Video: Quantum Field Theory plus Course materials

Lecture 01 – Introductory remarks on quantum field theory and classical field theory

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David Tong: Lectures on Quantum Field Theory

Video Lectures on Quantum Field Theory

These are videos of the lectures given at the Perimeter Institute PSI programme in 2009. Each video is in wmv format and somewhere around 130 Mb. More formats are available for download at the Perimeter Institute webpage here. http://pirsa.org/index.php?p=speaker&name=David_Tong

The lectures follow the printed notes which are available on the main quantum field theory webpage. http://www.damtp.cam.ac.uk/user/tong/qft.html

David Tong: Lectures on Quantum Field Theory

Video Lectures on Quantum Field Theory

These are videos of the lectures given at the Perimeter Institute PSI programme in 2009. Each video is in wmv format and somewhere around 130 Mb. More formats are available for download at the Perimeter Institute webpage here. http://pirsa.org/index.php?p=speaker&name=David_Tong

The lectures follow the printed notes which are available on the main quantum field theory webpage. http://www.damtp.cam.ac.uk/user/tong/qft.html

 

Double Quantum dots and electron spin control

The terminology makes it appear as if he is talking about a FET with source, drain and gate.

A lecture explaining Double Quantum Dots during the 2011 Undergraduate School on Experimental Quantum Information Processing (USEQIP) at the Institute for Quantum Computing.

Series of USEQIP 2011 series of videos

For more:
http://iqc.uwaterloo.ca/conferences/useqip2011
iqc.uwaterloo.ca
www.facebook.com/QuantumIQC
Twitter: @QuantumIQC

Video: Erann Gats explanation of quantum entanglement, measurement and interpretations

Using transmissive polarized sheets

    

 

Polarizer material experiment @ see 15:00 to 16:00 into the video below

—– 0 deg |  —- 90 deg | = nothing comes out.

—– 45 deg | —– 0 deg |  —– 90 deg | = ~nothing comes out.  I am calling the leakage "0"

 —– 0 deg |  —– 90 deg | —– 45 deg | = ~nothing comes out.

 —– 0 deg | —– 45 deg | —– 90 deg |  = 1/4 intensity 

1/4 intensity is due to electric field vector being diminished 2 times by square root of 2. Electric field is thus 1/2 and intensity will be the square of this at a value of 1/4.  

Later in the talk Garrett uses a polarization rotator. This takes the output of one orthogonal polarizer and spins it 90 degrees so that it aligns with the second polarizer giving no relative loss to a single sheet of polarizer material.  A single sheet of course has a loss of 1/2 when fed with unpolarized light. See image below.

 

 

David Mermin's "Stuff Left Behind" in terms of Von Neuman entropy.

It is highly recommend you watch David Mermin's "Stuff Left Behind" presentation before you watch this presentation.  Mermin's work is like chapter 1 and this is like chapter 2.

Ron Garrett aka Erann Gat quantum video on quantum mechanics.   It helps make quantum mechanics more clear by using very accessible experiments that use light as the test subject.

 

Research Links

Von Neumann Entropy

Where lambda are eigenvalues of the system.  Very similar to Shannon entropy but I suppose with complex values.

Notes

  • The polarizer experiments that he shows are quite interesting.  
  • This  presentation builds on David Mermin presentation is like a second chapter to that
  • The 3 particle correlation shown near the end is the David Mermin "Stuff Left Behind" presentation

 

 

Quantum entanglement is not as out of the ordinary as you might think

Simplification using single particle experiment explanations

Consider a single particle source.  The particle is equally likely to emit in any direction.  That situation is depicted below
   

What you imagine is that a localized particle emanates from the emitter and you detect it somewhere on your ring of detectors surrounding your experimental set up.  You can use your detectors ringing the emitter to verify that emissions are equally probable at any angle.   I imagine the situation differently.  What I imagine is below:

 
The concentric blue rings depict the phase waves of de broglie  propagating outwards from the emitter. They have no preference in direction.  They propagate in all directions.   When they encounter the ring of detectors one of the detectors detects the particle.   Now something has to prevent all the other detectors from firing and saying they also have detected the particle.  This would violate conservation of energy and what ever other conservation laws.  This is the "collapse" into the measured state above.

Note that this "communication" or universal book keeping function occurs in similar method as entanglement experiments show.  The instant the particle interacts with one detector all other detectors are prohibited from detecting the instant the particle is detected.  An instantaneous non communication book keeping function occurs just like described in polarized entangled photon experiments.   

This thought experiment reduces thinking about entanglement to how the universe uses book keeping functions across space to maintain conservation laws.   Let us apply this to the double slit experiment.   Most explanations of the double slit experiment leave you with the paradox of saying "It looks like 1 particle went through both slits".  Where as the two slit experiment possibly demonstrates the book keeping aspect.

