An asymptotic error bound for testing multiple quantum hypotheses

We consider the decision problem between a finite number of states of a finite quantum system, when an arbitrary large number of copies of the system is available for measurements. We provide an upper bound on the asymptotic exponential decay of the averaged probability of rejecting the true state. It represents a generalized quantum Chernoff distance of a finite set of states. As our main result we prove that the bound is sharp in the case of pure states.

Jan 11, 20103 citations

Generalized quantum Chernoff bound

Kun Fang, Masahito Hayashi

arXiv:2508.12889IEEE International Symposium on Information Theory (ISIT)Jun 1, 20260 citations

An asymptotic error bound for testing multiple quantum hypotheses

Michael Nussbaum, Arleta Szko La

Published Jan 1, 2011• 17 citations

OpenAlex

Abstract

Related papers

An asymptotic error bound for testing multiple quantum hypotheses

Michael Nussbaum, Arleta Szkoła

We consider the problem of detecting the true quantum state among r possible ones, based of measurements performed on n copies of a finite-dimensional quantum system. A special case is the problem of discriminating between r probability measures on a finite sample space, using n i.i.d. observations. In this classical setting, it is known that the averaged error probability decreases exponentially with exponent given by the worst case binary Chernoff bound between any possible pair of the r probability measures. Define analogously the multiple quantum Chernoff bound, considering all possible pairs of states. Recently, it has been shown that this asymptotic error bound is attainable in the case of r pure states, and that it is unimprovable in general. Here we extend the attainability result to a larger class of r-tuples of states which are possibly mixed, but pairwise linearly independent. We also construct a quantum detector which universally attains the multiple quantum Chernoff bound up to a factor 1/3.We consider the problem of detecting the true quantum state among r possible ones, based of measurements performed on n copies of a finite-dimensional quantum system. A special case is the problem of discriminating between r probability measures on a finite sample space, using n i.i.d. observations. In this classical setting, it is known that the averaged error probability decreases exponentially with exponent given by the worst case binary Chernoff bound between any possible pair of the r probability measures. Define analogously the multiple quantum Chernoff bound, considering all possible pairs of states. Recently, it has been shown that this asymptotic error bound is attainable in the case of r pure states, and that it is unimprovable in general. Here we extend the attainability result to a larger class of r-tuples of states which are possibly mixed, but pairwise linearly independent. We also construct a quantum detector which universally attains the multiple quantum Chernoff bound up to a factor 1/3.

arXiv:1112.1529The Annals of StatisticsDec 1, 201120 citations

Attainment of the multiple quantum Chernoff bound for certain ensembles of mixed states

Michael Nussbaum

We consider the problem of detecting the true quantum state among r possible ones, based on measurements performed on n of copies of a finite dimensional quantum system. It is known that the exponent for the rate of decrease of the averaged error probability cannot exceed the multiple quantum Chernoff bound (MQCB) defined as the worst case (smallest) quantum Chernoff distance between any possible pair of the r states. This error exponent is attainable for r pure states, but for the general case of mixed states only attainability up to a factor 1/3 is known. Here we show that the MQCB is attainable for mixed states if there is a pair which is closer in quantum Chernoff distance than 1/6 times the distance between all other pairs.We consider the problem of detecting the true quantum state among r possible ones, based on measurements performed on n of copies of a finite dimensional quantum system. It is known that the exponent for the rate of decrease of the averaged error probability cannot exceed the multiple quantum Chernoff bound (MQCB) defined as the worst case (smallest) quantum Chernoff distance between any possible pair of the r states. This error exponent is attainable for r pure states, but for the general case of mixed states only attainability up to a factor 1/3 is known. Here we show that the MQCB is attainable for mixed states if there is a pair which is closer in quantum Chernoff distance than 1/6 times the distance between all other pairs.

arXiv:1308.6563Aug 29, 20133 citations

Multiple Quantum Hypothesis Testing: One-Shot Pairwise Bounds and Sharp Asymptotics

