June 2022
Abstracts of the QSIT/Quantum Center, ETH Zurich Lunch Seminar, Thursday, June 2, 2022
A Loophole-Free Bell Test with Superconducting Circuits
Simon Storz – Quantum Device Lab (Wallraff group), ETH Zurich
The remarkable feature of quantum physics not to follow the principle of locality can be demonstrated experimentally using Bell tests. Over the past 50 years, this litmus-test of quantum physics was explored with a variety of quantum systems. But only relatively recently, loophole-free Bell tests were conducted successfully with spins in nitrogen-vacancy centers, with optical photons and neutral atoms. In this talk, I demonstrate a loophole-free violation of Bell's inequality with superconducting circuits, by entangling qubits housed in cryogenic systems separated by a distance of 30 meters and connected through a unique cryogenic microwave quantum link. Our experiment enables future work in superconducting circuits on quantum communication protocols, computing and fundamental physics making use of non-locality as a resource.
Experimental investigation of vacuum field correlations in causally disconnected space-time regions
Alexa Herter – Quantum Optoelectronics Group (Faist group), ETH Zurich
Despite the absence of any photons, the ground state of light contains energy, which manifests itself in electric field fluctuations. The effects of these so-called vacuum fluctuations can be seen in the Casimir force or the Lamb shift in Hydrogen Atoms. Nevertheless, commonly used optical intensity detectors are insensitive to the vacuum field due to the impossibility of extracting energy from the ground state of light.
On the other hand, electro-optic sampling has enabled the direct detection of vacuum fluctuations by measuring the electric field in the THz and mid-infrared frequency range instead of its intensity. With electro-optic sampling, we are able to measure the temporal correlation of the ground state fluctuations in spatially separated points, providing insights into the causal and non-causal connections of the vacuum field. This constitutes an experimental analogy of the famous Feynman’s “Two atom problem” and contributes to the quantum field theory from an experimental side.