Dynamical Acoustic Control of Resonance Fluorescence from a Strongly Driven Two-Level System

Abstract

Resonance fluorescence from a single two-level system is a cornerstone of quantum optics. In the strong driving regime, its emission spectrum exhibits the iconic Mollow triplet, with each spectral component corresponding to a transition between distinct atom-photon dressed states. Here, we experimentally study the resonance fluorescence spectrum under a novel driving configuration in which a second gigahertz-frequency field drives the Rabi transition between two atom-photon dressed states. Our experiment is performed on a single semiconductor quantum dot strongly driven by a laser and a surface acoustic wave. We observe emission spectra that are significantly altered from the standard Mollow triplet, including the dynamical cancellation of resonance fluorescence at the central emission frequency. These spectra are explained by a theoretical model that incorporates the hybridization of the two-level system, the optical field, and the acoustic field. Motivated by this model, we experimentally validate the condition for optimal cooling of acoustic phonons in an emitter-optomechanical system. Our results offer new insights into the quantum interactions among single two-level systems, optical fields, and acoustic fields in the strong driving limit, with important applications in nonclassical acoustic state generation, quantum transduction, and quantum sensing of thermal motions.

Figures (4)

• Figure 1: A quantum dot implementing a two-level system with its frequency modulated by a surface acoustic wave.a, Schematic of a strongly driven quantum dot with Rabi transition between optically dressed states induced by a surface acoustic wave via dynamical frequency modulation. b, Photoluminescence spectra of the quantum dot as a function of the bias voltage. We operate our experiments at a bias voltage of 0.6 V (black dashed line), where the quantum dot is doped with a single electron. c, Intensity of the quantum dot resonance fluorescence as a function of the frequency of a weak excitation laser (i.e. the absorption spectrum of the quantum dot), showing a transition linewidth of 678 MHz. d, Optical microscope image of the device used for launching and confining the surface acoustic wave. SAW: surface acoustic wave. IDT: interdigital transducer. CPW: coplanar waveguide. p- and n-contacts: ohmic contacts to the p- and n-doped layers. e, Absorption spectra of the quantum dot as a function of the acoustic driving strength $\Omega_\text{S}$ (see Supplementary Section 1).
• Figure 2: Resonance fluorescence spectroscopy of a single quantum dot under various driving conditions.a, Energy levels of the atom-photon dressed states and allowed electric dipole transitions between the dressed states. In the absence of the acoustic drive (left panel), the two transition dipoles that contribute to the central peak of the Mollow triplet oscillate independently, giving rise to a simple intensity summation of their emission at the central frequency. In the presence of the acoustic drive (right panel), these two transition dipoles interfere destructively, resulting in the elimination of central emission peak at the Rabi resonance condition. b, Experimentally measured resonance fluorescence spectra as a function of the optical Rabi frequency $\Omega_\text{L}$ when the laser is resonant with the quantum dot, showing the standard Mollow triplets. c, Same measurement as in b, but with the acoustic drive fixed at $\Omega_\text{S}/2\pi=1.75$ GHz. Black dashed circle marks the dynamical cancellation of emission at the central frequency. d, Calculated spectra with the same parameters in c. e Measured spectra as a function of the laser detuning $\Delta$ in the absence of the acoustic drive, showing the detuned Mollow triplets. The Rabi frequency is fixed at $\Omega_\text{L}/2\pi=2.625$ GHz. f, Same measurement as in e, but with the acoustic drive fixed at $\Omega_\text{S}/2\pi=1.75$ GHz. Black dashed circles mark the dynamical cancellation of emission at the laser frequency. g, Calculated spectra with the same parameters in f.
• Figure 3: The doubly dressed state picture.a, Energy levels of the atom-photon-phonon system at Rabi resonance. The optical coupling $\hat{H}_\text{L}$ creates the atom-photon dressed states $\ket{\pm,n',m}=\frac{1}{\sqrt{2}}\left(\ket{g,n+1,m}\pm\ket{e,n,m}\right)$ from the bare states, separated by the optical Rabi frequency $\Omega_\text{L}$. The acoustic coupling $\hat{H}_\text{S}$ further lifts the degeneracy between states $\ket{-,n',m+1}$ and $\ket{+,n',m}$, creating the doubly dressed states $\ket{\widetilde{\pm},n',m'}=\frac{1}{\sqrt{2}}\left(\ket{+,n',m}\pm\ket{-,n',m+1}\right)$, separated by the acoustic driving strength $\Omega_\text{S}$. The dipole matrix elements of the transitions $\ket{\widetilde{\pm},n',m'}\to\ket{\widetilde{\pm},n'-1,m'}$ are zero (red dashed arrows), explaining the elimination of central spectral line at the Rabi resonance condition. The other two transitions, labeled "a" and "b" (red solid arrows), give rise to two spectral lines that anti-cross each other due to the acoustic dressing. b,c, Predicted transition frequencies of the resonance fluorescence spectra by the doubly dressed state picture (dashed lines), overlaid with the experimentally measured spectra shown in Figs. \ref{['fig2']}c and \ref{['fig2']}f, respectively.
• Figure 4: Optimal condition for optical cooling of acoustic phonons via a single quantum dot. a, Extracted phonon cooling rate from the measured resonance fluorescence spectra as a function of the optical Rabi frequency $\Omega_\text{L}$ and laser detuning $\Delta$. b, Calculated phonon cooling rate with the same parameters in a. Black dashed lines in a and b highlight the Rabi resonance condition, where the generalized Rabi frequency $\Omega_\text{R}$ matches the phonon frequency $\omega_\text{S}$.