[Paper Review] Hybrid acousto-optical swing-up state control in a quantum dot

Mateusz Kuniej, Paweł Machnikowski+1 more|arXiv (Cornell University)|Feb 12, 2024

Spectroscopy Techniques in Biomedical and Chemical ResearchBiochemistry, Genetics and Molecular Biology3 citations

TL;DR

This paper proposes a hybrid acousto-optical swing-up scheme to deterministically prepare exciton and biexciton states in quantum dots using a single optical or acoustic pulse, leveraging detuned excitation to avoid filtering losses. It demonstrates that GaAs/AlGaAs quantum dots can achieve near-decoherence-free exciton preparation at liquid nitrogen temperatures, enabling high-fidelity state preparation for quantum information applications.

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.

Motivation & Objective

• To overcome the limitations of resonant excitation schemes in quantum dots, which require spectral filtering that reduces photon yield.
• To develop a non-resonant, deterministic state preparation method that avoids filtering and incoherent relaxation paths.
• To explore the use of acoustic fields as a tunable control parameter for selective excitation of excitonic states.
• To evaluate phonon-induced decoherence in InAs/GaAs and GaAs/AlGaAs quantum dots under realistic conditions.
• To identify material platforms where near-decoherence-free state preparation is feasible at experimentally accessible temperatures.

Proposed method

• Proposes a hybrid acousto-optical swing-up protocol using detuned optical and acoustic fields to drive coherent Rabi-like oscillations between ground, exciton, and biexciton states.
• Utilizes detuned excitation to avoid resonant filtering issues, with the detuning modulated via strain-induced shifts from acoustic waves or optical frequency tuning.
• Models the system as a three-level Hamiltonian with coupling to phonons via deformation potential and piezoelectric effects, using a spectral density approach to calculate decoherence.
• Derives the fidelity of state preparation using a general expression involving spectral densities and correlation functions, accounting for phonon bath effects.
• Computes phonon spectral densities using material parameters from InAs/GaAs and GaAs/AlGaAs quantum dots, including wave function form factors and phonon dispersion.
• Evaluates temperature dependence of decoherence by integrating Bose-Einstein distributions over phonon modes across LA, TA1, and TA2 branches.

Experimental results

Research questions

• RQ1 Can a single acoustic or optical pulse be used to selectively prepare either the exciton or biexciton state in a quantum dot without requiring two precisely timed pulses?
• RQ2 How does acoustic modulation of the detuning compare to optical detuning in terms of fidelity and control over excitonic state preparation?
• RQ3 What is the impact of phonon-induced decoherence on state preparation fidelity in InAs/GaAs and GaAs/AlGaAs quantum dots at finite temperatures?
• RQ4 At what temperature can GaAs/AlGaAs quantum dots achieve near-decoherence-free exciton preparation with current acoustic modulation capabilities?
• RQ5 Can the hybrid acousto-optical scheme enable deterministic generation of polarization-entangled photon pairs without spectral filtering?

Key findings

• The hybrid acousto-optical swing-up scheme enables deterministic preparation of exciton and biexciton states using only one optical pulse and one acoustic mode, or vice versa, by modulating the detuning.
• For GaAs/AlGaAs quantum dots, the exciton state preparation fidelity remains nearly decoherence-free even at liquid nitrogen temperatures (77 K), due to favorable phonon spectral density and coupling parameters.
• InAs/GaAs quantum dots exhibit stronger phonon-induced decoherence due to higher deformation potential and electron-hole localization, limiting performance at higher temperatures.
• The spectral density analysis shows that piezoelectric and deformation potential contributions are both significant, with the latter dominating in GaAs-based systems.
• At 4 K, the total phonon spectral density for GaAs/AlGaAs QDs peaks around 1.5 THz, with a broader distribution than in InAs/GaAs, indicating better coherence properties.
• Temperature dependence analysis reveals that decoherence increases with temperature, but remains negligible for GaAs/AlGaAs at 77 K, making it a promising platform for room-temperature-compatible quantum devices.