Recent content by Tspirit

Homework Statement In Gerry's book "Introductory quantum optics", Chapter 8.5 Decoherence, Page 207, there is a calculation which doesn't give the detail derivation, who can give me the calculation from (8.26) to (8.27)? Homework Equations The coherent state is defined by...

Homework Statement I am studying Gerry's <Introductory Quantum Optics>, in which there is an integral (Eq. 4.37) $$\intop_{-infinity}^{+infinity}\frac{[sin(\triangle t/2)]^{2}}{\triangle^{2}}d\triangle=\frac{\pi}{2}t.$$ I don't know how to get the result of the right side. Homework Equations I...

Thank you very much, Cthugha. Your reply is of great help. If the mean photon number of a single photon state in the free space is meaningless, how can we understand the operator equation of <n>=<1|n|1>=1? Can I think that there is only one photon in unlimited-short integration time? Or for...

I am studying Quantum Optics. A single photon state will give the mean photon number of 1, as shown the following equation: $$<\hat{n}>=<1|\hat{n}|1>=1.$$ For a two-photon number state, the similar calculation will be $$<\hat{n}>=<2|\hat{n}|2>=2.$$ And for a coherent state, it is...

Homework Statement I am reading the book of Gerry and Knight "Introductory Quantum Optics" (2004). In page 60, Chapter 3.7, there is two equation referring Fourier Transformation in the complex plane as follows: $$g(u)=\int f(\alpha)e^{\alpha^{*}u-\alpha u^{*}}d^{2}\alpha, (3.94a)$$...

Just non-relativity. I am a graduate student. Thank you.

I want a QM textbook which introduces detail knowledge of density matrix and trace (i.e. the average), who can recommend one for me? Thank you.

Yes, that is. All of the functions should be around the horizontal axis.

Homework Statement In Griffiths' book "Introduction to Quantum Mechanics", Section 2.3, Chapter 2, the Fig. 2.7 gives the plots of the wave function (##\psi_{n}##) and its modulus of the harmonics oscillator, see the Appendix. With the order (##n##) increasing, they become both higher. However...

Indeed, it's a simpler method.

Thank you! I have found the problem I met. In fact, I want to prove the following equation $$e^{x^{2}}=\sum\frac{x^{2n}}{n!},$$ but didn't succeed at first. Now I can. This is the process. Adopting the Taylor expansion of the left, with the derivertives $$...

Homework Statement In the Griffiths book <Introduction to QM>, Section 2.3.2: Analytic method (for The harmonic oscillator), there is an equation (##\xi## is very large) $$h(\xi)\approx C\sum\frac{1}{(j/2)!}\xi^{j}\approx C\sum\frac{1}{(j)!}\xi^{2j}\approx Ce^{\xi^{2}}.$$ How to understand the...

I made a mistake. Yes, you are right. But what I want is controllable current which can transmit information, just like telephone or fiber optics. I have no idea if a stream of electrons in vacuum can do this.

For electrical current, it can't propagate in space because it need moving of charge carriers such as electrons. For light radiation, it can. However, it can't turn the corner and hence can't realize free transmission of information with arbitrary directions.

Thank you for your kind help. I seem to get the point: superconductivity is a behavior of charge carriers and happens when the resistance of their moving is zero. The propagation of light don't need the help of the moving of something, so there is no corresponding resistance and thus...