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Universal control of quantum systems is a major goal to be achieved for quantum information processing, which demands thorough understanding of fundamental quantum mechanics and promises applications of quantum technologies. So far, most…

Quantum Physics · Physics 2019-02-05 Ling Hu , Xianghao Mu , Weizhou Cai , Yuwei Ma , Yuan Xu , Haiyan Wang , YiPu Song , Chang-Ling Zou , Luyan Sun

To decide whether a quantum channel is degradable is relatively easy: one has to find at least one example of a degrading quantum channel. But in general, no conclusive criterion exists to show the opposite. Using elementary methods we…

Quantum Physics · Physics 2015-12-18 Kamil Bradler

We present a new application of harmonic analysis to quantum information by constructing intriguing classes of quantum channels stemming from specific representations of multiplier algebras over locally compact groups $G$. Beginning with a…

Mathematical Physics · Physics 2015-06-11 Jason Crann , Matthias Neufang

We investigate the set of quantum channels acting on a single qubit. We provide an alternative, compact generalization of the Fujiwara-Algoet conditions for complete positivity to non-unital qubit channels, which we then use to characterize…

Quantum Physics · Physics 2014-04-29 Daniel Braun , Olivier Giraud , Ion Nechita , Clement Pellegrini , Marko Znidaric

Shallow quantum circuits have attracted increasing attention in recent years, due to the fact that current noisy quantum hardware can only perform faithful quantum computation for a short amount of time. The constant-depth quantum circuits…

Quantum Physics · Physics 2025-11-11 Yangjing Dong , Fengning Ou , Penghui Yao

Pauli channels are ubiquitous in quantum information, both as a dominant noise source in many computing architectures and as a practical model for analyzing error correction and fault tolerance. Here we prove several results on efficiently…

Quantum Physics · Physics 2022-02-23 Steven T. Flammia , Joel J. Wallman

The quantum query complexity of evaluating any read-once formula with n black-box input bits is Theta(sqrt(n)). However, the corresponding problem for read-many formulas (i.e., formulas in which the inputs have fanout) is not well…

Quantum Physics · Physics 2012-09-06 Andrew M. Childs , Shelby Kimmel , Robin Kothari

At the interface of machine learning and quantum computing, an important question is what distributions can be learned provably with optimal sample complexities and with quantum-accelerated time complexities. In the classical case, Klivans…

Quantum Physics · Physics 2023-11-08 Siyi Yang , Naixu Guo , Miklos Santha , Patrick Rebentrost

We establish the first general connection between the design of quantum algorithms and circuit lower bounds. Specifically, let $\mathfrak{C}$ be a class of polynomial-size concepts, and suppose that $\mathfrak{C}$ can be PAC-learned with…

Quantum Physics · Physics 2021-12-03 Srinivasan Arunachalam , Alex B. Grilo , Tom Gur , Igor C. Oliveira , Aarthi Sundaram

Coherent superposition is a key feature of quantum mechanics that underlies the advantage of quantum technologies over their classical counterparts. Recently, coherence has been recast as a resource theory in an attempt to identify and…

The results of quantum process tomography on a three-qubit nuclear magnetic resonance quantum information processor are presented, and shown to be consistent with a detailed model of the system-plus-apparatus used for the experiments. The…

This tutorial offers a quick, hands-on introduction to solving Quadratic Unconstrained Binary Optimization (QUBO) models on currently available quantum computers and their simulators. We cover both IBM and D-Wave machines: IBM utilizes a…

Quantum Physics · Physics 2025-06-18 Arul Mazumder , Sridhar Tayur

Motivated by limitations on the depth of near-term quantum devices, we study the depth-computation trade-off in the query model, where the depth corresponds to the number of adaptive query rounds and the computation per layer corresponds to…

Quantum Physics · Physics 2023-12-08 Uma Girish , Makrand Sinha , Avishay Tal , Kewen Wu

We analyze a class of quantum operations based on a geometrical representation of $d-$level quantum system (or qudit for short). A sufficient and necessary condition of complete positivity, expressed in terms of the quantum Fourier…

Quantum Physics · Physics 2009-11-10 Runyao Duan , Zhengfeng Ji , Yuan Feng , Mingsheng Ying

In the problem of quantum channel discrimination, one distinguishes between a given number of quantum channels, which is done by sending an input state through a channel and measuring the output state. This work studies applications of…

Quantum Physics · Physics 2022-09-08 Andrey Kardashin , Anna Vlasova , Anastasiia Pervishko , Dmitry Yudin , Jacob Biamonte

One of the key challenges in quantum machine learning is finding relevant machine learning tasks with a provable quantum advantage. A natural candidate for this is learning unknown Hamiltonian dynamics. Here, we tackle the supervised…

Quantum Physics · Physics 2025-06-23 Alice Barthe , Mahtab Yaghubi Rad , Michele Grossi , Vedran Dunjko

We study space-bounded communication complexity for unitary implementation in distributed quantum processors, where we restrict the number of qubits per processor to ensure practical relevance and technical non-triviality. We model…

Quantum Physics · Physics 2025-11-07 Longcheng Li , Xiaoming Sun , Jialin Zhang , Jiadong Zhu

This work investigates the application of quantum machine learning techniques for classical and quantum communication across different qubit channel models. By employing parameterized quantum circuits and a flexible channel noise model, we…

Quantum Physics · Physics 2023-07-14 Lakshika Rathi , Stephen DiAdamo , Alireza Shabani

We prove a $k^{-\Omega(\log(\varepsilon_2 - \varepsilon_1))}$ lower bound for adaptively testing whether a Boolean function is $\varepsilon_1$-close to or $\varepsilon_2$-far from $k$-juntas. Our results provide the first superpolynomial…

Data Structures and Algorithms · Computer Science 2023-04-24 Xi Chen , Shyamal Patel

Quantum machine learning has become an area of growing interest but has certain theoretical and hardware-specific limitations. Notably, the problem of vanishing gradients, or barren plateaus, renders the training impossible for circuits…

Quantum Physics · Physics 2023-08-31 Mo Kordzanganeh , Pavel Sekatski , Leonid Fedichkin , Alexey Melnikov