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Laser & Photonics Review

Coherent Manipulation of a Quantum Dot with Few Photons in a Low‐Reflectivity Micropillar Cavity

Jiajun Wang, Bang Ye Wu, Xu‐Jie Wang, Guoqi Huang, Li Liu, Hanqing Liu, Haiqiao Ni, Zhichuan Niu, Zhiliang L. Yuan

Published Nov 14, 2025• 0 citations
Publisher

Abstract

ABSTRACT Bidirectional coherent control between photonic and matter qubits in solid‐state quantum networks demand a tailored photon‐emitter interface that can operate at the few‐photon level. Cavity‐coupled quantum dots with high input coupling efficiency provides a viable path toward such interface. However, reflection from the bare cavity can contaminate, or even overwhelm, the desired output photons that have interacted with the emitter. To overcome this problem, we implement a low‐reflectivity ( 1%) quantum dot‐micropillar cavity system with 97% input coupling efficiency. We achieve an optical nonlinearity threshold of 5.6 incident photons per pulse while maintaining high antibunching fidelity ( 0.2), measured at a pulse duration of twice the quantum dot exciton lifetime. Furthermore, we observe quantum dot transition inversion at 9 photons when the pulse duration is reduced to roughly match the quantum dot lifetime. This highly efficient photon‐emitter interface paves the way for key quantum photonic resources and functionalities.

DOI
10.1002/lpor.202501778

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ABSTRACT Bidirectional coherent control between photonic and matter qubits in solid‐state quantum networks demand a tailored photon‐emitter interface that can operate at the few‐photon level. Cavity‐coupled quantum dots with high input coupling efficiency provides a viable path toward such interface. However, reflection from the bare cavity can contaminate, or even overwhelm, the desired output photons that have interacted with the emitter. To overcome this problem, we implement a low‐reflectivity ( 1%) quantum dot‐micropillar cavity system with 97% input coupling efficiency. We achieve an optical nonlinearity threshold of 5.6 incident photons per pulse while maintaining high antibunching fidelity ( 0.2), measured at a pulse duration of twice the quantum dot exciton lifetime. Furthermore, we observe quantum dot transition inversion at 9 photons when the pulse duration is reduced to roughly match the quantum dot lifetime. This highly efficient photon‐emitter interface paves the way for key quantum photonic resources and functionalities.
Giant optical nonlinearity is observed under both continuous wave and pulsed excitation in a deterministically coupled quantum dot-micropillar system, in a pronounced strong-coupling regime. Using absolute reflectivity measurements we determine the critical intracavity photon number as well as the input and output coupling efficiencies of the device. Thanks to a near-unity input-coupling efficiency, we demonstrate a record nonlinearity threshold of only 8 incident photons per pulse. The output-coupling efficiency is found to strongly influence this nonlinearity threshold. We show how the fundamental limit of single-photon nonlinearity can be attained in realistic devices, which would provide an effective interaction between two coincident single-photons.
In a quantum network based on atoms and photons, a single atom should control the photon state and, reciprocally, a single photon should allow the coherent manipulation of the atom. Both operations require controlling the atom environment and developing efficient atom-photon interfaces, for instance by coupling the natural or artificial atom to cavities. So far, much attention has been drown on manipulating the light field with atomic transitions, recently at the few-photon limit. Here we report on the reciprocal operation and demonstrate the coherent manipulation of an artificial atom by few photons. We study a quantum dot-cavity system with a record cooperativity of 13. Incident photons interact with the atom with probability 0.95, which radiates back in the cavity mode with probability 0.96. Inversion of the atomic transition is achieved for 3.8 photons on average, showing that our artificial atom performs as if fully isolated from the solid-state environment.
Quantum dots coupled to high-Q cavities can induce optical transparency that provides photon switching capabilities. However, the optical access to such cavities can be inefficient due to their restrictive optical modes. Here, we observe optical transparency of ∼ 80% induced by a quantum dot coupled to a cavity with an efficient optical access, the low-Q bullseye cavity, due to the destructive interference of reflected light. Together with optical lifetimes of quantum dots as short as 80 ps, and the coherent manipulation capabilities of their spin, the transparency induced by coupling these dots to bullseye cavities makes them promising for quantum technologies.
Abstract Hybrid quantum interfaces that combine the fast, deterministic single-photon emission of semiconductor quantum dots (QDs) with the long-lived quantum memories of atomic vapors represent a promising route towards scalable quantum networks and distributed quantum computing. However, the realization of such interfaces is fundamentally limited by the stringent spectral matching required between the narrow optical transitions of atomic systems and the intrinsically variable emission of QDs. Moreover, achieving bright QD emission requires integration into an efficient light-collecting structure. In this work, we present a systematic investigation of three tuning mechanisms for cavity-enhanced QDs embedded in micropillar cavities: thermal tuning, in situ laser processing, and nitrogen gas deposition. We experimentally evaluated the applicability of each method and characterized their tuning ranges and precisions. All three methods enable reliable and precise wavelength shifts, even for QDs in larger micropillars. These results provide practical strategies for achieving spectral resonance between QD emitters and atomic vapor lines, paving the way for tunable solid-state-atomic hybrid platforms for photon storage, synchronization, and interfacing in hybrid quantum systems.
Coherent control of quantum emitters is essential for scalable quantum photonic technologies. The recently proposed swing up of the quantum emitter population (SUPER) scheme allows efficient and coherent state preparation via off-resonant, red-detuned laser pulses, simplifying laser suppression and enhancing photon collection. We present a systematic study of SUPER excitation applied to a single GaAs quantum dot in a low- Q micropillar cavity. We first identify the optimal excitation conditions for SUPER, and then compare the key figures of merit against the well-established two-photon excitation (TPE). Despite requiring higher excitation powers, SUPER achieves near-unity population inversion of the exciton state ( ∼ 95 % ) and high single-photon purity ( g ( 2 ) = 0.03 ) comparable to that under TPE, while also exhibiting a shortened decay time ( ∼ 200 ps) reducing the time jitter in the exciton population. A polarization-resolved analysis reveals that when both excitation and collection are aligned with one of the exciton dipoles, SUPER results in highly polarized single-photon emission, exceeding the resonant TPE saturation by a factor of 1.45. Under optimized excitation conditions, we also observe biexciton preparation via a distinct SUPER resonance, constituting an experimental demonstration of biexciton preparation using SUPER. These findings are in good agreement with a proposed four-level theoretical model that incorporates the biexciton state. Furthermore, we report that, strikingly, a slight misalignment of laser polarization induces an additional SUPER resonance that selectively populates the orthogonal exciton dipole, without altering the nominal excitation polarization. This unexpected behavior reveals a new degree of freedom for coherent state preparation. Our findings establish the SUPER scheme as a versatile tool for state-selective exciton and biexciton control, with strong potential for quantum photonic applications.
Solid-state quantum emitters have long been recognized as the ideal platform to realize integrated quantum photonic technologies. We demonstrate that a self-assembled negatively charged quantum dot (QD) in a low Q-factor photonic micropillar is a suitable design for deterministic polarization switching and spin-photon entanglement. We show this by measuring a shift in phase of an input single photon of at least 2π/3. As we explain in the text, this is strong experimental proof that input photons can interact with the emitter deterministically. A deterministic photon-emitter interaction is a viable and scalable means to achieve several vital functionalities such as single photon switches and entanglement gates. Our experimentally determined value is limited by mode mismatch between the input laser and the cavity, QD spectral fluctuations, and spin relaxation. When on-resonance we estimate that up to ∼80% of the collected photons couple into the cavity mode and have interacted with the QD and undergone a phase shift of π.