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Description
Quantum emitters in transition metal dichalcogenides (TMDs), such as WSe2, are promising sources of single photons for quantum technologies, where one qubit is encoded in the quantum state of a single photon. The layered nature of TMDs allows straightforward fabrication and seamless integration of the source with other photonic structures. However, both the total efficiency (defined as the number of collected photons per excitation trigger) and the indistinguishability of emitted photons must be increased close to unity to scale up the number of available qubits.
High collection efficiency from WSe2 emitters coupled to a photonic cavity was recently demonstrated thanks to an excellent control of the emission dynamics [1]. On the other hand, a significant challenge is to find efficient and scalable solutions to control the excitation dynamics, namely, to excite the emitter on-demand and with near unity fidelity. It is widely accepted that resonant excitation poses a fundamental limitation to the efficiency due to polarization filtering of the outgoing single photons, while pumping into a higher energy state limits the indistinguishability significantly. Thus, identifying suitable non-resonant excitation schemes and assessing their performance is of the utmost importance.
In this work [2], we investigate the excitation dynamics of WSe2 emitters under different schemes, unveiling the critical role of phonons on the state preparation fidelity. We develop a quantitative theory of WSe2 emitters interacting with 2D acoustic phonons, and fit the parameters to our own experimental results. Crucially, the model shows that phonon coupling in this platform is an order of magnitude stronger compared to established InAs/GaAs quantum dot emitters, in agreement with recent experiments [3].
Using our detailed phonon theory, we assess the performance of different state-preparation protocols. We show, for example, that the well-known Rabi oscillations are strongly suppressed by phonon scattering in WSe2. On the other hand, near-resonant phonon-assisted excitation [4] allows to prepare the exciton state with fidelity larger than 99\%. We also discuss how to excite WSe2 emitters with the so-called SUPER scheme [5], where the impact of phonon coupling is crucial but often under-estimated [6]. Finally, we provide a quantitative description of the spectral broadening induced by phonon coupling, which sets fundamental limitations on the single-photon indistinguishability.
This work provides fundamental insights into the physics of phonon coupling in WSe2 emitters, offering an avenue to control the excitation process.
[1] J.-C. Drawer et al., Nano Lett. 23, 8683 (2023).
[2] L. Vannucci et al., Phys. Rev. B 109, 245304 (2024).
[3] V. N. Mitryakhin et al., Phys. Rev. Lett. 132, 206903 (2024).
[4] S. E. Thomas et al., Phys. Rev. Lett. 126, 233601 (2021).
[5] T. Bracht et al, PRX Quantum 2, 040354 (2021).
[6] L. Vannucci and N. Gregersen, Phys. Rev. B 107, 195306 (2023).
