Abstract
In this note, we show that O(log (1/ε)) rounds of parallel repetition with a threshold suffice to reduce completeness and soundness error to ε for single-prover quantum interactive proof systems. This improves on a previous O(log (1/ε) log log (1/ε)) bound from Hornby (2018), while also simplifying its proof. A key element in our proof is a concentration bound from Impagliazzo and Kabanets (2010).