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Masahito Hayashi

Publications and source records attributed to Masahito Hayashi.

At least 91 records · Page 5Linked to original sources
arXiv2023

Measurement-Device-Independent Detection of Beyond-Quantum State

In quantum theory, a quantum state on a composite system of two parties realizes a non-negative probability with any measurement element with a tensor product form. However, there also exist non-quantum states which satisfy the above condition. Such states are called beyond-quantum states, and cannot be detected by standard Bell tests. To distinguish a beyond-quantum state from quantum states, we propose a measurement-device-independent (MDI) test for beyond-quantum state detection, which is composed of quantum input states on respective parties and quantum measurements across the input system and the target system on respective parties. The performance of our protocol is independent of the forms of the tested states and the measurement operators, which provides an advantage in practical scenarios. We also discuss the importance of tomographic completeness of the input sets to the detection.

quant-ph↗
arXiv2023

Iterative minimization algorithm on a mixture family

Iterative minimization algorithms appear in various areas including machine learning, neural networks, and information theory.The em algorithm is one of the famous iterative minimization algorithms in the area of machine learning, and the Arimoto-Blahut algorithm is a typical iterative algorithm in the area of information theory.However, these two topics had been separately studied for a long time. In this paper, we generalize an algorithm that was recently proposed in the context of the Arimoto-Blahut algorithm.Then, we show various convergence theorems, one of which covers the case when each iterative step is done approximately.Also, we apply this algorithm to the target problem of the em algorithm, and propose its improvement. In addition, we apply it to other various problems in information theory.

cs.IT↗
arXiv2023

Robust and efficient verification of graph states in blind measurement-based quantum computation

Blind quantum computation (BQC) is a secure quantum computation method that protects the privacy of clients. Measurement-based quantum computation (MBQC) is a promising approach for realizing BQC. To obtain reliable results in blind MBQC, it is crucial to verify whether the resource graph states are accurately prepared in the adversarial scenario. However, previous verification protocols for this task are too resource consuming or noise susceptible to be applied in practice. Here, we propose a robust and efficient protocol for verifying arbitrary graph states with any prime local dimension in the adversarial scenario, which leads to a robust and efficient protocol for verifying the resource state in blind MBQC. Our protocol requires only local Pauli measurements and is thus easy to realize with current technologies. Nevertheless, it can achieve the optimal scaling behaviors with respect to the system size and the target precision as quantified by the infidelity and significance level, which has never been achieved before. Notably, our protocol can exponentially enhance the scaling behavior with the significance level.

quant-ph↗
arXiv2023

Stochastic behavior of outcome of Schur-Weyl duality measurement

We focus on the measurement defined by the decomposition based on Schur-Weyl duality on $n$ qubits. As the first setting, we discuss the asymptotic behavior of the measurement outcome when the state is given as the permutation mixture $ρ_{mix,n,l}$ of the state $| 1^{l} \, 0^{n-l} \rangle := | 1 \rangle^{\otimes l} \otimes |0\rangle^{\otimes (n-l)}$. In contrast, when the state is given as the Dicke state $|Ξ_{n,l}\rangle$, the measurement outcome takes one deterministic value. These two cases have completely different behaviors. As the second setting, we study the case when the state is given as the tensor product of the permutation mixture $ρ_{mix,k,l}$ and the Dicke state $| Ξ_{n-k,m-l} \rangle$. We derive various types of asymptotic distribution including a kind of central limit theorem when $n$ goes to infinity.

math-ph↗
arXiv2023

Covert communication with Gaussian noise: from random access channel to point-to-point channel

We propose a covert communication protocol for the spread-spectrum multiple random access with additive white Gaussian noise (AWGN) channel. No existing paper has studied covert communication for the random access channel. Our protocol assumes binary discrete phase-shift keying (BPSK) modulation, and it works well under imperfect channel state information (I-CSI) for both the legitimate and adversary receivers, which is a realistic assumption in the low power regime. Also, our method assumes that the legitimate users share secret variables in a similar way as the preceding studies. Although several studies investigated the covert communication for the point-to-point communication, no existing paper considers the covert communication under the above uncertainty assumption even for point-to-point communication. Our protocol under the above uncertainty assumption allows O(n) legitimate senders and O(n/log n) active legitimate senders. Furthermore, our protocol can be converted to a protocol for point-to-point communication that works under the above uncertainty assumption.

cs.IT↗
arXiv2023

Non-Adaptive Coding for Two-Way Wiretap Channel with or without Cost Constraints

This paper studies the secrecy results for the two-way wiretap channel (TW-WC) with an external eavesdropper under a strong secrecy metric. Employing non-adaptive coding, we analyze the information leakage and the decoding error probability, and derive inner bounds on the secrecy capacity regions for the TW-WC under strong joint and individual secrecy constraints. For the TW-WC without cost constraint, both the secrecy and error exponents could be characterized by the conditional Rényi mutual information in a concise and compact form. And, some special cases secrecy capacity region and sum-rate capacity results are established, demonstrating that adaption is useless in some cases or the maximum sum-rate that could be achieved by non-adaptive coding. For the TW-WC with cost constraint, we consider the peak cost constraint and extend our secrecy results by using the constant composition codes. Accordingly, we characterize both the secrecy and error exponents by a modification of Rényi mutual information, which yields inner bounds on the secrecy capacity regions for the general discrete memoryless TW-WC with cost constraint. Our method works even when a pre-noisy processing is employed based on a conditional distribution in the encoder and can be easily extended to other multi-user communication scenarios.

