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Quantum optics

Light particles interacting with matter

Quantum optics describes how individual quanta of light, the photons, interact with atoms, molecules and larger pieces of matter. We focus on studies of light interacting with nanoscale systems, in both experiment and theory. Our motivation for this is to create and study hybridized quantum states between electrons and photons. We also aim for example to increase the coherence of these states and their interaction strength to build electro-optical systems, devices and sensors.

Research areas:

Microwave photonics

Microwave photons are one of the main interaction media in solid-state quantum devices such as superconducting and semiconducting qubits. We study experimentally and theoretically microwave photons interacting with electrons in semiconductor nanostructures in so-called circuit quantum electrodynamics (cQED) setup. For the electronic part of the system, we focus on using quantum dots that enable to build photodetectors in the microwave domain and strong coherent coupling between electric charge and microwave photons in the electrical circuits.

Close-up of an electronic chip.
A microwave photodiode device converting microwave photons into an electrical current. By W. Khan.

Many-Body Physics of Finite Quantum Systems

Research in this area sets focus on the theory of quantum-optically confined systems of ultra-cold atoms and molecules and related nanostructures. We work on novel quantum systems at the crossover between the few- and many-body limit, studying precursors of phase transitions and hitherto unknown states of quantum matter, such as self-bound bosonic quantum droplets or dipolar supersolidity. We focus on fundamental theoretical questions while working closely in contact with experiment.

The upper part represents the experiment with a laser that shines on the 2D trap with atoms. In the lower part you can see how the atoms act when they pair, while the water represents their properties as suprafluids. Illustration: Jonas Ahlstedt.
Artist view of a quantum optical trap with ultra-cold fermions. (J. Ahlsted, Lund Bioimaging Centre).

Quantum Light Spectroscopy

The essential quantum resource behind the envisioned quantum light spectroscopy is the photons’ time-frequency entanglement.  The idea lies in simultaneously high temporal and spectral resolution achievable in a single measurement, as no time-frequency uncertainty applies to the time-frequency entangled pairs. Furthermore, since coincidences of two photons are measured, the background can be suppressed, allowing superior sensitivity.

We develop detectors and spectroscopy tapping into the quantum properties of the entangled photons and single photon detectors with high quantum efficiency. These techniques hold the promise to provide access to nontrivial quantum dynamics with superior sensitivity as compared to the common spectroscopies made with classical light fields.

imagination of an entangled photon
Entangled photons, dance in the night, Two souls bound, in quantum delight. Separated by distance, yet always near, Their fates entwined, forever dear. Entangled photon poesy by ChatGPT and imagination of an entangled photon pair by Midjourney AI text-to-image converter

Key publications:

Contact persons:


Microwave Quantum Photonics for Quantum Technology and Fundamental Physics (QPHOTON)

European Research Council Consolidator Grant