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:This talk will give an overview of recent work in quantum engineering with trapped ions and the exciting prospects that steady progress in this field has opened up for future research. Internal states of trapped ions have remarkable quantum coherence that lies at the heart of both the currently most precise atomic clocks and their excellent suitability as the physical keepers of quantum information. The ions' charge offers a strong handle to confine them in deep trapping potentials for very long times and to move them and manipulate their quantum state of motion with great precision. Most importantly, Coulomb coupling between several ions is utilized for high quality quantum logic gates and for producing entangled quantum states of unprecedented complexity. Optical transitions efficiently couple trapped ions to the electromagnetic vacuum that provides an almost perfect entropy sink. This enables precise initialization of internal and motional degrees of freedom without the need for low temperature experiments. The unique combination of features of trapped ions has recently led to advances in several fields, especially in quantum information processing and precision tests of fundamental physics. Perhaps most notably, it has spawned a multitude of novel experimental techniques that could also be leveraged (for example) towards quantum-enabled sensors, quantum simulation, novel spectroscopy methods, cavity QED with ions, coupling atomic physics systems to solid-state systems and the quantum coherence of well isolated mesoscopic systems. All these possibilities have in common that they expand our ability to control the quantum world. If history is any guide, such expanded abilities might well lead to more, possibly unforeseen applications and intriguing insights into some of the most fundamental questions. [more]
Abstract:Bose-Einstein condensates of atoms with non-zero spin constitute not only an optimal scenario to investigate fundamental properties of magnetic superfluids, but also an ideal system for the study of macroscopic amplification of quantum and classical fluctuations. This is strikingly manifested in a sample initially prepared in the m = 0 state, where spin-changing collisions triggered by quantum fluctuations may lead to the creation of correlated pairs in m = ± 1. We show that the pair creation efficiency is strongly influenced by the interplay between the external trapping potential and the Zeeman Effect and reflects the confinement-induced magnetic-field dependence of elementary spin excitations of the trapped condensate. Remarkably, pair production in our experiments is characterized by a multi-resonant dependence on the magnetic field. Pair creation at these resonances acts as strong parametric matter-wave amplifier. Depending on the resonance condition, this amplification can be extremely sensitive or insensitive to the presence of seed atoms. We show that pair creation at a resonance which is insensitive to the presence of seed atoms is triggered by quantum fluctuations and thus the system acts as a matter-wave amplifier for the vacuum state. [more]
Prof. Rubiola has worked on various topics of electronics and metrology, navigation systems, time and frequency comparisons, and Cs frequency standards. His main fields of interest are precision electronics form dc to microwaves and phase noise metrology, which include frequency synthesis, high spectral purity oscillators, photonic systems, sophisticated instrumentation, and noise. He has developed a new generation of instruments for AM/PM noise measurement with ultimate sensitivity, based on synchronous detection of the error signal in a sophisticated version of the Wheatstone bridge, and on a variety of signal-processing methods. The course will consist of three lectures Dec 2nd: General metrology of amplitude and phase noise Dec 9th: The origin of frequency instability and noise in oscillators Dec 11th: The cross-spectrum experimental method [more]
Prof. Rubiola has worked on various topics of electronics and metrology, navigation systems, time and frequency comparisons, and Cs frequency standards. His main fields of interest are precision electronics form dc to microwaves and phase noise metrology, which include frequency synthesis, high spectral purity oscillators, photonic systems, sophisticated instrumentation, and noise. He has developed a new generation of instruments for AM/PM noise measurement with ultimate sensitivity, based on synchronous detection of the error signal in a sophisticated version of the Wheatstone bridge, and on a variety of signal-processing methods. The course will consist of three lectures Dec 2nd: General metrology of amplitude and phase noise Dec 9th: The origin of frequency instability and noise in oscillators Dec 11th: The cross-spectrum experimental method [more]
Abstract:Hybrid quantum systems, which combine ultra-cold atoms with solid state devices, have attracted considerable attention in the last few years. Promising applications are in the areas of precision sensing and quantum information processing. I report on our experimental efforts towards the realization of such systems based on ultracold atoms, superconductors and carbon nanotubes. The cold atom/superconductor experiment consists of a rubidium BEC apparatus and a thermally shielded helium flow cryostat at 4.2 K in the same ultrahigh vacuum system. Atom clouds are loaded into a magnetic microtrap formed near a superconducting niobium wire. We observe the impact of the Meissner effect on the trap parameters and measure the spin coherence of atoms near the superconductor. The measured coherence times are the longest yet observed in the vicinity of a highly conducting material and confirm the suppression of Johnson noise in superconductors. The results have implications for the development of coherently coupled cold atom/solid state quantum devices, in which cold atoms serve as long term quantum memory. In a second experiment, we investigate the interaction between ultracold atoms and carbon nanotubes. Free standing single nanotubes, periodic structures, and “carpets” of nanotubes are grown on the surface of an atom chip. We observe the scattering of ultracold atoms on the nanotubes. In addition, we describe a novel atom detector based on field ionization of ground state atoms near carbon nanotubes and subsequent ion counting. [more]
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