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arXiv:2606.05033

Crossover from Rabi oscillations to adiabatic population switching in the Faraday optical control of quantum dot spins

Jan M. Kaspari, Zhe Xian Koong, Dorian A. Gangloff, Michał Gawełczyk, Doris E. Reiter

cond-mat.mes-hallquant-phSubmitted Jun 3, 2026• Announced Jun 4, 2026• 0 citations
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Abstract

Stimulated Raman transitions in Faraday geometry allow for simultaneous single-shot qubit readout and qubit control. It involves driving an unbalanced $Λ$ system via an auxiliary excited state. Due to the simultaneous driving of both transitions with unequal detuning, the resulting time-dependent Stark shift gives rise to additional resonance conditions beyond the conventional picture. We identify a distinct regime in which repeated passages through avoided crossings lead to step-like population inversion arising from Landau-Zener-Stückelberg interference. By changing the detuning beatnote, we demonstrate a controlled continuous crossover from Rabi-like oscillations to adiabatic population switching. These findings establish the oscillating Stark shift as a mechanism for engineering and controlling spin dynamics in Faraday geometry.

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Stimulated Raman transitions in Faraday geometry allow for simultaneous single-shot qubit readout and qubit control. It involves driving an unbalanced ΛΛΛ system via an auxiliary excited state. Due to the simultaneous driving of both transitions with unequal detuning, the resulting time-dependent Stark shift gives rise to additional resonance conditions beyond the conventional picture. We identify a distinct regime in which repeated passages through avoided crossings lead to step-like population inversion arising from Landau-Zener-Stückelberg interference. By changing the detuning beatnote, we demonstrate a controlled continuous crossover from Rabi-like oscillations to adiabatic population switching. These findings establish the oscillating Stark shift as a mechanism for engineering and controlling spin dynamics in Faraday geometry.
Abstract Solid-state spins are promising as interfaces from stationary qubits to single photons for quantum communication technologies. Semiconductor quantum dots have excellent optical coherence, exhibit near-unity collection efficiencies when coupled to photonic structures, and possess long-lived spins for quantum memory. However, the incompatibility of performing optical spin control and single-shot readout simultaneously has been a challenge faced by almost all solid-state emitters. To overcome this, we leverage light-hole mixing to realize a highly asymmetric lambda system in a negatively charged heavy-hole exciton in Faraday configuration. By compensating GHz-scale differential Stark shifts, induced by unequal coupling to Raman control fields, and by performing nuclear-spin cooling, we achieve quantum control of an electron-spin qubit with a π-pulse contrast of 97.4% while preserving spin-selective optical transitions with a cyclicity of 471 (50). We demonstrate this scheme for both GaAs and InGaAs quantum dots, and show that it is compatible with the operation of a nuclear quantum memory. Our approach thus enables repeated emission of indistinguishable photons together with qubit control, as required for single-shot readout, photonic cluster-state generation, and quantum repeater technologies.
Solid-state spins are promising as interfaces from stationary qubits to single photons for quantum communication technologies. Semiconductor quantum dots have excellent optical coherence, exhibit near-unity collection efficiencies when coupled to photonic structures, and possess long-lived spins for quantum memory. However, the incompatibility of performing optical spin control and single-shot readout simultaneously has been a challenge faced by almost all solid-state emitters. To overcome this, we leverage light-hole mixing to realize a highly asymmetric lambda system in a negatively charged heavy-hole exciton in Faraday configuration. By compensating GHz-scale differential Stark shifts, induced by unequal coupling to Raman control fields, and by performing nuclear-spin cooling, we achieve quantum control of an electron-spin qubit with a π-pulse contrast of 97.4% while preserving spin-selective optical transitions with a cyclicity of 471 (50). We demonstrate this scheme for both GaAs and InGaAs quantum dots, and show that it is compatible with the operation of a nuclear quantum memory. Our approach thus enables repeated emission of indistinguishable photons together with qubit control, as required for single-shot readout, photonic cluster-state generation, and quantum repeater technologies.
Landau-Zener (LZ) transition has received renewed interest as an alternative approach to control single-qubit states. An LZ transition occurs when a system passes through an avoided crossing that arises from quantum mechanical coupling of two levels, taking the system to a coherent superposition of the two states. Then, multiple LZ transitions induce interference known as Landau-Zener-Stückelberg (LZS) interference whose amplitude strongly depends on the velocity or adiabaticity of the passage. Here, we study the roles of LZ transitions and LZS interference in coherent charge oscillations of a one-electron semiconductor double quantum dot by time-domain experiments using standard rectangular voltage pulses. By employing density matrix simulations, we show that, in the standard setup using rectangular pulses, even a small distortion of the pulse can give rise to LZ transitions and hence LZS interference, which significantly enhances the measured oscillation amplitude. We further show experimentally that the nature of the coherent charge oscillations changes from Rabi-type to LZS oscillations with increasing pulse distortion. Our results thus demonstrate that it is essential to take into account LZS interference for both precise control of charge qubits and correct interpretation of measurement results.
We report Ramsey interference in the excitonic population of a negatively charged quantum dot measured in resonant fluorescence. Our experiments show that the decay time of the Ramsey interference is limited by the spectral width of the transition. Applying a vertical magnetic field induces Zeeman split transitions that can be addressed by changing the laser detuning to reveal two-, three-, and four-level system behavior. We show that under finite field the phase-sensitive control of two optical pulses from a single laser can be used to prepare both population and spin states simultaneously. We also demonstrate the coherent optical manipulation of a trapped spin in a quantum dot in a Faraday geometry magnetic field.
A new regime of coherent quantum dynamics of a qubit is realized at low driving frequencies in the strong driving limit. Coherent transitions between qubit states occur via the Landau-Zener process when the system is swept through an energy-level avoided crossing. The quantum interference mediated by repeated transitions gives rise to an oscillatory dependence of the qubit population on the driving-field amplitude and flux detuning. These interference fringes, which at high frequencies consist of individual multiphoton resonances, persist even for driving frequencies smaller than the decoherence rate, where individual resonances are no longer distinguishable. A theoretical model that incorporates dephasing agrees well with the observations.
This paper studies the carrier-phonon dynamics in the optical control of the spin states in a single doped semiconductor quantum dot by means of a perturbation theory describing the open system evolution under arbitrary driving and a correlation expansion technique. This paper considers the phonon-induced decoherence accompanying a single-qubit gate: an arbitrary rotation between two selected electron spin states performed via stimulated adiabatic Raman transitions and virtual excitation of a trion state. The error of the quantum gate as well as the population and coherence dynamics is calculated depending on the driving duration and detuning and study the possible reduction of the phonon decoherence.