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We consider realistic measurement systems, where measurements are accompanied by decoherence processes. The aim of this work is the construction of methods and algorithms for precise quantum measurements with fidelity close to the…

Quantum Physics · Physics 2017-01-10 Yu. I. Bogdanov , B. I. Bantysh , N. A. Bogdanova , A. B. Kvasnyy , V. F. Lukichev

The resource theoretic measure of quantum coherence is basis dependent, and the amount of coherence contained in a state is different in different bases. We obtained analytical solutions for the maximum coherence by optimizing the reference…

Quantum Physics · Physics 2017-11-13 Ming-Liang Hu , Shu-Qian Shen , Heng Fan

The problem of deciding whether a set of quantum measurements is jointly measurable is known to be equivalent to determining whether a quantum assemblage is unsteerable. This problem can be formulated as a semidefinite program (SDP).…

We describe two procedures which, given access to one copy of a quantum state and a sequence of two-outcome measurements, can distinguish between the case that at least one of the measurements accepts the state with high probability, and…

Quantum Physics · Physics 2017-04-18 Aram W. Harrow , Cedric Yen-Yu Lin , Ashley Montanaro

The impossibility of deterministic and error-free discrimination among nonorthogonal quantum states lies at the core of quantum theory and constitutes a primitive for secure quantum communication. Demanding determinism leads to errors,…

Quantum Physics · Physics 2021-12-21 M. A. Solís-Prosser , O. Jiménez , A. Delgado , L. Neves

We consider the problem of determining the mixed quantum state of a large but finite number of identically prepared quantum systems from data obtained in a sequence of ideal (von Neumann) measurements, each performed on an individual copy…

Quantum Physics · Physics 2009-11-10 Franz Embacher , Heide Narnhofer

Recently, a technique known as quantum symmetry test has gained increasing attention for detecting bipartite entanglement in pure quantum states. In this work we show that, beyond qualitative detection, a family of well-defined measures of…

Quantum Physics · Physics 2025-11-12 Xiaoyu Liu , Jordi Tura , Albert Rico

Quantum bits, or qubits, are the fundamental building blocks of present quantum computers. Hence, it is important to be able to characterize the state of a qubit as accurately as possible. By evaluating the qubit characterization problem…

Quantum Physics · Physics 2024-02-27 Bacui Li , Lorcan O. Conlon , Ping Koy Lam , Syed M. Assad

We investigate the issue of assisted coherence distillation in the asymptotic limit (considering infinite copies of the resource states), by coordinately performing the identical local operations on the auxiliary systems of each copy. When…

Quantum Physics · Physics 2022-08-24 Huang-Qiu-Chen Wang , Qi Luo , Qi-Ping Su , Yong-Nan Sun , Nengji Zhou , Li Yu , Zhe Sun

How many copies of a quantum process are necessary and sufficient to construct an approximate classical description of it? We extend the result of Surawy-Stepney, Kahn, Kueng, and Guta (2022) to show that…

Quantum Physics · Physics 2024-01-31 Aadil Oufkir

As an analogy of best separable approximation (BSA) in the framework of entanglement theory, here we concentrate on the notion of best incoherent approximation, with application to characterizing and quantifying quantum coherence. From both…

Quantum Physics · Physics 2020-09-16 Yao Yao , Dong Li , C. P. Sun

One of the primary objectives in the field of quantum state learning is to develop algorithms that are time-efficient for learning states generated from quantum circuits. Earlier investigations have demonstrated time-efficient algorithms…

Quantum Physics · Physics 2024-02-14 Nai-Hui Chia , Ching-Yi Lai , Han-Hsuan Lin

Given a single copy of a mixed state of the form \rho=\lambda\rho_1+(1-\lambda)\rho_2, what is the optimal measurement to estimate the parameter \lambda, if \rho_1 and \rho_2 are known? We present a general strategy to obtain the optimal…

Quantum Physics · Physics 2007-06-13 Thomas Konrad , Otfried Gühne , Jürgen Audretsch , Hans J. Briegel

In the realm of quantum information processing, the efficient characterization of entangled states poses an overwhelming challenge, rendering the traditional methods including quantum tomography unfeasible and impractical. To tackle this…

Quantum Physics · Physics 2025-12-09 Ye-Chao Liu , Jiangwei Shang

We prove a lower bound on the number of copies needed to test the property of a multipartite quantum state being product across some bipartition (i.e. not genuinely multipartite entangled), given the promise that the input state either has…

Quantum Physics · Physics 2024-06-25 Benjamin D. M. Jones , Ashley Montanaro

In this paper we consider the problem of unambiguous discrimination between a set of linearly independent pure quantum states. We show that the design of the optimal measurement that minimizes the probability of an inconclusive result can…

Quantum Physics · Physics 2016-11-17 Yonina C. Eldar

We formulate an algorithm to lower bound the fidelity between quantum many-body states only from partial information, such as the one accessible by few-body observables. Our method is especially tailored to permutationally invariant states,…

Quantum Physics · Physics 2020-08-19 Matteo Fadel , Albert Aloy , Jordi Tura

In the quantum state tomography problem, one wishes to estimate an unknown $d$-dimensional mixed quantum state $\rho$, given few copies. We show that $O(d/\epsilon)$ copies suffice to obtain an estimate $\hat{\rho}$ that satisfies…

Quantum Physics · Physics 2015-09-15 Ryan O'Donnell , John Wright

The Groverian entanglement measure introduced earlier for pure quantum states [O. Biham, M.A. Nielsen and T. Osborne, Phys. Rev. A 65, 062312 (2002)] is generalized to the case of mixed states, in a way that maintains its operational…

Quantum Physics · Physics 2009-11-11 Daniel Shapira , Yishai Shimoni , Ofer Biham

We study the problem of universal quantum cloning -- taking several identical copies of a pure but unknown quantum state and producing further copies. While it is well known that it is impossible to perfectly reproduce the state, how well…

Quantum Physics · Physics 2016-08-09 Alastair Kay