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arXiv:2512.16016 · Physical review. B./Physical review. B

Stationary two-qubit entanglement mediated by one-dimensional plasmonic nanoarrays

Luke C. Ugwuoke, Tjaart P. J. Krüger, Mark S. Tame

quant-phSubmitted Dec 17, 2025• Announced Dec 19, 2025• 0 citations• Revised Jul 20, 2026 (v2)
v1 · Dec 17, 2025v2 · Jul 20, 2026
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Abstract

Entanglement is one of the key measures of quantum correlations present in nanophotonic systems, with promising applications in quantum optics and beyond. Previous studies have shown that the degree of entanglement between two quantum dot qubits is preserved when a metal nanoparticle is used to mediate the interactions between the qubits. In this work, we investigate long-range plasmonic mediation of qubit--qubit entanglement by studying the impact of the number of mediating metal nanoparticles on stationary concurrence. Collinear and periodically spaced metal nanoparticles that satisfy the weak-coupling approximation are considered. An effective model that enables the derivation of the mediated interactions within the framework of cavity quantum electrodynamics is employed. Under weak driving at the single particle resonance frequency, the model shows that odd-number arrays are more robust to entanglement decay. We attribute this to strong inter-qubit dissipative coupling as a result of a hybridized dipole plasmon resonating with the driving frequency in odd-number arrays. These arrays can sustain non-vanishing stationary entanglement beyond an inter-qubit spacing of one micron, opening up the possibility of independent spatial optical probing of each quantum dot.

Journal reference
Physical Review B 114, 065410 (2026)
DOI
10.1103/vm4t-x91b
Comments
12 pages, 8 figures

