Weak measurement
View article: Entanglement transition from variable-strength weak measurements
Entanglement transition from variable-strength weak measurements Open
We show that weak measurements can induce a quantum phase transition of interacting many-body systems from an ergodic thermal phase with a large entropy to a nonergodic localized phase with a small entropy, but only if the measurement stre…
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No-Go Theorem for the Characterization of Work Fluctuations in Coherent Quantum Systems Open
An open question of fundamental importance in thermodynamics is how to describe the fluctuations of work for quantum coherent processes. In the standard approach, based on a projective energy measurement both at the beginning and at the en…
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Aspects of quantum work Open
Various approaches of defining and determining work performed on a quantum system are compared. Any operational definition of work, however, must allow for two facts: first, that work characterizes a process rather than an instantaneous st…
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Direct Measurement of the Density Matrix of a Quantum System Open
One drawback of conventional quantum state tomography is that it does not readily provide access to single density matrix elements since it requires a global reconstruction. Here, we experimentally demonstrate a scheme that can be used to …
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Detecting Large Quantum Fisher Information with Finite Measurement Precision Open
We propose an experimentally accessible scheme to determine the lower bounds on the quantum Fisher information (QFI), which ascertains multipartite entanglement or usefulness for quantum metrology. The scheme is based on comparing the meas…
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Ultrasensitive and real-time detection of chemical reaction rate based on the photonic spin Hall effect Open
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. However, the precise and real-time detection of the reaction rate remains challenging due to its fast and dynamical pr…
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Quantum Backaction Evading Measurement of Collective Mechanical Modes Open
The standard quantum limit constrains the precision of an oscillator position measurement. It arises from a balance between the imprecision and the quantum backaction of the measurement. However, a measurement of only a single quadrature o…
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Quantum Criticality Under Decoherence or Weak Measurement Open
Decoherence inevitably happens when a quantum state is exposed to its environment, which can affect quantum critical points (QCPs) in a nontrivial way. As was pointed out in the recent literature on (1+1)d conformal field theory (CFT) [Gar…
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Self-testing quantum states and measurements in the prepare-and-measure scenario Open
The goal of self-testing is to characterize an a priori unknown quantum\nsystem based solely on measurement statistics, i.e. using an uncharacterized\nmeasurement device. Here we develop self-testing methods for quantum\nprepare-and-measur…
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Natural Framework for Device-Independent Quantification of Quantum Steerability, Measurement Incompatibility, and Self-Testing Open
We introduce the concept of assemblage moment matrices, i.e., a collection of matrices of expectation values, each associated with a conditional quantum state obtained in a steering experiment. We demonstrate how it can be used for quantum…
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Measuring Incompatible Observables by Exploiting Sequential Weak Values Open
One of the most intriguing aspects of quantum mechanics is the impossibility of measuring at the same time observables corresponding to noncommuting operators, because of quantum uncertainty. This impossibility can be partially relaxed whe…
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Direct quantum process tomography via measuring sequential weak values of incompatible observables Open
The weak value concept has enabled fundamental studies of quantum measurement and, recently, found potential applications in quantum and classical metrology. However, most weak value experiments reported to date do not require quantum mech…
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Weak value beyond conditional expectation value of the pointer readings Open
It is argued that a weak value of an observable is a robust property of a\nsingle pre- and post-selected quantum system rather than a statistical\nproperty. During an infinitesimal time a system with a given weak value affects\nother syste…
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Incompatibility robustness of quantum measurements: a unified framework Open
In quantum mechanics performing a measurement is an invasive process which generally disturbs the system. Due to this phenomenon, there exist incompatible quantum measurements, i.e. measurements that cannot be simultaneously performed on a…
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Experimental Demonstration of Direct Path State Characterization by Strongly Measuring Weak Values in a Matter-Wave Interferometer Open
A method was recently proposed and experimentally realized for characterizing a quantum state by directly measuring its complex probability amplitudes in a particular basis using so-called weak values. Recently, Vallone and Dequal [Phys. R…
