Atom Arrays Suppress Light Transmission, Enabling Multi-Photon Generation

Resonantly driven atoms within a waveguide exhibit suppressed transmission and enhanced photon bunching as their number increases. Transmission occurs solely when all atoms are excited, facilitating the generation of heralded multi-photon states with potential applications in long-distance quantum communication and precision measurement.

The controlled interaction of light and matter at the nanoscale is fundamental to advances in quantum technologies. Researchers are continually seeking methods to manipulate photons – fundamental particles of light – to create and control quantum states for applications ranging from secure communication to precision sensing. A new study by Zeidan Zeidan, Therese Karmstrand, Maryam Khanahmadi, and Göran Johansson, all affiliated with the Department of Microtechnology and Nanoscience (MC2) at Chalmers University of Technology, and in Karmstrand’s case, also with the Theoretical Quantum Physics Laboratory at RIKEN, details a method for achieving enhanced photon bunching using coherently driven atoms within a waveguide. Their work, entitled ‘Superbunching from coherently driven atoms in a waveguide’, demonstrates that by carefully controlling the interaction, transmission through the system becomes dominated by the emission of multiple photons simultaneously, a process with potential applications in generating complex quantum states and enhancing the range of quantum communication.

Atomic Arrays Induce Superbunched Photon Emission in Waveguide Quantum Optics

Increasing the number of identical two-level atoms within a one-dimensional waveguide actively suppresses light transmission while simultaneously enhancing photon bunching, according to new research. The findings demonstrate a transition towards a regime of predominantly incoherent, superbunched photon scattering, offering a novel mechanism for generating multi-photon states.

The study details how photons scatter from an array of identical, resonantly driven two-level atoms confined within a waveguide – a structure that guides electromagnetic waves. When illuminated by a weak coherent light source, researchers observed that increasing the number of atoms progressively diminishes transmitted light. Simultaneously, the probability of detecting photons arriving in clusters – termed ‘photon bunching’ – increases markedly.

This behaviour arises because transmission only occurs when all atoms within the array are simultaneously excited. This collective excitation requirement fundamentally alters the scattering process, shifting it from a regime where photons propagate individually to one where they emerge in correlated groups. This contrasts with typical waveguide quantum optics, which often focuses on single-photon effects.

To rigorously support these observations, the researchers employed techniques from queueing theory and Markov chains. These mathematical frameworks model the arrival of photons and the transitions between atomic energy levels. The resulting equations quantify the relationship between the probability of detecting a photon, the rate at which photons arrive at the system (the ‘drive field’s arrival rate’), and the time elapsed. Mathematical tools such as the Chernoff bound and Stirling’s formula were used to simplify complex calculations and establish bounds on the detection probability.

The research establishes a pathway for generating ‘heralded’ multi-photon states – states where the presence of multiple photons is confirmed by a detection event. These states have significant potential for applications in long-distance quantum communication, where the reliable transmission of quantum information requires the generation and detection of entangled photons, and precision metrology, where multi-photon states can enhance measurement accuracy.

Future investigations will focus on the scalability of this multi-photon generation scheme with increased atomic number and waveguide length. Understanding the impact of imperfections, such as atomic disorder and decoherence (the loss of quantum coherence), on the fidelity of the generated multi-photon states will also be crucial.