cs.IT↗
arXiv2023

Tight Cramér-Rao type bounds for multiparameter quantum metrology through conic programming

In the quest to unlock the maximum potential of quantum sensors, it is of paramount importance to have practical measurement strategies that can estimate incompatible parameters with best precisions possible. However, it is still not known how to find practical measurements with optimal precisions, even for uncorrelated measurements over probe states. Here, we give a concrete way to find uncorrelated measurement strategies with optimal precisions. We solve this fundamental problem by introducing a framework of conic programming that unifies the theory of precision bounds for multiparameter estimates for uncorrelated and correlated measurement strategies under a common umbrella. Namely, we give precision bounds that arise from linear programs on various cones defined on a tensor product space of matrices, including a particular cone of separable matrices. Subsequently, our theory allows us to develop an efficient algorithm that calculates both upper and lower bounds for the ultimate precision bound for uncorrelated measurement strategies, where these bounds can be tight. In particular, the uncorrelated measurement strategy that arises from our theory saturates the upper bound to the ultimate precision bound. Also, we show numerically that there is a strict gap between the previous efficiently computable bounds and the ultimate precision bound.

quant-ph↗
arXiv2023

Tight Exponential Analysis for Smoothing the Max-Relative Entropy and for Quantum Privacy Amplification

The max-relative entropy together with its smoothed version is a basic tool in quantum information theory. In this paper, we derive the exact exponent for the asymptotic decay of the small modification of the quantum state in smoothing the max-relative entropy based on purified distance. We then apply this result to the problem of privacy amplification against quantum side information, and we obtain an upper bound for the exponent of the asymptotic decreasing of the insecurity, measured using either purified distance or relative entropy. Our upper bound complements the earlier lower bound established by Hayashi, and the two bounds match when the rate of randomness extraction is above a critical value. Thus, for the case of high rate, we have determined the exact security exponent. Following this, we give examples and show that in the low-rate case, neither the upper bound nor the lower bound is tight in general. This exhibits a picture similar to that of the error exponent in channel coding. Lastly, we investigate the asymptotics of equivocation and its exponent under the security measure using the sandwiched Rényi divergence of order $s\in (1,2]$, which has not been addressed previously in the quantum setting.

quant-ph↗
arXiv2023

Detection of Beyond-Quantum Non-locality based on Standard Local Quantum Observables

Device independent detections of quantum non-locality like Bell-CHSH inequality are important methods to detect quantum non-locality because the whole protocol can be implemented by uncertified local observables. However, this detection is not sufficient for the justification of standard quantum theory, because there are theoretically many types of beyond-quantum non-local states in General Probabilistic Theories. One important class is Entanglement Structures (ESs), which contain beyond-quantum non-local states even though their local systems are completely equivalent to standard quantum systems. This paper shows that any device independent detection cannot distinguish beyond-quantum non-local states from standard quantum states. To overcome this problem, this paper gives a device dependent detection based on local observables to distinguish any beyond-quantum non-local state from all standard quantum states. Especially, we give a way to detect any beyond-quantum non-local state in two-qubit ESs by observing only spin observables on local systems.

quant-ph↗
arXiv2023

Oblivious Quantum Computation and Delegated Multiparty Quantum Computation

We propose a new concept, oblivious quantum computation, which requires performing oblivious transfer with respect to the computation outcome of the quantum computation, where the secrecy of the input qubits and the program to identify the quantum gates are required. Exploiting quantum teleportation, we propose a two-server protocol for this task, which realizes an exponential improvement for the communication complexity over the simple application of two-server (quantum) oblivious transfer to the sending of the computation result. Also, we discuss delegated multiparty quantum computation, in which, several users ask multiparty quantum computation to server(s) only using classical communications. We propose a two-server protocol for the latter task as well.

quant-ph↗
arXiv2023

Prior Entanglement Exponentially Improves One-Server Quantum Private Information Retrieval for Quantum Messages

Quantum private information retrieval (QPIR) for quantum messages is a quantum communication task, in which a user retrieves one of the multiple quantum states from the server without revealing which state is retrieved. In the one-server setting, we find an exponential gap in the communication complexities between the presence and absence of prior entanglement in this problem with the one-server setting. To achieve this aim, as the first step, we prove that the trivial solution of downloading all messages is optimal under QPIR for quantum messages, which is a similar result to that of classical PIR but different from QPIR for classical messages. As the second step, we propose an efficient one-server one-round QPIR protocol with prior entanglement by constructing a reduction from a QPIR protocol for classical messages to a QPIR protocol for quantum messages in the presence of prior entanglement.

