Testing quantum fault tolerance on small systems

Understand

We extensively test a recent protocol to demonstrate quantum fault tolerance on three systems: (1) a real-time simulation of five spin qubits coupled to an environment with two-level defects, (2) a real-time simulation of transmon quantum computers, and (3) the 16-qubit processor of the IBM Q Experience.

• In the simulations, the dynamics of the full system is obtained by numerically solving the time-dependent Schr\"odinger equation.
• We find that the fault-tolerant scheme provides a systematic way to improve the results when the errors are dominated by the inherent control and measurement errors present in transmon systems.
• However, the scheme fails to satisfy the criterion for fault tolerance when decoherence effects are dominant.