Electrical Control of Optically Active Single Spin Qubits in ZnSe

TL;DR

This work demonstrates electrical control of single donor-bound excitons in ZnSe quantum wells by applying lateral electric fields via patterned surface electrodes. The DC Stark effect enables tuning of emission energies over a broad range to overcome inhomogeneous broadening, while the field stabilizes the local charge environment, halving the optical linewidth and suppressing spectral wandering. A two-state trap model qualitatively captures how trap dynamics respond to electrical and optical stabilization, linking occupancy probabilities to spectral properties. The findings suggest that electrical control can simultaneously optimize spectral addressability and spin coherence, with potential routes to transform-limited emission via device redesign such as Schottky diodes for out-of-plane fields. Overall, electrical tuning and stabilization emerge as powerful strategies for impurity-based quantum emitters in ZnSe.

Abstract

Electrons bound to shallow donors in ZnSe quantum wells are promising candidates for optically addressable spin qubits and single-photon sources. However, their optical coherence and indistinguishability are often limited by spectral broadening arising from charge fluctuations in the local environment. Here, we report electrical control of single donor qubits in ZnSe quantum wells. The applied field induces a DC Stark shift that tunes the emission energy over a range exceeding 30 times the inhomogeneous linewidth, effectively compensating for emitter-to-emitter variations. Concurrently, the field stabilizes trap occupancy, yielding a twofold reduction in optical linewidth and the suppression of spectral wandering. A statistical model based on trap dynamics qualitatively reproduces these observations and elucidates the mechanism of field-assisted charge noise suppression. Our results identify electrical control as a versatile pathway to significantly improve optical and spin addressability.

Figures (3)

• Figure 1: Device illustration and magneto spectroscopy characterization. (a) Schematic of device geometry, consisting of ZnMgSe/ZnSe:Cl/ZnMgSe quantum well, ZnSe buffer, AlO$_x$ capping and GaAs substrate, with electrodes on the top and connections. (b) Crystal structure Zn(blue)Se(pink) with Cl(green) as a substitutional donor and bound electron (yellow). (c) Optical microscope image of the fabricated electrodes. The gold-colored regions highlight the patterned electrodes, designed for lateral electric field application. (d) Photoluminescence spectrum of donor-bound exciton in Voigt configuration shows four distinct peaks with two orthogonal polarization.
• Figure 2: Characterization of the Stark shift in a single bound exciton. (a) Photoluminescence bias map. (b) Integrated intensity as a function of the applied bias. (c) Full width at half maximum of the emission line as a function of the applied bias.
• Figure 3: Manipulation of charge environment around donor site. (a) Emission spectrum under resonant excitation of the free exciton line for different electric fields. (b) The narrowing effect from the electric field suggests an optimal field of around 35 V is suitable to stabilize the bound exciton emission. The theoretical curve corresponds to about 18 traps distributed in the region of 3n m to 5n m from donor with average trap depth of 0.3eV and initial occupancy of 0.35. We extract these values based on a numerical fit constrained by the donor's effective Bohr radius and typical defect densities in ZnSe. (c) Emission spectra recorded for varying weak above-band excitation powers in the absence of an electric field. (d) Dynamics of linewidth and central wavelength as a function of different above-band intensities. The theoretical curves correspond to an average saturation power of 1 nW and an initial trap occupancy of about 0.4. We extract these values based on a numerical fit to a statistical model. (e) The electric field stabilizes the fluctuating traps by polarizing the occupancy probability toward 0. (f) The process of filling trap states and eliminating the fluctuating charge environment through free carrier injection pushes occupancy toward unity.