Quantum Field Measurements in the Fewster-Verch Framework
Jan Mandrysch, Miguel Navascués
November 19, 2024
The Fewster-Verch (FV) framework was introduced as a prescription to define
local operations within a quantum field theory (QFT) that are free from
Sorkin-like causal paradoxes. In this framework the measurement device is
modeled via a probe QFT that, after interacting with the target QFT, is subject
to an arbitrary local measurement. While the FV framework is rich enough to
carry out quantum state tomography, it has two drawbacks. First, it is unclear
if the FV framework allows conducting arbitrary local measurements. Second, if
the probe field is interpreted as physical and the FV framework as fundamental,
then one must demand the probe measurement to be itself implementable within
the framework. That would involve a new probe, which should also be subject to
an FV measurement, and so on. It is unknown if there exist non-trivial FV
measurements for which such an "FV-Heisenberg cut" can be moved arbitrarily far
away. In this work, we advance the first problem by proving that measurements
of locally smeared fields fit within the FV framework. We solve the second
problem by showing that any such field measurement admits a movable
FV-Heisenberg cut.
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