## Fault-Tolerant Dynamic Hamiltonian Engineering of Spin Ensembles

**Speaker:**Joonhee Choi, Harvard University

**When:**April 12, 2019 (Fri), 12:00PM to 01:00PM (add to my calendar)

**Location:**SCI 352

**Hosted by:**Alexander Sushkov

*This event is part of the Biophysics/Condensed Matter Seminar Series. *

Robust control of quantum dynamics lies at the heart of many applications of quantum physics, ranging from quantum metrology to many-body quantum simulations. Periodic (Floquet) driving is a powerful tool for engineering bare system Hamiltonians into desired target Hamiltonians while suppressing unwanted coupling to the environment. However, the fidelity of such Hamiltonian engineering is typically limited due to imperfections and inhomogeneities both in the system itself and in the manipulation of the quantum state. Robust ensemble spin engineering in disordered systems with strong interaction and imperfect spin control thus remains an open challenge. We introduce a powerful framework for the design of pulse sequences that are fault-tolerant to imperfections, for reliable and efficient quantum control of interacting many-body systems. Our formalism treats leading order imperfection effects in a simple fashion and uses a description of the system based on time-domain transformations of the S^z Pauli spin operator. We use the formalism to design control sequences for the protection of quantum coherence, for optimal quantum sensing and for the simulation of engineered many-body Hamiltonians, all realized in the presence of interactions and imperfections. Our method is applicable to a wide range of physical systems with different dominant energy scales and we demonstrate its efficacy by implementing robust sequences in a dense ensemble of nitrogen-vacancy centers in diamond.