Abstract: The ability to prepare ground states of many-body Hamiltonians on quantum devices is of central importance for a variety of tasks and applications in quantum computation and quantum simulation. In this talk I will describe a simple, flexible, and robust protocol to prepare low-energy states of arbitrary Hamiltonians on either digital or analog quantum hardware. The protocol is inspired by the “adiabatic demagnetization” technique used to cool solid state systems to extremely low temperatures. A constant fraction of the available qubits serve as a renewable bath, enabling the cooling process to be run in a cyclic fashion. Measurements of the bath spins at the end of each cycle provide information on the progress of cooling. Importantly, we find that the performance of the algorithm in the presence of a finite error rate depends on the nature of the excitations of the system: systems with topological excitations (which cannot be created or destroyed individually) are fundamentally more difficult to cool than systems with trivial local excitations. This difference is reflected both in the form of the approach to the steady state (exponential vs. power law) and the scaling of the steady state energy density with the rate of imposed errors/noise. Intriguingly, we show that this challenge can be overcome by encoding the system’s degrees of freedom into those of the quantum simulator in a non-local manner by the introduction of gauge fields, which act as a reservoir for removing excitations while maintaining locality of the implementation.
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The talk will start at 12:30 pm, but lunch will be provided at 12:00 pm.