Periodic Reporting for period 1 - SuperWave (Superatom Waveguide Quantum Electrodynamics)
Période du rapport: 2023-11-01 au 2025-04-30
The past decade has seen remarkable advances in the field of quantum non-linear optics, where individual photons are made to strongly interact which each other. Such strong photon-photon interactions are of both fundamental and technological interest: They are the prerequisite for implementing deterministic quantum logic gate operations for processing optical quantum information. Moreover, photons that strongly interact via a quantum nonlinear medium exhibit complex out-of-equilibrium quantum dynamics that enable one to tailor and control the photon statistics of light. Quantum non-linear effects have been successfully demonstrated with few photons in a number of experimental platforms, which exploit resonant enhancement of emitter-photon coupling via high-finesse optical cavities, collective response of ensembles of strongly interacting Rydberg atoms, so-called superatoms, or efficient coupling of single quantum emitters to guided light in the realm of waveguide quantum electrodynamics (QED). However, it remains a formidable challenge to reach the true many-body regime of quantum non-linear optics, where strong interactions and entanglement between many photons and many quantum emitters give rise to exotic quantum phases of light, such as photonic molecules or fermionic subradiant states. The objective of SuperWave is to realize this regime by synergizing superatoms and waveguide QED. By uniting the expertise and experimental methods of three teams that have previously driven these fields independently, we will develop near-ideal fiber-coupled nonlinear quantum devices. Their implementation will mark a major breakthrough in quantum optics and constitute a key resource in quantum sensing, quantum metrology, quantum communication, as well as quantum simulations. We will illustrate this great potential through a number of hallmark experiments such as the coherent fragmentation of a classical light pulse into its highly nonclassical photon number components.
During the first 18 months of the ERC Synergy Grant, the project has established a robust foundation for planned research activities. The initial period focused primarily on technological achievements forming the basis for main research goals. Central activities included fabrication and testing of novel nanofibers suitable for integration with ultracold atom ensembles. Through close collaboration between UBER (Berlin) and UBO (Bonn), nanofibers with ~50% transmission at near-UV wavelengths for ~100-nm-diameter fibers were produced. Notably, the project achieved, to our knowledge for the first time, fabrication of nanofibers from photonic crystal fibers. These fibers were transferred to UBO for characterization of photodarkening susceptibility using a dedicated vacuum test setup constructed under Berlin's guidance.
The TU WIEN theoretical team developed approaches for describing both experimental setups. Simulation methods were implemented to study coupling between fiber-guided photons and superatom ensembles under realistic conditions, including various broadening effects and trapping geometries. A detailed numerical model describing the Berlin experiment accounted for lattice defects and quantum mechanical motion. The Bonn and Vienna teams implemented a thorough simulation of the proposed fiber-atom interface, providing essential input for finalizing experiment design and benchmarking results.
The experimental apparatus for producing ultracold Ytterbium atoms was constructed, with Rydberg excitation successfully demonstrated (without nanofiber integration). Optimization of this setup was published in a peer-reviewed article. At UBER, a novel magic-wavelength nanofiber-based two-color dipole trap was demonstrated, enabling trapping with deep sub-λ/2 spacing—a significant technological advancement creating prerequisites for selective radiance implementation.
The Vienna team achieved notable theoretical results. Effects of strong direct interactions between quantum emitters on cooperative radiance in regular arrays were studied, with findings published in Physical Review Letters. These calculations demonstrated that interactions can induce superradiance under conditions typically showing weak cooperative decay. Additionally, open many-body dynamics of laser-driven Rydberg atoms were investigated, revealing novel quantum time crystal phases in regular atom arrays, published in Nature Physics and on arXiv.
The project established a structured collaboration framework between UBER, UBO, and TU WIEN, with UBER leading nanofiber fabrication, UBO conducting characterization and experimental implementation, and TU WIEN providing theoretical support. Personnel mobility facilitated knowledge transfer, with UBO members trained in Berlin for handling fragile nanofibers. Regular virtual and occasional in-person interactions ensured close coordination. The consortium held two meetings to discuss progress and research directions. This collaborative approach enabled significant cross-fertilization between atomic physics, quantum optics, and fiber optics, leading to transformative outcomes not achievable through individual efforts.
