Coherent Heteronuclear Spin Dynamics in an Ultracold Spinor Mixture

We report the observation of coherent heteronuclear spin dynamics driven by interspecies spin-spin interaction in an ultracold spinor mixture, which manifests as periodical and well-correlated spin oscillations between two atomic species. In particular, we investigate the magnetic field dependence of the oscillations and find a resonance behavior which depends on both the linear and quadratic Zeeman effects and the spin-dependent interaction. We also demonstrate a unique knob for controlling the spin dynamics in the spinor mixture with species-dependent vector light shifts.

Figure 1

Magnetic energy diagram for two heteronuclear spin-changing processes. For the process in Eq. (2) (blue curve), $\mathrm{\Delta }E$ has a zero-crossing point at $B_0=1.69\mathrm{G}$. Spin-changing process $|0,1⟩\leftrightarrow |1,0⟩$ (red dashed curve) has a large detuning near $B_0$ and is greatly suppressed.

Figure 2

Coherent heteronuclear spin dynamics at $B=1.9\mathrm{G}$. (a),(b), evolution of the fractional spin population of Rb (circle) and Na (square). (c),(d), magnetization oscillations of Rb and Na. The oscillation amplitudes differences are due to the number imbalance. Inset: evolution of total magnetization. Solid lines are sinusoidal fitting.

Figure 3

Dependence of heteronuclear spin dynamics on external magnetic field $B$. (a) Spin oscillations at $B=1.5$ (top), 1.7 (middle), and 1.9 G (bottom) for $|-1⟩$ of Rb (red circle) and $|0⟩$ of Na (blue squares). The solid curves are for eye guiding and error bars are from statistics of several shots. (b) Magnetic energy $\mathrm{\Delta }E$ vs $B$. (c),(d) Spin oscillation amplitudes (c) and periods (d) extracted from the Rb data. Solid blue lines are calculations based on many-body kinetic equations using experimental atomic conditions without fitting parameters. Error bars for both the amplitude and the period are from fitting of the oscillations and represent 1 standard deviation. Mechanisms for the observed damping in the oscillations will be investigated in future works.

Figure 4

Optical control of coherent heteronuclear spin dynamics with vector light shift. (a) Modified dependence of $\mathrm{\Delta }E$ on $B$ with light induced effective magnetic field $B_{\mathrm{ac}}$ on Rb. (b) Resonance positions as observed in the period vary with changing $B_{\mathrm{ac}}$. Solid curves are to guide the eye and error bars are from fitting of the oscillations. $B_{\mathrm{ac}}$ is calculated based on the measured light intensity $I$ and $\wp$.