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arXiv:2605.22226

Geometric Construction of Optimal Teleportation Witnesses

Yanning Jia, Fenzhuo Guo, Mengxuan Bai, Mengyan Li, Haifeng Dong, Fei Gao

quant-phSubmitted May 21, 2026• Announced May 22, 2026• 0 citations
v1 · May 21, 2026v2 · Oct 20, 2026
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Abstract

Not all entangled states are useful for quantum teleportation. We present a geometric method to construct optimal teleportation witnesses, which provide operational necessary and sufficient criteria for identifying the teleportation usefulness of arbitrary two-qudit entangled states. Specifically, by developing a two-layer iterative cutting-plane algorithm to solve the shortest distance problem from the target state $ρ$ to the convex set $S$ of useless states, we obtain the projection point $σ^* \in S$ and then construct the optimal teleportation witness from the projection geometry. Moreover, the shortest distance $D(ρ)$ obtained during this construction also serves as a necessary and sufficient criterion for usefulness. We apply our method to identify the teleportation usefulness of three classes of entangled states.

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Not all entangled states are useful for quantum teleportation. We present a geometric method to construct optimal teleportation witnesses, which provide operational necessary and sufficient criteria for identifying the teleportation usefulness of arbitrary two-qudit entangled states. Specifically, by developing a two-layer iterative cutting-plane algorithm to solve the shortest distance problem from the target state ρρρ to the convex set SSS of useless states, we obtain the projection point σ∗∈Sσ^* \in Sσ∗∈S and then construct the optimal teleportation witness from the projection geometry. Moreover, the shortest distance D(ρ)D(ρ)D(ρ) obtained during this construction also serves as a necessary and sufficient criterion for usefulness. We apply our method to identify the teleportation usefulness of three classes of entangled states.
Teleportation witnesses are Hermitian operators which can identify useful entanglement for quantum teleportation. Here we provide a systematic method to construct teleportation witnesses from entanglement witnesses corresponding to general qudit systems. The witnesses so constructed are shown to be optimal for qubit and qutrit systems and therefore detect the largest set of states useful for teleportation within a given class. We demonstrate the action of the witness pertaining to different classes of states in qubits and qutrits. Decomposition of the witness in terms of spin operators facilitates experimental identification of useful resources for teleportation.
Constructing optimal entanglement witnesses for arbitrary quantum systems remains a formidable challenge, hindered by the structural complexity of high-dimensional quantum state spaces. In this work, we overcome this barrier by introducing a unified framework for constructing geometrically optimal witnesses capable of identifying arbitrary entanglement structures. By leveraging the geometric properties of a target quantum state relative to a specific entanglement structure in Hilbert-Schmidt space, these witnesses are constructed in an efficient and effective manner. Among all nontrivial witnesses, they provide maximal distinguishability between the target state and the set of states without the desired entanglement structure. As a result, our approach enables the universal detection of bipartite, multipartite, and high-dimensional entanglement. To demonstrate its experimental feasibility, we apply the framework to a four-qubit nuclear spin quantum system. Compared to existing methods, our approach offers enhanced noise robustness, broader detection universality, and improved construction efficiency, providing a powerful and versatile tool for advancing the characterization and understanding of entanglement in quantum systems.
The ability of entangled states to act as a resource for teleportation is linked to a property of the fully entangled fraction. We show that the set of states with their fully entangled fraction bounded by a threshold value required for performing teleportation is both convex and compact. This feature enables the existence of Hermitian witness operators, the measurement of which could distinguish unknown states useful for performing teleportation. We present an example of such a witness operator illustrating it for different classes of states.
We investigate two-copy scenario of quantum teleportation based on Bell measurements. The detailed protocol is presented and the general expression of the corresponding optimal teleportation fidelity is derived, which is given by the two-copy fully entangled fraction that is invariant under local unitary transformations. We prove that under a specific case of the protocol, which is significant for improving the optimal fidelity, the set of states with their two-copy fully entangled fractions bounded by a threshold value that required for useful two-copy teleportation is convex and compact. Hence the witness operators exist to separate states that are useful for two-copy teleportation from the rest ones. Moreover, we show that the optimal fidelity of two-copy teleportation surpasses that of the original one copy teleportation.
We investigate two-channel scenarios of optimal quantum teleportation based on Bell measurements and GHZ measurements. The detailed protocols are presented and the general expressions of the optimal teleportation fidelities are derived, which turn out to be functions of two-channel fully entangled fractions -- invariants under local unitary transformations. We prove that the set of states which are useful for two-channel teleportation is convex and compact. Hence witness operators exist to separate states that are useful for optimal teleportation from the rest ones. Moreover, we show that our two-channel teleportation fidelity is better than the usual one channel ones. The corresponding experimental schemes for two-channel teleportation of photon states are also presented.