Quantum Information

.Scalar quantum field theories can possess metastable vacuum states which decay through thermal and quantum fluctuations. In space, the decay of the metastable vacuum proceeds through the creation and subsequent expansion of bubbles containing a new phase, which coalesce and eventually complete the phase transition. Vacuum decay is a non-perturbative and non-linear dynamical problem, making it the perfect candidate for quantum simulators. Understanding this process has phenomenological implications for early Universe cosmology, including observables such as a stochastic gravitational wave background, meaning there may be novel ways to use quantum simulators to make predictions for observational cosmology. In this talk I will first describe theoretical work developing observables for vacuum decay, including nucleation site correlation functions and bubble nucleation pre-cursors. I will then describe experimental efforts within the Quantum Simulators for Fundamental Physics consortium to develop analog quantum simulators of vacuum decay with cold atomic gasses. Such experiments will allow us to empirically test early Universe physics in tabletop experiments.

Scaling up the Hilbert space of a quantum computer is essential to demonstrate quantum advantage over classical computing. Other than packing more quantum information carrier in a quantum computing system, one avenue for increasing the quantum computing Hilbert space is by encoding more logical states per quantum information carrier (making it a qudit), rather than a traditional 2-state qubit encoding. Trapped ions typically exhibit multiple (meta)stable electronic energy states that are suitable for logical state encodings and are a suitable platform for qudit applications. In this talk, I present our work on realizing a 25-level trapped 137Ba+ ion qudit, which is the maximal encoding allowed by the single-shot readout protocol that we employ. We show that the harnessing of these additional logical states per ion can be done by just adding a few more lasers to the control system, without any trapping architecture modification compared to a qubit system. I will also present the experimental challenges and limitations, fundamental and technical, relevant to realizing a 25-level trapped 137Ba+ ion qudit.