Abstract In traditional quantum metrology protocols, the initial multipartite entangled pure quantum probes are considered to be isolated, i.e., free of quantum many-body effects. Here, we study the impact of inherent many-body effects such as interaction with noisy environment and nonlocal interactions among particles on metrologically resourceful multipartite entanglement of initially mixed quantum probes. In this regard, we employ an information-theoretic multipartite entanglement measure as a figure-of-merit. The inevitable interaction with the noisy environment leads to disentanglement in multipartite quantum probes which restricts its metrological advantage. For this, we use entanglement dissociation to derive bounds on the multipartite entanglement measure that can identify the relevant entanglement structure under global as well as local noisy evolution. Furthermore, we investigate nonlocal interactions in terms of their entangling capability in a multipartite quantum probe. We show that such nonlocal interactions can be exploited as a valuable resource that exhibits better precision scaling in mixed-state quantum metrology. Moreover, we numerically observe these results for GHZ-W class states.
Abstract In traditional quantum metrology protocols, the initial multipartite entangled pure quantum probes are considered to be isolated, i.e., free of quantum many-body effects. Here, we study the impact of inherent many-body effects such as interaction with noisy environment and nonlocal interactions among particles on metrologically resourceful multipartite entanglement of initially mixed quantum probes. In this regard, we employ an information-theoretic multipartite entanglement measure as a figure-of-merit. The inevitable interaction with the noisy environment leads to disentanglement in multipartite quantum probes which restricts its metrological advantage. For this, we use entanglement dissociation to derive bounds on the multipartite entanglement measure that can identify the relevant entanglement structure under global as well as local noisy evolution. Furthermore, we investigate nonlocal interactions in terms of their entangling capability in a multipartite quantum probe. We show that such nonlocal interactions can be exploited as a valuable resource that exhibits better precision scaling in mixed-state quantum metrology. Moreover, we numerically observe these results for GHZ-W class states.
Abstract We consider quantum metrology with several copies of bipartite and multipartite quantum states. We characterize the metrological usefulness by determining how much the state outperforms separable states. We identify a large class of entangled states that become maximally useful for metrology in the limit of large number of copies, even if the state is weakly entangled and not even more useful than separable states. This way we activate metrologically useful genuine multipartite entanglement. Remarkably, not only that the maximally achievable metrological usefulness is attained exponentially fast in the number of copies, but it can be achieved by the measurement of few simple correlation observables. We also make general statements about the usefulness of a single copy of pure entangled states. We surprisingly find that the multiqubit states presented in Hyllus et al (2010 Phys. Rev. A 82 012337), which are not useful, become useful if we embed the qubits locally in qutrits. We discuss the relation of our scheme to error correction, and its possible use for quantum metrology in a noisy environment.
Multipartite entanglement is the premier resource for quantum technologies. Yet, its exact quantification in the laboratory is notoriously challenging, typically requiring the full knowledge of high dimensional quantum states. Here, we construct observable bounds to multipartite entanglement for systems of arbitrary size, which are functions of the local and global state purities, and correlation functions. First, we derive experimentally accessible upper and lower limits to both the bipartite entanglement of formation and the squashed entanglement of bipartite systems, by leveraging cornerstone results of quantum information theory: the entropy strong subadditivity inequality and the Koashi-Winter monogamy relation. Then, we convert them into bounds to the entanglement up to degree k for arbitrary states, and to the genuine k-partite entanglement, by employing a recently proposed method. Finally, we analytically and numerically test these results, by bounding the multipartite entanglement of several relevant states and mixtures, including the important classes of GHZ, Dicke, W states, and random pure states.
Quantum many-body interactions can induce quantum entanglement among particles, rendering them valuable resources for quantum-enhanced sensing. In this work, we establish a link between the bound on the growth of the quantum Fisher information and the Lieb-Robinson bound, which characterizes the operator growth in locally interacting quantum many-body systems. We show that for initial separable states, despite the use of local many-body interactions, the precision cannot surpass the shot noise limit at all times. This conclusion also holds for an initial state that is the nondegenerate ground state of a local and gapped Hamiltonian. These findings strongly hint that when one can only prepare separable initial states, nonlocal and long-range interactions are essential resources for surpassing the shot noise limit. This observation is confirmed through numerical analysis on the long-range Ising model. Our results bridge the field of many-body quantum sensing and operator growth in many-body quantum systems and open the possibility to investigate the interplay between quantum sensing and control, many-body physics and information scrambling.
Quantifying multipartite entanglement in quantum many-body systems and hybrid quantum computing architectures is a fundamental yet challenging task. In recent years, thermodynamic quantities such as the maximum extractable work from an isolated system (the ergotropy) have allowed for entanglement measures that are operationally more accessible. However, these measures can be restrictive when applied to systems governed by Hamiltonians with strong collective or interparticle interactions. Motivated by advances in quantum simulators, we propose a framework that circumvents these restrictions by evaluating global and local ergotropy either through controlled quenching of interactions or by measuring suitable local observables only. We show that this formalism allows us to correctly estimate genuine multipartite entanglement in both stationary and time-evolved states of systems with strong interactions, including parametrized quantum states simulated on a quantum circuit with varying circuit depth and noise. We demonstrate its applicability to realistic physical models, namely, the Tavis-Cummings model, the three-level Dicke model, and the transverse-field Ising model, highlighting its potential as a versatile tool for characterizing entanglement in near-term quantum simulators.
Quantum mechanical systems can be used to out perform classical ones in several tasks. For instance, quantum correlations can be employed to beat the shot-noise limit in metrology protocols. Such parameter estimation methods are crucial for both advances in science and the development of technologies. Almost all quantum technologies operate with some level of noise and how quantum-enhancement fares in the presence of noise is still unclear. Here we show that, when a system in mixed multipartite quantum state is used to estimate a parameter, the information must be decoded by coherent interactions between the parts of the probe. On the other hand, noiseless quantum metrology protocols are adaptively additive for any pure entangled states, that is, no coherent processing is necessary in this case. This leads to an operational interpretation for the ability of performing coherent interactions in noisy parameter estimation and highlights a cornerstone difference between mixed and pure states. This result has fundamental importance in the search for the source of quantum advantage and it also has practical relevance for the designing of new high-precision-measurement devices.
The ability to preserve multipartite entanglement in noisy environments is central to advancing quantum information processing. In this work, we develop a semiclassical theoretical model of three entangled qubits exposed to local Markov noise environments with tunable statistical correlations between noise sources. We show that such correlations can significantly influence the dynamics of multipartite entanglement, in some cases slowing its decay and, under ideal conditions, even enabling full preservation. Using tripartite negativity as an entanglement measure, we derive analytical results for the GHZ and W states, demonstrating their contrasting responses to correlated and anticorrelated noise. Our analysis identifies regimes in which multipartite entanglement can be sustained despite environmental interactions, offering new insight into how noise correlations may serve as a resource for protecting quantum coherence in multi-qubit systems.