Chris Fechisin

Chris Fechisin

PhD student at the University of Maryland with a focus on topological quantum matter

Publications

Noninvertible Symmetry-Protected Topological Order in a Group-Based Cluster State

The cluster state is the simplest example of SPT order, protected by a $\mathbb{Z}_2\times\mathbb{Z}_2$ symmetry. In this work, we show that a generalized cluster state with fusion category symmetry $G\times\text{Rep}(G)$ shares many qualitative features with the ordinary cluster state and should be thought of as an SPT protected by a non-invertible symmetry.

Christopher Fechisin, Nathanan Tantivasadakarn, Victor V. Albert. (2025). Noninvertible Symmetry-Protected Topological Order in a Group-Based Cluster State. Phys. Rev. X 15, 011058.

SPT Phases cond-mat hep-th

Disclinations, dislocations, and emanant flux at Dirac criticality

We study the effects of lattice rotational and translational symmetries on Dirac cones in lattice models and the Dirac fermion field theories to which they flow in the continuum. In particular, we find that models defined on lattices with defects flow to field theories with additional magnetic flux, the amount of which is determined by universal topological data. We use defect conformal field theory to identify observables sensitive to this additional flux and then measure it in critical lattice models.

Maissam Barkeshli, Christopher Fechisin, Zohar Komargodski, Siwei Zhong. (2025). Disclinations, dislocations, and emanant flux at Dirac criticality. Preprint arXiv: 2501.13866.

SPT Phases Crystalline Symmetries cond-mat hep-th

Instability of steady-state mixed-state symmetry-protected topological order to strong-to-weak spontaneous symmetry breaking

In this work, we interrogate the analogy between (i) pure state SPTs as ground states of local Hamiltonians and (ii) mixed state SPTs as steady states of local Lindbladians. We construct a Lindbladian which hosts a simple mixed-state SPT within its steady-state subspace, then add symmetric local perturbations to see if the new steady states lie in the same mixed-state phase as the original. We find that for generic symmetric perturbations, the answer is no, due to the onset of strong-to-weak spontaneous symmetry breaking.

Jeet Shah, Christopher Fechisin, Yu-Xin Wang, Joseph T. Iosue, James D. Watson, Yan-Qi Wang, Brayden Ware, Alexey V. Gorshkov, Cheng-Ju Lin. (2024). Instability of steady-state mixed-state symmetry-protected topological order to strong-to-weak spontaneous symmetry breaking. Preprint arXiv:2410.12900.

Mixed States SPT Phases cond-mat quant-ph

Quantum Non-Demolition Photon Counting in a 2d Rydberg Atom Array

Rydberg arrays exhibit remarkable many-body physics due to strong Rydberg-Rydberg interactions which are possible between their constituent atoms. We present a protocol which leverages this physics to non-destructively count photons by temporarily storing them in the array.

Christopher Fechisin, Kunal Sharma, Przemyslaw Bienias, Steven L. Rolston, J. V. Porto, Michael J. Gullans, Alexey V. Gorshkov. (2022). Quantum Non-Demolition Photon Counting in a 2d Rydberg Atom Array. Preprint arXiv:2210.10798.

Mixed States quant-ph