Quantum nondemolition (QND) measurement is a special type of measurement of a quantum system in which the uncertainty of the measured observable does not increase from its measured value during the subsequent normal evolution of the system. This necessarily requires that the measurement process preserve the physical integrity of the measured system, and moreover places requirements on the relationship between the measured observable and the self-Hamiltonian of the system. In a sense, QND measurements are the "most classical" and least disturbing type of measurement in quantum mechanics. Most devices capable of detecting a single particle and measuring its position strongly modify the particle's state in the measurement process, e.g. photons are destroyed when striking a screen. Less dramatically, the measurement may simply perturb the particle in an unpredictable way; a second measurement, no matter how quickly after the first, is then not guaranteed to find the particle in the same location. Even for ideal, "first-kind" projective measurements in which the particle is in the measured eigenstate immediately after the measurement, the subsequent free evolution of the particle will cause uncertainty in position to quickly grow. In contrast, a momentum (rather than position) measurement of a free particle can be QND because the momentum distribution is preserved by the particle's self-Hamiltonian p2/2m. Because the Hamiltonian of the free particle commutes with the momentum operator, a momentum eigenstate is also an energy eigenstate, so once momentum is measured its uncertainty does not increase due to free evolution. Note that the term "nondemolition" does not imply that the wave function fails to collapse. QND measurements are extremely difficult to carry out experimentally. Much of the investigation into QND measurements was motivated by the desire to avoid the standard quantum limit in the experimental detection of gravitational waves. The general theory of QND measurements was laid out by Braginsky, Vorontsov, and Thorne following much theoretical work by Braginsky, Caves, Drever, Hollenhorts, Khalili, Sandberg, Thorne, Unruh, Vorontsov, and Zimmermann. (Wikipedia).
Quantum Operators for measurements of Energy, Position, and Momentum in Quantum Physics. My Patreon page is at https://www.patreon.com/EugeneK
From playlist Physics
Understanding Quantum Mechanics #1: It’s not about discreteness
This must be one of the most common misunderstandings about quantum mechanics, that quantum mechanics is about making things discrete. But is an understandable misunderstanding because the word “quantum” suggests that quantum mechanics is about small amounts of something. Indeed, if you as
From playlist Understanding Quantum Mechanics
What is the quantum measurement problem?
Subscribe to our YouTube Channel for all the latest from World Science U. Visit our Website: http://www.worldscienceu.com/ Like us on Facebook: https://www.facebook.com/worldscienceu Follow us on Twitter: https://twitter.com/worldscienceu
From playlist Science Unplugged: Quantum Mechanics
In Quantum Mechanics, can something be in two places at the same time?
Subscribe to our YouTube Channel for all the latest from World Science U. Visit our Website: http://www.worldscienceu.com/ Like us on Facebook: https://www.facebook.com/worldscienceu Follow us on Twitter: https://twitter.com/worldscienceu
From playlist Science Unplugged: Quantum Mechanics
Will This LIGHT Experiment Be Successful?!? #Quantum #Mechanics #Physics #Energy #NicholasGKK #Shorts
From playlist Quantum Mechanics
Quantum Measurements are Entanglement
How entanglement destroys interference, and why all quantum measurements are a form of entanglement. My Patreon page is at https://www.patreon.com/EugeneK
From playlist Physics
Limits on spectral resolution measurements by (...) - A. Retzker - PRACQSYS 2018 - CEB T2 2018
Alex Retzker (D Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem, Israel) / 04.07.2018 Limits on spectral resolution measurements by quantum probes for nano NMR The limits of frequency resolution in nano NMR experiments have been discussed extensively in recent years
From playlist 2018 - T2 - Measurement and Control of Quantum Systems: Theory and Experiments
Are You GOOD At Quantum Physics?
