Continuous Superradiant Laser Achieves Tens of Picowatts Power with Sub-Millihertz Linewidth

Superradiance, a phenomenon where atoms collectively emit light, promises powerful and coherent laser sources, but sustaining continuous operation has remained a significant challenge. Jana El Badawi, Marion Delehaye, and Bruno Bellomo, from Université Marie et Louis Pasteur and associated research institutions, now present a theoretical framework for achieving precisely that, demonstrating how sequential transport of atoms can enable continuous superradiant laser operation. Their work identifies the specific conditions under which this process yields stable, low-noise emission with power levels reaching tens of picowatts, and importantly, reveals the robustness of this approach even with variations in atomic properties. This research establishes a pathway towards practical superradiant lasers, potentially impacting fields requiring highly coherent and stable light sources, and opens new avenues for exploring collective atomic phenomena.

Superradiance and Coherent Light Source Limits

This extensive collection of research focuses on achieving highly coherent light sources, pushing the boundaries of laser stability and coherence. The central concept involves leveraging superradiance, a phenomenon where collective atomic behavior enhances coherence, with the goal of building optical atomic clocks and frequency standards with unprecedented stability. The compilation demonstrates a strong theoretical foundation alongside significant experimental progress in this field. The research encompasses theoretical underpinnings of superradiance and quantum optics, experimental realization of superradiant lasers, and applications to optical clocks and frequency standards.

Strontium emerges as a particularly useful atomic species due to its favorable properties for optical clock applications. The emphasis throughout is on achieving extremely high coherence in the emitted light, crucial for enhancing optical clock stability. The collection highlights the active nature of this field, with many references dating from 2015 to 2024, and provides a clear picture of current research in superradiance, quantum optics, and precision measurement.

Atomic Synchronization in Continuous Superradiant Lasers

Scientists have developed a theoretical framework to explore a continuous superradiant laser, mirroring an experimental setup. The study focuses on ensembles of atoms interacting with a Fabry-Perot cavity, employing an open system approach to identify conditions for achieving laser power levels of tens of picowatts with a sub-millihertz linewidth. Researchers discovered that the laser’s performance remains remarkably robust due to the synchronization of atomic dipoles. The team utilized a two-site configuration, where atoms couple equally to the cavity, but with potentially different detunings and ensemble sizes.

Analysis revealed that synchronization leads to a single, narrow spectral line whose central frequency corresponds to a weighted average of the two ensemble frequencies, demonstrating the potential for continuous superradiant emission through sequential loading of atoms. Precise control of the relative frequencies of the two ensembles is required to maintain laser stability. To address computational challenges, scientists implemented the second-order cumulant expansion, a powerful approximation method that simplifies calculations without sacrificing crucial quantum correlations. This technique truncates correlations at second order, significantly reducing computational cost while preserving accuracy, and conserves total phase invariance, ensuring the accuracy of phase-dependent terms.

Continuous Superradiance in a Fabry-Perot Cavity

Scientists have achieved continuous superradiant laser emission using sequentially-emitting ensembles of atoms coupled to a Fabry-Perot cavity. This research demonstrates a pathway towards sustained laser operation at extremely low power levels, reaching tens of picowatts, while maintaining an exceptionally narrow linewidth of less than one millihertz. Experiments revealed the robustness of the laser’s performance even with variations in atomic frequency and coupling strength to the cavity. Synchronization of the atomic dipoles plays a crucial role in maintaining stable emission despite these perturbations.

Furthermore, the research demonstrates that by carefully controlling the relative frequencies of the two atomic ensembles, continuous superradiant emission can be reliably achieved. Data confirms that the system’s performance is accurately modeled using the second-order cumulant expansion, a computational technique that significantly reduces complexity while preserving key quantum correlations. This method provides more accurate results than traditional approaches like mean-field or Langevin-based methods. Analysis of the cavity spectrum reveals that the laser operates with a narrow linewidth and predictable power output.

Atomic Synchronization Enables Narrow-Band Superradiance

This theoretical study investigates a continuous superradiant laser created using sequentially-loaded atomic ensembles within an optical cavity. The research demonstrates that, under specific conditions, this laser can achieve picowatt power levels with a remarkably narrow spectral linewidth, potentially suitable for precision applications. The team identified a parameter space where the laser’s performance is robust even with variations in atomic coupling and frequency broadening, due in part to the synchronization of atomic dipoles. Crucially, the study reveals that when two ensembles of atoms with slightly different frequencies are used, synchronization can lead to a single, narrow spectral line whose frequency is the weighted average of the two ensembles’ frequencies. This finding suggests that sequential loading of atoms is a viable approach to achieving continuous superradiant emission, provided the relative frequencies of the ensembles are carefully controlled. Future work could explore the impact of more complex detuning profiles and variations in coupling strength to further refine the laser design and optimise its performance.