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arXiv:2304.04274 · Physical Review Letters

Resource-Efficient High-Dimensional Entanglement Detection via Symmetric Projections

Simon Morelli, Marcus Huber, Armin Tavakoli

Published Oct 25, 2023• 28 citations
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Abstract

We introduce two families of criteria for detecting and quantifying the entanglement of a bipartite quantum state of arbitrary local dimension. The first is based on measurements in mutually unbiased bases and the second is based on equiangular measurements. Both criteria give a qualitative result in terms of the state's entanglement dimension and a quantitative result in terms of its fidelity with the maximally entangled state. The criteria are universally applicable since no assumptions on the state are required. Moreover, the experimenter can control the trade-off between resource-efficiency and noise-tolerance by selecting the number of measurements performed. For paradigmatic noise models, we show that only a small number of measurements are necessary to achieve nearly-optimal detection in any dimension. The number of global product projections scales only linearly in the local dimension, thus paving the way for detection and quantification of very high-dimensional entanglement.

DOI
10.1103/physrevlett.131.170201

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Abstract The characterization of high-dimensional entanglement plays a crucial role in the field of quantum information science. Conventional entanglement criteria measuring coherent superpositions of multiple basis states face experimental bottlenecks on most physical platforms due to limited multi-channel control. Here, we introduce a practically efficient detection strategy based on randomized product projections. We show that the first-order moments of such projections can be used to estimate entanglement fidelity, thereby enabling practical and efficient certification of the Schmidt number (SN) in high-dimensional bipartite systems. By constructing optimal observables, it is sufficient to merely measure a single basis state, substantially reducing experimental overhead. Moreover, we present an algorithm to obtain a lower bound of the SN with a high confidence level from a limited number of experimental data. Our results open up resource-efficient experimental avenues to detect high-dimensional entanglement and test its implementations in modern information technologies.
Mutually unbiased bases, mutually unbiased measurements and general symmetric informationally complete measurements are three related concepts in quantum information theory. We investigate multipartite systems using these notions and present some criteria detecting entanglement of arbitrary high dimensional multi-qudit systems and multipartite systems of subsystems with different dimensions. It is proved that these criteria can detect the k -nonseparability ( k is even) of multipartite qudit systems and arbitrary high dimensional multipartite systems of m subsystems with different dimensions. We show that they are more efficient and wider of application range than the previous ones. They provide experimental implementation in detecting entanglement without full quantum state tomography.
We investigate correlations among complementary observables. In particular, we show how to take advantage of mutually unbiased bases for the efficient detection of entanglement in arbitrarily high-dimensional, multipartite, and continuous-variable quantum systems. The introduced entanglement criteria are relatively easy to implement experimentally since they require only a few local measurement settings. In addition, we establish a link between the separability problem and the maximum number of mutually unbiased bases---opening an additional avenue in this long-standing open problem.
Abstract The detection of quantum entanglement represents a fundamental challenge in quantum measurement theory within the context of quantum information science. In this work, we propose a family of separability criteria based on mutually unbiased equiangular tight frames [IEEE Trans. Inf. Theory 67 , 1656–1667 (2021)], which constitute a natural generalization of both mutually unbiased bases and equiangular tight frames. The proposed criteria are applicable to a broad class of quantum systems, including bipartite systems with equal or unequal subsystem dimensions, as well as multipartite systems with heterogeneous dimensional components. In the examined cases, namely isotropic, Bell-diagonal, and Werner states, the proposed entanglement detection criteria demonstrate superior performance relative to several established methods. Crucially, these criteria rely solely on a small set of local measurements, which significantly enhances their experimental feasibility for the characterization of entanglement in unknown quantum states. Overall, the MUETF-based criteria provide more robust and versatile tools for entanglement verification across diverse quantum architectures.
Abstract Methods of quantum information processing often appear in terms of specially selected states. For example, mutually unbiased bases (MUBs) and symmetric informationally complete measurements are widely applied. Finite frames have found use in many areas including quantum information. Due to its specific inner structure, a single equiangular tight frame (ETF) allows one to formulate criteria to detect non-classical correlations. This study aims to approach entanglement detection with the use of mutually unbiased ETFs. Such frames are an interesting generalization of widely recognized MUBs. It still uses rank-one operators, but the number of outcomes can exceed the dimensionality. Several approaches are considered including separability criteria and entanglement witnesses. Separability criteria for multipartite systems are finally obtained.
Existing methods for deciding whether a bipartite quantum state is separable or entangled typically fall into one of two categories: they are either complete but require access to an explicit density matrix followed by numerical optimization, or they can be evaluated directly by measuring the quantum system but are incomplete, in the sense that they cannot detect all forms of entanglement. In this work, we overcome both limitations in a unified framework. First, we bypass numerical optimization by deriving separability criteria in the form of universal bounds on tensor powers of separable states. We prove that these bounds are complete: every entangled state violates them for sufficiently large tensor powers. Second, we explicitly construct a corresponding complete family of nonlinear entanglement witnesses, which can detect all forms of entanglement without requiring an explicit density matrix. The witnesses we construct are moreover basis-independent, in the sense that they are invariant under conjugation by local unitaries. Altogether, our results expand the toolbox for entanglement detection in arbitrary local dimensions in a manifestly invariant way.