arXiv subjects

Donghoon Ha

Publications and source records attributed to Donghoon Ha.

At least 19 recordsLinked to original sources

arXiv2026

(2,m)-threshold quantum data hiding

We consider multiparty quantum state discrimination and present a multiparty quantum data-hiding scheme for one classical bit to be shared among multiple parties. In the proposed scheme, any pair of parties can collaborate to perfectly recover the hidden bit through a joint measurement, whereas measurements based on local operations and classical communication(LOCC) performed even by all parties reveal only an arbitrarily small amount of information. We further provide bounds on the optimal LOCC discrimination of multiparty quantum states. The proposed scheme can be implemented using only separable states of low-dimensional quantum systems, enhancing its practical feasibility.

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arXiv2025

Quantum data hiding with two-qubit separable states

We consider the discrimination of two-party quantum states and provide a quantum data-hiding scheme using two-qubit separable states. We first provide a bound on the optimal local discrimination of two-party quantum states, and establish a sufficient condition under which a two-party quantum state ensemble can be used to construct a data-hiding scheme. We illustrate this condition with examples of two-qubit state ensembles consisting of two orthogonal separable states. As our data-hiding scheme can be implemented with separable states of the lowest possible dimension, its practical realization becomes significantly more attainable.

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arXiv2025

Factorizability of optimal quantum sequence discrimination under maximum-confidence measurements

We consider the discrimination of quantum sequences under maximum-confidence measurements and show that the optimal discrimination of a quantum sequence ensemble can always be factorized into that of each individual ensemble. In other words, the optimal quantum sequence discrimination under maximum-confidence measurements can be achieved just by performing a maximum-confidence discrimination independently at each step of the quantum sequence. We also show that the maximum confidence of identifying a quantum sequence is to achieve the maximum confidence of identifying each state comprising the quantum sequence. We further provide a necessary and sufficient condition for the optimal quantum state discrimination under maximum-confidence measurements.

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arXiv2025

Factorizability of multi-party quantum sequence discrimination under local operations and classical communication

We consider multi-party quantum sequence discrimination under local operations and classical communication(LOCC), and provide conditions under which the optimal LOCC discrimination of a multi-party quantum sequence ensemble can be factorized into that of each individual ensemble. In other words, the optimal LOCC discrimination of a multi-party quantum sequence ensemble can be achieved just by performing optimal LOCC discrimination independently at each step of the quantum sequence. We also illustrate through examples of multi-party quantum states that such factorizability of optimal LOCC discrimination is possible. We further establish a necessary and sufficient condition under which the optimal LOCC discrimination of a multi-party quantum state ensemble can be realized just by guessing the state with the largest probability. Our results can provide a useful application to investigate the fundamental limits of quantum data hiding.

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arXiv2025

Quantum data-hiding scheme using orthogonal separable states

We consider bipartite quantum state discrimination and present a quantum data-hiding scheme utilizing an orthogonal separable state ensemble. Using a bound on local minimum-error discrimination, we provide a sufficient condition for the separable state ensemble to be used in constructing a quantum data-hiding scheme. Our results are illustrated with various examples in bipartite quantum systems. As our scheme employs separable states of low-dimensional quantum systems, it becomes more feasible for practical implementation.

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arXiv2024

Postmeasurement information and nonlocality of quantum state discrimination

In quantum state discrimination, nonlocality arises when optimal discrimination cannot be achieved using only local operations and classical communication. It has recently been shown that postmeasurement information identifying the subensemble containing the prepared state can either annihilate or create such nonlocality. Here, we demonstrate that these effects can depend critically on how the original ensemble is partitioned into subensembles. We derive sufficient conditions under which different ensemble partitions lead to the annihilation or creation of nonlocality upon the revelation of postmeasurement information. We further construct explicit bipartite quantum state ensembles satisfying these conditions, thereby illustrating the partition-dependent nature of nonlocality in quantum state discrimination.

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arXiv2024

Entanglement witness and nonlocality in confidence of measurement from multipartite quantum state discrimination

We consider multipartite quantum state discrimination and provide a specific relation between the properties of entanglement witness and quantum nonlocality inherent in the confidence of measurements. We first provide the definition of the confidence of measurements as well as its useful properties for various types of multipartite measurements. We show that globally maximum confidence that cannot be achieved by local operations and classical communication strongly depends on the existence of entanglement witness. We also provide conditions for an upper bound on maximum of locally-achievable confidences. Finally, we establish a method in terms of entanglement witness to construct quantum state ensemble with nonlocal maximum confidences.

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arXiv2024

Multi-player quantum data hiding by nonlocal quantum state ensembles

We provide multi-player quantum data hiding based on nonlocal quantum state ensembles arising from multi-party quantum state discrimination. Using bounds on local minimum-error discrimination of multi-party quantum states, we construct a multi-player quantum data-hiding scheme. Our data-hiding scheme can be used to hide multiple bits, asymptotically, unless all the players collaborate. We also illustrate our results by examples of nonlocal quantum state ensembles.

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arXiv2023

Nonlocal quantum state ensembles and quantum data hiding

We consider the discrimination of bipartite quantum states and establish a relation between nonlocal quantum state ensemble and quantum data hiding processing. Using a bound on optimal local discrimination of bipartite quantum states, we provide a sufficient condition for a bipartite quantum state ensemble to be used to construct a quantum data-hiding scheme. Our results are illustrated by examples in multidimensional bipartite quantum systems.

