Small particles respond to light through electric and magnetic patterns called multipoles. Their interference determines the direction of scattered light and affects the decay of nearby emitters. Larger nanoantenna arrays, metasurfaces, and other nanophotonic systems demand increasingly costly simulations to meet strict performance and reliability requirements. We show how to represent these responses with quantum bits (qubits) and use quantum circuits to calculate scattering and the Purcell effect, the change in an emitter's decay rate caused by its surroundings. The circuits can encode known multipoles or estimate unknown ones from Maxwell's equations at the particle surface. We test the method against classical theory using an ideal quantum simulator and real IBM and IonQ quantum computers. For a silicon nanoparticle of radius 78 nm illuminated at 679 nm, IonQ gives a forward directivity of 2.984, close to the ideal dipolar value 3, quantifying the concentration of scattered light in the forward direction. For an emitter 10 nm from a gold nanoparticle and emitting at 510 nm, IBM measurements yield a calculated total decay rate 20.48 times its vacuum value versus 20.47 from theory, with correction for errors in reading the qubit states. We also establish how the number of multipoles and the required accuracy set the demands on qubits and measurements. These results motivate quantum-assisted design studies of directional radiation and emitter decay in nanophotonic systems.
Small particles respond to light through electric and magnetic patterns called multipoles. Their interference determines the direction of scattered light and affects the decay of nearby emitters. Larger nanoantenna arrays, metasurfaces, and other nanophotonic systems demand increasingly costly simulations to meet strict performance and reliability requirements. We show how to represent these responses with quantum bits (qubits) and use quantum circuits to calculate scattering and the Purcell effect, the change in an emitter's decay rate caused by its surroundings. The circuits can encode known multipoles or estimate unknown ones from Maxwell's equations at the particle surface. We test the method against classical theory using an ideal quantum simulator and real IBM and IonQ quantum computers. For a silicon nanoparticle of radius 78 nm illuminated at 679 nm, IonQ gives a forward directivity of 2.984, close to the ideal dipolar value 3, quantifying the concentration of scattered light in the forward direction. For an emitter 10 nm from a gold nanoparticle and emitting at 510 nm, IBM measurements yield a calculated total decay rate 20.48 times its vacuum value versus 20.47 from theory, with correction for errors in reading the qubit states. We also establish how the number of multipoles and the required accuracy set the demands on qubits and measurements. These results motivate quantum-assisted design studies of directional radiation and emitter decay in nanophotonic systems.
In this paper, we study the collective effects which appear as a pair of quantum emitters is positioned in close vicinity to a plasmonic nanoparticle. These effects include multipole-multipole interaction and collective decay, the strengths and rates of which are modified by the presence of the nanoparticle. As a result, entanglement is generated between the quantum emitters, which survives in the stationary state. To evaluate these effects, we exploit the Green's tensor-based quantization scheme in the Markovian limit, taking into account the corrections from light-matter coupling channels higher than the electric dipole. We find these higher-order channels to significantly influence the collective rates and degree of entanglement, and in particular, to qualitatively influence their spatial profiles. Our findings indicate that, apart from quantitatively modifying the results, the higher-order interaction channels may introduce asymmetry into the spatial distribution of the collective response.
It is now well established that radiative decay of quantum emitters can be strongly modified by their environment. In this paper, we present an exact—within the weak-coupling approximation—multipole expression to compute the Lamb (frequency) shift induced by an arbitrary set of resonant scatterers on a nearby quantum emitter, using multiscattering theory. We also adopt a quasi-normal mode description to account for the line shape of the Lamb shift spectrum in the near field of a plasmonic nanosphere. It is then shown that the Lamb shift resonance can be blueshifted as the size of the nanoparticle increases, suggesting that nanoparticles may be used to tune this resonant interaction. Finally, a realistic calculation of the Lamb shift is made for a dimer configuration.
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 develop a framework that computes two-photon spontaneous emission (TPSE) spectra of a quantum emitter near an arbitrarily shaped nanostructure. The model considers the interaction up to the electric quadrupolar order, which is relevant for nanophotonic structures sustaining strongly confined fields that are used to enhance and to tailor spontaneous emission processes. Moreover, we consider interference effects between multipolar two-photon emission channels, for the first time to our knowledge. First, we show for a s → s transition of a hydrogen atom placed under a silver plasmonic nanodisk a substantial enhancement in the photon-pair emission rates by 5 and 11 orders of magnitude for the two-electric dipole (2ED) and two-electric quadrupole (2EQ) transitions, respectively. Then for the same emitter under a plasmonic graphene nanotriangle, we demonstrate a breakdown of the electric dipole approximation in the TPSE process where the interference between the 2ED and 2EQ transitions is important, as it increases the total rate by 63 %. Third, we explore platforms where entangled photons of different energy are emitted in the far-field in different directions. In the end, our framework is a complete tool to design emitters and nanostructures for the TPSE process, leading to a rich assortment of functional nanoantennas.
Quantum nanophotonics enables advanced functionalities in information processing and sensing by providing control over quantum-light emission. Introducing time modulation into nanophotonic environments adds an additional dimension, enabling dynamic reconfiguration of the local density of optical states (LDOS), access to Floquet harmonics, and simultaneous control of emission rate, spectrum, and direction, capabilities that are fundamentally inaccessible in static platforms. Designing such systems requires self-consistent treatment of temporal modulation, electrodynamics, and quantum dynamics. Here, we extend a quantum-electromagnetic framework by coupling time-modulated Maxwell electrodynamics, solved using an anisotropic discrete dipole approximation, with a harmonic-resolved Gorini–Kossakowski–Sudarshan–Lindblad master equation. This Floquet–Lindblad–DDA approach captures the quantum feedback induced by temporal modulation and enables evaluation of harmonic-resolved populations, radiated and dissipated power, Purcell enhancement, and quantum efficiency. We applied the method to control the emission of a diamond NV center using voltage-driven Pockels modulation of a barium titanate nanoantenna array. The optimized structure achieves Purcell enhancements exceeding 5000 and routes more than 75% of the power to the n = +1 Floquet harmonic, enabling electronic beam steering by more than 50°. These results demonstrate a platform for programmable quantum-light emission based on time-modulated nanophotonics.
Manipulating photoluminescence from solid-state quantum emitters (QEs) on demand is of central importance for advanced quantum nanophotonic technologies. In comparison with conventional free-space approaches relying on bulky optical components, emitter-integrated metasurfaces provide a compact and efficient route for shaping photon emission directly at the source. Recent progress has established a common platform in which QE-excited surface plasmon polaritons (SPPs) are transformed by surrounding metasurfaces into free-space radiation with tailored propagation direction, polarization state, relative intensity, and spatial structure. This review highlights two complementary strategies that have recently been utilized for shaping quantum emission. The first is emitter-coupled meta-optics, which enables versatile photon sources with arbitrary polarization states, off-normal directionality, and multichannel emission by means of phase-engineered anisotropic meta-atoms. The second is vectorial scattering holography, including multiplexed implementations, which allows direct reconstruction of arbitrarily structured and polarization-multiplexed emission from individual nanodiamonds. Together, these approaches unlock unprecedented degrees of freedom for nanoscale light shaping and provide a promising route toward scalable quantum photonic devices and high-capacity information processing.