Decoherence and Quantum Error Correction

A. K. Ekert, Kalle‐Antti Suominen, Martin Bodo Plenio +5 more

Dave Bacon

In Chapter 1 we saw that open quantum systems could interact with an environment and that this coupling could turn pure states into mixed states. This process will detrimentally impact any quantum computation, because it can lessen or destroy the interference effects that are vital to distinguishing a quantum computer from a classical computer. The problem of overcoming this effect is called the decoherence problem . Historically, the problem of overcoming decoherence was thought to be a major obstacle towards building a quantum computer. However, it was discovered that, under suitable conditions, the decoherence problem could be overcome. The main idea behind how this can be achieved is through the theory of quantum error correction (QEC). In this chapter we give an introduction into the way in which the decoherence problem can be overcome via the method of QEC. It is important to note that the scope of the introduction is not comprehensive, and focuses only on the basics of QEC without reference to the notion of fault-tolerant quantum computation, which is covered in Chapter 5. Quantum error correction should be thought of as a (major) tool in this larger theory of fault-tolerant quantum computing.

János A. Bergou, Mark S. Hillery

Jincheng Zhang

This paper investigates adaptive optimization techniques for quantum error correction (QEC) codes. The core claim is that dynamic adjustment of QEC parameters, guided by estimates of decoherence probabilities, can significantly enhance the efficiency of quantum information transmission. The proposed mechanism utilizes real-time adjustments to the code's redundancy, encoding scheme, and error correction protocols, adapting to varying noise environments and qubit states. Traditional QEC approaches typically employ fixed parameters, lacking the crucial element of adaptability. This research addresses this limitation by introducing a framework for continuous optimization based on accurate decoherence probability assessment. The framework involves estimating the decoherence probability (Pd) of individual qubits, which is then used to dynamically modify key parameters of the QEC code. Specifically, we explore adjusting the code rate (R), the minimum distance (d) of the code, and the choice of error correction scheme. The optimization algorithm aims to minimize the overall error rate while maintaining a desired level of performance. This work presents a novel approach to QEC, promising improved robustness and efficiency in quantum communication and computation. The key mathematical components of this work are presented below.

Wen-Ching Li

Alexey A. Melnikov, Leonid Evgenevich Fedichkin

We considered the interaction of semiconductor quantum register with noisy environment leading to various types of qubit errors. We analysed both phase and amplitude decays during the process of electron-phonon interaction. The performance of quantum error correction codes (QECC) which will be inevitably used in full scale quantum information processors was studied in realistic conditions in semiconductor nanostructures. As a hardware basis for quantum bit we chose the quantum spatial states of single electron in semiconductor coupled double quantum dot system. The modified 5- and 9-qubit quantum error correction (QEC) algorithms by Shor and DiVincenzo without error syndrome extraction were applied to quantum register. 5-qubit error correction procedures were implemented for Si charge double dot qubits in the presence of acoustic phonon environment. ¬-matrix, Choi{Jamio lkowski state and measure of decoherence techniques were used to quantify qubit faulttolerance. Our results showed that the introduction of above quantum error correction techniques at small phonon noise levels provided quadratic improvement of output error rates. The effciency of 5-qubits quantum error correction algorithm in semiconductor quantum information processors was demonstrated.