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This paper explores as didactically as possible the fundamental principles of both classical and quantum metrology, focusing on the Cram\'er-Rao Bound and how it defines the maximum precision in parameter estimation, taking into account…

Quantum Physics · Physics 2024-12-13 Leonardo A. M. Souza

Multiparameter quantum estimation is made difficult by the following three obstacles. First, incompatibility among different physical quantities poses a limit on the attainable precision. Second, the ultimate precision is not saturated…

Quantum Physics · Physics 2022-03-14 Jisho Miyazaki , Keiji Matsumoto

Although quantum metrology allows us to make precision measurement beyond the standard quantum limit, it mostly works on the measurement of only one observable due to Heisenberg uncertainty relation on the measurement precision of…

Quantum Physics · Physics 2018-06-06 Jiamin Li , Yuhong Liu , Liang Cui , Nan Huo , Syed M Assad , Xiaoying Li , Z. Y. Ou

We investigate the localization of two incoherent point sources with arbitrary angular and axial separations in the paraxial approximation. By using quantum metrology techniques, we show that a simultaneous estimation of the two separations…

Quantum Physics · Physics 2019-04-17 Carmine Napoli , Samanta Piano , Richard Leach , Gerardo Adesso , Tommaso Tufarelli

In this paper we explore the possibility of performing Heisenberg limited quantum metrology of a phase, without any prior, by employing only maximally entangled states. Starting from the estimator introduced by Higgins et al. in New J.…

Quantum Physics · Physics 2020-10-27 Federico Belliardo , Vittorio Giovannetti

Randomized measurements are useful for analyzing quantum systems especially when quantum control is not fully perfect. However, their practical realization typically requires multiple rotations in the complex space due to the adoption of…

Quantum Physics · Physics 2025-08-28 Jin-Min Liang , Satoya Imai , Shuheng Liu , Shao-Ming Fei , Otfried Gühne , Qiongyi He

We show that the quantum angle measurement for x-polarized photon number states results in an angle which will never correspond to the y-axis for an odd number of photons; yet for an even number of photons it always can. The analogy of this…

Quantum Physics · Physics 2015-12-01 Scott Roger Shepard

A recently proposed phase-estimation protocol that is based on measuring the parity of a two-mode squeezed-vacuum state at the output of a Mach-Zehnder interferometer shows that Cram\'{e}r-Rao bound sensitivity can be obtained [P.\ M.\…

Quantum Physics · Physics 2013-09-10 Keith R. Motes , Petr M. Anisimov , Jonathan P. Dowling

When standard light sources are employed, the precision of the phase determination is limited by the shot noise. Quantum entanglement provides means to exceed this limit with the celebrated example of N00N states that saturate the ultimate…

Quantum Physics · Physics 2010-06-01 M. Kacprowicz , R. Demkowicz-Dobrzanski , W. Wasilewski , K. Banaszek , I. A. Walmsley

The use of special quantum states to achieve sensitivities below the limits established by classically behaving states has enjoyed immense success since its inception. In bosonic interferometers, squeezed states, number states and cat…

High-sensitivity accelerometers and gravimeters, achieving the ultimate limits of measurement sensitivity are key tools for advancing both fundamental and applied physics. While numerous platforms have been proposed to achieve this goal,…

Quantum Physics · Physics 2026-02-24 Salman Sajad Wani , Saif Al-Kuwari , Arshid Shabir , Paolo Vezio , Francesco Marino , Mir Faizal

The quantum limit is a fundamental lower bound on the uncertainty when estimating a parameter in a system dominated by the minimum amount of noise (quantum noise). For the first time, we derive and demonstrate a quantum limit for…

Signal Processing · Electrical Eng. & Systems 2025-05-12 Huwei Wang , Roman Ermakov , Francesco Da Ros , Darko Zibar

Precise estimation of physical parameters underpins both scientific discovery and technological development. A central goal of quantum metrology and sensing is to exploit quantum resources like entanglement to devise optimal strategies for…

Quantum Physics · Physics 2026-03-09 Zhao-Yi Zhou , Da-Jian Zhang

In quantum phase estimation, the Heisenberg limit provides the ultimate accuracy over quasi-classical estimation procedures. However, realizing this limit hinges upon both the detection strategy employed for output measurements and the…

Quantum Physics · Physics 2024-07-23 Hanan Saidi , Hanane El Hadfi , Abdallah Slaoui , Rachid Ahl Laamara

We investigate quantum dynamical systems defined on a finite dimensional Hilbert space and subjected to an interaction with an environment. The rate of decoherence of initially pure states, measured by the increase of their von Neumann…

Quantum Physics · Physics 2009-11-10 Robert Alicki , Artur Lozinski , Prot Pakonski , Karol Zyczkowski

Quantum properties of the probes used to estimate a classical parameter can be used to attain accuracies that beat the standard quantum limit. When qubits are used to construct a quantum probe, it is known that initializing $n$ qubits in an…

Quantum Physics · Physics 2009-11-13 Anil Shaji , Carlton M. Caves

It has recently been argued that the inability to measure the absolute phase of an electromagnetic field prohibits the representation of a laser's output as a quantum optical coherent state. This argument has generally been considered…

Quantum Physics · Physics 2009-11-10 Kae Nemoto , Samuel L. Braunstein

In quantum mechanics, geometry has been demonstrated as a useful tool for inferring non-classical behaviors and exotic properties of quantum systems. One standard approach to illustrate the geometry of quantum systems is to project the…

Studies of quantum metrology have shown that the use of many-body entangled states can lead to an enhancement in sensitivity when compared to product states. In this paper, we quantify the metrological advantage of entanglement in a setting…

We introduce new formulations of the quantum Cram\'{e}r-Rao bound (QCRB) and the Holevo Cram\'{e}r-Rao bound (HCRB) in multi-parameter quantum metrology via purification, where we show their values for any mixed state are connected to that…

Quantum Physics · Physics 2026-05-06 Sisi Zhou