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Quantum state tomography (QST) represents an essential tool for the characterization, verification, and validation (QCVV) of quantum processors. Only for a few idealized scenarios, there are analytic results for the optimal measurement set…

Quantum Physics · Physics 2022-12-27 Violeta N. Ivanova-Rohling , Niklas Rohling , Guido Burkard

Besides quantum entanglement and steering, quantum coherence has also been identified as a useful quantum resource in quantum information. It is important to investigate the evolution of quantum coherence in practical quantum channels. In…

Quantum Physics · Physics 2021-10-29 Haijun Kang , Dongmei Han , Na Wang , Yang Liu , Shuhong Hao , Xiaolong Su

Quantum illumination (QI) is an entanglement-based protocol for improving lidar/radar detection of unresolved targets beyond what a classical lidar/radar of the same average transmitted energy can do. Originally proposed by Lloyd as a…

Quantum Physics · Physics 2024-09-20 Jeffrey H. Shapiro

The estimation of parameters characterizing dynamical processes is central to science and technology. The estimation error changes with the number N of resources employed in the experiment (which could quantify, for instance, the number of…

Quantum Physics · Physics 2012-01-10 B. M. Escher , R. L. de Matos Filho , L. Davidovich

Any quantum device that amplifies coherent states of a field while preserving their phase generates noise. A nonlinear, phase-invariant amplifier may generate less noise, over a range of input field strengths, than any linear amplifier with…

Condensed Matter · Physics 2009-10-22 Dmitri Kouznetsov , Roberto Ortega , Daniel Rohrlich

Quantum metrology aims at achieving enhanced performance in measuring unknown parameters by utilizing quantum resources. Thus, quantum metrology is an important application of quantum technologies. Photonic systems can implement these…

Quantum Physics · Physics 2023-05-18 Madhura Ghosh Dastidar , Aprameyan Desikan , Vidya Praveen Bhallamudi

The phase of an optical field inside a linear amplifier is widely known to diffuse with a diffusion coefficient that is inversely proportional to the photon number. The same process occurs in lasers which limits its intrinsic linewidth and…

Quantum Physics · Physics 2019-11-06 A. Chia , M. Hajdusek , R. Fazio , L. C. Kwek , V. Vedral

Entangled photons are widely used in quantum technologies. Many photonic experiments generate them with probabilistic photon-pair sources that can be modeled as squeeze operators. In practice, these sources are usually treated in the…

Quantum Physics · Physics 2026-05-05 Carlos Ruiz-Gonzalez , Mario Krenn , Xuemei Gu

We discuss the effects of imperfect photon detectors suffering from loss and noise on the reliability of linear optical quantum computers. We show that for a given detector efficiency, there is a maximum achievable success probability, and…

Quantum Physics · Physics 2012-05-18 Scott Glancy , J. M. LoSecco , H. M. Vasconcelos , C. E. Tanner

Standard system identification methods often provide inconsistent estimates with closed-loop data. With the prediction error method (PEM), this issue is solved by using a noise model that is flexible enough to capture the noise spectrum.…

Systems and Control · Computer Science 2018-09-07 Miguel Galrinho , Cristian R. Rojas , Hakan Hjalmarsson

The purpose of a phase-preserving linear amplifier is to make a small signal larger, regardless of its phase, so that it can be perceived by instruments incapable of resolving the original signal, while sacrificing as little as possible in…

Quantum Physics · Physics 2013-03-26 Carlton M. Caves , Joshua Combes , Zhang Jiang , Shashank Pandey

Quantum nonlinear operations for harmonic oscillator systems play a key role in the development of analog quantum simulators and computers. Since a variety of strong highly nonlinear operations are unavailable in the existing physical…

Quantum Physics · Physics 2017-09-25 Kimin Park , Petr Marek , Radim Filip

Noise is the main obstacle for the realization of fault tolerant quantum information processing and secure communication over long distances. In this work, we propose a communication protocol relying on simple linear optics that optimally…

Quantum Physics · Physics 2015-06-16 Mikael Lassen , Adriano Berni , Lars S. Madsen , Radim Filip , Ulrik L. Andersen

Non-Hermitian quantum systems, governed by nonunitary evolution, offer powerful tools for manipulating quantum states through engineered loss. A prime example is coherent absorption, where quantum states undergo phase-dependent partial or…

The two-way capacities of quantum channels determine the ultimate entanglement and secret-key distribution rates achievable by two distant parties that are connected by a noisy transmission line, in absence of quantum repeaters. Since…

Quantum Physics · Physics 2025-01-27 Francesco Anna Mele , Ludovico Lami , Vittorio Giovannetti

We theoretically and experimentally investigate conditional enhancement of overall coherence of quantum states by probabilistic quantum operations that apply to the input state a quantum filter diagonal in the basis of incoherent states. We…

Quantum Physics · Physics 2021-08-03 Robert Stárek , Michal Mičuda , Michal Kolář , Radim Filip , Jaromír Fiurášek

In this paper, we propose to use the discretized version of the so-called Enhanced Gaussian Noise (EGN) model to estimate the non-linearity effects of fiber on the performance of optical coherent and uncompensated transmission (CUT)…

Signal Processing · Electrical Eng. & Systems 2020-02-19 Ramin Hashemi , Mehdi Habibi , Hamzeh Beyranvand , Ali Emami , Mahdi Hashemi , Davood Ranjbar Rafie

In many practical applications, quantum algorithms require several qubits, significantly more than those available with current noisy intermediate-scale quantum processors. Distributed quantum computing (DQC) is considered a scalable…

Quantum Physics · Physics 2026-03-02 Michele Bandini , Davide Ferrari , Stefano Carretta , Michele Amoretti

Noiseless subsystems offer a general and efficient method for protecting quantum information in the presence of noise that has symmetry properties. A paradigmatic class of error models displaying non-trivial symmetries emerges under…

Quantum networking at many scales will be critical to future quantum technologies and experiments on quantum systems. Photonic links enable quantum networking. They will connect co-located quantum processors to enable large-scale quantum…

Quantum Physics · Physics 2024-03-21 Jason Saied , Jeffrey Marshall , Namit Anand , Shon Grabbe , Eleanor G. Rieffel