Our team studies the quantum physics of superconducting electronic circuits and their interaction with quantum electromagnetic fields in a state-of-the-art research environment at the Department of Physics of ETH Zurich and at the ETH Zurich - Paul Scherrer Institute Quantum Computing Hub. At the fundamental level, our research is positioned at the intersections of mesoscopic condensed matter physics, atomic physics, and quantum optics, where physical systems with intriguing properties and exciting applications can be realized. In our work, we are exploring quantum information science with superconducting circuits both at the fundamental level and for applications in quantum computing, quantum communication, quantum simulation, and quantum sensing.

In the context of quantum information science, we control the dynamics of quantum systems, consisting of tens of qubits, to investigate their complex physical properties and explore their use in quantum information processing. A focus research theme of our lab is the exploration of quantum error correction, a striking theoretical concept to correct errors that occur in quantum information processing systems. Those errors are due to decoherence of their constituent components, the qubits, and our limited ability to perfectly control them. Over the past 25 years, extraordinary progress in the improvement of coherence properties, control, and readout has turned superconducting circuits into one of the most promising architectures for constructing quantum information processors. In recent years, the focus has shifted from implementing near-term intermediate-scale quantum algorithms to realizing fault-tolerant quantum computation. For applications such as quantum chemistry or factoring, this requires fault-tolerant quantum processors that operate many thousands of physical qubits. In our lab, we explore the essential elements required to realize error-corrected quantum computing hardware. Recently, we have demonstrated key features of quantum error correction by realizing for the first time repeated quantum error correction in a distance-three surface code device based on 17 superconducting qubits (Nature 605, 669--674 (2022)). We have also performed lattice surgery on such a code to entangle two repetition-code logical qubits (arXiv:2501.04612). The results of this research are highly relevant for the development of quantum hardware for fault-tolerant quantum computation.

Our lab also studies the fundamental physics of light-matter interaction in the context of cavity quantum electrodynamics (QED). The strong coherent coupling between a single quantum two-level system and a single mode of a quantized electromagnetic field allows us to explore interactions in solid-state electronic circuits on the single-photon level. This field of research founded in 2004 is known as circuit quantum electrodynamics, or short circuit QED (Rev. Mod. Phys. 93, 025005 (2021)). Circuit QED has enabled the study of a wide range of quantum optical phenomena in superconducting electronics circuits at a level of detail and control which rivals approaches in other physical systems, such as atoms, molecules, semiconductor quantum dots or nitrogen-vacancy centers. Commonly, in circuit QED the quantum physics of radiation fields localized in transmission line cavities is investigated through its interaction with individual or collections of superconducting qubits or multi-level systems.

Pioneering work performed in our laboratory since 2010 has enabled the detailed study of quantum properties of propagating microwave fields. Instead of using photo-detectors, ubiquitous at optical frequencies, we instantaneously detect amplitude and phase of propagating quantum fields versus time, which we first amplify using linear or parametric amplifiers. We are then able to measure higher order correlation functions and to perform full quantum state tomography on propagating modes, even in the presence of significant noise added by the amplifiers.

Since 2009, we have explored the use of circuit QED with physical systems that have transitions in the microwave regime, creating hybrid quantum systems. We have realized hybrid quantum systems in which we control and detect the quantum properties of semiconductor quantum dots or Rydberg atoms. In an effort to develop novel measurement and instrumentation technologies, we realize applications of quantum electronic circuits as sensitive, possibly quantum limited, nano-electronic measurement devices and detectors. In particular, we have successfully developed parametric amplifiers, single-photon detectors, single-photon sources, and digital electronics to perform real-time analysis of acquired data at high sustained data rates.