Hao-Chung Cheng, Po-Chieh Liu

We consider Bayesian discrimination among multiple quantum states and establish a dimension-free one-shot upper bound on the minimum probability of error in terms of the sum of pairwise errors. This resolves a conjecture of Audenaert and Mosonyi [J. Math. Phys. 55 (2014)] and improves the multiple quantum Chernoff bound of Li [Ann. Statist. 44 (2016)] by removing its dimension-dependent prefactor. In the asymptotic many-copy regime, our bound proves the achievability of the multiple quantum Chernoff distance for arbitrary separable Hilbert spaces, thereby settling the previously open infinite-dimensional case, and further yields constant-factor sharp asymptotics for the optimal error probability. In binary quantum hypothesis testing, we prove that the minimum error probability is characterized, up to universal constants, by a trace harmonic-mean quantity. Consequently, the optimal binary quantum error probability is within a factor of two of the optimal classical error probability for the associated Nussbaum-Szkoła distributions, complementing the lower bound of Nussbaum and Szkoła [Ann. Statist. 37 (2009)].We consider Bayesian discrimination among multiple quantum states and establish a dimension-free one-shot upper bound on the minimum probability of error in terms of the sum of pairwise errors. This resolves a conjecture of Audenaert and Mosonyi [J. Math. Phys. 55 (2014)] and improves the multiple quantum Chernoff bound of Li [Ann. Statist. 44 (2016)] by removing its dimension-dependent prefactor. In the asymptotic many-copy regime, our bound proves the achievability of the multiple quantum Chernoff distance for arbitrary separable Hilbert spaces, thereby settling the previously open infinite-dimensional case, and further yields constant-factor sharp asymptotics for the optimal error probability. In binary quantum hypothesis testing, we prove that the minimum error probability is characterized, up to universal constants, by a trace harmonic-mean quantity. Consequently, the optimal binary quantum error probability is within a factor of two of the optimal classical error probability for the associated Nussbaum-Szkoła distributions, complementing the lower bound of Nussbaum and Szkoła [Ann. Statist. 37 (2009)].

quant-pharXiv:2606.06246Jun 5, 20260 citations

Discriminating quantum states: The multiple Chernoff distance

Ke Li

We consider the problem of testing multiple quantum hypotheses $\{\rho_{1}^{\otimes n},\ldots,\rho_{r}^{\otimes n}\}$ , where an arbitrary prior distribution is given and each of the $r$ hypotheses is $n$ copies of a quantum state. It is known that the minimal average error probability $P_{e}$ decays exponentially to zero, that is, $P_{e}=\exp\{-\xi n+o(n)\}$ . However, this error exponent $\xi$ is generally unknown, except for the case that $r=2$ . In this paper, we solve the long-standing open problem of identifying the above error exponent, by proving Nussbaum and Szkoła’s conjecture that $\xi=\min_{i\neq j}C(\rho_{i},\rho_{j})$ . The right-hand side of this equality is called the multiple quantum Chernoff distance, and $C(\rho_{i},\rho_{j}):=\max_{0\leq s\leq1}\{-\log\operatorname{Tr}\rho_{i}^{s}\rho_{j}^{1-s}\}$ has been previously identified as the optimal error exponent for testing two hypotheses, $\rho_{i}^{\otimes n}$ versus $\rho_{j}^{\otimes n}$ . The main ingredient of our proof is a new upper bound for the average error probability, for testing an ensemble of finite-dimensional, but otherwise general, quantum states. This upper bound, up to a states-dependent factor, matches the multiple-state generalization of Nussbaum and Szkoła’s lower bound. Specialized to the case $r=2$ , we give an alternative proof to the achievability of the binary-hypothesis Chernoff distance, which was originally proved by Audenaert et al.We consider the problem of testing multiple quantum hypotheses $\{\rho_{1}^{\otimes n},\ldots,\rho_{r}^{\otimes n}\}$, where an arbitrary prior distribution is given and each of the $r$ hypotheses is $n$ copies of a quantum state. It is known that the minimal average error probability $P_{e}$ decays exponentially to zero, that is, $P_{e}=\exp\{-\xi n+o(n)\}$. However, this error exponent $\xi$ is generally unknown, except for the case that $r=2$. In this paper, we solve the long-standing open problem of identifying the above error exponent, by proving Nussbaum and Szkoła’s conjecture that $\xi=\min_{i\neq j}C(\rho_{i},\rho_{j})$. The right-hand side of this equality is called the multiple quantum Chernoff distance, and $C(\rho_{i},\rho_{j}):=\max_{0\leq s\leq1}\{-\log\operatorname{Tr}\rho_{i}^{s}\rho_{j}^{1-s}\}$ has been previously identified as the optimal error exponent for testing two hypotheses, $\rho_{i}^{\otimes n}$ versus $\rho_{j}^{\otimes n}$. The main ingredient of our proof is a new upper bound for the average error probability, for testing an ensemble of finite-dimensional, but otherwise general, quantum states. This upper bound, up to a states-dependent factor, matches the multiple-state generalization of Nussbaum and Szkoła’s lower bound. Specialized to the case $r=2$, we give an alternative proof to the achievability of the binary-hypothesis Chernoff distance, which was originally proved by Audenaert et al.

