Smash!

Let's talk about collisions. Pretty much all physics experiments can be broken down into two categories: scattering (for example, particle accelerators) and interference (for example, Young's double slit experiment).

Example of a scattering experiment. I have been trying to convince the guys in the lab next door (who are actually working on an interference experiment) that they need to buff up and dress like this in the lab. Incidentally, the laser safety glasses that he is wearing are correct for the wavelength of light being emitted in the tube, if I compare them to a similar model from Thorlabs.

In certain regimes, the line between the two kinds of experiments gets kind of hazy. You see, there is this thing called wave-particle duality. Sometimes, matter acts like a particle (like little balls smashing into each other), and other times the same matter can act like a wave (like ripples in water overlapping with other ripples, making an interference pattern). This is true even for some large molecules. It is most definitely true for cold atoms, like the ones I am working on.

In our lab, we are doing scattering experiments. We take two clouds of very cold atoms (less than a microkelvin!) and smash them against each other. However, they are so cold that they no longer behave like particles, as your everyday gas would. They instead act like waves and interfere with each other! The way they behave when they collide is nothing like what would happen to a particle. It looks like this:

These are two clouds of atoms trapped in some laser beams. They are about 400 nK and there are half a million atoms in each cloud. We accelerate one cloud towards the other and then release them from their trap so they can expand after the collision. The expanding halo is made up of scattered atoms.

These atoms are moving at pedestrian speeds. If we increase the collision energy a little bit more, the pattern of scattered atoms will look a bit different and develops lobes in funny places. It's one of the things next on the agenda, so watch this space!

I will add a final note about particle accelerator experiments. To do interesting physics and make a name for yourself, it's all about going for extremes. For example, the LHC was made to do higher energy collisions than any other existing accelerator. The other, often forgotten, end of the spectrum is the super slow collision regime. That's where we're at! We're doing the slowest, lowest possible energy collisions! That's pretty extreme.

2011 in Review

It has been 5 months since my last post. That's quite a long time! I have some good reasons for this. In fact, the one new year's resolution I have this year is to write more regularly!

At the end of every year (or start of the next one), I like to review the year and see how things have come along. This time, in particular, perhaps you can see why I haven't really had time for posting much. Also, this year I had two major (only) activities: physics and Taekwon-Do.


2011 In Review

Overall, the year can be summed up in one word: intense.

Let's break it down. 2011 was welcomed at a beach in Napier, after having driven for 12 hours around the East Cape of New Zealand. The next few days were spent traveling around the South Island with one of my close friends and my newly acquired husband. It was a nice trip, but made me realise that I don't really like road trip vacations. Sure, you see a lot, but it's tiring, and I would much rather go somewhere new and spend a few days getting to know the place instead of always being on the move.

Some time in 2010, I decided that 2011 would be the year that I go for my 2nd degree (dan) black belt in Taekwon-Do. Black belt gradings are pretty tough and require a lot of preparation and 100% commitment. I was mentally prepared to start training at the beginning of 2011, and a grading was scheduled for April. I began training 5 or 6 days a week and was generally enjoying myself with it. In March, the ITF Taekwon-Do World Championships were held in Wellington, and at the last minute I got flights to go watch. I'm glad I went, because I found it quite inspirational in regard to my own training.

During these few months, my new supervisor and I were trying to improve our experimental setup and figure out why we couldn't make Bose-Einstein condensates (BECs). We pulled things apart, put them back together, replaced electronics, optimised parameters, etc, but no luck. Even though we were making improvements, BEC still eluded us. It was good to go to training at the end of the day because I could physically vent all my mental frustration and not bring it home with me!

As I'm sure everyone knows, on February 22nd, an earthquake hit Christchurch. We felt it here in Dunedin, which is around 4.5 hours drive away. It was an aftershock of a quake in September, but that earthquake only caused some damage. This time, people died. Friends' homes were destroyed. The whole central city was closed down due to damage and unstable buildings. You hear about disasters around the world all the time and see the damage on TV. Somehow I always felt disconnected from them. This time, it was in my own back yard and my own friends that were affected. It was heartwarming to see all the volunteer initiatives to help Christchurch residents, and it definitely restored some of my faith in humanity! Unfortunately, they are still being shaken by earthquakes and jerked around by politics and insurance companies. I really hope they get a break soon!

