Anti-Parity-Time Symmetric Optics via Flying Atoms

Abstract: The recently-developed notion of 'parity-time (PT) symmetry' in optical systems with a controlled gain-loss interplay has spawned an intriguing way of achieving optical behaviors that are presently unattainable with standard arrangements. In most experimental studies so far, however, the implementations rely highly on the advances of nanotechnologies and sophisticated fabrication techniques to synthesize solid-state materials. Here, we report the first experimental demonstration of optical anti-PT symmetry, a counterpart of conventional PT symmetry, in a warm atomic-vapor cell. By exploiting rapid coherence transport via flying atoms, our scheme illustrates essential features of anti-PT symmetry with an unprecedented precision on phase-transition threshold, and substantially reduces experimental complexity and cost. This result represents a significant advance in non-Hermitian optics by bridging a firm connection with the field of atomic, molecular and optical physics, where novel phenomena and applications in quantum and nonlinear optics aided by (anti-)PT symmetry could be anticipated.

• The paper presents the inaugural experimental demonstration of anti-PT symmetry using flying atoms in a warm Rubidium vapor cell.
• It employs rapid atomic coherence transport and a dual-channel EIT configuration to precisely measure a 30.5 Hz phase transition between unbroken and broken phases.
• The findings pave the way for innovative non-Hermitian and quantum optics applications, potentially advancing quantum computing and information science.

Anti-Parity-Time Symmetric Optics with Flying Atoms: An Overview

The paper "Anti-Parity-Time Symmetric Optics via Flying Atoms" provides the inaugural experimental realization of optical anti-parity-time (anti-PT) symmetry in a system characterized by a warm atomic vapor cell. This study signifies an important step forward in non-Hermitian optics, particularly by leveraging flying atomic coherence as a minimalistic medium, significantly reducing experimental complexity and cost compared to alternative solid-state approaches.

Experimental Setup and Methodology

The experimental framework is anchored in rapid coherence transport within a wall-coated warm Rubidium (Rb) vapor cell, designed to preserve atomic quantum states over multiple wall collisions. The setup employs a standard electromagnetically induced transparency (EIT) configuration within two spatially separated optical channels. By controlling these parameters precisely, the experiment achieves a high-resolution observation of the phase transition associated with anti-PT symmetry, offering unparalleled precision in measuring the threshold of this transition.

Theoretical and Experimental Contributions

The theoretical underpinnings rest on exploiting the anti-commutation relation of an anti-PT symmetric Hamiltonian with the PT operator, contrasting conventional PT symmetry. Here, the employed non-Hermitian Hamiltonian is marked by mediating atomic coherence through moving atoms. The investigation offers crucial insights into the spectral evolution of anti-PT symmetric systems, delineating an unbroken and a broken phase distinctly through the spectral behavior of eigen-EIT supermodes as a function of probe detuning.

The experimental data robustly corroborates theoretical predictions, showcasing significant quantitative agreements, such as the remarkably precise phase breaking observed at 2Δ₀ ≈ 30.5 Hz. This accuracy highlights the potential of atom-photon interactions in revealing subtle non-Hermitian phenomena and guides easy replication through relatively affordable and simple microwell-equipped setups.

Implications and Future Directions

The study's results punctuate a promising intersection between non-Hermitian optical physics and atomic, molecular, and optical (AMO) physics. It opens potential for novel explorations in quantum and nonlinear optics applications, particularly in the realms of slow/fast light and quantum information science. Given the feasibility shown through the warm atomic vapor medium, this work points to future investigations involving spatially dependent PT symmetries and suggests novel methodologies for studying photon-based nonlinear optics at minimal light levels—potentially moving towards single-photon level explorations.

Challenges remain in transitioning theoretical frameworks to viable experimental approaches, especially regarding complex symmetry manipulations in dynamic environments. Nonetheless, the insights gained establish this anti-PT symmetric system as a versatile platform to deepen our understanding of non-Hermitian physics across quantum optics, possibly transforming the scope for innovative applications in quantum computing and communication.

In summary, this paper successfully bridges a fundamental gap in non-Hermitian optics, advancing both theoretical understanding and practical implementation. By utilizing atom-based mediators, this approach sets the stage for fresh innovations in the study and application of non-Hermitian systems, encouraging future research endeavors in expanding this groundwork into new domains and utilizing varying media and couplings.