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Colloquium: Eklund Student Lectures

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Rui-xing Zhang and Aishwarya Kumar, The Pennsylvania State University
26 April 2018 from 3:45 PM to 4:45 PM
117 Osmond Laboratory
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Quantum computing with neutral atoms: Quantum gates and Maxwell’s demon

Aishwarya Kumar

 I will describe our progress in building a quantum computer based on Cesium atoms trapped in a 3D optical lattice. We can cool ~90% of the atoms to the 3D vibrational ground state of the trap and execute site selective single qubit gates with high fidelity (0.996) and low crosstalk (0.002). Using site selective state flips and state dependent lattice translations, we move single atoms to generate perfectly filled registers of neutral atoms. This sorting process is an implementation of a Maxwell’s demon that reduces the total entropy of the system by a factor of 2.44 and initializes the quantum computer.


Topological Insulators of Bosons

Ruixing Zhang

Symmetry protected topological (SPT) states are exotic quantum states of matter, whose topological properties are only well-defined in the presence of some symmetries. Recent years have witnessed the great power of state-of-the-art first-principle methods in predicting fermionic SPT materials, such as electronic topological insulators. Finding their boson analogs, however, is a much harder problem, as strong interactions are required to prevent bosons from condensing. So far, there is no successful experimental realization of any bosonic SPT state in two or higher dimensions. We studied the bilayer graphene system under a tilted magnetic field and found a fascinating interplay between the correlation effects and topology. In particular, the Coulomb interaction is found to gap out the fermionic degrees of freedom on the boundary. However, both spin and charge conservation symmetry protect a pair of helical boson modes to be gapless, which resembles a bosonic version of the electronic topological insulators. This proposal serves as the first material realization of a two-dimensional bosonic SPT state. I will also discuss various experimental consequences to reveal the “smoking-gun” signal of the bosonic SPT physics.