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Ask how the quantum compression of ensembles of pure states is affected by the availability of entanglement, and in settings where the encoder has access to side information. We find the optimal asymptotic quantum rate and the optimal…

Quantum Physics · Physics 2020-05-22 Zahra Baghali Khanian , Andreas Winter

The state overlap, quantified via $\tr[\rho \sigma]$, is a metric widely used to assess the closeness between two quantum states $\rho$ and $\sigma$. Although global state overlap alone does not directly capture entanglement properties, we…

Quantum state tomography is the problem of estimating a given quantum state. Usually, it is required to run the quantum experiment - state preparation, state evolution, measurement - several times to be able to estimate the output quantum…

General Physics · Physics 2025-04-30 Shibdas Roy , Filippo Caruso , Srushti Patil , Anumita Mukhopadhyay

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

We revisit the basic problem of quantum state certification: given copies of unknown mixed state $\rho\in\mathbb{C}^{d\times d}$ and the description of a mixed state $\sigma$, decide whether $\sigma = \rho$ or $\|\sigma -…

Quantum Physics · Physics 2021-11-12 Sitan Chen , Jerry Li , Ryan O'Donnell

We study the distinguishability of bipartite quantum states by Positive Operator-Valued Measures with positive partial transpose (PPT POVMs). The contributions of this paper include: (1). We give a negative answer to an open problem of [M.…

Quantum Physics · Physics 2014-04-02 Nengkun Yu , Runyao Duan , Mingsheng Ying

We show that combining randomized measurement protocols with importance sampling allows for characterizing entanglement in significantly larger quantum systems and in a more efficient way than in previous work. A drastic reduction of…

Quantum Physics · Physics 2023-01-26 Aniket Rath , Rick van Bijnen , Andreas Elben , Peter Zoller , Benoît Vermersch

We present a scheme for speeding up quantum measurement. The scheme builds on previous protocols that entangle the system to be measured with ancillary systems. In the idealised situation of perfect entangling operations and no decoherence,…

The problem of determining whether a given quantum state is entangled lies at the heart of quantum information processing, which is known to be an NP-hard problem in general. Despite the proposed many methods such as the positive partial…

Quantum Physics · Physics 2018-07-18 Sirui Lu , Shilin Huang , Keren Li , Jun Li , Jianxin Chen , Dawei Lu , Zhengfeng Ji , Yi Shen , Duanlu Zhou , Bei Zeng

We study a generalization of entanglement testing which we call the "hidden cut problem." Taking as input copies of an $n$-qubit pure state which is product across an unknown bipartition, the goal is to learn precisely where the state is…

Quantum Physics · Physics 2024-10-17 Adam Bouland , Tudor Giurgica-Tiron , John Wright

Quantum entanglement is a crucial resource for learning properties from nature, but a precise characterization of its advantage can be challenging. In this work, we consider learning algorithms without entanglement to be those that only…

Quantum Physics · Physics 2024-10-21 Senrui Chen , Changhun Oh , Sisi Zhou , Hsin-Yuan Huang , Liang Jiang

A quantum metrology protocol for parameter estimation is typically comprised of three stages: probe state preparation, sensing and then readout, where the time required for the first and last stages is usually neglected. In the present work…

Quantum Physics · Physics 2018-01-11 Anthony J. Hayes , Shane Dooley , William J. Munro , Kae Nemoto , Jacob Dunningham

The most simplest form of quantum network is an one dimensional quantum network with a single player in each node. In remote entanglement distribution each of the players carry out measurement at the intermediate nodes to produce an…

Quantum Physics · Physics 2023-06-27 Ganesh Mylavarapu , Indranil Chakrabarty , Kaushiki Mukherjee , Minyi Huang , Junde Wu

Despite the central importance of quantum entanglement in quantum technologies, the understanding of the optimal ways to exploit it is still beyond our reach, and even measuring entanglement in an operationally meaningful way is…

Quantum Physics · Physics 2026-04-03 Ludovico Lami , Mario Berta , Bartosz Regula

Impossibility of cloning and deleting of unknown states are important restrictions on processing of information in the quantum world. On the other hand, a known quantum state can always be cloned or deleted. However if we restrict the class…

Quantum Physics · Physics 2009-10-31 Michal Horodecki , Aditi Sen De , Ujjwal Sen

Quantum mechanics put restriction on performing some task which we can do classically. One such restriction is that we cannot copy an arbitrary quantum state. This is known as No-cloning theorem. Although quantum mechanics forbid us to…

Quantum Physics · Physics 2009-02-11 Satyabrata Adhikari

The phenomenon of quantum entanglement marks one of the furthest departures from classical physics and is indispensable for quantum information processing. Despite its fundamental importance, the distribution of entanglement over long…

Quantum Physics · Physics 2021-07-27 Sebastian Ecker , Philipp Sohr , Lukas Bulla , Marcus Huber , Martin Bohmann , Rupert Ursin

Quantum state tomography serves as a key tool for identifying quantum states generated in quantum computers and simulators, typically involving local operations on individual particles or qubits to enable independent measurements. However,…

Quantum Gases · Physics 2026-03-26 Giacomo Marmorini , Takeshi Fukuhara , Daisuke Yamamoto

Careful tailoring the quantum state of probes offers the capability of investigating matter at unprecedented precisions. Rarely, however, the interaction with the sample is fully encompassed by a single parameter, and the information…

Quantum entanglement is an indispensable resource for many significant quantum information processing tasks. However, because of the noise in quantum channels, it is difficult to distribute quantum entanglement over a long distance in…

Quantum Physics · Physics 2018-01-31 Zhaofeng Su , Ji Guan , Lvzhou Li