arXiv:1508.06624The Annals of StatisticsJul 7, 201651 citations

Asymptotically optimal discrimination between multiple pure quantum states

Michael Nussbaum, Arleta Szkoła

Jan 11, 20103 citations

Generalized quantum Chernoff bound

Kun Fang, Masahito Hayashi

We consider the task of distinguishing whether a quantum system is prepared in a state from one of several sets of quantum states. Assuming their convexity and stability under tensor product, we prove that the optimal error exponent for discrimination is precisely given by the regularized quantum Chernoff divergence between the sets, thereby establishing a generalized quantum Chernoff bound for the discrimination of multiple sets of quantum states. This extends the classical and quantum Chernoff bounds to the general setting of composite and correlated quantum hypotheses. Furthermore, leveraging minimax theorems, we show that discriminating between sets of quantum states is no harder than discriminating between their worst-case elements in terms of error probability. This implies the existence of an optimal state-agnostic test that achieves the minimum error probability for all states in the sets, matching the performance of the optimal state-dependent test for the most difficult pair of states. We provide explicit characterizations of the optimal state-agnostic test in the binary composite case. Finally, we show that the maximum overlap between a pure state and a set of free states, a quantity that frequently arises in quantum resource theories, is equal to the quantum Chernoff divergence between the sets, thereby providing an operational interpretation of this quantity in the context of symmetric hypothesis testing.We consider the task of distinguishing whether a quantum system is prepared in a state from one of several sets of quantum states. Assuming their convexity and stability under tensor product, we prove that the optimal error exponent for discrimination is precisely given by the regularized quantum Chernoff divergence between the sets, thereby establishing a generalized quantum Chernoff bound for the discrimination of multiple sets of quantum states. This extends the classical and quantum Chernoff bounds to the general setting of composite and correlated quantum hypotheses. Furthermore, leveraging minimax theorems, we show that discriminating between sets of quantum states is no harder than discriminating between their worst-case elements in terms of error probability. This implies the existence of an optimal state-agnostic test that achieves the minimum error probability for all states in the sets, matching the performance of the optimal state-dependent test for the most difficult pair of states. We provide explicit characterizations of the optimal state-agnostic test in the binary composite case. Finally, we show that the maximum overlap between a pure state and a set of free states, a quantity that frequently arises in quantum resource theories, is equal to the quantum Chernoff divergence between the sets, thereby providing an operational interpretation of this quantity in the context of symmetric hypothesis testing.

arXiv:2508.12889IEEE International Symposium on Information Theory (ISIT)Jun 1, 20260 citations

We consider the problem of testing multiple quantum hypotheses

\{\rho_{1}^{\otimes n},\ldots,\rho_{r}^{\otimes n}\}

, where an arbitrary prior distribution is given and each of the

r

hypotheses is

n

copies of a quantum state. It is known that the minimal average error probability

P_{e}

decays exponentially to zero, that is,

P_{e}=\exp\{-\xi n+o(n)\}

. However, this error exponent

\xi

is generally unknown, except for the case that

r=2

. In this paper, we solve the long-standing open problem of identifying the above error exponent, by proving Nussbaum and Szkoła’s conjecture that

\xi=\min_{i\neq j}C(\rho_{i},\rho_{j})

. The right-hand side of this equality is called the multiple quantum Chernoff distance, and

C(\rho_{i},\rho_{j}):=\max_{0\leq s\leq1}\{-\log\operatorname{Tr}\rho_{i}^{s}\rho_{j}^{1-s}\}

has been previously identified as the optimal error exponent for testing two hypotheses,

\rho_{i}^{\otimes n}

versus

\rho_{j}^{\otimes n}

. The main ingredient of our proof is a new upper bound for the average error probability, for testing an ensemble of finite-dimensional, but otherwise general, quantum states. This upper bound, up to a states-dependent factor, matches the multiple-state generalization of Nussbaum and Szkoła’s lower bound. Specialized to the case

r=2

, we give an alternative proof to the achievability of the binary-hypothesis Chernoff distance, which was originally proved by Audenaert et al.