Title: Finite-temperature states on a trapped-ion quantum computer
Speaker: Norbert M. LinkeAffiliations: Duke Univ. / Univ. of Maryland
Time: Oct.20th 10:00am
Venue: New Science Building(理科楼）C109
Abstract: Our experiment consists of a chain of 171Yb+ ions with individual Raman beam addressing and individual readout. This fully connected system can be configured to run any sequence of single- and two-qubit gates, making it in effect an arbitrarily programmable digital quantum computer. The high degree of control can be used for digital, but also for analog and hybrid quantum simulations. We also add a classical optimization layer to our quantum stack to realize variational optimization methods allowing us to make thermofield double states, which provide thermal subsystems at arbitrary temperatures . We use this capability for different studies with finite-temperature states, such as mapping out partition functions in an XXZ spin-chain  and measuring the decay out-of-time-ordered correlators in an Ising model system . Finally, we present a new pairwise-parallel entangling gate that effectively improves many characteristics of trapped ion quantum computers by up to a factor of two, lowering the physical errors for the above applications .
 D. Zhu et al., Proc. Natl. Acad. Sci. 117 (41) 25402-25406 (2020);
 A. Francis et al., Sci. Adv. 7 (34), eabf2447 (2021);
 A. M. Green et al., Phys. Rev. Lett. 128, 140601 (2022);
 Y. Zhu et al., Adv. Quantum Technol. 020324 (2023).
About the speaker: Norbert M. Linke is an Assistant Professor of Physics at the Duke Quantum Center (DQC), Duke University, North Carolina, USA, working on quantum applications of trapped ions, including quantum computing. Born in Munich, Germany, he graduated from the University of Ulm, and received his doctorate at the University of Oxford, UK, working on micro-fabricated ion-traps and microwave-addressing of ions. He spent four years as a post-doc and research scientist in the group of Chris Monroe at the University of Maryland's Joint Quantum Institute where he led a project that turned a physics experiment into a programmable quantum computer. He became an assistant professor at UMD in 2019 and transferred to the DQC in 2022.