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In the field of quantum reservoir computing (QRC), many different computational models and architectures have been proposed. From these models, we identify feedback-based models -- which use a feedback mechanism to re-embed classical…

Quantum Physics · Physics 2026-05-18 Erik L. Connerty , Ethan N. Evans

We study the estimation of the overlap between two unknown pure quantum states of a finite dimensional system, given $M$ and $N$ copies of each type. This is a fundamental primitive in quantum information processing that is commonly…

While real quantum devices have been increasingly used to conduct research focused on achieving quantum advantage or quantum utility in recent years, executing deep quantum circuits or performing quantum machine learning with large-scale…

Quantum Physics · Physics 2026-04-06 Yoshiaki Kawase

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…

We experimentally implement a machine-learning method for accurately identifying unknown pure quantum states. The method, called single-shot measurement learning, achieves the theoretical optimal accuracy for $\epsilon = O(N^{-1})$ in state…

Quantum Physics · Physics 2021-05-05 Sang Min Lee , Hee Su Park , Jinhyoung Lee , Jaewan Kim , Jeongho Bang

We propose and analyze quantum state estimation (tomography) using continuous quantum measurements with resource limitations, allowing the global state of many qubits to be constructed from only measuring a few. We give a proof-of-principle…

Quantum Physics · Physics 2020-04-13 Areeya Chantasri , Shengshi Pang , Teerawat Chalermpusitarak , Andrew N. Jordan

The experimental realization of increasingly complex quantum states underscores the pressing need for new methods of state learning and verification. In one such framework, quantum state tomography, the aim is to learn the full quantum…

Quantum Physics · Physics 2025-01-30 Antonio Anna Mele , Yaroslav Herasymenko

To use quantum systems for technological applications we first need to preserve their coherence for macroscopic timescales, even at finite temperature. Quantum error correction has made it possible to actively correct errors that affect a…

Quantum Physics · Physics 2017-03-24 Benjamin J. Brown , Daniel Loss , Jiannis K. Pachos , Chris N. Self , James R. Wootton

Quantum state tomography is the fundamental physical task of learning a complete classical description of an unknown state of a quantum system given coherent access to many identical samples of it. The complexity of this task is commonly…

Quantum Physics · Physics 2026-05-25 Yanglin Hu , Enrique Cervero-Martín , Elias Theil , Laura Mančinska , Marco Tomamichel

Acquiring information about an unknown qubit in a superposition of two states is essential in any computation process. Quantum measurement, or sharp measurement, is usually used to read the information contents of that unknown qubit system.…

Quantum Physics · Physics 2017-04-26 Ahmed Younes

Quantum reservoir computing has emerged as a promising machine learning paradigm for processing temporal data on near-term quantum devices, as it allows for exploiting the large computational capacity of the qubits without suffering from…

Quantum Physics · Physics 2025-08-21 Emanuele Ricci , Francesco Monzani , Luca Nigro , Enrico Prati

The information carrier of today's communications, a weak pulse of light, is an intrinsically quantum object. As a consequence, complete information about the pulse cannot, even in principle, be perfectly recorded in a classical memory. In…

Quantum Physics · Physics 2007-05-23 Brian Julsgaard , Jacob Sherson , J. Ignacio Cirac , Jaromir Fiurasek , Eugene S. Polzik

We initiate the study of sample-optimal quantum state tomography with minimal disturbance to the samples. Can we efficiently learn a precise description of a quantum state through sequential measurements of samples while at the same time…

Quantum Physics · Physics 2025-06-06 Josep Lumbreras , Mikhail Terekhov , Marco Tomamichel

Quantum computers are now on the brink of outperforming their classical counterparts. One way to demonstrate the advantage of quantum computation is through quantum random sampling performed on quantum computing devices. However, existing…

Quantum tomography is a crucial tool for characterizing quantum states and devices and estimating nonlinear properties of the systems. Performing full quantum state tomography on an $N_\mathrm{q}$ qubit system requires an exponentially…

Quantum Physics · Physics 2025-09-09 Zhixin Song , Hang Ren , Melody Lee , Bryan Gard , Nicolas Renaud , Spencer H. Bryngelson

Full quantum tomography of high-dimensional quantum systems is experimentally infeasible due to the exponential scaling of the number of required measurements on the number of qubits in the system. However, several ideas were proposed…

Quantum Physics · Physics 2021-01-20 G. I. Struchalin , Ya. A. Zagorovskii , E. V. Kovlakov , S. S. Straupe , S. P. Kulik

In the device-independent approach to quantum information theory, quantum systems are regarded as black boxes which, given an input (the measurement setting), return an output (the measurement result). These boxes are then treated…

This study proposes a new approach to quantum state recovery following measurement. Specifically, we introduce a special operation that transfers the probability amplitude of the quantum state into its orthogonal complement. This operation…

Quantum Physics · Physics 2025-10-03 Taiga Suzuki , Masayuki Ohzeki

We use a meta-learning neural-network approach to analyse data from a measured quantum state. Once our neural network has been trained it can be used to efficiently sample measurements of the state in measurement bases not contained in the…

Quantum Physics · Physics 2021-07-01 Alistair W. R. Smith , Johnnie Gray , M. S. Kim

While the no-cloning theorem forbids the perfect replication of quantum information, it is sometimes possible to produce large numbers of replicas with vanishingly small error. This phenomenon, known as quantum superreplication, can take…

Quantum Physics · Physics 2018-05-09 Giulio Chiribella , Yuxiang Yang