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Entanglement is one of the key measures of quantum correlations present in nanophotonic systems, with promising applications in quantum optics and beyond. Previous studies have shown that the degree of entanglement between two quantum dot qubits is preserved when a metal nanoparticle is used to mediate the interactions between the qubits. In this work, we investigate long-range plasmonic mediation of qubit--qubit entanglement by studying the impact of the number of mediating metal nanoparticles on stationary concurrence. Collinear and periodically spaced metal nanoparticles that satisfy the weak-coupling approximation are considered. An effective model that enables the derivation of the mediated interactions within the framework of cavity quantum electrodynamics is employed. Under weak driving at the single particle resonance frequency, the model shows that odd-number arrays are more robust to entanglement decay. We attribute this to strong inter-qubit dissipative coupling as a result of a hybridized dipole plasmon resonating with the driving frequency in odd-number arrays. These arrays can sustain non-vanishing stationary entanglement beyond an inter-qubit spacing of one micron, opening up the possibility of independent spatial optical probing of each quantum dot.
We theoretically investigate a general scheme for determining quantum entanglement of two detuned quantum dots (QDs) mediated by plasmon nanoparticle for weakly driven dissipative systems. By adiabatically eliminating the field operators, an effective model is proposed to find the underlying mechanism for this determination. Two specific hybrid systems composed of two QDs and a metallic nanoparticle (MNP) are considered. In the QD-MNP-QD system, the concurrence maxima generated by the detunings are several times larger than those in the resonance condition because of the robust superposition between the two separated entangled states. However, in the MNP-QD-QD system, the detunings generally reduce entanglement because the dipole-dipole interaction strongly suppresses the superposition of the entangled states. Moreover, the plateau of large concurrence exists for a broad range of parameters in both cases. The scheme is robust to dissipative systems and paves the way to improve entanglement in quantum information devices at the nanoscale.
The generation of quantum entanglement is important for a wide range of quantum technology protocols. In nanophotonics, a promising platform for quantum technologies, entanglement generation via plasmon-mediated coupling in quantum dot qubits is often modeled within the dipole limit, where only dipolar plasmons of the mediating nanoparticle are considered, and the local response approximation, where nonlocal corrections are ignored. However, multipolar effects manifest strongly at coupling distances less than the nanoparticle size, while nonlocal optical effects stem from a size-induced dielectric response. We investigated these two important effects in the generation of two-qubit entanglement mediated by plasmonic coupling. A cavity quantum electrodynamic approach is employed, where the induced plasmonic effects lead to modified transition rates in the dynamics of the coupled quantum dot qubits. We find that multipolar modes and size-dependent damping lead to entanglement decay at small coupling distances and limit mediated entanglement with certain particle sizes. We discuss potential implications of multipolar modes in entanglement-based quantum sensing.
We investigate relaxation dynamics in the system of two identical quantum dipole emitters (QDEs) located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. Considering one QDE to be brought into an optically active excited state and weakly coupled to the resonant LSP, we show that a stable superposition state of two QDEs is formed during the transition time, which is much shorter than the QDE spontaneous decay time and determined by the efficiency of resonant interaction between the QDEs and induced LSP. It is elucidated that the superposition state is established as a result of redistribution of the energy of the initially excited QDE so that the corresponding steady-state QDE fields induced at the MNP site cancel each other. The degree of steady-state entanglement characterized by the concurrence is found dependent only on the ratio of distances between the QDEs and the MNP, reaching its maximum value of $\ensuremath{\sim}0.65$, when the separation between the MNP and the initially excited QDE is larger by $\ensuremath{\sim}20%$ than the distance from the other QDE to the MNP.
Although the enhanced near fields produced by plasmon resonances in metal nanoparticles can enable strong local light-matter interactions, the strong dissipation of plasmon resonances would seem to be incompatible with quantum-mechanical phenomena such as entanglement. Counter to this intuition, the dissipation can in fact lead to the production of transient entanglement between the occupation states of dots coupled to a common plasmonic system. Building on previous results that showed entanglement between pairs of dots, we scale to larger systems of two, three, and more closely spaced dots. Moreover, we show that tuning the degree of coupling between each dot and the common plasmonic nanostructure enables entanglement to be created in the case where the entire system begins in its ground state and is excited by a single laser pulse. Entanglement is achieved without the need for the dots to be individually addressable, and without the need for controlled quantum gates, postselective measurements, or engineering of the dissipative environment. Through analytical solutions and numerical simulation of a model Hamiltonian based on a cavity-quantum-electrodynamics approach, we determine system configurations that maximize pairwise entanglement among the quantum dots, illustrating in principle the potential for true “quantum plasmonics.
We introduce a scheme for generating entanglement between two quantum dots using a plasmonic waveguide made from an array of metal nanoparticles. We show that the scheme is robust to loss, enabling it to work over long distance plasmonic nanoparticle arrays, as well as in the presence of other imperfections such as the detuning of the energy levels of the quantum dots. The scheme represents an alternative strategy to the previously introduced dissipative driven schemes for generating entanglement in plasmonic systems. Here, the entanglement is generated by using dipole-induced interference effects and detection-based postselection. Thus, contrary to the widely held view that loss is major problem for quantum plasmonic systems, we provide a robust-to-loss entanglement generation scheme that could be used as a versatile building block for quantum state engineering and control at the nanoscale.
We investigate the long-range coupling of individual atoms coupled to plasmon modes of metallic nanostructures. Placing a pair of emitters along a thin metallic wire, we observe a strong, wire- mediated long-range interaction between the emitters. As a result, super- and subradiance can occur over distances large compared to the resonant wavelength. The states with enhanced or suppressed decay rate are the symmetric or anti-symmetric single-excitation states. Coupling more atoms to a wire network with a nontrivial coupling topology leads to interesting entangled subradiant states of the system. A similar long-range superradiance effect can be observed when two emitters are coupled by a metamaterial slab (also known as a perfect lens) having a refractive index n=-1. Besides the modification of decay rates, dipole-dipole shifts enter due to the plasmon-mediated interaction. Based on the superradiance effect, we propose setups for building a two-qubit quantum phase gate for quantum emitters coupled by a nanowire and a perfect lens, respectively, where the qubits are strongly interacting and individually addressable at the same time.