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arXiv:quant-ph/0702065

Noise thresholds for entanglement purification

Peter P. Rohde

Published Feb 7, 2007• 0 citations
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Abstract

We consider the effects of gate noise on the operation of an entanglement purification protocol. We characterize the performance of the protocol by two measures, the minimum purifiable input state fidelity, and the maximum output state fidelity. Both these measures are a function of gate error rate. For sufficiently large gate error rate these two measures converge, defining a threshold on gate error rates. Numerically, we estimate this threshold to be $9.2\times 10^{-2}$, which is achievable with many present day experimental architectures. (This paper is written in an experimental rapid communication format).

DOI
10.48550/arxiv.quant-ph/0702065

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We study the stability under quantum noise effects of the quantum privacy amplification protocol for the purification of entanglement in quantum cryptography. A systematic numerical study of the impact of all possible single-qubit noise channels is performed. We find that both the qualitative behavior of the fidelity of the purified state as a function of the number of purification steps and the maximum level of noise that can be tolerated by the protocol strongly depend on the specific noise channel. These results provide valuable information for experimental implementations of the quantum privacy amplification protocol.
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In this article, we present a novel idea for entanglement purification with joint measurements, the joint entanglement purification protocol(joint-EPP). In some quantum communication tasks using entangled pairs, one party holds the whole entangled pairs at the final stage, he or she is able to perform joint measurements on the pairs. In this situation the proposed joint-EPP can improve the entanglement purification by allowing a higher tolerated error rate, faster convergence which uses less steps to achieve a high fidelity, and higher production rate which produces more number of good entangled pairs from a given number of bad entangled pairs. We have established the general correspondence between linear classical codes and the joint-EPP. It has been shown that the joint-EPP can correct errors as long as the error threshod is no larger than 0.5. The joint-EPP works even for fidelity less than 0.5 as long as it is larger than 0.25. We give several concrete examples, definitions and applications of the joint-EPP.
Entanglement purification protocols, designed to improve the fidelity of Bell states over quantum networks for inter-node communications, have attracted significant attention over the last few decades. These protocols have great potential to resolve a core challenge in quantum networking of generating high-fidelity Bell states. However, previous studies focused on the theoretical discussion with limited consideration of realistic errors. Studies of dynamically selecting the right purification protocol under various realistic errors that occur in practice have yet to be performed. In this work, we study the performance of various purification protocols under realistic errors by conducting density matrix simulations over a large suite of error models. Based on our findings of how specific error channels affect the performance of purification protocols, we propose a module that can be embedded in the quantum network. This module determines and selects the appropriate purification protocol, considering not only expected specifications from the network layer but also the capabilities of the physical layer. Finally, the performance of our proposed module is verified using two benchmark categories. Compared with the default approach and exhaustive search approach, we show a success rate approaching 90% in identifying the optimal purification protocol for our target applications.
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In this paper, we propose a novel bipartite entanglement purification protocol built upon hashing and upon the guessing random additive noise decoding (GRAND) approach recently devised for classical error correction codes. Our protocol offers substantial advantages over existing hashing protocols, requiring fewer qubits for purification, achieving higher fidelities, and delivering better yields with reduced computational costs. We provide numerical and semi-analytical results to corroborate our findings and provide a detailed comparison with the hashing protocol of Bennet et al. Although that pioneering work devised performance bounds, it did not offer an explicit construction for implementation. The present work fills that gap, offering both an explicit and more efficient purification method. We demonstrate that our protocol is capable of purifying states with noise on the order of 10% per Bell pair even with a small ensemble of 16 pairs. The work explores a measurement-based implementation of the protocol to address practical setups with noise. This work opens the path to practical and efficient entanglement purification using hashing-based methods with feasible computational costs. Compared to the original hashing protocol, the proposed method can achieve some desired fidelity with a number of initial resources up to one hundred times smaller. Therefore, the proposed method seems well-fit for future quantum networks with a limited number of resources and entails a relatively low computational overhead.