How Quickly Can You Solve THIS Quantum Physics Problem?!? #Quantum #Mechanics #Light #Frequency #NicholasGKK #Shorts
From playlist Quantum Mechanics
Physics - Ch 66 Ch 4 Quantum Mechanics: Schrodinger Eqn(63 of 92) Transmission vs Reflection-Classic
Visit http://ilectureonline.com for more math and science lectures! In this video I will explain what happens in the “real” (non-quantum mechanic) world when a particle comes upon a barrier or a step-function where the energy of the particle is related to the potential of that step. With
From playlist PHYSICS 66.1 QUANTUM MECHANICS - SCHRODINGER EQUATION
In this video, we review the quantum measurement operator and quantum measurement in the Wolfram Quantum Framework. We discuss the implementation of both projective measurements and also POVMs. For more info and examples, please visit the Wolfram Quantum Framework resource page: https://wo
From playlist Daily Study Group: Quantum Computation Framework
Classical Verification of Quantum Computations - Urmila Mahadev
Computer Science/Discrete Mathematics Seminar I Topic: Classical Verification of Quantum Computations Speaker: Urmila Mahadev Affiliation: UC Berkeley Date: November 26, 2018 For more video please visit http://video.ias.edu
From playlist Mathematics
Observers Disturb What They Measure | Understanding the Quantum World
What if you could exist in two places at once and give a random answer as to which of the two locations you are? Particles can, and "both" isn't an acceptable answer, making quantum mechanics a difficult field of study. Prepare to take "please only check one" to a whole new level. This vi
From playlist Science
The measurement problem and some mild solutions by Dustin Lazarovici ( Lecture - 01)
21 November 2016 to 10 December 2016 VENUE Ramanujan Lecture Hall, ICTS Bangalore Quantum Theory has passed all experimental tests, with impressive accuracy. It applies to light and matter from the smallest scales so far explored, up to the mesoscopic scale. It is also a necessary ingredie
From playlist Fundamental Problems of Quantum Physics
Dynamical model selection and estimation near the (...) - J. Ralph - Workshop 2 - CEB T2 2018
Jason Ralph (Univ. Liverpool) / 06.06.2018 Dynamical model selection and estimation near the quantum-classical boundary Joint work with Marko Toros, Simon Maskell, Kurt Jacobs and Hendrik Ulbricht. We discuss a general method of model selection from experimentally recorded time-trace dat
From playlist 2018 - T2 - Measurement and Control of Quantum Systems: Theory and Experiments
Stefanie Barz: Photonic graph states and their applications in quantum network
Recording during the meeting "9th International Conference on Quantum Simulation and Quantum Walks" the January 21, 2020 at the Centre International de Rencontres Mathématiques (Marseille, France) Filmmaker: Guillaume Hennenfent Find this video and other talks given by worldwide mathematic
From playlist Mathematical Physics
For more information visit: http://bit.ly/28C3_information To download the video visit: http://bit.ly/28C3_videos Playlist 28C3: http://bit.ly/28C3_playlist Speaker: Robert Helling How quantum information differs from classical Quantum systems can have very different properties
From playlist 28C3: Behind Enemy Lines
The Language of Quantum Physics is Strange | PHYSICS EXPLAINED
This is how Quantum Physicists communicate their ideas Hi guys, so I wanted to make a video explaining some of the notation used by quantum physicists to describe their ideas. There is a reason why things are written the way they are, and it is interesting to see these reasons, in my opin
From playlist Quantum Physics by Parth G
Stanford Seminar - How to Compute with Schrödinger's Cat: An Introduction to Quantum Computing
"How to Compute with Schrödinger's Cat: An Introduction to Quantum Computing" - Eleanor Rieffel of NASA Ames Research & Wolfgang Polak, Independent Consultant About the talk: The success of the abstract model of classical computation in terms of bits, logical operations, algorithms, and
From playlist Engineering
Energy Of A Photon (Quantum Physics)
This video will explain how to deal with photons, as quantized wave packets of light. #physics #math #science #engineering #quantum #tiktok #NicholasGKK #shorts
From playlist Quantum Mechanics
Verifier-on-a-Leash: new schemes for verifiable (...) - S. Jeffery - Main Conference - CEB T3 2017
Stacey Jeffery (CWI Amsterdam) / 15.12.2017 Title: Verifier-on-a-Leash: new schemes for verifiable delegated quantum computation, with quasilinear resources Abstract: The problem of reliably certifying the outcome of a computation performed by a quantum device is rapidly gaining relevan
From playlist 2017 - T3 - Analysis in Quantum Information Theory - CEB Trimester