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Linear and Multilinear Algebra

Research problems on numerical ranges in quantum computing

David W. Kribs, Aron Pasieka, Martin Laforest, Colm A. Ryan, Marcus Palmer Da Silva

Published Jun 22, 2009• 27 citations
Publisher

Abstract

We describe some instances in quantum information processing where numerical range techniques arise. We focus on two basic settings: higher-rank numerical ranges and their relevance in theoretical quantum error correction, and the classical numerical range and its use for comparing quantum information processing operations. We present the basic theory, discuss examples and formulate open problems.

DOI
10.1080/03081080802677441

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We describe some instances in quantum information processing where numerical range techniques arise. We focus on two basic settings: higher-rank numerical ranges and their relevance in theoretical quantum error correction, and the classical numerical range and its use for comparing quantum information processing operations. We present the basic theory, discuss examples and formulate open problems.
We solve the fundamental quantum error correction problem for bi-unitary channels on two-qubit Hilbert space. We construct qubit codes for such channels on arbitrary dimension Hilbert space, and identify correctable codes for Pauli-error models not detected by the stabilizer formalism. This is accomplished through an application of a new tool for error correction in quantum computing called the ``higher-rank numerical range''. We describe its basic properties and discuss possible further applications.
We give a short introduction to quantum computing and its relation to numerical analysis. We survey recent research on quantum algorithms and quantum complexity theory for two basic numerical problems – high dimensional integration and approximation. Having matching upper and lower complexity bounds for the quantum setting, we are in a position to compare them with those for the classical deterministic and randomized setting, previously obtained in information-based complexity theory. This enables us to assess the possible speedups quantum computation could provide over classical deterministic or randomized algorithms for these numerical problems.
The rank-k numerical range has a close connection to the construction of quantum error correction code for a noisy quantum channel. For a noisy quantum channel, a quantum error correcting code of dimension k exists, if and only if the associated joint rank-k numerical range is non-empty. In this paper, the no- tion of joint rank-k numerical range is generalized, and some state- ments of (2011, Generalized numerical ranges and quantum error correction, J. Operator Theory, 66: 2, 335-351.) are extended.