Why error-prone quantum measurements have outcomes

Stefanie J. Beale, Joel J. Wallman

Measurements are a vital part of any quantum computation, whether as a final step to retrieve results, as an intermediate step to inform subsequent operations, or as part of the computation itself (as in measurement-based quantum computing). However, measurements, like any aspect of a quantum system, are highly error-prone and difficult to model. In this paper, we introduce a new technique based on randomized compiling to transform errors in measurements into a simple form that removes particularly harmful effects and is also easy to analyze. In particular, we show that our technique reduces generic errors in a computational basis measurement to act like a confusion matrix, i.e. to report the incorrect outcome with some probability, and as a stochastic channel that is independent of the measurement outcome on any unmeasured qudits in the system. We further explore the impact of errors on indirect measurements and demonstrate that a simple and realistic noise model can cause errors that are harmful and difficult to model. Applying our technique in conjunction with randomized compiling to an indirect measurement undergoing this noise results in an effective noise which is easy to model and mitigate.

Yu Watanabe

Alastair A. Abbott, Cristian S. Calude, Karl Svozil

Abdullah Ash Saki, Mahabubul Alam, Junde Li +1 more

Quantum computers are built with fragile and noise/error-prone qubits. Some prominent errors include, decoherence/dephasing, gate error, readout error, leakage, and crosstalk. Furthermore, the qubits vary in terms of their quality. Some qubits are healthy whereas others prone to errors. This presents an opportunity to exploit good quality qubits to improve the computation outcome. This chapter reviews the state-of-the-art mapping techniques for error tolerance. We take quantum benchmarks as well as approximate algorithms for applications covering MaxCut, object detection and factorization to illustrate various optimization challenges and opportunities.

Giovanni Acampora, Autilia Vitiello

Recently, a significant interest is arising in developing techniques capable of correcting errors in noisy quantum computations without using additional quantum resources. These techniques, known as mitigation methods, are aimed at post-processing the quantum outcome without working at quantum hardware level. Among the most error-prone operations on the current quantum devices, there is surely the quantum measurement. Currently, the most popular mitigation method for quantum measurement error consists of computing a so-called mitigation matrix to be applied on the results outputted by a quantum processor to transform them and make them closer to the ideal ones. In this paper, a new measurement error mitigation method based on a competent memetic algorithm is proposed to generate an appropriate mitigation matrix. As shown in the experimental session, the proposed measurement error mitigation method shows better results when compared with the conventional method and the state of the art among the evolutionary approaches.

Leonardo Vanni, Roberto Laura