Colloquia


Colloquia

We plan to return partly to in-person talks. These talks will be held in the interim lecture hall B 0.32 at MPQ and can additionally be attended online. Some talks remain online only.

2G regulations apply to in-person talks, i.e. every time you wish to participate in person, you will have to prove, e.g. with the CovPass-App, that you are vaccinated or recovered.Whether facemasks have to be worn inside the lecture hall will be communicated in the the e-mail announcement for each talk separately. In any case, you will need a medical facemask in the hallway. Audience not affiliated with MPQ are welcome to join in person as long as they meet 2G criteria.

Details on how to participate online are distributed via the mailing lists [wiss-mpq] and [Mpq-colloquium-stream]. To receive this information, please register using the adjacent link.

Scientific organization of the talks:  Dr. Stephan Dürr and Dr. Thomas Udem

Abstract. Molecular hydrogen ions (H_2^+, HD^+, ...) are the simplest molecules, and their simplicity makes them interesting systems for fundamental physics studies and for methodological investigations in the novel field of cold molecules.The energies of molecular hydrogen ions, in particular the rotational and vibrational energies (in atomic units) are functions of the particle masses (electron, proton, deuteron), the Coulomb interaction, and to a lesser extent the magnetic properties of these particles. Significant theoretical advances now permit to calculate these energies ab-initio with an inacccuracy below 1 part in 10^9. This includes important contributions from relativistic and QED corrections.The dependence of transition energies on the electron-to-proton mass ratio makes these molecules also candidates for a laboratory search for a possible time-dependence of this fundamental constant. In this talk I will describe the status of the Düsseldorf experiment on precision laser spectroscopy of sympathetically cooled HD+, including the most recent developments towards enhanced precision. [more]
Abstract:Controlling quantum degrees of freedom in solids is an outstanding challenge in physics. Owing to strong interaction with the solid environment usually dephasing in fast and hence control is imperfect. Spins have turned out to be ideal candidates for solid state quantum systems, especially when incorporated into an otherwise spin free lattice made up from carbon like e.g. in diamond. Diamond has outstanding material properties, including ultrahardness and higher thermal conductivity than any other solid material. In addition, diamond has recently become much more attractive for solid-state electronics, with the development of techniques to grow high-purity, single-crystal synthetic diamonds and insert suitable impurities into them (doping). Pure diamond is an electrical insulator, but doped with boron, it can become a semiconductor with outstanding properties. It could be used for detecting ultraviolet light, ultraviolet light-emitting diodes and optics, and high-power microwave electronics. But the application that has many researchers excited is quantum spintronics, which could lead to a practical quantum computer, ultra¬secure communication and has the potential for revolutionizing imaging schemes. This is based on the fact that spins in diamond are exceptionally well shielded from their environment, allowing e.g. multipartite entangled states to be observed over ms in a room temperature solid [1]. The very same fact renders electron spins in diamond to be exceptionally high resolution magnetic field sensors [2]. The talk will highlight recent achievements in solid-state quantum physics with diamond, which may also have important spin off to other areas like e.g. biophysics. [1] P. Neumann et al. “Multipartite entanglement among single spins in diamond” Science 320 (2008) 1326[2] G. Balasubramanian “Nanoscale imaging magnetometry with diamond spins under ambient conditions” Nature 455 (2008) 648 [more]
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