quant-ph↗
arXiv2023

Efficient algorithms for quantum information bottleneck

The ability to extract relevant information is critical to learning. An ingenious approach as such is the information bottleneck, an optimisation problem whose solution corresponds to a faithful and memory-efficient representation of relevant information from a large system. The advent of the age of quantum computing calls for efficient methods that work on information regarding quantum systems. Here we address this by proposing a new and general algorithm for the quantum generalisation of information bottleneck. Our algorithm excels in the speed and the definiteness of convergence compared with prior results. It also works for a much broader range of problems, including the quantum extension of deterministic information bottleneck, an important variant of the original information bottleneck problem. Notably, we discover that a quantum system can achieve strictly better performance than a classical system of the same size regarding quantum information bottleneck, providing new vision on justifying the advantage of quantum machine learning.

quant-ph↗
arXiv2023

Unified Approach to Secret Sharing and Symmetric Private Information Retrieval with Colluding Servers in Quantum Systems

This paper unifiedly addresses two kinds of key quantum secure tasks, i.e., quantum versions of secret sharing (SS) and symmetric private information retrieval (SPIR) by using multi-target monotone span program (MMSP), which characterizes the classical linear protocols of SS and SPIR. SS has two quantum extensions; One is the classical-quantum (CQ) setting, in which the secret to be sent is classical information and the shares are quantum systems. The other is the quantum-quantum (QQ) setting, in which the secret to be sent is a quantum state and the shares are quantum systems. The relation between these quantum protocols and MMSP has not been studied sufficiently. We newly introduce the third setting, i.e., the entanglement-assisted (EA) setting, which is defined by modifying the CQ setting with allowing prior entanglement between the dealer and the end-user who recovers the secret by collecting the shares. Showing that the linear version of SS with the EA setting is directly linked to MMSP, we characterize linear quantum versions of SS with the CQ ad QQ settings via MMSP. Further, we introduce the EA setting of SPIR, which is shown to link to MMSP. In addition, we discuss the quantum version of maximum distance separable codes.

quant-ph↗
arXiv2023

Special functions in quantum phase estimation

This paper explains existing results for the application of special functions to phase estimation, which is a fundamental topic in quantum information. We focus on two special functions. One is prolate spheroidal wave function, which approximately gives the maximum probability that the difference between the true parameter and the estimate is smaller than a certain threshold. The other is Mathieu function, which exactly gives the optimum estimation under the energy constraint. It also characterizes the uncertainty relation for the position and the momentum for periodic functions.

quant-ph↗
arXiv2023

Analytical calculation formulas for capacities of classical and classical-quantum channels

We derive an analytical calculation formula for the channel capacity of a classical channel without any iteration while its existing algorithms require iterations and the number of iteration depends on the required precision level. Hence, our formula is its first analytical formula without any iteration. We apply the obtained formula to examples and see how the obtained formula works in these examples. Then, we extend it to the channel capacity of a classical-quantum (cq-) channel. Many existing studies proposed algorithms for a cq-channel and all of them require iterations. Our extended analytical algorithm have also no iteration and output the exactly optimum values.

cs.IT↗
arXiv2022

Pseudo standard entanglement structure cannot be distinguished from standard entanglement structure

An experimental verification of the maximally entangled state ensures that the constructed state is close to the maximally entangled state, but it does not guarantee that the state is exactly the same as the maximally entangled state. Further, the entanglement structure is not uniquely determined in general probabilistic theories even if we impose that the local subsystems are fully equal to quantum systems. Therefore, the existence of the maximally entangled state depends on whether the standard entanglement structure is valid. To examine this issue, we introduce pseudo standard entanglement structure as a structure of quantum composite system under natural assumptions based on the existence of projective measurements and the existence of approximations of all maximally entangled standard states. Surprisingly, there exist infinitely many pseudo standard entanglement structures different from the standard entanglement structure. In our setting, any maximally entangled state can be arbitrarily approximated by an entangled state that belongs to our obtained pseudo standard entanglement structure. That is, experimental verification does not exclude the possibility of our obtained pseudo standard entanglement structure that is different from the standard entanglement structure. On the other hand, such pseudo structures never possess global unitary symmetry, i.e., global unitary symmetry is essential condition for the standard entanglement structure.

quant-ph↗
arXiv2022

Two-Server Oblivious Transfer for Quantum Messages

Oblivious transfer is considered as a cryptographic primitive task for quantum information processing over quantum network. Although it is possible with two servers, any existing protocol works only with classical messages. We propose two-server oblivious transfer protocols for quantum messages.

quant-ph↗
arXiv2022

Significance improvement by randomized test in random sampling without replacement

This paper studies one-sided hypothesis testing under random sampling without replacement. That is, when $n+1$ binary random variables $X_1,\ldots, X_{n+1}$ are subject to a permutation invariant distribution and $n$ binary random variables $X_1,\ldots, X_{n}$ are observed, we have proposed randomized tests with a randomization parameter for the upper confidence limit of the expectation of the $(n+1)$th random variable $X_{n+1}$ under a given significance level $δ>0$. Our proposed randomized test significantly improves over deterministic test unlike random sampling with replacement.

math.ST↗