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arXiv:1903.08667 · Physical Review Letters

Enhanced Multiqubit Phase Estimation in Noisy Environments by Local Encoding

Massimiliano Proietti, Martin Ringbauer, Francesco Graffitti, Peter Barrow, Alexander Pickston, Dmytro O. Kundys, Daniel Cavalcanti, Leandro Aolita, Rafael Chaves, Alessandro Fedrizzi

Published Nov 1, 2019• 13 citations
arXivHTMLPDF

Abstract

The first generation of multiqubit quantum technologies will consist of noisy, intermediate-scale devices for which active error correction remains out of reach. To exploit such devices, it is thus imperative to use passive error protection that meets a careful trade-off between noise protection and resource overhead. Here, we experimentally demonstrate that single-qubit encoding can significantly enhance the robustness of entanglement and coherence of four-qubit graph states against local noise with a preferred direction. In particular, we explicitly show that local encoding provides a significant practical advantage for phase estimation in noisy environments. This demonstrates the efficacy of local unitary encoding under realistic conditions, with potential applications in multiqubit quantum technologies for metrology, multipartite secrecy, and error correction.

DOI
10.1103/physrevlett.123.180503

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The first generation of multiqubit quantum technologies will consist of noisy, intermediate-scale devices for which active error correction remains out of reach. To exploit such devices, it is thus imperative to use passive error protection that meets a careful trade-off between noise protection and resource overhead. Here, we experimentally demonstrate that single-qubit encoding can significantly enhance the robustness of entanglement and coherence of four-qubit graph states against local noise with a preferred direction. In particular, we explicitly show that local encoding provides a significant practical advantage for phase estimation in noisy environments. This demonstrates the efficacy of local unitary encoding under realistic conditions, with potential applications in multiqubit quantum technologies for metrology, multipartite secrecy, and error correction.
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Quantum computation promises unprecedented computational power, but its realization faces significant challenges, primarily due to the extreme sensitivity of quantum states to environmental noise and decoherence. Traditional quantum error correction schemes, while theoretically sound, often require a substantial overhead in terms of qubit resources and complex control, hindering practical implementation. This work proposes a novel approach to quantum computation that leverages topological protection to achieve self-correcting quantum circuits. We demonstrate that by carefully designing quantum circuits based on topological phases, we can inherently minimize the impact of local perturbations and enable the system to actively correct errors without requiring explicit error detection and correction cycles. The core idea revolves around encoding quantum information in topological states, where information is localized and protected from local noise. This approach offers a pathway towards more robust and scalable quantum computation, potentially reducing the resource overhead associated with traditional error correction. We outline a framework for designing such circuits and discuss the key theoretical considerations underpinning this methodology. Further investigation into specific circuit architectures and their performance characteristics is warranted.
Abstract Heisenberg scaling characterizes the ultimate precision of parameter estimation enabled by quantum mechanics, which represents an important quantum advantage of both theoretical and technological interest. Here, we present a comprehensive and rigorous study of the attainability of strong, global notions of Heisenberg scaling (in contrast to the commonly studied local estimation based on e.g. quantum Fisher information) in the fundamental problem of quantum metrology, in noisy environments. As our first contribution, we formally define two useful notions of Heisenberg scaling in global estimation respectively based on the average estimation error and the limiting distribution of estimation error (which we highlight as a practically important figure of merit). A main result of this work is that for the standard phase damping noise, an O ( n −1 ) noise rate is a necessary and sufficient condition for attaining global Heisenberg scaling. We first prove that O ( n −1 ) is an upper bound on the noise rate for Heisenberg scaling to be possible, and then show by constructing a ‘robust’ estimation procedure that global Heisenberg scaling in both senses can indeed be achieved under Θ( n −1 ) noise. In addition, we provide a practically more friendly adaptive protocol using only an one-qubit memory, which achieves global Heisenberg scaling in terms of limiting distribution as well under O ( n −1 ) noise.
Quantum metrology overcomes standard precision limits and plays a central role in science and technology. Practically, it is vulnerable to imperfections such as decoherence. Here we demonstrate quantum metrology for noisy channels such that entanglement with ancillary qubits enhances the quantum Fisher information for phase estimation but not otherwise. Our photonic experiment covers a range of noise for various types of channels, including for two randomly alternating channels such that assisted entanglement fails for each noisy channel individually. We simulate noisy channels by implementing space-multiplexed dual interferometers with quantum photonic inputs. We demonstrate the advantage of entanglement-assisted protocols in a phase estimation experiment run with either a single-probe or multiprobe approach. These results establish that entanglement with ancillae is a valuable approach for delivering quantum-enhanced metrology. Our approach to entanglement-assisted quantum metrology via a simple linear-optical interferometric network with easy-to-prepare photonic inputs provides a path towards practical quantum metrology.
This paper presents a novel approach to quantum error correction leveraging the topological properties of quantum entanglement. Traditional quantum error correction codes rely on local operations, which are often inefficient and vulnerable to noise. We propose a scheme utilizing multi-body quantum entanglement networks to encode and decode quantum information, capitalizing on the inherent topological protection offered by entanglement. The core mechanism involves the exchange of entangled states to effectively mitigate the impact of noise, achieving robust quantum information transfer without the constraints of localized operations. This work introduces a fundamentally new paradigm for quantum communication, offering a more reliable pathway for transmitting quantum information in the presence of environmental noise. The proposed method aims to overcome the limitations of existing error correction techniques by exploiting the intrinsic robustness of entanglement, paving the way for more practical and scalable quantum communication systems. The key advantage lies in the absence of the need for local quantum gates, which are often a significant bottleneck in quantum communication. We demonstrate, theoretically, the potential for enhanced error correction performance through the strategic manipulation of entangled states.