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Advanced Quantum Technologies

Molecular Polaritons at the Quantum Frontier: From Cavity QED Foundations to Photonic Qubit Architectures

Krunal Modi, Ruzhi Zhang, Muhammad Usman, Chaofu Sun, Bin Ni, Brij Mohan, Keyur Bhatt, Bin Xu, X L Liu, Jichuan Xiong

Published Jun 1, 2026• 0 citations
Publisher

Abstract

ABSTRACT Molecular polaritons, hybrid quasiparticles formed through the strong coupling between molecular transitions and confined electromagnetic modes, have opened a new era by the combination of quantum electrodynamics (QED) with molecular photonics. This review deals with the theoretical, computational, and experimental developments that have put molecular polaritons at the forefront of next‐generation quantum information processing, photonics, and molecular‐scale qubit engineering. Starting from the Pauli–Fierz Hamiltonian, and other QED‐like macroscopic, ab initio, and QED‐coupled‐cluster methods which provide chemically accurate descriptions of correlated electron–photon states. A major focus is placed on dipole‐mediated quantum gates using rotational and polaritonic qubits, where long‐range dipole–dipole interactions enable scalable, room‐temperature logic operations. The article further discusses cutting‐edge spectroscopic methods such as 2D femtosecond stimulated Raman scattering, ultrafast pump‐probe, and cavity‐enhanced Raman reveals dark‐state dynamics, coherence transfer, and vacuum‐modified photo dynamics. Finally, we highlight recent advances in implementing polariton‐based logic gates, qubit analogs, and entanglement schemes that preserve coherence. Together, these advances establish molecular polaritons as chemically versatile and technologically promising candidates for on‐chip quantum logic and room‐temperature quantum photonic circuits, uniting the experimental realizations with quantum optical theory to chart a pathway for scalable, tunable, and coherent quantum information technologies.

