Berlin 2024 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 18: Superconductivity: Poster

TT 18.36: Poster

Monday, March 18, 2024, 15:00–18:00, Poster C

Topological quantum phase transitions of toric code states under weak measurement — •Finn Eckstein, Guo-Yi Zhu, and Simon Trebst — Institute for Theoretical Physics, University of Cologne, Germany

The toric code is a paradigmatic model for topological order and robust quantum memory that has been seminal in the conceptualisation of fault-tolerant quantum computation. But while toric code states are stable to Pauli noise and exhibit a finite error threshold, they are inherently unstable when the syndrome measurements are infinitesimally tuned away from a strong (projective) measurement to weak measurements. Here we expand on this long-known observation and investigate toric code states when introducing weak measurements of individual qubits. We analytically demonstrate that, for varying the measurement angle on the Bloch sphere, the quantum problem can be exactly mapped to a classical Ashkin-Teller model subject to non-Hermitian random bond couplings (which originate from the anyon statistics of the toric code). By combining state-of-the-art hybrid tensor network / Monte Carlo numerical simulations we chart out the entanglement phase diagram and its topological quantum phase transitions.

Keywords: Toric code; Weak measurement; Measurement Induced Phasetransition; Monitored Quantum Circuits; Nishimori physics