背景和原罪


最近的一个热门新闻是29岁的清华研究生,工作5年后当上了县级市市长。这样的新闻总能让人产生自卑感,也就会有很多人挖他的负面材料,比如是否有后台,有家庭背景什么的。现在发现,都没有,他唯一的背景就是他是清华毕业的高材生,所以地方上很重视他。接下来,更重量级的负面材料来了,有人发现,他硕士期间发表的一篇论文超过50%抄袭了他人的文章。这就是出名的代价,也是他的原罪。如果清华按照规章制度的话,论文抄袭最严重的处罚是可以追回学位的。那么这条原罪就直指周市长的硕士学位以及清华背景。问题是,清华敢这么做么,这个先例能开么?官员中的那些硕士博士有几个的学位论文是自己写的,又有多少是抄袭而来的,大家都心知肚明。

最近出了很多类似的新闻,什么80后的副厅级干部,80后的教授博导。少年成名,虽然是意气风发,却也少不了被人盯上,挖出原罪来。说实话,有背景的人,耳濡目染,从小立志,就会很注意约束自己。而没有大志向的人,往往对自己也没有高要求,容易犯些小错误。这对一般人来说,什么也不是。可是对于名人来说,就是原罪。人们常说的从小立志,立大志,果然是有道理的。另外,我妈妈从小教育我不要当第一,第一太辛苦了,当第二就很好了。立大志,少出风头,这就是我的体会。

New paper: cooling limits and measurement of optomechanical oscillator


New paper dance now.

arXiv:0906.1379

Title: Phase noise and laser cooling limits of opto-mechanical oscillators
Author: Zhang-qi Yin

Abstract: The noise from laser phase fluctuation sets a major technical obstacle to cool the nano-mechanical oscillators to the quantum region. We propose a cooling configuration based on the opto-mechanical coupling with two cavity modes to significantly reduce this phase noise. After optimization of the cavity parameters, we show through simple arguments that the intrinsic cooling limit of the opto-mechanical oscillator is set by $T_{\text{env}}/Q$, where $T_{\text{env}}$ is the environment temperature and $Q$ is the mechanical quality factor. We also discuss detection of the phonon number when the mechanical oscillator is cooled near the quantum region and specify the required conditions for this detection.

Update in 17th June: Today I found a similar paper published in PRL: Three-Mode Optoacoustic Parametric Amplifier: A Tool for Macroscopic Quantum Experiments, by Chunnong Zhao and et al.. The earlier version of the paper was posted in arXiv:0710.2383v3, which didn’t investigate the phase noise in detail and was already cited in my paper.

Several interesting papers in the last months


It has been for a long time since my last post on quantum physics. Here I select some interesting papers on cavity and optomechanics.

One most interesting paper I read in the last month is from Prof. Vahala and Prof. Painter’s groups. They demonstrated that micro-mechanical oscillator can be driven and cooled by the optical gradient force, other than traditional scattering radiation pressure. This approach makes it possible that photon momentum to be transferred over a length scale approaching the wavelength of light. They use double-disk structure, which provides back-action several orders larger than the previous one. They also demonstrate the cooling factor of 13 dB under heavily damped conditions (mechanical Q=4).

Another paper is discussing the proposal for a search for the cosmic axions using an optical cavity.  Axions, which were postulated 30 years ago, remain an attractive candidate for the cold dark matter of the universe. The proposal uses some stokes-like processes to detect the axions. The axions are absorbed by an optical cavity field of frequency \omega_o. The sidebands \omega_\pm = \omega_0 \pm \omega_a appear on the carrier. The displacement of the sidebands is the axion frequency \omega=E_a=m. The proposal is very sensitive.

The last one is discussing the possibility of realizing the strong coupling between a mechanical oscillator and a single atom, from Prof. Kimble’s group. The strong coupling between a cavity mode and a single atom has been accomplished for about 10 years. Once the strong coupling between a mechanical oscillator and a single atom was realized, there are countless application the the technique. Everything you have done in the Cavity-QED systems can be transferred to the optomechanical plus atomic systems. It allows us to coherent manipulation, preparation and measurement  of micromechanical objects.