Non-Markovian memory in a measurement-based quantum computer

TL;DR

This paper analyzes how non-Markovian environments affect the fidelity of single-qubit gates in measurement-based quantum computing, revealing the importance of timing in measurements for optimal performance.

Contribution

It provides analytical solutions for gate fidelities under non-Markovian noise and highlights the critical role of measurement timing in such environments.

Findings

Fidelity is identical for X and Z gates under these conditions.

Fast measurements do not always mean high fidelity, nor slow measurements low.

Optimal measurement timing varies significantly in non-Markovian environments.

Abstract

We study the exact open system dynamics of single qubit gates during a measurement-based quantum computation considering non-Markovian environments. We obtain analytical solutions for the average gate fidelities and analyze it for amplitude damping and dephasing channels. We show that the average fidelity is identical for the X-gate and Z-gate and that neither fast application of the projective measurements necessarily implies high gate fidelity, nor slow application necessarily implies low gate fidelity. Indeed, for highly non-Markovian environments, it is of utmost importance to know the best time to perform the measurements, since a huge variation in the gate fidelity may occur given this scenario. Furthermore, we show that while for the amplitude damping the knowledge of the dissipative map is sufficient to determine the best measurement times, i.e. the best times in which measures are taken, the same is not necessarily true for the phase damping. To the later, the time of the set of measures becomes crucial since a phase error in one qubit can fix the phase error that takes place in another.