# About anti bunching and bunching

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1. Mar 21, 2015

### Lizzie Mann

Why the plots of a second-order intensity correlation function appear both Bunching and Antibunching?

I thought only anti bunching would occur, because the system is a quantum-sized system and all the phenomena happened in a microscopic way.

Why bunching effect still happens in a quantum-sized cavity? Why it depends on the driving strength to get results of bunching or anti bunching?

Last edited by a moderator: Apr 1, 2015
2. Mar 24, 2015

### soarce

Can you provide a reference on the physical phenomena which you mentioned?

It's true that at fundamental level the photon emission from a single source display quantum behaviour, i.e. antibunching. But a pure quantum effect may lead to photon bunching, see for instance the Dick superradiance. Maybe in your system there is some additional effect which can favour photon bunching.

3. Mar 24, 2015

### Cthugha

That is hard to say. You do not even mention the exact system you have in mind. Both bunching and antibunching may show up depending on the processes taking place. Take for example a single colloidal quantum dot. It is a single emitter, so it will show antibunching. However, it is also subject to blinking - there are some trap states leading to longer periods, when the quantum dot is simply dark. This leads to bunching as the dot is in the bright state when it emits a photon and it is way more likely that another photon will be emitted shortly afterwards, if the QD is already in the bright state. As these effects occur on different time scales, both bunching and antibunching will be visible.

4. Mar 24, 2015

### Lizzie Mann

Yes, actually this question arose when I was reading the paper I uploaded and it is about dressed states and superposition.
Here is a link to this paper:http://www.sciencedirect.com/science/article/pii/S0030401809010542
The whole paper is talking about quantum-sized cavity and atom and photon transitions. So it confuses me that at the end, the paper said that the second-order correlation function for strong excitation exhibits photon bunching...

Last edited by a moderator: May 7, 2017
5. Mar 24, 2015

### Lizzie Mann

Thank you, it is really interesting and helpful for me to get to know that. But by trap states, I was wondering if it is the same thing as Blockade? Like when a photon is passing by a system, it will blockade the transition of another photon? Did you mean that when the quantum dot is in the bright state, the bunching effect then will definitely happen?

Here is another link to it:http://www.sciencedirect.com/science/article/pii/S0030401809010542
In this paper, when the second correlation function is derived, it is divided into the strong excitation correlation function and the weak excitation correlation function, and it says that when the system is in strong excitation, bunching effect happens. and when the system is in weak excitation, anti bunching exhibits. So it confused me so much...Does it mean that classical effect still happens in quantum world?

Last edited by a moderator: May 7, 2017
6. Mar 24, 2015

### soarce

From figure 5: In the low strength field regime ($\mathcal{E}/\kappa$ small) the photon bunching occurrs due to the two-photon emission. For strong field regime things are more complicated because the intermediate state splits and interferrence effects occurrs.

7. Mar 24, 2015

### Lizzie Mann

Thanks a lot for your answer~But can scientists do experiments to perform the bunching and anti bunching effect from one quantum system currently? Or currently it is just theoretical study of these two phenomena?

8. Mar 25, 2015

### Cthugha

I do not think, the situation discussed by Carmichael in the paper you quoted has been directly tested in an experiment yet. It is not quite trivial to measure photon statistics due to probably low counting rates and high sensitivity to stray light and realizing a multiphoton transition in the strong coupling regime is even less trivial.

But in general, bunching and antibunching can of course be seen for one quantum system (which I assume is supposed to mean a single emitter). The antibunching effect simply comes from the fact that you have a single emitter. Any intrinsic excess noise will introduce bunching, so if you have a noisy single emitter, you may get both effects if the timescales are completely different. See for example " Bunching and antibunching in the fluorescence of semiconductor nanocrystals" by G. Messin et al., Optics Letters 26, 1891 (2001). http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-26-23-1891
There are free copies of this paper available on the web.

There are also papers on the transition from antibunching to bunching for atoms in a cavity, but that involves more than one atom.

9. Mar 26, 2015

### Lizzie Mann

Thank you so much for your answer, it really helps me a lot!

10. Mar 29, 2015

### Lizzie Mann

hi I was thinking about your answer the other day, and I think it makes a lot of sense...but if the situation discussed in Carmichael's paper is hardly going to be experimentally performed, then what is the purpose of this paper's work if it is just a theoretical study and even does not have a chance to be experimentally observed? I thought scientists study anti bunching effect theoretically only because they want to actually see and control the effect someday in the future...so it confuses me again...and I really want to consult about your opinion, thanks a lot @@Cthugha

Last edited by a moderator: May 7, 2017
11. Apr 1, 2015

### Cthugha

Well, the effect of antibunching has been seen routinely in a lot of labs. Any "true" single emitter, e.g. a single atom or quantum dot, will show it. The problem with those sources is that they do not really work in a deterministic manner. During each excitation cycle, a single photon may or may not be emitted by the system. Also, the direction is not necessarily well defined. Creating heralded single photons from entangled photon pairs is not better in that respect.

Photon blockade (Birnbaum et al., Nature 436, 87-90 (2005)) is a different beast. You need a medium which is linear already at the single photon level. So the presence of a single photon shifts the energy levels of the system so strongly that the shift is larger than one linewidth. So, if you have an incoming beam of light, only the first photon will enter the system and the others will not be able to, because the energy level of the system has already shifted. So, this non-linear system may convert a stream of photons into single photons. This is possible, but hard to do. Real single-photon non-linear media have only been demonstrated recently. See, for example, the results of the Lukin group. Now, what Carmichael investigates, is what happens if the energy levels of the system shift due to the presence of a photon and you also have photons of that new energy present. The system will shift away further, you get pretty complex non-linearities and complex behaviour. This is not impossible to realize, but there are not that many groups in the world that have the necessary equipment to perform experiments like that. So I suppose these groups will do experiments like that sometime, but they will finish doing all the easier experiments first.

12. Apr 3, 2015