Increasing error tolerance in quantum computers with dynamic bias arrangement

• Main Authors: Bombín, Hector, Dawson, Chris, Nickerson, Naomi, Pant, Mihir, Sullivan, Jordan
• Format: Journal Article
• Language: English
• Published: 28-03-2023
• Subjects: Physics - Quantum Physics
• DOI: 10.48550/arxiv.2303.16122

Many quantum operations are expected to exhibit bias in the structure of
their errors. Recent works have shown that a fixed bias can be exploited to
improve error tolerance by statically arranging the errors in beneficial
configurations. In some cases an error bias can be dynamically reconfigurable,
an example being linear optical fusion where the basis of a fusion failure can
be chosen before the measurement is made. Here we introduce methods for
increasing error tolerance in this setting by using classical decision-making
to adaptively choose the bias in measurements as a fault tolerance protocol
proceeds. We study this technique in the setting of linear optical fusion based
quantum computing (FBQC). We provide examples demonstrating that by dynamically
arranging erasures, the loss tolerance can be tripled when compared to a static
arrangement of biased errors while using the same quantum resources: we show
that for the best FBQC architecture of Bartolucci et al. (2023) the threshold
increases from $2.7\%$ to $7.5\%$ per photon with the same resource state by
using dynamic biasing. Our method does not require any specific code structure
beyond having a syndrome graph representation. We have chosen to illustrate
these techniques using an architecture which is otherwise identical to that in
Bartolucci et al. (2023), but deployed together with other techniques, such as
different fusion networks, higher loss thresholds are possible.