Hybrid acousto-optical swing-up state control in a quantum dot

Abstract

State transfer between different quantum systems is key for successful quantum technologies. Over long distances, photons are irreplaceable, but on short ranges in miniaturized complex devices or hybrid systems, coupling via orders of magnitude shorter-wavelength acoustic waves has great potential. With interfaces to light, acoustic waves, and more, optically active quantum dots (QDs) are essential for multi-component systems. Here, we propose a hybrid acousto-optical method for non-resonant QD charge state control, extending the recent all-optical swing-up state preparation. We show that exciton and biexciton states, or other superpositions of charge states, can be prepared. Each field can act as a trigger, allowing for the implementation of either an optically gated acoustic control or the opposite scheme, where an optical pulse controls the transition during acoustic modulation. Thus, we introduce acoustic state control into a system that lacks direct acoustic coupling between the states. The method does not rely on pulse shaping and is expected to work with arbitrary pulse shapes as long as the optical dressing is performed quasi-adiabatically. Evaluating the phonon impact, we find an almost decoherence-free exciton preparation even at elevated temperatures with current QD and acoustic technology. This approach may also pave the way for optically controlled entanglement between emitters and acoustic modes, and further on-chip state transfer via quantum acoustic buses.

Figures (6)

• Figure 1: Schematic energy structure of the studied three-level system with external fields. (a) Ground $\ket{\mathrm{g}}$ and two excited levels, $\ket{\mathrm{x}}$ and $\ket{\mathrm{xx}}$, corresponding to the exciton and biexciton in a QD. Acoustic modulation of the excited states is marked with green and violet arrows. Two optical driving cases are marked: $\ket{\mathrm{x}}$ preparation (red arrow) and $\ket{\mathrm{xx}}$ preparation (blue arrow); (b) Dressed-states picture with acoustic field frequencies tuned for $\ket{\mathrm{g}}$--$\ket{\mathrm{x}}$ (green arrow) and $\ket{\mathrm{g}}$--$\ket{\mathrm{xx}}$ (violet arrow) transitions.
• Figure 2: Optically gated acoustic control. Exciton preparation with quasi-continuous optical coupling and acoustic $\pi$-rotation control pulse: (a) envelopes of acoustic and optical pulses, (b) bare states occupations; inset shows state evolution on the Bloch sphere, (c) occupations of the dressed states. Parameters used: $\hbar\Delta = 1.75$ meV, $\hbar A_{\mathrm{L}} = 1.75$ meV, $\sigma_{\mathrm{L}} = 11.7$ ps, $\hbar A_{\mathrm{ac}} = 0.35$ meV, $\sigma_{\mathrm{ac}} = 8.36$ ps, $\hbar\omega_{\mathrm{ac}} = 2.474$ meV, $\kappa_{\mathrm{L}} = 3.34$ ps, and $\kappa_{\mathrm{ac}} = 1.67$ ps.
• Figure 3: Acoustically gated optical control: exciton preparation. (a) Optimal acoustic-field parameters for exciton preparation. Occupation of the exciton state $\ket{\mathrm{x}}$ as a function of acoustic field parameters for a Gaussian optical pulse ($\hbar\Delta = 1.75$ meV, $\hbar A_{\mathrm{L}} = 1.75$ meV, $\sigma_{\mathrm{L}} = 11.7$ ps) and constant envelope of acoustic driving. We mark a point corresponding to the maximum occupation (black circle) and a point given by analytical prediction [Eq. \ref{['eq:omega-ac']} and Eq. \ref{['eq:acousticAmplitudeCondition']}] for flat-top pulses (white circle). (b) Evolution of bare states occupation in the two-level system (left axis) and external field amplitudes (right axis) for acoustic field parameters corresponding to the black circle in panel (a).
• Figure 4: Biexciton preparation.(a) Occupation of the biexciton as a function of acoustic field parameters for a Gaussian optical pulse with ($\hbar\Delta_{\mathrm{xx}} = -2.5$ meV, $\hbar A_{\mathrm{L}} = 1.5$ meV, $\sigma_{\mathrm{L}} = 11.7$ ps) and constant envelope of acoustic driving. The black circle marks the optimal parameters. (b) Evolution of state occupations in the three-level system (left axis) and external field amplitudes (right) for acoustic field parameters corresponding to the black circle in panel (a).
• Figure 5: Impact of laser pulse duration. (a) Maximal post-pulse occupation of the desired state and (b) the fidelity of this final state calculated as a function of the laser pulse duration $\sigma_{\mathrm{L}}$. Solid (dashed) lines correspond to GaAs (InAs) QDs; red (blue) lines are for the exciton (biexciton) state. Recombination times used: $\tau_{\mathrm{x}}^{\mathrm{(GaAs)}}=0.426$ ns, $\tau_{\mathrm{xx}}^{\mathrm{(GaAs)}}=0.39$ ns Heyn2012, $\tau_{\mathrm{x}}^{\mathrm{(InAs)}}=1.22$ ns, $\tau_{\mathrm{xx}}^{\mathrm{(InAs)}}=0.76$ ns Feucker2008. The vertical dashed line marks $\sigma_{\mathrm{L}}=11.7$ ps, while the pale red (blue) vertical dotted line marks the optimal value for the $\ket{\text{x}}$ ($\ket{\text{xx}}$) state.