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IQIM Postdoctoral and Graduate Student Seminar

Friday, October 14, 2022
12:00pm to 1:00pm
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East Bridge 114
Topological order from finite-depth circuits and measurements: from theory to quantum devices
Nat Tantivasadakarn, Sherman Fairchild Postdoctoral Scholar,

Abstract: A fundamental distinction between many-body quantum states are those with short- and long-range entanglement (SRE and LRE). The latter, such as cat states, topological order, or critical states cannot be created by finite-depth circuits. Remarkably, examples are known where LRE is obtained by performing single-site measurements on SRE states such as preparing the toric code from measuring a sublattice of a 2D cluster state. I will present a general framework of how and why these known protocols give rise to long range entanglement based on interpreting the cluster state measurement as implementing the non-local Kramers-Wannier transformation. This provides a scalable and practical way to ``gauge" a symmetry using only finite-depth circuits and measurements, and moreover allows us to go beyond the preparation of stabilizer states. In addition, we find a complexity hierarchy on long-range entangled states based on the minimal number of measurement layers required to create the state. I will argue that certain phases of matter cannot be prepared using any finite number of layers, while remarkably certain non-Abelian topological orders can be prepared in a single round of measurement. As an application, I will outline how current NISQ devices, ranging from Rydberg atom arrays to Google's quantum processors, can scalably prepare a large class of exotic phases such as non-Abelian topological order and even fracton phases.
This talk is based on 2112.01519, 2112.03061, 2209.03964, and 2209.06202

Lunch will be provided, following the talk, on the lawn outside the Bridge arcade.

Attendees joining in person must demonstrate that they comply with Caltech's vaccination requirements (present Caltech ID or AWS ID or vaccination and booster confirmation).

For more information, please contact Marcia Brown by phone at 626-395-4013 or by email at [email protected].