Two entangle Photons

What about the case of 2 entangle photons?   They are created coherently and are assumed identical and indistinguishable.   Their phase waves travel out concentrically and totally overlapping as shown above in the second diagram.   The book keeping rules can not discern if it is received photon number 1 or photon number 2.   In fact it is even meaningless to talk about photon number 1 and 2.  They are identical in every way.  Thus the results of 1 hitting the detector are no different from 2 hitting the detector.  Thus what you measure for 1 is what you will measure for 2.   The book keeping detectors first detect one photon then the second.   Since the book keeping conservations laws govern the detection of the second photon they must see a redundant identical measurement with same instantaneous resolution.  The mechanism is the book keeping principles this resolution occurs instantaneously instead of propagating at the speed of light.  It is only after detection measurement that the "particle" is localized.  Conservation book keeping forces this localization.  

Why does quantum computing appear to be able to do something standard computing based on thermodynamic electronics can not ?

What is the reason for quantum computing being able to do more than classical thermodynamic computing? Quantum computing harnesses physical conservation laws that we have up till now not harnesses in regular calculations. These laws do not propagate at the speed of light but rather instantaneously as a conservation law "book keeping" function.

Quantum Entanglement of Photons demonstrated in relatively low cost set up

  • Louis DeBroglie does not get the credit he deserves for original thinking in quantum machanics – DeBroglie thesis paper   – he won the Nobel Prize in 1929 for very good reasons which you will see if you read his thesis paper.
  • I am looking for the single photon counter used in this experimental setup

PowerPoint presentation of experiment Uses an SPCM-APD  ( Single Photon Counting Module – Avalanch Photo Detector )

One of the experimenters

Relatively simple setup uses spontaneous parametric downconversion of photon to create 2 photons that are entangled.  Then these are sent to 2 single photon detectors.   If you have any of the parts or pieces of this setup for sale I would be interested in buying.     

Summary Outline of Richard Feynmans Thesis – Framework for learning QED and Quantum Mechanics in general

He was a fun guy.

 A reasonable strategy for learning QED would be to try to recreate Richard Feynman's path of discovery that lead him to his thesis paper.   If you are an electrical or computer engineer you should probably set about the task of learning the subject for sooner or later quantum computing and nanotechnology are going to go mainstream.  If I am successful in learning this subject it will mark the first time I have not been at least 10 years behind the technology curve when it finally hits.

Research Links

— The following summary is from his Nobel prize address in 1965 and yields some insight as to how he went about the problem of reformulating QED into a more usable form.   It includes some information about the wrong turns he took which of course is very instructive in and of itself. —

My Guide to all things Richard Feynman

Wikipedia entry  – with a list of papers at the bottom.

Selected papers of Richard Feynman

Feynman related book bit torrents  – includes the Feynman lectures on physics 1, 2, 3 –  Buy a hard copy because they are great but when traveling soft copy is the way to go.

Feynman lectures on computation  – hard copy on Amazon – Bittorrent   – Of course, we might get useful ideas from studying how the brain works, but we must remember that automobiles do not have legs like cheetahs nor do airplanes flap their wings!

Video: KITP Lecture : Putting Weirdness to Work: Quantum Information Science

boxes and soxes

Backup copy: Putting quantum weirdness to work: Quantum Information Science

Quantum physics, information theory, and computer science are among the crowning intellectual achievements of the 20th century. Now, a new synthesis of these themes is underway. The emerg- ing field of quantum information science is providing important insights into fundamental issues at the interface of computation and physical science, and may guide the way to revolutionary technological advances. The quantum laws that govern atoms and other tiny objects differ radically from the classical laws that govern our ordinary experience. In particular, quantum information (information en- coded in a quantum system) has weird properties that contrast sharply with the familiar properties of classical information. Physicists, who for many years have relished this weirdness, have begun to recognize in recent years that we can put the weirdness to work: There are tasks involving the acquisition, transmission, and processing of information that are achievable in principle because Nature is quantum mechanical, but that would be impossible in a less weird classical world. John Preskill will describe the properties of quantum bits ("qubits"), the indivisible units of quantum infor- mation, and explain the essential ways in which qubits differ from classical bits. For one thing, it is impossible to read or copy the state of a qubit without disturbing it. This property is the basis of "quantum cryptography," wherein the privacy of secret information can be founded on principles of fundamental physics. Qubits can be "entangled" with one another. This means that the qubits can exhibit subtle quantum correlations that have no classical analogue; roughly speaking, when two qubits are en- tangled, their joint state is more definite than the state of either qubit by itself. Because of quantum entanglement, a vast amount of classical information would be needed to describe completely the quantum state of just a few hundred qubits. Therefore, a "quantum computer" operating on just a few hundred qubits could perform tasks that ordinary digital computers could not possibly emulate. 

Links

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