Linear Optical Logical Bell State Measurements with Optimal Loss-Tolerance Threshold
Paul Hilaire, Yaron Castor, Edwin Barnes, Sophia E. Economou, Frédéric Grosshans · PRX Quantum · 2023
Quantum threshold theorems impose hard limits on the hardware capabilities to process quantum information.We derive tight and fundamental upper bounds to loss-tolerance thresholds in different linearoptical quantum information processing settings through an adversarial framework, taking into account the intrinsically probabilistic nature of linear optical Bell measurements.For logical Bell state measurements-ubiquitous operations in photonic quantum information-we demonstrate analytically that linear optics can achieve the fundamental loss threshold imposed by the no-cloning theorem even though, following the work of Lee et al. [Phys.Rev. A 100, 052303 (2019)] the constraint was widely assumed to be stricter.We spotlight the assumptions of the latter publication and find their bound holds for a logical Bell measurement built from adaptive physical linear-optical Bell measurements.We also give an explicit even stricter bound for nonadaptive Bell measurements.