Complete coherent control, initialisation, manipulation, and readout of a single electron spin bound to an impurity within zinc selenide has been achieved. This enables detailed investigation of the donor’s spin dynamics including relaxation times and Rabi oscillations; it also reveals coherent population trapping, a quantum state where excitation is suppressed, and hyperfine interactions between electrons and atomic nuclei. These findings establish isolated optical donors as promising building blocks for solid-state qubits with potential applications in scalable quantum technologies.

Complete light-based control over an individual electron’s spin within zinc selenide was demonstrated by both initiating and reading its state optically. Controlling single spins, the fundamental units of quantum information, with light offers a pathway to building scalable quantum technologies. The team observed key behaviours like ‘Rabi oscillations’, demonstrating precise manipulation of the spin, alongside evidence of interactions between electrons and atomic nuclei within the material itself.

Researchers from the University of Maryland and Forschungszentrum Jülich achieved complete light-based control over an individual electron’s spin within zinc selenide; this represents a sharp step towards building scalable quantum technologies. They demonstrated optical initialisation, setting the initial state of the spin, coherent manipulation using precisely timed laser pulses, and readout to determine its final state.

A key concept is ‘hyperfine interaction,’ which can be understood as tiny magnets within atoms subtly influencing the behaviour of the electron’s magnetic moment, much like nearby metal objects slightly deflect a compass needle. This precise control was evidenced by observing phenomena such as ‘Rabi oscillations’, akin to gently rocking a pendulum back and forth with predictable results, alongside evidence of interactions between electrons and atomic nuclei in the material itself.

Coherent Control Reveals Fast Spin Dynamics and Nuclear Access in Zinc Selenide

Spin relaxation dropped from unquantified levels to an experimentally determined 18.5 ±3.8μs, establishing a lower bound of 0.51ms for the intrinsic spin flip process, a threshold crossed through achieving coherent control absent in prior single donor level demonstrations. The University of Maryland team completed optical initialisation, manipulation, and readout of individual electron spins within zinc selenide using picosecond laser pulses tuned to exploit spin-selective exciton transitions; Rabi oscillations and Ramsey interference confirmed precise adjustments to these spin states. This breakthrough reveals hyperfine interactions between electrons and chlorine nuclei, suggesting potential access to nuclear spin as additional quantum memory, thus positioning ZnSe donors as promising solid-state qubits for scalable quantum technologies.

An inhomogeneous dephasing time of 21.9ns further characterised the newly controlled quantum state, complementing the established spin relaxation time. Utilising this nuclear spin could provide increased storage capacity for quantum information; high-contrast coherent population trapping was also demonstrated, forming an optically controlled ‘dark state’ insensitive to excitation, vital for protecting fragile states from environmental noise.

Optical Initialisation and Readout of Donor Spins via Off-Resonant Exciton Transitions

The team employed spin-selective exciton transitions, special ways electrons within impurities interact with light, to initialise and read out individual donor spins in zinc selenide. Carefully tuned picosecond optical pulses delivered *off*-resonance (slightly detuned from exact excitation energies) allowed precise control without directly exciting unwanted states. This approach bypasses the need for traditional microwave manipulation, opening avenues towards fully integrated photonic quantum technologies; subtle differences in how electron spin affects light absorption and emission enabled scientists to manipulate the spin state using only photons.

Zinc selenide nanoposts were fabricated, each approximately 200 nanometres in diameter containing between two and three chlorine atoms, within a density δ-doped layer of around ten billion impurities per square centimetre, this isolation technique enables individual optical donors. Measurements occurred at 3.6 Kelvin utilising confocal magnetooptical microscopy with high numerical aperture lenses for efficient photon collection. The fabrication process bypassed previous limitations caused by charge noise.

Optical Control Versus Hyperfine Limits in Zinc Selenide Qubits

Creating strong qubits that can be precisely controlled and reliably read out is essential for scalable quantum technologies; this work addresses key challenges achieving such control within solid-state materials through complete optical manipulation of an electron spin trapped inside zinc selenide. Despite advances demonstrated via techniques like Rabi oscillations and population trapping, inherent hyperfine interactions between electrons and chlorine nuclei present as impurities limit information stability within the qubit, these create slight variations in energy levels. This demonstration of fully optically controlled coherent manipulation bypasses microwave control previously required in solid-state qubit research.

Confirming precise adjustment of the quantum state without external magnetic fields or radiofrequency signals represents an advance towards scalable photonic quantum technologies while also revealing opportunities to use nuclear spins for increased storage capacity. Mitigating the influence of these hyperfine effects on coherence times remains crucial; exploring methods to manage them will be key going forward. The team’s work not only demonstrates complete optical control but also highlights how managing these interactions could unlock even greater potential from zinc selenide qubits, paving the way toward robust and reliable quantum information processing. Further investigation into optimising this delicate balance between control and stability is essential for realising fully functional solid-state quantum devices.

Researchers demonstrated optical initialization, coherent control, and readout of a single electron spin bound to an impurity within zinc selenide. This achievement means that the qubit’s state can be manipulated using light alone, bypassing previous reliance on microwave signals, a step towards more scalable solid-state quantum technologies.

The study resolved spin relaxation dynamics and observed Rabi oscillations as well as population trapping with picosecond optical pulses at 3.6 Kelvin. While hyperfine interactions with chlorine nuclei currently limit information storage time, these results identify isolated impurities in II-VI semiconductors as a promising platform for optically active qubits.

👉 More information
🗞 Coherent Optical Control of a Single Donor Electron Spin
✍️ Yuxi Jiang, Amirehsan Alizadehherfati, Jasvith R. Basani and Edo Waks (University of Maryland); Christine Falter, Nils von den Driesch, Yurii Kutovyi, Jan Seelbinder and Alexander Pawlis (Forschungszentrum Jülich and RWTH Aachen University)
🧠 ArXiv: https://arxiv.org/abs/2610.36423

More like this