Cavity-free -Type Coherent Population Trapping Advances Microwave Sensing with Δ System Precision

The pursuit of increasingly sensitive microwave sensors drives innovation in fields ranging from medical diagnostics to materials science, and researchers are now exploring novel approaches to atomic control for these devices. Ido Fridman, Shemuel Sternklar, and Eliran Talker, all from Ariel University, demonstrate a new technique using atomic systems without the need for confining optical cavities, a significant simplification in sensor design. Their work focuses on manipulating the quantum properties of atoms to enhance sensitivity to microwave fields, achieving what is known as coherent population trapping. The team’s findings reveal a strong link between microwave field characteristics and the resulting atomic coherence, paving the way for smaller, more robust atomic clocks and potentially revolutionising microwave sensing platforms.

Researchers observe that the coherent population trapping (CPT) resonance exhibits a pronounced dependence on the microwave power and detuning, resulting in measurable changes in resonance contrast, linewidth, and center frequency. To explain these effects, they develop a numerical density-matrix model, incorporating the microwave coupling strength into the ground-state coherence calculations, capturing the essential physics of this system. The excellent agreement between theory and experiment establishes a robust framework for microwave control of cavity-free atomic systems.

Rubidium Cascade System and EIT Modelling

The research focuses on a three-level Rubidium atom, a Δ-type system where two ground states connect to a single excited state, crucial for creating interference effects. The system utilizes a coupling field to drive transitions and a microwave field to coherently drive transitions between ground states. This configuration allows investigation of interactions between these fields and the Rubidium atoms, potentially achieving effects like electromagnetically induced transparency or slow light. Detunings, representing the difference between field and atomic transition frequencies, and Rabi frequencies, quantifying the interaction strength between fields and atoms, are key parameters. Velocity averaging accounts for Doppler broadening due to atomic motion. Appendixes detail the derivation of the Bloch equations and the calculation of the microwave Rabi frequency.

Microwave Control of Atomic Coherence Demonstrated

Scientists have demonstrated precise control over atomic coherence using a cavity-free microwave field, achieving a breakthrough in manipulating the quantum states of atoms without confining structures. The research team investigated a Δ-type system, where two ground states are coupled by a microwave field, exhibiting heightened sensitivity to external parameters. Experiments revealed a pronounced dependence of coherent population trapping (CPT) resonance on both microwave power and detuning, resulting in measurable shifts in resonance contrast, linewidth, and center frequency. Specifically, changes in resonance contrast were linked to microwave field strength, while linewidths narrowed or broadened with detuning, and the resonance center frequency predictably shifted with microwave parameter alterations.

To explain these observations, scientists developed a detailed numerical model based on the density-matrix formalism, explicitly incorporating the microwave coupling strength into the ground-state coherence calculations. The model accurately predicted the experimental results, establishing a robust framework for controlling Δ-type atomic systems in open space. This breakthrough delivers a pathway towards compact and enhanced atomic clocks, as well as improved platforms for sensitive microwave vector sensing, potentially impacting fields like navigation and fundamental physics research. This cavity-free approach offers a simpler and more versatile method for manipulating atomic states compared to traditional cavity-based systems, opening new avenues for quantum technologies.

Microwave Control of Atomic Coherence in Free Space

This research presents a combined theoretical and experimental investigation of a three-level atomic system interacting with microwave fields, achieved without the use of confining cavities. Scientists demonstrate that the coherent population trapping response is significantly affected by both the strength and frequency of the applied microwave field, observing changes in resonance contrast, linewidth, and central frequency. The team developed a numerical model that accurately captures the observed behaviour, particularly when the microwave field aligns with the optical axis, and successfully reproduces experimental results in near-zero detuning conditions. A key achievement lies in the elimination of traditional metallic resonators, allowing direct measurement of the spatial properties of microwave fields and offering potential for compact, open-space vector microwave sensors.

While the current work focuses on sensitivity to a single component of the microwave field, it establishes a pathway towards full vector reconstruction, including measurements of direction, polarization, and field gradients. Researchers acknowledge that further theoretical analysis is needed to fully account for the complex dependence of the CPT resonance on microwave frequency, and note the current experimental setup is limited to externally controlled signals. These findings demonstrate the potential of cavity-free atomic systems for advanced microwave sensing and quantum-enhanced field measurements.