In an article recently published in the journal Nature Communications, researchers proposed an innovative approach for the selective preparation and potential “immortalization" of selected plasmon-exciton polariton states through quantum nanoplasmonic coherent perfect absorption (CPA).
Temporal snapshots of the time-harmonic electric near-field components Ex in (a, b) and Ez in (c, d), magnified in the nanogap-QE region (marked by black boxes), are displayed at the respective critical wavelengths for qnCPA. The two polariton states are distinguished by the nature of the phase relationship between the local nanocavity and QE fields, namely an in-phase relation for the upper polariton (a,c) and an anti-phase relation for the lower polariton (b,d). Image Credit: https://www.nature.com/articles/s41467-024-50574-9
Background
In condensed-matter quantum optics, quantum electrodynamic strong coupling represents a technologically compelling and fundamentally significant regime of light-matter interaction. In this regime, the confined photonic mode of an optical resonator becomes deeply entangled with the phononic or electronic excitations of matter. This interaction leads to the formation of polaritons or dressed states, which exhibit a dual light-matter character.
In the collective many-emitter regime, strong coupling between phononic or electronic transitions and optical modes significantly alters phenomena such as polaron photoconductivity, ground-state chemical reactivity, and exciton transport. This allows for the manipulation of non-equilibrium material properties based on the delocalized nature of mixed light-matter states.
These advancements can drive the development of sophisticated polariton-enabled chemistry protocols and cavity-enhanced optoelectronic devices. At the single-emitter level, achieving strong coupling is essential for photonic quantum information processing, enabling applications like quantum sensing and single-qubit coherent control.
However, despite the crucial role of light-matter superposition states in quantum information processing, challenges persist. Material dissipation and environment-induced decoherence can undermine the coherence of light-matter polaritons over time. Therefore, the key challenges are selectively preparing, sustaining, and protecting these hybrid light-matter states to fully exploit the potential of strong-coupling-enabled photonic quantum technologies.
The Proposed Approach
In this study, researchers proposed the use of CPA under near-field driving to prepare and protect a single quantum emitter’s polaritonic states interacting with a plasmonic nanocavity at room temperature. CPA is the time-reversed lasing analog at the threshold. To achieve lasing, the active medium-supported gain within an optical resonator must be adequately high to realize the lasing threshold, thereby giving rise to a coherent outgoing mode.
In contrast, an optical resonator’s intrinsic losses must possess a specific critical value to realize an incoming coherent mode’s total reflectionless absorption for a CPA system. Although CPA has been originally conceptualized and investigated in the classical optics domain, recent studies have focused on harnessing and elucidating CPA in the quantum regime.
In this work, researchers investigated a novel principle to selectively initialize and preserve the strongly coupled light-matter states’ coherence by leveraging the unidirectional, non-perturbing, and frequency-specific energy transfer characteristics of quantum nanoplasmonic CPA.
Specifically, the proposed CPA scheme utilized an inherent frequency specificity to selectively initialize the coupled systems in a chosen plasmon-emitter-dressed state. This method employed unidirectional, non-perturbing, and coherent near-field energy transfer from a nearby plasmonic waveguide, which effectively stabilized the dressed state against dynamic dissipation in ambient conditions.
Study Significance
Researchers demonstrated that the quantum nanoplasmonic CPA regime could selectively lock a nanocavity-quantum emitter system into either the lower or upper plasmon-emitter polariton state under plasmonic single-mode waveguide driving.
In this regime, coupling the nanocavity-quantum system to a plasmonic nanowire waveguide enabled unique initialization of the lower or upper plasmon-emitter polaritons. The absence of a reflection signal at the polariton excitation energy indicated a one-way feeding mechanism, effectively locking the strongly coupled system within the chosen dressed state.
The CPA’s intrinsic non-bonding condition was crucial, as it allowed effective decoupling of the waveguide from the nanocavity-quantum emitter system. This decoupling ensured that the polaritons remained unaffected by the driving waveguide, preserving their coherence. Importantly, the waveguide decoupling and feeding mechanisms provided a promising approach for maintaining polariton states over time.
The dressed state could be sustained coherently in dynamic equilibrium, where the inherent dissipations of the quantum emitter and plasmonic resonator were counterbalanced by near-field, non-perturbing energy delivery, feeding the polaritonic system at an optimal rate. This method contrasts with simple, resonant driving using continuous-wave, weak laser light, which cannot achieve stationary dressed-state populations.
Moreover, the proposed scheme obviates the need for cryogenic cooling and stringent isolation from environmental effects to preserve individual quantum states. Instead, it leverages dynamic dissipation under ambient conditions by strategically interacting with plasmon interference to establish the quantum nanoplasmonic CPA regime.
To summarize, this study established a previously unexplored quantum state preparation and coherence preservation paradigm in plasmonic cavity quantum electrodynamics, offering compelling prospects for room-temperature-viable and novel quantum nanophotonic technologies.
Journal Reference
Lai, Y. et al. (2024). Room-temperature quantum nanoplasmonic coherent perfect absorption. Nature Communications, 15(1), 1-8. DOI: 10.1038/s41467-024-50574-9, https://www.nature.com/articles/s41467-024-50574-
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