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arXiv2023

Entanglement witness and multipartite quantum state discrimination

We consider multipartite quantum state discrimination and show that the minimum-error discrimination by separable measurements is closely related to the concept of entanglement witness. Based on the properties of entanglement witness, we establish some necessary and/or sufficient conditions on minimum-error discrimination by separable measurements. We also provide some conditions on the upper bound of the maximum success probability over all possible separable measurements. Our results are illustrated by examples of multidimensional multipartite quantum states. Finally, we provide a systematic way in terms of the entanglement witness to construct multipartite quantum state ensembles showing nonlocality in state discrimination.

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arXiv2022

Bipartite quantum state discrimination and decomposable entanglement witness

We consider bipartite quantum state discrimination using positive-partial-transpose measurements and show that minimum-error discrimination by positive-partial-transpose measurements is closely related to entanglement witness. By using the concept of decomposable entanglement witness, we establish conditions on minimum-error discrimination by positive-partial-transpose measurements. We also provide conditions on the upper bound of the maximum success probability over all possible positive-partial-transpose measurements. Finally, we illustrate our results using examples of multidimensional bipartite quantum states.

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arXiv2022

Bound on optimal local discrimination of multipartite quantum states

We consider the unambiguous discrimination of multipartite quantum states and provide an upper bound for the maximum success probability of optimal local discrimination. We also provide a necessary and sufficient condition to realize the upper bound. We further establish a necessary and sufficient condition for this upper bound to be saturated. Finally, we illustrate our results using examples in multidimensional multipartite quantum systems.

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arXiv2022

Qubit State Discrimination using Post-measurement Information

We consider the optimal discrimination of nonorthogonal qubit states with post-measurement information and provide an analytic structure of the optimal measurements. We also show that there is always a null optimal measurement when post-measurement information is given. Further, in discriminating four states using post-measurement information, we analytically provide the optimal probability of correct guessing and show that the uniqueness of optimal measurement is equivalent to the non-existence of non-null optimal measurement with post-measurement information.

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arXiv2021

Bound on local minimum-error discrimination of bipartite quantum states

We consider the optimal discrimination of bipartite quantum states and provide an upper bound for the maximum success probability of optimal local discrimination. We also provide a necessary and sufficient condition for a measurement to realize the upper bound. We further establish a necessary and sufficient condition for this upper bound to be saturated. Finally, we illustrate our results using an example.

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arXiv2021

Locking and unlocking of quantum nonlocality without entanglement in local discrimination of quantum states

The phenomenon of nonlocality without entanglement(NLWE) arises in discriminating multi-party quantum separable states. Recently, it has been found that the post-measurement information about the prepared subensemble can lock or unlock NLWE in minimum-error discrimination of non-orthogonal separable states. Thus, it is natural to ask whether the availability of the post-measurement information can influence on the occurrence of NLWE even in other state-discrimination strategies. Here, we show that the post-measurement information can be used to lock as well as unlock the occurrence of NLWE in terms of optimal unambiguous discrimination. Our results can provide a useful application for hiding or sharing information based on non-orthogonal separable states.

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arXiv2021

Complete analysis to minimum-error discrimination of mixed four qubit states with arbitrary prior probabilities

In this work, we provide a complete analysis to minimum-error discrimination of mixed four qubit states with arbitrary prior probabilities. For the complete anaysis, the most important work to do is to find the necessary and sufficient conditions for the existence of null measurement operator. From the geometric structure of qubit states, we obtain the analytic condition for deciding the existence of a null operator in minimum-error measurement for mixed four qubit states, which also gives the necessary and sufficient conditions for every optimal POVM to have non-zero elements. Using the condition, we completely analyze minimum-error discrimination of mixed four qubit states with arbitrary prior probabilities.

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arXiv2021

Annihilating and creating nonlocality without entanglement by postmeasurement information

Nonlocality without entanglement (NLWE) is a nonlocal quantum phenomenon that arises in separable state discrimination. We show that the availability of the postmeasurement information about the prepared subensemble can affect the occurrence of NLWE in discriminating nonorthogonal nonentangled states. We provide a two-qubit state ensemble consisting of four nonorthogonal separable pure states and show that the postmeasurement information about the prepared subensemble can annihilate NLWE. We also provide another two-qubit state ensemble consisting of four nonorthogonal separable states and show that the postmeasurement information can create NLWE. Our result can provide a useful method to share or hide information using nonorthogonal separable states.

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arXiv2021

Quantum nonlocality without entanglement depending on nonzero prior probabilities in optimal unambiguous discrimination

Nonlocality without entanglement(NLWE) is a nonlocal phenomenon that occurs in quantum state discrimination of multipartite separable states. In the discrimination of orthogonal separable states, the term NLWE is used when the quantum states cannot be discriminated perfectly by local operations and classical communication. In this case, the occurrence of NLWE is independent of nonzero prior probabilities of quantum states being prepared. Recently, it has been found that the occurrence of NLWE can depend on nonzero prior probabilities in minimum-error discrimination of nonorthogonal separable states. Here, we show that even in optimal unambiguous discrimination, the occurrence of NLWE can depend on nonzero prior probabilities. We further show that NLWE can occur regardless of nonzero prior probabilities, even if only one state can be locally discriminated without error. Our results provide new insights into classifying sets of multipartite quantum states in terms of quantum state discrimination.

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