Mini-symposium on quantum optics

13:10 - 13:50 David Zueco, University of Zaragoza 
Van der Waals quantum electrodynamics

In quantum electrodynamics (QED), light typically refers to confined photons in cavities and waveguides, while matter corresponds to localized quantum emitters. These architectures have enabled key advances in solid-state quantum technologies, but their scalability is limited by the photonic nature of light. In this talk, I propose replacing photons with magnons—the quanta of spin waves—hosted in van der Waals (vdW) antiferromagnetic  insulators. This approach enables the exploration of cavity QED with magnetic molecules as emitters and 2D materials containing magnons. These 2D materials support the formation of nanometric magnonic resonators, offering low-loss confinement and versatile control through stacking, topology, and interface engineering. This provides a means to control spin-wave emission and to mediate strong light-matter interactions at the nanoscale, closely resembling the paradigms of structured baths in conventional waveguide QED architectures. We term this platform VdW-QED.

13:50 - 14:30 Peter Rabl, TU Munich / Walther-Meißner-Institute
Autonomous entanglement distribution in squeezed and thermal photonic reservoirs 

I will discuss the autonomous distribution of entanglement in quantum networks driven by squeezed or thermal light. First, I will review our previous work on generating tunable multi-qubit entangled states in a dual-rail waveguide QED system by simply driving the atoms with a two-mode squeezed photon source. I will then show that even a purely thermal photon source can generate highly entangled states between two spatially separated qubits, provided the photonic reservoir is sufficiently narrow-band, i.e., strongly non-Markovian. I will explain the underlying mechanisms that lead to this surprising effect and discuss how it could potentially be used as a purely passive scheme to entangle superconducting qubits via room-temperature Johnson–Nyquist noise.

14:30 - 15:00 Coffee

15:00 - 15:40 Carlos Sánchez Muñoz, CSIC
Strategies toward quantum optics in the terahertz regime

Terahertz (THz) radiation has promising applications across a range of fields, including food science, medical diagnostics, biology, high-bandwidth communication, and security. However, the development of quantum technologies in the THz regime remains at a nascent stage compared to their counterparts in the visible and microwave domains. This lag is largely due to the lack of bright and efficient photonic transitions at THz frequencies.

In this talk, I present our theoretical proposals aimed at realizing quantum-optical platforms operating in the THz regime. Our approach leverages the permanent dipole moment of a single polar quantum emitter to induce THz transitions between optically dressed states, alongside the design of hybrid cavity systems. We demonstrate how these concepts can be used to engineer on-demand single-photon sources, as well as to mediate entanglement between quantum emitters via THz photonic modes. These developments point toward novel quantum-optical platforms that offering an strategic compromise between the limitations of the visible spectrum (e.g., nanometric precision and material absorption) and those of the microwave regime (e.g., scalability and the need for millikelvin cooling).

15:40 - 16:20 Peter Samuelsson, Lund University
Wigner-function formalism for the detection of single microwave pulses in a resonator-coupled double quantum dot

Semiconductor double quantum dots (DQD) coupled to superconducting microwave resonators offer a promising platform for the detection of single microwave photons. In previous works, the photodetection was studied for a monochromatic source of microwave photons. Here, we theoretically analyze the photodetection of single microwave pulses. The photodetection in this case can be seen as a nonlinear filtering process of an incoming signal, the pulse, to an outgoing one, the photocurrent. This analogy to signal processing motivated the derivation of a Wigner-function formalism which provides a compelling visualization of the time and frequency properties of the photodetector for low intensities. We find a trade-off between detecting the time and the frequency of the incoming photons, in agreement with the time-energy uncertainty relation. As the intensity of the source increases, the photodetection is influenced by coherent Rabi oscillations of the DQD. Our findings give insight into the time-dependent properties of microwave photons interacting with electrons in a DQD-resonator hybrid system and provide guidance for experiments on single microwave pulse detection.

Zenelaj et al., Phys. Rev. Research 7, 013305 (2025)