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📚 Journals Refereed

Physical Review X, Physical Review Letters, Physical Review B

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📅 Events Organized

UMD Condensed Matter Theory Student Seminar

Founder & Organizer · January-April 2025

Weekly research seminar featuring UMD students and postdocs

Harvard Society of Physics Students Chilloquium

Co-Founder & Organizer · June 2020-May 2021

Weekly undergraduate-oriented career and research talks by external and internal faculty

^{Recordings Available Online}

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

Christopher Fechisin, Kunal Sharma, Przemyslaw Bienias, Steven L. Rolston, J. V. Porto, Michael J. Gullans, Alexey V. Gorshkov

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.

Mixed States quant-ph

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

Christopher Fechisin, Nathanan Tantivasadakarn, Victor V. Albert

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.

SPT Phases cond-mat hep-th

Instability of steady-state mixed-state symmetry-protected topological order to 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

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.

Mixed States SPT Phases cond-mat quant-ph

Disclinations, dislocations, and emanant flux at Dirac criticality

Maissam Barkeshli, Christopher Fechisin, Zohar Komargodski, Siwei Zhong

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.

SPT Phases Crystalline Symmetries cond-mat hep-th

Mixed-state phase transitions induced by power-law quantum channels

Christopher Fechisin, Jeet Shah, Tsung-Cheng Lu, Zhi-Yuan Wei, Yu-Xin Wang, Alexey V. Gorshkov, Cheng-Ju Lin

Open quantum systems can exhibit inherently mixed quantum orders, such as strong-to-weak spontaneous symmetry breaking (SW-SSB), which have no analogue in pure states. It is generally expected that a finite-depth local quantum channel cannot induce a phase transition to SW-SSB in one spatial dimension. We circumvent this obstruction by applying a long-range quantum channel to a family of pure states, finding trivial, mixed SPT, and SW-SSB phases in various parameter regimes.

Mixed States SPT Phases cond-mat quant-ph

A Clifford hierarchy stabilizer formalism (with applications to twisted quantum doubles)

Christopher Fechisin, Kieran Cooney, Mathi Raja, Kyle Kawagoe, Victor V. Albert, Dominic Williamson, Seth Musser

We introduce a stabilizer formalism based on the Clifford hierarchy, which generalizes the Pauli stabilizer formalism by combining Pauli-X operators with diagonal operators drawn from a fixed level of the Clifford hierarchy on prime-dimensional qudits. This yields a natural class of beyond-Pauli stabilizer models, including many twisted quantum double phases. Using this framework and focusing on a minimal example, we construct a logical qudit and an explicit non-Clifford transversal logical gate.

cond-mat quant-ph

Teaching experience 1

Undergraduate course, University 1, Department, 2014

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Teaching experience 2

Workshop, University 1, Department, 2015

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