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Many-Body Chern Number from Statistical Correlations of Randomized Measurements Open
One of the main topological invariants that characterizes several topologically ordered phases is the many-body Chern number (MBCN). Paradigmatic examples include several fractional quantum Hall phases, which are expected to be realized in…
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Experiment Investigating the Connection between Weak Values and Contextuality Open
Weak value measurements have recently given rise to a great amount of interest in both the possibility of measurement amplification and the chance for further quantum mechanics foundations investigation. In particular, a question emerged a…
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Monitored open fermion dynamics: Exploring the interplay of measurement, decoherence, and free Hamiltonian evolution Open
The interplay of unitary evolution and local measurements in many-body\nsystems gives rise to a stochastic state evolution and to measurement-induced\nphase transitions in the pure state entanglement. In realistic settings,\nhowever, this …
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Noisy Quantum Metrology Enhanced by Continuous Nondemolition Measurement Open
We show that continuous quantum nondemolition (QND) measurement of an atomic ensemble is able to improve the precision of frequency estimation even in the presence of independent dephasing acting on each atom. We numerically simulate the d…
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Feedback-Induced Quantum Phase Transitions Using Weak Measurements Open
We show that applying feedback and weak measurements to a quantum system induces phase transitions beyond the dissipative ones. Feedback enables controlling essentially quantum properties of the transition, i.e., its critical exponent, as …
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Direct Reconstruction of the Quantum Density Matrix by Strong Measurements Open
New techniques based on weak measurements have recently been introduced to the field of quantum state reconstruction. Some of them allow the direct measurement of each matrix element of an unknown density operator and need only O(d) differ…
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Detecting topological invariants in chiral symmetric insulators via losses Open
We show that the bulk winding number characterizing one-dimensional topological insulators with chiral symmetry can be detected from the displacement of a single particle, observed via losses. Losses represent the effect of repeated weak m…
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Detecting metrologically useful asymmetry and entanglement by a few local measurements Open
Important properties of a quantum system are not directly measurable, but\nthey can be disclosed by how fast the system changes under controlled\nperturbations. In particular, asymmetry and entanglement can be verified by\nreconstructing t…
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Sustained State-Independent Quantum Contextual Correlations from a Single Ion Open
We use a single trapped-ion qutrit to demonstrate the quantum-state-independent violation of noncontextuality inequalities using a sequence of randomly chosen quantum nondemolition projective measurements. We concatenate 53×10^{6} sequenti…
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Incoherent Qubit Control Using the Quantum Zeno Effect Open
The quantum Zeno effect is the suppression of Hamiltonian evolution by repeated observation, which pins the system to an eigenstate of the measurement observable. Using measurement alone, control of the state can be achieved if the observa…
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Contextual Wavefunction collapse: an integrated theory of quantum measurement Open
This paper is an in depth implementation of the proposal that the quantum\nmeasurement issue can be resolved by carefully looking at top-down contextual\neffects within realistic measurement contexts. The specific setup of the\nmeasurement…
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Measurement-Induced Strong Kerr Nonlinearity for Weak Quantum States of Light Open
Strong nonlinearity at the single photon level represents a crucial enabling tool for optical quantum technologies. Here we report on experimental implementation of a strong Kerr nonlinearity by measurement-induced quantum operations on we…
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Quasi-probability distributions for observables in dynamic systems Open
We develop a general framework to investigate fluctuations of non-commuting observables. To this end, we consider the Keldysh quasi-probability distribution (KQPD). This distribution provides a measurement-independent description of the ob…
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Protecting weak measurements against systematic errors Open
In this work, we consider the systematic error of quantum metrology by weak\nmeasurements under decoherence. We derive the systematic error of maximum\nlikelihood estimation in general to the first-order approximation of a small\ndeviation…
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Determination of weak values of quantum operators using only strong measurements Open
Weak values have been shown to be helpful especially when considering them as\nthe outcomes of weak measurements. In this paper we show that in principle, the\nreal and imaginary parts of the weak value of any operator may be elucidated\nf…