Cavity Quantum Electrodynamics

Project members Leiden: Henk Snijders, Dapeng Ding, Michiel de Dood, Wolfgang Löffler, Martin van Exter, Dirk Bouwmeester


Project members UCSB (Santa Barbara): John Frey, Justin Norman, John Bowers, Dirk Bouwmeester


cqed scheme01 Here we investigate coupling of a single electronic system (quantum dots, ions) to photons within optical micro cavities. Such systems are an essential building block for quantum information hardware, such as quantum memories, quantum repeaters, photonic two-qubit quantum gates, electronic qubit – photonic qubit gateways, and as a means to generate entangled photons on demand. We investigate currently two different electronic systems: Rare-earth ions in a dielectric host material, and self-assembled quantum dots in GaAs-based heterostructures. In both cases, we have developed high-quality optical micro cavities to enable efficient light-matter interaction on the single photon level. These systems give rise to exciting cavity quantum electrodynamics (CQED) effects, which are currently under very active investigation by a number of groups worldwide.


Quantum dot cavity-QED

The picture above an exemplary CQED system with a quantum dot: Two exciton transitions in a InAs quantum dot give rise to a V-level system. If it is embedded in a high-quality optical cavity, photons are made to interact with the electronic transitions efficiently. A consequence is that one obtains new quasi particles with simultaneous photonic and electronic properties, polaritons.


cqed qds A hallmark of CQED effects is the suppression of the cavity transmission on resonance by the presence of a single quantum dot. It is then easy to see how we can realise a simple quantum gate based on this "photon blockade" effect: If we have sent a photon in the system shortly before, the quantum dot is effectively switched off and cavity transmission restored. This works of course in reflection in the exactly opposite way.




cqed samplescheme To obtain such high-quality cavity-quantum dot devices, we have developed an optimal system which enables polarization degenerate high-Q optical cavity modes together with electrical tuneability of the quantum dot emission energy; this is essential to bring the quantum dot into resonance with the optical cavity mode. Exceptional is here also that we can use the cavities both in transmission and reflection geometry, enabling photonic quantum gates that are in principle free of loss. The picture shows a cross-sectional view of our device.


Rare-earth ion cavity-QED

cqed rareearth We also investigate rare-earth ions in optical ring cavities, see the figure on the right. Rare-earth ions enable inner-shell transitions that are shielded from the environment, leading to exceptional coherence properties. Such systems are ideal quantum memories, and we study how integrated optical cavities can be used to enhance interaction of single photons with the quantum memory.