DOI
10.1002/qute.202500837

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ABSTRACT Molecular polaritons, hybrid quasiparticles formed through the strong coupling between molecular transitions and confined electromagnetic modes, have opened a new era by the combination of quantum electrodynamics (QED) with molecular photonics. This review deals with the theoretical, computational, and experimental developments that have put molecular polaritons at the forefront of next‐generation quantum information processing, photonics, and molecular‐scale qubit engineering. Starting from the Pauli–Fierz Hamiltonian, and other QED‐like macroscopic, ab initio, and QED‐coupled‐cluster methods which provide chemically accurate descriptions of correlated electron–photon states. A major focus is placed on dipole‐mediated quantum gates using rotational and polaritonic qubits, where long‐range dipole–dipole interactions enable scalable, room‐temperature logic operations. The article further discusses cutting‐edge spectroscopic methods such as 2D femtosecond stimulated Raman scattering, ultrafast pump‐probe, and cavity‐enhanced Raman reveals dark‐state dynamics, coherence transfer, and vacuum‐modified photo dynamics. Finally, we highlight recent advances in implementing polariton‐based logic gates, qubit analogs, and entanglement schemes that preserve coherence. Together, these advances establish molecular polaritons as chemically versatile and technologically promising candidates for on‐chip quantum logic and room‐temperature quantum photonic circuits, uniting the experimental realizations with quantum optical theory to chart a pathway for scalable, tunable, and coherent quantum information technologies.
Abstract Quantum nanophotonics places nanoscale structuring in direct dialogue with photonic quantum information—compressing functionality to the few-nanometre, few-femtosecond frontier while retaining energy efficiency, speed and room-temperature operation. We highlight nanoplasmonic cavity-QED architectures in which extreme mode confinement delivers strong coupling under ambient conditions, enabling ultrafast single-photon emission and near-field multipartite entanglement using industry-grade near-field transducers that nanofocus guided light at practical efficiencies. We set these advances against the arc from early plasmonic cQED proposals and single-emitter Purcell studies to modern time-domain measurements that resolve sub-picosecond polariton/Rabi dynamics—establishing a clear route from concept to device. In parallel, we point to low-loss, high-index Mie resonators whose spectrally sharp electric and magnetic modes afford narrow-band coherent control, filtering and radiation-pattern engineering, and which naturally co-integrate in hybrid metal–dielectric stacks that combine ultrastrong local coupling with low-loss routing and storage. Finally, we discuss quantum nanoplasmonic coherent perfect absorption (qnCPA)—a waveguide-fed, non-perturbing protocol that selectively prepares and protects plasmon–emitter dressed states via dissipation-assisted, unidirectional feeding. Together with macroscopic QED and quantum quasinormal-mode quantization, which regularize open, lossy resonators and clarify when loss can be a resource, these developments chart robust, chip-scale routes to room-temperature quantum technologies.
Strong light-matter coupling gives rise to polaritons - hybrid excitations whose mixed photonic and matter character enables control over optical, electronic and chemical properties. This Feature Article surveys the main architectures supporting polariton formation, including photonic microcavities, plasmonic nanostructures, open cavities and metasurfaces, and outlines how inorganic semiconductors, organic aggregates and hybrid systems access strong and ultrastrong coupling. Key phenomena such as coherent dynamics, vibronic interactions, dark-state reservoirs and polariton-mediated energy and electron transport are discussed, together with the experimental and theoretical tools used to study them. We highlight examples where strong coupling modifies charge transport, energy flow and chemical reactivity, and we summarize emerging regimes, including intermediate and dark-strong coupling, that broaden the landscape of hybrid light-matter physics.
The field of Polaritonic Chemistry studies molecules strongly coupled to the light field of optical cavities. The resulting modification of the potential energy landscape has been demonstrated to enable control over the chemical and physical properties of materials and molecular ensembles. This thesis extends the Tavis–Cummings model to describe molecules under strong light–matter coupling, incorporating static dipole moments and dipole self-energy contributions derived from the Pauli–Fierz Hamiltonian. These additional terms are shown to be essential for reproducing cavity-modified molecular dynamics and spectra. Simulations on the nuclear wavefunction propagation of MgH+ molecules demonstrate the impact of these terms, while an effective two-level system model accurately captures the behavior of large ensembles. Beyond single excitations, the thesis also explores the higher excitation manifolds of the Tavis-Cummings model, which reveals that allowing for more than a single excitation makes the reaction of the involved polaritons entropically more favorable. Open-system simulations highlight how the coherence of the system's initial state governs decay pathways and enables long-lived energy storage. Finally, a multilevel vibrational model coupled to a two-mode cavity is introduced, where a Raman scheme enables selective mixing of vibrational states. The simulation results show that continuous pumping can drive molecules into specific vibrational states while suppressing electronic excitation, both for single molecules and small ensembles. Together, these results provide new theoretical insights into the mechanisms by which optical cavities reshape molecular energy landscapes. The results suggest approaches for controlling photonic, electronic, and vibrational dynamics in strongly coupled systems, contributing to the theoretical foundation of polariton chemistry.
In the field of polaritonic chemistry, strong light-matter interactions are used to alter chemical reactions inside optical cavities. To understand these processes, the development of reliable theoretical models is essential. While traditional methods have to balance accuracy and system size, new developments in quantum computing offer a path for accurate calculations on currently available quantum devices. Here, we introduce the quantum electrodynamics unitary coupled cluster (QED-UCC) method combined with the Variational Quantum Eigensolver algorithm, as well as the quantum electrodynamics equation-of-motion (QED-EOM) method formulated in the qubit basis that allow accurate calculations of ground-state and excited-state properties of strongly coupled light-matter systems suitable for quantum computers. These methods show excellent agreement with the exact reference results and can outperform their traditional counterparts when strong electronic correlations become significant. This work sets the stage for future developments of polaritonic quantum chemistry methods suitable for both classical and quantum computers.
Cavity QED, wherein a quantum emitter is coupled to electromagnetic cavity modes, is a powerful platform for implementing quantum sensors, memories, and networks. However, due to the fundamental trade-off between gate fidelity and execution time, as well as limited scalability, the use of cavity QED for quantum computation was overtaken by other architectures. Here, we introduce a new element into cavity QED—a free charged particle, acting as a flying qubit. Using free electrons as a specific example, we demonstrate that our approach enables ultrafast, deterministic, and universal discrete-variable quantum computation in a cavity-QED-based architecture, with potentially improved scalability. Our proposal hinges on a novel excitation blockade mechanism in a resonant interaction between a free-electron and a cavity polariton. This nonlinear interaction is faster by several orders of magnitude with respect to current photon-based cavity-QED gates, enjoys wide tunability and can demonstrate fidelities close to unity. Furthermore, our scheme is ubiquitous to any cavity nonlinearity, either due to light-matter coupling as in the Jaynes-Cummings model or due to photon-photon interactions as in a Kerr-type many-body system. In addition to promising advancements in cavity-QED quantum computation, our approach paves the way towards ultrafast and deterministic generation of highly entangled photonic graph states and is applicable to other quantum technologies involving cavity QED. Published by the American Physical Society 2024
Molecular polaritons within the mid-infrared regime have emerged as a source for modifying and manipulating molecular and photonic properties. However, the development of new methodologies for photon generation is still a challenge in nanophotonics. We propose a molecular model based on the Holstein-quantum-Rabi Hamiltonian, which also incorporates realistic dipole moments and nonadiabatic couplings among electronic excited states, to study the ultrafast photodynamics of diatomic molecules in confined electromagnetic fields within quantized cavities. In addition to vibronic transitions due to intrinsic nonadiabatic couplings, two types of light-induced crossings emerge: one type is located at molecular nuclear geometries where the rotating wave approximation is fulfilled, and another type appears at different geometries where counter-rotating transitions may occur. We make a comprehensive study of polariton photodynamics within a time window of a few tens of femtoseconds, where dissipative mechanisms do not influence the polariton photodynamics. We stress the dramatic change of the polariton energy spectrum as a function of the Huang-Rhys factor when nonadiabatic couplings are included in the model. We conclude that both the molecular nonadiabatic couplings and, more specifically, the counter-rotating couplings in the cavity-molecule interaction play a crucial role in converting vibronic energy into photons through excited dressed states. We also show that the sign of the Huang-Rhys factor has a significant impact on this photon conversion. Our work paves the way for the development of many-photon generation powered by strong light-matter interaction, along with potential applications using alkaline earth monohydride molecules.