Day 2 Dec-3 2021
Session 4 14:00-14:45

Coherent errors in quantum error correction and fault-tolerant quantum computation

Dong Liu
Tsinghua University & Beijing Academy of Quantum Information Sciences, China

Quantum error correction (QEC) is the key for the fault-tolerant quantum computation, and their experimental realization will be the next milestone. A remarkable result of QEC is the error threshold theorem, which is established on stochastic error models. However, non-stochastic errors or coherent errors may dominate the quantum computing chips, and cannot be excluded. Therefore, we study the performance of quantum error correction codes (QECCs) under the non-stochastic single qubit coherent errors and detection-induced coherent errors due to the imperfectness of practical implementations of stabilizer measurements, after running a quantum circuit. Considering the most promising surface code, we find that the detection-induced coherent error will result in undetected error terms, which will accumulate and evolve into logical errors. However, we show that this kind of errors will be alleviated by increasing the code size, akin to eliminating other types of errors discussed previously. We also find that with both the single qubit coherent errors and detection-induced coherent errors, the exact surface code becomes an approximate QECC.

In the last few minutes, I will briefly present the new quantum software package—Qcover, which is under development in our group. The core of Quantum Approximate Optimization Algorithm (QAOA) is to search the optimal parameters that minimize the expectation value of target Hamiltonian via variational method. The Qcover present here, can efficiently simulate QAOA process to obtain the optimal parameters based on graph algorithm. It will accelerates the coming of quantum advantage with the assistant of NISQ hardware.

Dr. Dong Liu is an associate professor at Tsinghua University and a research scientist at Beijing Academy of Quantum Information Sciences. He got his B.S. and PhD degrees at Peking University and Duke University, and worked as a postdoc researcher at Michigan State University and Microsoft Station Q. He joined Tsinghua University in 2018 as a faculty member. He became an adjunct scientist at BAQIS in 2020 and is leading a research group of quantum computer operating system.

He mostly focused on the theory of quantum devices physics, quantum computer architecture, topological quantum computation, and non-equilibrium condensed matter physics.