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When the dynamics of a quantum system of interest is known, an informationally-complete set of observables is not needed for state reconstruction via tomographic techniques: letting the system evolve before performing the measurement allows…

Quantum Physics · Physics 2026-02-17 Marco Peruzzo , Tommaso Grigoletto , Francesco Ticozzi

Computing the state of a quantum mechanical many-body system composed of indistinguishable particles distributed over a multitude of modes is one of the paradigmatic test cases of computational complexity theory: Beyond well-understood…

Complete characterization of states and processes that occur within quantum devices is crucial for understanding and testing their potential to outperform classical technologies for communications and computing. However, solving this task…

Quantum Physics · Physics 2020-05-07 E. S. Tiunov , V. V. Tiunova , A. E. Ulanov , A. I. Lvovsky , A. K. Fedorov

The duration, strength and structure of memory effects are crucial properties of physical evolution. Due to the invasive nature of quantum measurement, such properties must be defined with respect to the probing instruments employed. Here,…

Quantum Physics · Physics 2021-06-18 Yu Guo , Philip Taranto , Bi-Heng Liu , Xiao-Min Hu , Yun-Feng Huang , Chuan-Feng Li , Guang-Can Guo

Discrimination between unknown processes chosen from a finite set is experimentally shown to be possible even in the case of non-orthogonal processes. We demonstrate unambiguous deterministic quantum process discrimination (QPD) of…

Quantum Physics · Physics 2015-05-13 Anthony Laing , Terry Rudolph , Jeremy L. O'Brien

We describe a scheme for quantum error correction that employs feedback and weak measurement rather than the standard tools of projective measurement and fast controlled unitary gates. The advantage of this scheme over previous protocols…

Quantum Physics · Physics 2009-11-10 Mohan Sarovar , Charlene Ahn , Kurt Jacobs , Gerard J. Milburn

Conditional quantum optical processes enable a wide range of technologies from generation of highly non-classical states to implementation of quantum logic operations. The process fidelity that can be achieved in a realistic implementation…

Quantum Physics · Physics 2015-06-23 Merlin Cooper , Eirion Slade , Michal Karpinski , Brian J. Smith

Robust, accurate and efficient quantum tomography is key for future quantum technologies. Traditional methods are impractical for even medium sized systems and are not robust against noise and errors. Here we report on an experimental…

Quantum Physics · Physics 2016-07-27 Robert J. Chapman , Christopher Ferrie , Alberto Peruzzo

We briefly review single-qubit quantum process tomography for trace-preserving and nontrace-preserving processes, and derive explicit forms of the general constraints for fitting experimental data. These new forms provide additional insight…

Quantum Physics · Physics 2016-05-31 Ramesh Bhandari , Nicholas A. Peters

In this paper, we present a thought experiment that demonstrates that the equivalence of quantum reduced states and statistical mixed states of ensembles is not merely a simple mathematical formulation in quantum mechanics, but rather…

Quantum Physics · Physics 2025-04-18 Zhihong Zuo

Quantum sensing utilize quantum effects, such as entanglement and coherence, to measure physical signals. The performance of a sensing process is characterized by error which requires comparison to a true value. However, in practice, such a…

Quantum Physics · Physics 2024-10-29 Lian-Xiang Cui , Yi-Mu Du , C. P. Sun

The sensitivity of classical and quantum sensing is impaired in a noisy environment. Thus, one of the main challenges facing sensing protocols is to reduce the noise while preserving the signal. State of the art quantum sensing protocols…

Optics · Physics 2016-07-18 L. Cohen , Y. Pilnyak , D. Istrati , A. Retzker , H. S. Eisenberg

For a quantum system undergoing a unitary process work is commonly defined based on the Two Projective Measurement (TPM) protocol which measures the energies of the system before and after the process. However, it is well known that…

Quantum Physics · Physics 2017-11-22 P. Solinas , H. J. D. Miller , J. Anders

Determination of the quantum nature of correlations between two spatially separated systems plays a crucial role in quantum information science. Of particular interest is the questions of if and how these correlations enable quantum…

Quantum Physics · Physics 2017-09-27 Farid Shahandeh , Austin P. Lund , Timothy C. Ralph

In general, it is difficult to evaluate measurement errors when the initial and final conditions of the measurement make it impossible to identify the correct value of the target observable. Ozawa proposed a solution based on the operator…

Quantum Physics · Physics 2016-03-09 Masataka Iinuma , Yutaro Suzuki , Taiki Nii , Ryuji Kinoshita , Holger F. Hofmann

Throughout quantum mechanics there is statistical balance, in the collective response of an ensemble of systems to differing measurement types. Statistical balance is a core feature of quantum mechanics, underlying quantum mechanical…

Quantum Physics · Physics 2022-10-31 Brian Drummond

We celebrate this year hundred years of quantum mechanics but there is still no consensus regarding its interpretation and limitations. In this article we advocate the statistical contextual interpretation which is free of paradoxes. State…

Quantum Physics · Physics 2026-01-06 Marian Kupczynski

We present an experimental procedure to determine the usefulness of a measurement scheme for quantum error correction (QEC). A QEC scheme typically requires the ability to prepare entangled states, to carry out multi-qubit measurements, and…

Quantum Physics · Physics 2015-06-04 Gabrielle Denhez , Alexandre Blais , David Poulin

Characterizing noisy quantum processes is important to quantum computation and communication (QCC), since quantum systems are generally open. To date, all methods of characterization of quantum dynamics (CQD), typically implemented by…

Quantum Physics · Physics 2015-01-28 S. Omkar , R. Srikanth , S. Banerjee

We discuss strategies for quantum enhanced estimation of atomic transition frequencies with ions stored in Paul traps or neutral atoms trapped in optical lattices. We show that only marginal quantum improvements can be achieved using…

Quantum Physics · Physics 2012-04-23 U. Dorner