arXiv subjects

Anders Søndberg Sørensen

Publications and source records attributed to Anders Søndberg Sørensen.

22 records · Page 2Linked to original sources

arXiv2017

Multi-partite entanglement detection with non symmetric probing

We show that spin squeezing criteria commonly used for entanglement detection can be erroneous, if the probe is not symmetric. We then derive a lower bound on squeezing for separable states in spin systems probed asymmetrically. Using this we further develop a procedure that allows us to verify the degree of entanglement of a quantum state in the spin system. Finally, we apply our method for entanglement verification to existing experimental data, and use it to prove the existence of tri-partite entanglement in a spin squeezed atomic ensemble.

quant-ph↗

arXiv2014

Unraveling the mesoscopic character of quantum dots in nanophotonics

We provide a microscopic theory for semiconductor quantum dots that explains the pronounced deviations from the prevalent point-dipole description that were recently observed in spectroscopic experiments on quantum dots in photonic nanostructures. At the microscopic level the deviations originate from structural inhomogeneities generating a large circular quantum current density that flows inside the quantum dot over mesoscopic length scales. The model is supported by the experimental data, where a strong variation of the multipolar moments across the emission spectrum of quantum dots is observed. Our work enriches the physical understanding of quantum dots and is of significance for the fields of nanophotonics, quantum photonics, and quantum-information science, where quantum dots are actively employed.

cond-mat.mes-hall↗

arXiv2014

Probing electric and magnetic vacuum fluctuations with quantum dots

The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this paper we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonance. As a consequence, quantum dots can probe electric and magnetic fields simultaneously and can thus be applied for sensing the electromagnetic environment of complex photonic nanostructures. Our study opens the prospect of interfacing quantum dots with optical metamaterials for tailoring the electric and magnetic light-matter interaction at the single-emitter level.

quant-ph↗

arXiv2010

Strongly Modified Plasmon-Matter Interaction with Mesoscopic Quantum Emitters

Semiconductor quantum dots (QDs) provide an essential link between light and matter in emerging fields such as light-harvesting, all-solid-state quantum communication, and quantum computing. QDs are excellent single-photon sources and can store quantum bits for extended periods making them promising interconnects between light and matter in integrated quantum information networks. To this end the light-matter interaction strength must be strongly enhanced using nanophotonic structures such as photonic crystal cavities and waveguides or plasmonic nanowires. So far it has been assumed that QDs can be treated just like atomic photon emitters where the spatial properties of the wavefunction can be safely ignored. Here we demonstrate that the point-emitter description for QDs near plasmonic nanostructures breaks down. We observe that the QDs can excite plasmons eight times more efficiently depending on their orientation due to their mesoscopic character. Either enhancement or suppresion of the rate of plasmon excitation is observed depending on the geometry of the plasmonic nanostructure in full agreement with a new theory. This discovery has no equivalence in atomic systems and paves the way for novel nanophotonic devices that exploit the extended size of QDs as a resource for increasing the light-matter interaction strength.

cond-mat.mes-hall↗