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Quantum theory is commonly formulated in complex Hilbert spaces. However, the question of whether complex numbers need to be given a fundamental role in the theory has been debated since its pioneering days. Recently it has been shown that…

Generalized quantum measurements, described by positive operator-valued measures (POVMs), are essential for modeling realistic processes in open quantum systems. While quantum process tomography can fully characterize a POVM, it is…

Quantum Physics · Physics 2025-10-10 Sahil , Sohail

The measurement precision of modern quantum simulators is intrinsically constrained by the limited set of measurements that can be efficiently implemented on hardware. This fundamental limitation is particularly severe for quantum…

Quantum Physics · Physics 2020-07-01 Giacomo Torlai , Guglielmo Mazzola , Giuseppe Carleo , Antonio Mezzacapo

We develop an efficient algorithm for determining optimal adaptive quantum estimation protocols with arbitrary quantum control operations between subsequent uses of a probed channel. We introduce a tensor network representation of an…

We propose a new class of quantum computing algorithms which generalize many standard ones. The goal of our algorithms is to estimate probability distributions. Such estimates are useful in, for example, applications of Decision Theory and…

Quantum Physics · Physics 2007-05-23 Robert R. Tucci

We consider ontological models of a quantum system, assuming that not all probability distributions over the space $\Lambda$ of ontic states are preparable, only those belonging to a certain set C. We assume further that every POVM with a…

Quantum Physics · Physics 2022-05-10 Roderich Tumulka

The current shift in the quantum optics community towards large-size experiments -- with many modes and photons -- necessitates new classical simulation techniques that go beyond the usual phase space formulation of quantum mechanics. To…

We argue that measurement data in quantum physics can be rigorously interpreted only as a result of a statistical, macroscopic process, taking into account the indistinguishable character of identical particles. Quantum determinism is in…

General Physics · Physics 2025-07-22 Patrick Navez , Henni Ouerdane

Unitary transformations are routinely modeled and implemented in the field of quantum optics. In contrast, nonunitary transformations that can involve loss and gain require a different approach. In this theory work, we present a universal…

Quantum Physics · Physics 2018-04-17 Nora Tischler , Carsten Rockstuhl , Karolina Słowik

Non-classical states of light find applications in enhancing the performance of optical interferometric experiments, with notable example of gravitational wave-detectors. Still, the presence of decoherence hinders significantly the…

Quantum Physics · Physics 2018-08-17 R. Demkowicz-Dobrzanski , M. Jarzyna , J. Kolodynski

Considering the problem of sampling from the output photon-counting probability distribution of a linear-optical network for input Gaussian states, we obtain results that are of interest from both quantum theory and the computational…

Quantum Physics · Physics 2015-02-16 Saleh Rahimi-Keshari , Austin P. Lund , Timothy C. Ralph

Non-classical correlations in optical beams offer the unprecedented opportunity of surpassing conventional limits of sensitivity and resolution in optical measurements and imaging, especially but not only, when a low photon flux down to the…

Quantum Physics · Physics 2019-04-03 Ivano Ruo-Berchera , Ivo Pietro Degiovanni

It is usually believed that a picture of Quantum Mechanics in terms of true probabilities cannot be given due to the uncertainty relations. Here we discuss a tomographic approach to quantum states that leads to a probability representation…

Quantum Physics · Physics 2007-05-23 Michele Caponigro , Stefano Mancini , Vladimir I. Man'ko

The act of describing how a physical process changes a system is the basis for understanding observed phenomena. For quantum-mechanical processes in particular, the affect of processes on quantum states profoundly advances our knowledge of…

Quantum Physics · Physics 2017-10-20 Jen-Hsiang Hsieh , Shih-Hsuan Chen , Che-Ming Li

The technologies of quantum information and quantum control are rapidly improving, but full exploitation of their capabilities requires complete characterization and assessment of processes that occur within quantum devices. We present a…

Coherence is a cornerstone of quantum theory and a prerequisite for the advantage of quantum technologies. In recent work, the notion of coherence with respect to a general quantum measurement (POVM) was introduced and embedded into a…

Quantum Physics · Physics 2021-03-31 Felix Bischof , Hermann Kampermann , Dagmar Bruß

The operation of a quantum computer is considered as a general quantum operation on a mixed state on many qubits followed by a measurement. The general quantum operation is further represented as a Feynman-Vernon double path integral over…

Quantum Physics · Physics 2018-04-04 Erik Aurell

One of the fastest growing areas of interest in quantum computing is its use within machine learning methods, in particular through the application of quantum kernels. Despite this large interest, there exist very few proposals for relevant…

Quantum Physics · Physics 2023-10-12 Cassandra Bowie , Sally Shrapnel , Michael Kewming

In this paper a system-oriented formalism of Quantum Information Processing is presented. Its form resembles that of standard signal processing, although further complexity is added in order to describe pure quantum-mechanical effects and…

Quantum Physics · Physics 2007-05-23 Marcos Curty , David J. Santos

What is the right statistics for the measurements of arrival times of a quantum particle? Although this question is very old, it is still open. Usual experiments are performed in far-field regime and this question becomes unimportant, as a…

Quantum Physics · Physics 2014-02-17 Nicola Vona , Günter Hinrichs , Detlef Dürr