Around the end of March, our grading got postponed until July due to lack of numbers. I felt a little bummed, but was glad to have more time to train. I should add at this stage that not only do I practice Taekwon-Do, but I am the instructor of my university Taekwon-Do club, so my own personal training (usually at other clubs) is in addition to the two classes a week that I teach during the semester (though I have some very nice assistants!). By coincidence, around this time, a person I knew who is higher ranked than me who had quit Taekwon-Do a year before suddenly had plenty of time that needed occupying due to a change of personal circumstances. So I asked him to train me, initially just for fitness, and slowly (but unintentionally!) got him back into Taekwon-Do and he eventually joined my club and we became friends.

In May, we had our regional tournament. In the past, I was never a strong competitor, but the training payed off and I got a couple of medals! Our club also got 2nd place overall. My TKD returnee made a very good coach and helped all of us improve our sparring. Unfortunately, around this time, the July grading was canceled due to lack of numbers, so I had to wait until December to grade in the North Island (where there are many more people doing TKD, so the gradings are a lot more regular). A setback, but in the meantime, we would concentrate on the national tournament in August.

Back to the lab: we were dredging the bottom of the barrel. I pored over PhD theses and all kinds of stuff looking for problems other people had that prevented them from getting BEC. The game is to cool a cloud of atoms to almost absolute zero and still have enough atoms in your sample to do interesting experiments. We could get our atoms to less than a microkelvin, but then something would heat them up again, preventing us from reaching the density and temperature needed to form a condensate. In July, on an unusually cold weekend, we finally cracked it. This was an immense relief. The end of my PhD was finally in sight!

From that point on, things moved quickly. We moved into testing out our ultracold atom collider (I will do a post on this later). Just imagine a montage of happy physicists running experiments, collecting data, plotting graphs, writing papers, etc. Fun times! And for me, the evenings were filled with punching, kicking, breaking boards, running, sparring, etc. Personal social life: nil.

For once, our club had a decent contingent going to nationals. We trained together on Sunday mornings, doing 1.5 hours of some sort of sadistic running exercise devised by our coach (the returnee), followed by 1.5 hours of sparring training. The tournament went well. We didn't do spectacularly in terms of placings, but everyone did well. I was certainly very proud of everyone and myself!

Things in the lab plodded along for the rest of the year. We had a setback or two, but nothing dramatic. We submitted a paper on the collider recently. My first paper!

By November, I was starting to feel tired. Training 6 days a week and spending the rest of the time in the lab was getting exhausting! I felt ready, and just wanted to get the grading over with! I should note, at this point, that the first time I went for my black belt, I didn't pass. There were a number of reasons for it, but mainly I was just not that well prepared. 6 months later, I re-tested and I did pass, but the whole thing left me feeling like I just wasn't very good at Taekwon-Do. I became an instructor straight after getting my black belt, not because this was a personal aspiration, but out of necessity, because the previous instructor had finished his studies at university and was moving overseas, and I was the next most qualified person. At the time, I felt like I just barely made it to black belt and that I wasn't cut out for much more.

This year taught me that I am cut out for more. I passed my 2nd dan grading, and I got an A. I certainly didn't do it on my own. Everyone has people helping them for gradings, and I am very thankful for the people who helped me (other more senior instructors and also my personal coach). I now have more aspirations for competing and look forward to this year's tournaments and training some of my students for their black belt grading.

In the lab, perseverance has paid off. Every year, I wish for success in the lab. In 2011, it actually happened and that makes me very happy! The next few months will see the final push to finishing my PhD, which I look forward to very much!

2011 was an intense year. It was a year of sadness and stress for many of my friends. It was also a year of happy events for friends as well (five couples I am friends with got married, one of them expecting their first child any day now). It was a year of frustration in some areas, and ultimately a year of overcoming obstacles and learning that I can be better at whatever I want to be as long as I put in the effort.