Press release: Schrödinger's cat in an electron microscope

Nr. 116/2015 - 19.05.2015

Göttingen scientists create a pure superposition of free electron states

(pug) The term “Schrödinger's cat” illustrates the fundamental principle that, in quantum mechanics, a system can exist simultaneously in two mutually exclusive states. According to Schrödinger’s thought experiment, the cat is placed in a seemingly paradoxical superposition of being both dead and alive. Scientists at the University of Göttingen recently developed a new approach to generate a pure superposition of free electron states. The superposition consists of an electron moving simultaneously at a number of different velocities – an impossible situation in classical physics. The results were published in the scientific journal Nature.

For their experiment, the research group around Professor Claus Ropers and Dr. Sascha Schäfer at Göttingen University’s 4th Physical Institute developed an ultrafast transmission electron microscope to investigate how, on nanometre length scales, short electron pulses interact with intense light fields. “Close to the nanostructures, we observed that the electrons exchange multiple photons with the optical near-field and, consequentially, the electrons get accelerated or decelerated,” Professor Ropers explains. “In quantum mechanical terms, the exact number of exchanged photons is indeterminate, so that the electrons exist in a superposition of different velocities,” Dr. Schäfer adds.

The scientists were able to map out the quantum character of these states by observing so-called “Rabi oscillations”, where the distribution of electron velocities shows an oscillatory behaviour as a function of the light intensity. Based on their measurements, the Göttingen researchers predict that an electron pulse in such a superposition state evolves into a temporal comb structure, with the duration of its peaks shorter than one hundred attoseconds (an attosecond is one quintillionth or 10 to the power of 18 of a second). “We still need to experimentally demonstrate the attosecond comb structure. Nevertheless, our newly developed ultrafast transmission electron microscope already allows us to look at many dynamic processes on the microscopic scale,” adds Armin Feist, doctoral candidate and first author of the publication.

Original publication: Armin Feist et al. Quantum coherent optical phase modulation in an ultrafast transmission electron microscope. Nature (2015). www.nature.com/nature/journal/v521/n7551/full/nature14463.html

Contact:
Professor Claus Ropers and Dr. Sascha Schäfer
Georg-August-Universität Göttingen
Faculty of Physics – 4th Physical Institute
Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
Phone: +49 (0)551 39-4549 or -4576
E-mail: cropers@gwdg.de or schaefer@ph4.physik.uni-goettingen.de
Website: www.uni-goettingen.de/en/91116.html