November 2023

Abstracts of the Quantum Center Lunch Seminar

Date: Thursday, November 2, 2023
Place: ETH Zurich, Hönggerberg, HPF G 6
Time: 12:00 - 13:30

Stabilisation of cat-state manifolds using nonlinear interactions

Ivan Rojkov and Matteo Simoni - Trapped Ion Quantum Information (Home group), ETH Zurich

Schrödinger’s cat qubits are an interesting candidate for bosonic error-corrected quantum computation due to their robustness to oscillator dephasing errors. The simplest case, which includes superposition of two distinct coherent states has previously been demonstrated using engineered two-photon loss. We will present a generalisation of this scheme which uses interfering heating and cooling processes with different nonlinear dependence on the energy of the oscillator. Where these competing processes are equal in strength, we show that the steady states feature manifolds of multi-component cat states with discrete rotational symmetry. Furthermore the nature of the nonlinear dependency can be tuned to realize superpositions of squeezed states. We will outline an implementation of our scheme within a trapped ion system, where the desired nonlinear interaction naturally emerges from the spin-motion coupling of laser-driven ions outside the usual Lamb-Dicke regime of operation. Finally, we discuss the preparation, manipulation and measurement of these states as well as their robustness to some bosonic errors.

Quantum systems as gravitational sources: which quantum aspects of gravity can we test?

Flaminia Giacomini - Quantum Information Theory (Renner group), ETH Zurich

Understanding the fundamental nature of gravity at the interface with quantum theory is a major open question in theoretical physics. Recently, the study of gravitating quantum systems, for instance a massive quantum system prepared in a quantum superposition of positions and sourcing a gravitational field, has attracted a lot of attention: experiments are working towards realising such a scenario in the laboratory, and measuring the gravitational field associated to a quantum source is expected to give some information about quantum aspects of gravity. However, there are still open questions concerning the precise conclusions that these experiments could draw on the nature of gravity, such as whether experiments in this regime will be able to test more than the Newtonian part of the gravitational field.
In my talk, I will give an example of how quantum information tools such as communication protocols can contribute to identifying quantum aspects of gravity in low-energy (thought) experiments. I will then discuss directions of theoretical investigation that are needed to give a solid answer to current open questions.