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The method of classical shadows heralds unprecedented opportunities for quantum estimation with limited measurements [H.-Y. Huang, R. Kueng, and J. Preskill, Nat. Phys. 16, 1050 (2020)]. Yet its relationship to established quantum…

Quantum Physics · Physics 2021-07-19 Joseph M. Lukens , Kody J. H. Law , Ryan S. Bennink

Machine learning techniques have led to broad adoption of a statistical model of computing. The statistical distributions natively available on quantum processors are a superset of those available classically. Harnessing this attribute has…

The rapid advancement of quantum computing has led to an extensive demand for effective techniques to extract classical information from quantum systems, particularly in fields like quantum machine learning and quantum chemistry. However,…

Quantum Physics · Physics 2023-05-09 Yifei Chen , Zhan Yu , Chenghong Zhu , Xin Wang

We illustrate the application of Quantum Computing techniques to the investigation of the thermodynamical properties of a simple system, made up of three quantum spins with frustrated pair interactions and affected by a hard sign problem…

Weak quantum measurements enable real-time tracking and control of dynamical quantum systems, producing quantum trajectories -- evolutions of the quantum state of the system conditioned on measurement outcomes. For classical systems, the…

Quantum measurements are slow, while classical processors are fast, yet existing hybrid protocols never exploit this asymmetry. In this work, we propose an alternative formulation of classical estimators as online algorithms that are…

Quantum Physics · Physics 2026-03-30 Marwa Marso , Sabrina Herbst , Jadwiga Wilkens , Vincenzo De Maio , Ivona Brandic , Richard Kueng

Locally-biased classical shadows allow rapid estimation of energies of quantum Hamiltonians. Recently, derandomised classical shadows have emerged claiming to be even more accurate. This accuracy comes at a cost of introducing classical…

Quantum Physics · Physics 2021-05-27 Charles Hadfield

This thesis explores the application of the Symmetry-Breaking/Symmetry-Restoration methodology on quantum computers to better approximate a Hamiltonian's ground state energy within a variational framework in many-body physics. This involves…

Quantum Physics · Physics 2023-11-10 Andres Ruiz

Quantum simulation advantage over classical memory limitations would allow compact quantum circuits to yield insight into intractable quantum many-body problems, but the interrelated obstacles of large circuit depth in quantum time…

Quantum Physics · Physics 2024-05-02 Woo-Ram Lee , Ryan Scott , V. W. Scarola

State smoothing is a technique to estimate a state at a particular time, conditioned on information obtained both before (past) and after (future) that time. For a classical system, the smoothed state is a normalized product of the…

Quantum Physics · Physics 2024-04-04 Kiarn T. Laverick , Prahlad Warszawski , Areeya Chantasri , Howard M. Wiseman

We discuss how to calculate genuine multipartite quantum and classical correlations in symmetric, spatially invariant, mixed $n$-qubit density matrices. We show that the existence of symmetries greatly reduces the amount of free parameters…

Quantum Physics · Physics 2016-10-24 Gian Luca Giorgi , Steve Campbell

Although spin is a core property in fermionic systems, its symmetry can be easily violated in a variational simulation, especially when strong correlation plays a vital role therein. In this study, we will demonstrate that the broken…

Chemical Physics · Physics 2023-10-09 Takashi Tsuchimochi , Yuto Mori , Seiichiro L. Ten-no

Quantum computers are believed to bring computational advantages in simulating quantum many body systems. However, recent works have shown that classical machine learning algorithms are able to predict numerous properties of quantum systems…

Quantum Physics · Physics 2024-12-23 Riccardo Molteni , Casper Gyurik , Vedran Dunjko

Quantum computers and quantum algorithms have made great strides in the last few years and promise improvements over classical computing for specific tasks. Although the current hardware is not yet ready to make real impacts at the time of…

Quantum Physics · Physics 2024-08-28 Nils Quetschlich , Tobias Forster , Adrian Osterwind , Domenik Helms , Robert Wille

Error correction will add so much overhead to large quantum computations that we suspect the most efficient algorithms will use a classical co-processor to do as much work as possible. We present a method to offload portions of a quantum…

Quantum Physics · Physics 2020-08-12 Samuel Jaques , Craig Gidney

The classical shadow estimation protocol is a noise-resilient and sample-efficient quantum algorithm for learning the properties of quantum systems. Its performance depends on the choice of a unitary ensemble, which must be chosen by a user…

Quantum Physics · Physics 2024-01-10 Kaifeng Bu , Dax Enshan Koh , Roy J. Garcia , Arthur Jaffe

Improving the performance of quantum algorithms is a fundamental task to achieve quantum advantage. In many cases, extracting information from quantum systems poses an important challenge for practical implementations in real-world quantum…

Quantum Physics · Physics 2025-02-28 Leticia Bertuzzi , João P. Engster , Evandro C. R. da Rosa , Eduardo I. Duzzioni

We present shadow spectroscopy as a simulator-agnostic quantum algorithm for estimating energy gaps using very few circuit repetitions (shots) and no extra resources (ancilla qubits) beyond performing time evolution and measurements. The…

Quantum Physics · Physics 2025-04-10 Hans Hon Sang Chan , Richard Meister , Matthew L. Goh , Bálint Koczor

Extracting information efficiently from quantum systems is a major component of quantum information processing tasks. Randomized measurements, or classical shadows, enable predicting many properties of arbitrary quantum states using few…

Quantum mechanics provides cryptographic primitives whose security is grounded in hardness assumptions independent of those underlying classical cryptography. However, existing proposals require low-noise quantum communication and…