ELFT HÍRADÓ

[Janos Asboth <asboth.janos AT ttk.bme.hu>]

Dear Colleagues,

We have an online seminar this week at our Quantum Error Correction seminar
series at BME TTK Theor. Phys.

Friday, June 16, at 10:00 AM.
https://shorturl.at/yTV04

Dong E. Liu (Tsinghua University):
Lattice gauge theory and topological quantum error correction with quantum
deviations in the state preparation and error detection

Quantum deviations or coherent noise are a typical type of noise when
implementing gate operations in quantum computers, and their impact on the
performance of quantum error correction (QEC) is still elusive. Here [1],
we consider the topological surface code, with both stochastic noise and
coherent noise on the multi-qubit entanglement gates during stabilizer
measurements in both initial state preparation and error detection. We map
a multi-round error detection protocol to a three-dimensional statistical
mechanical model consisting of Z_2 gauge interactions and related the error
threshold to its phase transition point. Specifically, two error thresholds
are identified distinguishing different error correction performances.
Below a finite error threshold, in stark contrast to the case with only
stochastic errors, unidentifiable measurement errors can cause the failure
of QEC in the large code distance limit. This problem can only be fixed at
the perfect initial state preparation point. For a finite or small code
with distance d, we find that if the preparation error rate is below a
crossover scale ~1/\log(d), the logical errors can still be suppressed. We
conclude that this type of unavoidable coherent noise has a significant
impact on QEC performance, and becomes increasingly detrimental as the code
distance increases.

[1]: Y Zhao and DE Liu, arXiv:2301.12859

We welcome anybody who is interested.

Best,
 Janos Asboth