The lecture is accompanied by a Journal Club, where original scientific papers related to the topics from the lectures will be discussed. Usually the topic of the article will be related to the topics of the lecture in that week.

You should read the paper and understand the central topics before the journal club (rather than just bringing the printout), usually we also give some "questions" that you should try to find an answer for, in order to emphasize specific aspects of the paper or related topics.

1. The first paper in the club which we will discuss on May 11th demonstrates a quantum optics effect realized in a semiconductor implementation: "Ramsey fringes in a single InGaAs/GaAs quantum dot", Physica Status Solidi B 243, No. 10, 2229–2232 (2006). The DOI is: 10.1002/pssb.200668028
   - a quantum dot here is just a structure in a semiconductor which contains electrons and is so small that these have discrete energy levels similar to those in an atom. So, for our purposes it is just a generic two-level system - what exactly these two states look like does not matter for what is described. The same goes for the "photocurrent", which is a read-out method to measure the excited-state probability of the quantum dot.
   - What is the sequence of coupling pulses used here, and why is it two pi/2 pulses and not two or three pi pulses?
   - Why is there a "detuning" - what is detuned from what? And how does that relate to the voltage?
   - and, obviously: What is the result of the paper, and how does the approximate shape of the results shown in the graphs arise
2. The second paper is is about a very common kind of laser spectroscopy, the so-called saturated absorption spectroscopy: Opt Comm 31 28-30 (1979): doi:10.1016/0030-4018(79)90237-2. This type of spectroscopy was development over quite some time and it's explanation is scattered over many papers. But it should be straightforward to find a clear explanation on the web. 
   -Try to draw a schemactic of the setup. (Why isn't it printed in the paper?)
   -Why does this spectroscopy need at least two beams?
   -What are the laser powers in the two beams?
3. The third paper for May 25th is about coherent states. As we did not discuss all aspects of coherent optical fields yet, we will look instead into a different implementation, that of coherent states of atoms instead of photons. The paper is "Collaps and revival of a coherent matter wave field", Nature 419, 51-54 (2002). 
   - What is the equivalent of the electric field (observable) in this case of a coherent state of atoms?
   - What is measured and how?
   - Why is there an oscillation in the observed signal? In the beginning the signal is "high", why does it disappear - and then come back?
   - Bonus question: Can you explain Figure 1?
   - Bonus bonus question: This was originally proposed for photons but not observed. Why is it "easier" for atoms and what kind of physical system would you need to see this kind of effect with photons?
4. The paper for next week's journal club (June 1) is  Phys. Rev. Lett. 76, 1800–1803 (1996): Quantum Rabi Oscillation: A Direct Test of Field Quantization in a Cavity, written by a group in Paris in 1996. It looks into fundamental effects of the interaction of a two-level system with a quantized field.
   - What is the two-level system involved here?
   - How is the cavity coupling strength controlled?
   - What is the important progress over earlier work that made it possible to observe this effect for the first time?
5. In the Journal club on June 8 we will discuss the paper by Pinkse et al., Nature 404, 365-368 (2000). It combines optical potentials and cavity qed effects. 
   - We remind you of the usual questions: What did they do, how does it work, what did they find etc.
   - There are two kinds of motion that the atom is exhibiting once inside the cavity. What are they, and what causes them?
   - Why is the light only switched on after a trigger, why is it non on all the time (there is even more than on ereason)
   - Advanced: What is the experiment that people would have liked to do which is mentioned in the beginning of the paper? How would that have worked?
6. On June 22, we will discuss a true classic (and a very simple experiment), the paper "Measurement of subpicosecond time intervals between two photons by interference ", by   C. K. Hong, Z. Y. Ou, and L. Mandel, Phys. Rev. Lett. 59, 2044–2046 (1987) 
   Hint: The authors present their work as a new measurement method. But historically, that was not the big deal about this paper, but rather the results thez were able to measure with it. So, apart from the usual questions you should look at this
   - What is parametric down conversion? (use books or whatever resources - you only need an approximate understanding for this paper) In this particular paper, there is no real difference between "signal" and "idler", so don t be confused.
   - Why is the beam splitter needed for the measurement scheme described?
   - Interesting point: What would happen if the photons were randomly polarized and the beam splitter would split the beam by "sorting" the photons according to their polarization (vertical: reflected, horizontal: transmitted)?
7. On June 29, we will discuss a "local" paper: "Nonclassical radiation of a single stored ion", by Frank Diedrich and Herbert Walther,  Phys. Rev. Lett. 58, 203–206 (1987) 
   - Don't worry if you don't understand the details of the way the ion trap works, it is not central for the measurement.
   - Can you explain why the photons are antibunched in this case?
   - What is the quantity which is measured by the setup?
   - What is determining the antibunching time-span?
   - What is light with sub-poissonian statistics, how do they show they generate it, and why is it generated in this experiment?
8. The next paper deals with the creation and measurement of entanglement between photons: Experimental Entanglement Swapping: Entangling Photons that Never Interacted by Jian-Wei Pan et.al. Phys. Rev. Lett. 80, 3891 (1998)
   -How are photons created?
   -How do Photons 1 and 4 become entangled?
   -How do they prove the entanglement?
   -Why do they need four photon coincidences?
9. After several papers on photons we will in the next journal club look at an early experiment towards quantum computing with ion traps. In Laser addressing of individual ions in a linear ion trap H.C Nägerl and Coworkers in the group of R. Blatt in Innsbruck show the ability to address individual ions in the linear Paul trap using tightly focused laser beams: Phys. Rev. A. 60, 145 (1999)
10. On July 20 we will discuss the paper "Generation of Nonclassical Motional States of a Trapped Atom", Phys. Rev. Lett. 76, 1796–1799 (1996).
    - No cavity is used in this experiment - so what is the connection to cavity physics?
    - What is the observable? How is it measured and how does it depend on the quantum state?
    - Which is the motion state that corresponds most to a classical motion state?
    - Which is the state that corresponds most closely to a classical light field when talking about quantized photon states? Can you explain the differences?
11. The paper discussed on July 27 will be Cooling atoms in dark gravitational laser traps (Pis'ma Zh. Eksp. Teor. Fiz 61, No. 1 (1995)). Here, a simple and effective cooling scheme for atoms is presented.
    - Where does the potential come from that constitutes the "laser trap"? These are also called "optical dipole traps". Think about the dressed state pictures discussed earlier, and the interaction between the single atom and the cavity in an earlier journal club.
    - Why are there two potentials shown in the figure? What cuases the shape of them?
    - Reminder: What is optical pumping?
    - What is causing the cooling effect in the scheme shown?
    - And why do the authors call this a "dark" trap?
    - What is a Monte Carlo simulation, and what does it tell the authors?
    
    

You also may browse yourself in the journals, which you can access here. For the journal club the most relevant journals will be Physical Review Letters (PRL), Physical Review A (PRA), Reviews of Modern Physics (Rev. Mod. Phys), Nature and Science.