The TU WIEN theoretical team developed approaches for describing both experimental setups. Simulation methods were implemented to study coupling between fiber-guided photons and superatom ensembles under realistic conditions, including various broadening effects and trapping geometries. A detailed numerical model describing the Berlin experiment accounted for lattice defects and quantum mechanical motion. The Bonn and Vienna teams implemented a thorough simulation of the proposed fiber-atom interface, providing essential input for finalizing experiment design and benchmarking results.
The experimental apparatus for producing ultracold Ytterbium atoms was constructed, with Rydberg excitation successfully demonstrated (without nanofiber integration). Optimization of this setup was published in a peer-reviewed article. At UBER, a novel magic-wavelength nanofiber-based two-color dipole trap was demonstrated, enabling trapping with deep sub-λ/2 spacing—a significant technological advancement creating prerequisites for selective radiance implementation.
The Vienna team achieved notable theoretical results. Effects of strong direct interactions between quantum emitters on cooperative radiance in regular arrays were studied, with findings published in Physical Review Letters. These calculations demonstrated that interactions can induce superradiance under conditions typically showing weak cooperative decay. Additionally, open many-body dynamics of laser-driven Rydberg atoms were investigated, revealing novel quantum time crystal phases in regular atom arrays, published in Nature Physics and on arXiv.
The project established a structured collaboration framework between UBER, UBO, and TU WIEN, with UBER leading nanofiber fabrication, UBO conducting characterization and experimental implementation, and TU WIEN providing theoretical support. Personnel mobility facilitated knowledge transfer, with UBO members trained in Berlin for handling fragile nanofibers. Regular virtual and occasional in-person interactions ensured close coordination. The consortium held two meetings to discuss progress and research directions. This collaborative approach enabled significant cross-fertilization between atomic physics, quantum optics, and fiber optics, leading to transformative outcomes not achievable through individual efforts.
The fabrication of ultrathin nanofibers exhibiting ~50% transmission at near-UV wavelengths for diameters of approximately 100 nm represents a substantial technological advancement. Notably, the successful production of nanofibers from photonic crystal fibers—achieved for the first time to our knowledge—addresses critical challenges in fiber compatibility with ultracold atom systems. These developments necessitate significant adaptations to standard fiber pulling processes, providing new insights into photodarkening mechanisms relevant to near-UV applications.
The theoretical team at TU WIEN has developed novel methodologies that exceed conventional approaches in modeling light-matter interactions. Their implementation of simulation frameworks for describing coupling between fiber-guided photons and superatom ensembles—incorporating homogeneous/inhomogeneous broadening, trapping geometries, and collective dipole interactions—enables unprecedented predictive accuracy under realistic experimental conditions. Additionally, the discovery that strong interactions between quantum emitters can induce superradiance under conditions typically exhibiting weak cooperative decay (published in Phys. Rev. Lett. 134, 126901) represents a fundamental theoretical advance with implications for both atomic and solid-state systems.
Experimental progress includes the demonstration of a magic-wavelength nanofiber-based two-color dipole trap enabling atom trapping with deep sub-λ/2 spacing. This breakthrough overcomes previous limitations in spatial control and establishes a critical prerequisite for implementing selective radiance—a key project objective. The theoretical identification of novel quantum time crystal phases in laser-driven Rydberg atom arrays (reported in Nat. Phys. 20, 1389 and arXiv:2503.16141) further extends beyond conventional semiclassical frameworks, revealing emergent many-body dynamics in open quantum systems.
The theoretical team at TU WIEN has developed novel methodologies that exceed conventional approaches in modeling light-matter interactions. Their implementation of simulation frameworks for describing coupling between fiber-guided photons and superatom ensembles—incorporating homogeneous/inhomogeneous broadening, trapping geometries, and collective dipole interactions—enables unprecedented predictive accuracy under realistic experimental conditions. Additionally, the discovery that strong interactions between quantum emitters can induce superradiance under conditions typically exhibiting weak cooperative decay (published in Phys. Rev. Lett. 134, 126901) represents a fundamental theoretical advance with implications for both atomic and solid-state systems.
Experimental progress includes the demonstration of a magic-wavelength nanofiber-based two-color dipole trap enabling atom trapping with deep sub-λ/2 spacing. This breakthrough overcomes previous limitations in spatial control and establishes a critical prerequisite for implementing selective radiance—a key project objective. The theoretical identification of novel quantum time crystal phases in laser-driven Rydberg atom arrays (reported in Nat. Phys. 20, 1389 and arXiv:2503.16141) further extends beyond conventional semiclassical frameworks, revealing emergent many-body dynamics in open quantum systems.