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The time-symmetric formalism endows the weak measurement and its outcome, the weak value,many unique features. In particular, it allows a direct tomography of quantum states without resort to complicated reconstruction algorithms and…

Quantum Physics · Physics 2021-11-01 Liang Xu , Huichao Xu , Tao Jiang , Feixiang Xu , Kaimin Zheng , Ben Wang , Aonan Zhang , Lijian Zhang

The partial trace operation is usually considered in composite quantum systems, to reduce the state on a single subsystem. This operation has a key role in the decoherence effect and quantum measurements. However, partial trace operations…

Quantum Physics · Physics 2024-03-18 Quentin Ansel

Quantum theory has the property of "local tomography": the state of any composite system can be reconstructed from the statistics of measurements on the individual components. In this respect the holism of quantum theory is limited. We…

Quantum Physics · Physics 2015-05-19 Lucien Hardy , William K. Wootters

We derive a tight bound between the quality of estimating a quantum state by measurement and the success probability of undoing the measurement in arbitrary dimensional systems, which completely describes the tradeoff relation between the…

Quantum Physics · Physics 2012-10-12 Yong Wook Cheong , Seung-Woo Lee

One of the main postulates of quantum mechanics is that measurements destroy quantum coherence (wave function collapse). Recently it was discovered that in a many-body system dilute local measurements still preserve some coherence across…

Quantum Physics · Physics 2025-05-13 Aleksei Khindanov , Igor L. Aleiner , Lara Faoro , Lev B. Ioffe

Traditional uncertainty relations dictate a minimal amount of noise in incompatible projective quantum measurements. However, not all measurements are projective. Weak measurements are minimally invasive methods for obtaining partial state…

Quantum Physics · Physics 2021-03-15 Jonathan T. Monroe , Nicole Yunger Halpern , Taeho Lee , Kater W. Murch

Weak measurement is a standard measuring procedure with two changes: it is performed on pre- and post-selected quantum systems and the coupling to the measuring device is weakened. The outcomes of weak measurements, ``weak values'' are very…

High Energy Physics - Theory · Physics 2009-09-25 Lev Vaidman

Quantum mechanics does not permit joint measurements of non-commuting observables. However, it is possible to measure the weak value of a projection operator, followed by the precise measurement of a different property. The results can be…

Quantum Physics · Physics 2015-02-25 Holger F. Hofmann

The problem of feedback control of quantum systems by means of weak measurements is investigated in detail. When weak measurements are made on a set of identical quantum systems, the single-system density matrix can be determined to a high…

Quantum Physics · Physics 2009-10-31 Seth Lloyd , Jean-Jacques E. Slotine

The quantum measurement procedure based on the Lorentz transformation formalism and weak perturbation of the system is considered. In the simple case of a single-qubit it turns out that one can perform 4-dimension pseudo-rotation along with…

Quantum Physics · Physics 2019-06-18 Yu. I. Bogdanova , N. A. Bogdanova , B. I. Bantysh , Yu. A. Kuznetsov

We generalize the concept of a weak value of a quantum observable to cover arbitrary real positive operator measures. We show that the definition is operationally meaningful in the sense that it can be understood within the quantum theory…

Quantum Physics · Physics 2013-05-29 Erkka Haapasalo , Pekka Lahti , Jussi Schultz

We present a simple and efficient Bayesian recursive algorithm for the data-pattern scheme for quantum state reconstruction, which is applicable to situations where measurement settings can be controllably varied efficiently. The algorithm…

The implementation of weak-value amplification requires the pre- and post-selection of states of a quantum system, followed by the observation of the response of the meter, which interacts weakly with the system. Data acquisition from the…

Quantum Physics · Physics 2015-06-17 G. Bié Alves , B. M. Escher , R. L. de Matos Filho , N. Zagury , L. Davidovich

The statistical properties of photons are fundamental to investigating quantum mechanical phenomena using light. In multi-photon, two-mode systems, correlations may exist between outcomes of measurements made on each mode which exhibit…

Quantum Physics · Physics 2017-02-06 Evan Meyer-Scott , Johannes Tiedau , Georg Harder , Lynden K. Shalm , Tim J. Bartley

Experimental access to many-body quantum systems is often limited by measurement backaction, and key dynamical properties are typically obtained by perturbing a system and measuring its response. Here we replace this active paradigm with a…

Quantum Physics · Physics 2026-04-21 Emine Altuntas , Ian B. Spielman

The notion of weak measurement provides a formalism for extracting information from a quantum system in the limit of vanishing disturbance to its state. Here we extend this formalism to the measurement of sequences of observables. When…

Quantum Physics · Physics 2009-11-13 Graeme Mitchison , Richard Jozsa , Sandu Popescu

Measurement plays a quintessential role in the control of quantum systems. Beyond initialization and readout which pertain to projective measurements, weak measurements in particular, through their back-action on the system, may enable…

Quantum Physics · Physics 2022-06-07 Yunzhao Wang , Kyrylo Snizhko , Alessandro Romito , Yuval Gefen , Kater Murch

We propose to use quantum tomography to characterize the state of a perturbed Bose-Einstein condensate. We assume knowledge of the number of particles in the zero-wave number mode and of density distributions in space at different times,…

Other Condensed Matter · Physics 2009-11-10 Anders S. Mouritzen , Klaus Molmer

The standard approach to quantum measurement discrimination is to perform the given unknown measurement on a probe state, possibly entangled with an auxiliary system, and make a decision based on the measurement outcome obtained. In this…

Quantum Physics · Physics 2026-02-25 Charbel Eid , Marco Túlio Quintino

A theory of quantum measurement was introduced some time ago that was based on the notion of the so-called separation status. This separation status had a spatial, local character, so that the theory worked only in special cases.…

Quantum Physics · Physics 2016-06-14 Petr Hajicek