Greenaway, Sean

In the quantum simulation of physical systems, the evolution operator is typically implemented via a finite sequence of fundamental gates defined through the Suzuki-Trotter decomposition; the quality of the simulation increases with the circuit depth, however on NISQ devices this must be balanced against the adverse effects of increasing gate counts, fundamentally limiting what can be accurately simulated on current devices. In this work, a strategy for optimising the gate sequence generated by the Trotter decomposition is presented, in which both discrete optimisation of the gate ordering and continuous optimisation over the rotation angles are applied to produce a circuit which is able to achieve the greatest fidelity with as short a circuit as possible. These optimisations open up the possibility of observing more subtle, complex dynamics at short times and performing simulations for longer times than was previously believed to be possible with currently available quantum computers. Alongside an overview of the optimisation method, results from current NISQ devices will be presented comparing the performance of the optimised circuits with their Trotterised counterparts.

Knap, Michael

Kokail, Christian

van Bijnen, Rick

Vovrosh, Joseph

Confinement is a phenomenon that occurs when the attraction between two particles grows with their distance, most prominently found in quantum chromodynamics (QCD) between quarks. In condensed matter physics, similar phenomena appear in quantum spin chains, for example, in the one dimensional transverse field Ising model (TFIM) with an additional longitudinal field, famously observed via neutron scattering in the quantum material cobalt niobate or in optical lattice experiments. Confinement also drastically alters the non-equilibrium dynamics starting from selected initial states. Here, the physics of confinement in the TFIM is explored in relation to quantum simulation capabilities of state-of-the-art quantum computers. We report quantitative confinement signatures on an IBM quantum computer observed via two distinct velocities for information propagation from domain walls and their mesonic bound states. Our results are a crucial step for exploring non-perturbative quantum interaction phenomena which are beyond the capabilities of classical computers.

Zhao, Hongzheng

The concept of quantum many-body scars has recently been introduced to weakly break ergodicity and violate Eigenstate Thermalization Hypothesis. We propose a simple setup to generate quantum many-body scars in a doubly modulated Bose-Hubbard system which can be readily implemented in cold atomic gases. The dynamics is shown to be governed by kinetic constraints which appear via density assisted tunnelling in a high frequency expansion. We find the optimal driving parameters for the kinetically constrained hopping which leads to small isolated subspaces of scared eigenstates. The experimental signatures and the transition to fully thermalizing behavior as a function of driving frequency are analyzed.