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Paper 1

Simplified circuit-level decoding using Knill error correction

Ewan Murphy, Subhayan Sahu, Michael Vasmer

Year

2026

Journal

arXiv preprint

DOI

arXiv:2603.05320

arXiv

2603.05320

Quantum error correction will likely be essential for building a large-scale quantum computer, but it comes with significant requirements at the level of classical control software. In particular, a quantum error-correcting code must be supplemented with a fast and accurate classical decoding algorithm. Standard techniques for measuring the parity-check operators of a quantum error-correcting code involve repeated measurements, which both increases the amount of data that needs to be processed by the decoder, and changes the nature of the decoding problem. Knill error correction is a technique that replaces repeated syndrome measurements with a single round of measurements, but requires an auxiliary logical Bell state. Here, we provide a theoretical and numerical investigation into Knill error correction from the perspective of decoding. We give a self-contained description of the protocol, prove its fault tolerance under locally decaying (circuit-level) noise, and numerically benchmark its performance for quantum low-density parity-check codes. We show analytically and numerically that the time-constrained decoding problem for Knill error correction can be solved using the same decoder used for the simpler code-capacity noise model, illustrating that Knill error correction may alleviate the stringent requirements on classical control required for building a large-scale quantum computer.

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Paper 2

How Bohr's Copenhagen interpretation is realist and solves the measurement problem

Govind Krishnan.

Year

2023

Journal

arXiv preprint

DOI

arXiv:2308.00814

arXiv

2308.00814

The field of interpretation of quantum mechanics emerged in an attempt to solve the measurement problem. This turned on the perception that Niels Bohr avoided addressing the measurement problem by taking an instrumentalist view of quantum mechanics. I argue that this view is mistaken and Bohr's interpretation of quantum mechanics is realist. Moreover, Bohr's interpretation, which is different from textbook quantum mechanics (which is due more to Von Neumann and Paul Dirac), succeeds in solving the measurement problem. While the claim that Bohr dissolves the measurement problem within the limits of the epistemological framework he assumes has been made by a few authors, rarely has the case been made that Bohr's project unambiguously and completely overcomes the measurement problem. I make the strong case that Bohr eliminated the measurement problem altogether. For this, I put forward two new postulates through which to make sense of Bohr's interpretation. The article thus seeks to single out Bohr's interpretation from the various views that go together under the umbrella of orthodox quantum mechanics, and which have been traditionally considered susceptible to the measurement problem. It shows that Bohr's interpretation should be classified along with those like hidden variable theories, collapse models, modal interpretations etc., which offer a solution to the measurement problem and are committed to a realist ontology.

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