Dr. Alexander Grimm
Paul Scherrer Institut (PSD/LNQ), Bosonic Quantum Information group


Nanofabrication aspects of bosonic quantum information processing with Schrödinger-cat qubits.


Quantum two-level systems are routinely used to encode qubits but tend to be inherently fragile, leading to errors in the encoded information. Quantum error correction (QEC) addresses this challenge by encoding effective qubits into more complex quantum systems. Unfortunately, the hardware overhead associated with QEC can quickly become very large.
In contrast, a qubit that is intrinsically protected against a subset of quantum errors can be encoded into superpositions of two opposite-phase oscillations in a resonator, so-called Schrödinger-cat states [1]. This “Schrödinger-cat qubit” has the potential to significantly reduce the complexity of QEC. In a recent experiment, we have demonstrated the stabilization and operation of such a qubit through the interplay between Kerr nonlinearity and single-mode squeezing in a superconducting microwave resonator [2].
In this talk, I will review some key concepts of QEC and situate our approach within the field. Then, I will give an overview of the cat qubit, followed by an outlook on different applied and fundamental research directions it enables. I will in particular focus on the nanofabrication aspects that are relevant to the implementation of this type of qubit.

[1] Mirrahimi, M. et al. New J. Phys. 16, 045014 (2014).
[2] Grimm, A. , Frattini N.E., et al. Nature 584, 205–209 (2020).


Since July 2022 Alexander is the group leader of the bosonic quantum information group after joining the Paul Scherrer Institut as a tenure-track scientist in November 2019. He obtained his PhD for research done between 2011 and 2015 in the group of Max Hofheinz at CEA Grenoble. During this time, he experimentally demonstrated that inelastic Cooper pair tunneling through a voltage-biased Josephson junction can be leveraged to create a source of antibunched microwave radiation. As part of this effort, he developed a novel fabrication method for vertical NbN-MgO-NbN Josephson junctions. From 2016 to 2019 he was part of the group of Michel Devoret at Yale University as a postdoctoral associate, working on autonomous quantum error correction (QEC) in bosonic codes. There, he performed various QEC experiments including the demonstration and operation of a ‘’Kerr-cat qubit’’, a type of bosonic qubit which is encoded into superpositions of stabilized coherent states. For his contributions to the field of quantum information processing with non-linear effects in Josephson junctions he received the 2022 Nicholas Kurti prize.