Superfluorescence from Lead Halide Perovskite Quantum Dot Superlattices (1804.01873v1)

Abstract: An ensemble of emitters can behave significantly different from its individual constituents when interacting coherently via a common light field. After excitation, collective coupling gives rise to an intriguing many-body quantum phenomenon, resulting in short, intense bursts of light: so-called superfluorescence. Because it requires a fine balance of interaction between the emitters and their decoupling from the environment, together with close identity of the individual emitters, superfluorescence has thus far been observed only in a limited number of systems, such as atomic and molecular gases and semiconductor crystals, and could not be harnessed for applications. For colloidal nanocrystals, however, which are of increasing relevance in a number of opto-electronic applications, the generation of superfluorescent light was precluded by inhomogeneous emission broadening, low oscillator strength, and fast exciton dephasing. Using caesium lead halide (CsPbX3, X = Cl, Br) perovskite nanocrystals that are self-organized into highly ordered three-dimensional superlattices allows us to observe key signatures of superfluorescence: red-shifted emission with more than ten-fold accelerated radiative decay, extension of the first-order coherence time by more than a factor of four, photon bunching, and delayed emission pulses with Burnham-Chiao ringing behaviour at high excitation density. These mesoscopically extended coherent states can be employed to boost opto-electronic device performances and enable entangled multi-photon quantum light sources.

• The paper demonstrates that ordered CsPbX₃ quantum dot superlattices enable superfluorescence with a more than ten-fold reduction in radiative decay from 400 ps to 148 ps.
• It employs a self-assembly technique to create highly coherent three-dimensional arrays that enhance oscillator strength and minimize inhomogeneous broadening.
• The study observes photon bunching and Burnham–Chiao ringing, indicative of multi-photon emission with potential applications in high-brightness quantum light sources.

Overview of Superfluorescence from Lead Halide Perovskite Quantum Dot Superlattices

The paper "Superfluorescence from Lead Halide Perovskite Quantum Dot Superlattices" presents a significant advancement in the observation and utilization of superfluorescence (SF) in colloidal nanocrystal systems, specifically caesium lead halide (CsPbX₃, X = Cl, Br) perovskite quantum dots (QDs). The paper successfully demonstrates key SF characteristics in these systems, including red-shifted emission, accelerated radiative decay, extended coherence time, photon bunching, and delayed emission pulses with Burnham–Chiao ringing.

Methodology

The authors employ a self-assembly technique to create highly ordered, three-dimensional superlattices of CsPbX₃ nanocrystals. This structural organization fosters the cooperative interaction necessary for SF by maintaining high oscillator strength and limiting inhomogeneous broadening. The process relies on optimizing quantum dot dispersion and assembly conditions, which are critical for achieving the coherent coupling necessary for SF.

Key Findings

• Red-Shifted Emission and Radiative Decay: The superlattices exhibit emission shifted by 70-90 meV, distinct from non-coupled QDs. This cooperative emission shows a radiative decay time reduction from 400 ps to 148 ps, signifying a more than ten-fold speed-up in decay kinetics due to SF.
• Coherence Time: The SF-states exhibit a first-order coherence time that is expanded by over four times the coherence period of non-coupled QDs, indicating significant phase synchronization amongst the emitters.
• Photon Bunching and Burnham–Chiao Ringing: The paper observes photon bunching indicative of coherent multi-photon emission and characterizes oscillations in the emission under intense excitation, consistent with the Burnham–Chiao model.

Implications

This work is poised to impact opto-electronic applications, as the demonstrated SF behavior in QD superlattices opens pathways for developing high-brightness, multi-photon quantum light sources. The cooperative effects observed suggest potential utility in quantum information processing, with implications for entangled photon sources and quantum state manipulation.

Future Directions

The reproducibility of SF across different batches indicates scalability of the process, although optimization of synthesis and assembly remains an area for development. Future research might explore different material systems or synthesis techniques to enhance coupling strength and coherence across larger arrays, offering further control over emission phenomena. Additionally, integration into practical devices, such as ultrafast light-emitting diodes or coherent quantum light sources, would be a logical extension of this research.

In summary, this paper provides compelling evidence of superfluorescence in a new class of materials, highlighting the relevance and utility of quantum dot superlattices in advancing quantum optical technologies.