polarization and sense of propagation was theoretically examined in a nonlinear Kerr medium filling a cavity, and self-pulsing and chaos have been found [4].

S. Cecchi

Papers

Observation of Optical Tristability in Sodium Vapors

Multistability in a sodium filled Fabry-Perot: D1 line, hyperfine and Zeeman pumping

Intrinsic oscillations in the polarization of light transmitted by a sodium-filled Fabry–Perot resonator

Period Doubling and Intermittency in the Transmission of a Na Vapor-Filled Fabry-Perot

An experimental study of nonlinear effects in room temperature HgCdTe thermal optical bistability: Increasing absorption and self-defocusing