Posts in category Other funny things
Measuring entanglement
I cannot believe it myself, and it is hardly thustworthy to write about it on April 1, but please take it for a fact. I have attempted to experimentally quantify entanglement of photon pairs today. I did not do any experiments for more than thirty years.
Val Zwiller is to blame. When asked to provide an experimental setup for undegraduate lab practice, he could not come with any fresh idea. So he’s just slightly modified a setup of pioneering experiment of Alian Aspect who has quantified the violation of Bell inequality in 1981. He has invited me and Leo Kouwenhoven to "inagurate" – that’s how he put it – the experimental setup.
At 16:00 I was at his office. We brisky got to the measurement room. On the way Val asked me with soft heartfelt tone: " Do you believe in entanglement? Do you believe in non-locality?" This gave me a thrilling impression of being a part of important rite: he sounded like a priest asking faithful about their readiness. "I do. I do believe." I responded, trying to match the tone. I wanted to add that I believe in quantum mechanics, but, given the nature of the rite (where a participant should demonstrate a ritual doubt and sucsessfully overcome it by direct measurement) this would not sound polite.
Me and Leo have been supervised by Julia Cramer and another young lady. The setup was placed in two large plastic boxes alike my children use to store old toys. One box housed a blue laser, non-linear crystal to chop a blue photon into an entangled pair of red ones. The two go by two fibers to the second box where their polarizations have been rotated by changeable angles and finally get to photon counters. The computer gave coincidence counts, those depending on the rotation angles. The math to be made afterwards, and its significance is explained in http://en.wikipedia.org/wiki/CHSH_inequality.
There were about twenty curious people in the room, all irradiating excess heat. Val has attibuted the chaotic work of the setup to this mere circumstance. He kept re-tuning the fibers in the production box. He did it quickly and efficiently. I was turning polarizers. Leo read data and wrote it up. One needs to measure at four different positions of the polarizers. So we got 16 readings. After the experiment everybody was cheering while I had to do the math.
We did not manage to prove (our faithful devotion to ) quantum mechanics this time. This would happen if the final answer would exceed classical boundary of 2. Yet we got 1.91: Almost. Not bad for the first time.
Thanks very much, Val, Julia and all others involved: this was a wonderful and entertaining experience for me, and it will be fun for many generations of students.
Hangxing Xie
has received the title of Ph.D. today. I was in the commission. His research has been in the field of electron transport at interfaces of organic materials: it is an interesting and potentially important fact that such interfaces between practically insulating materials can provide electric conduction. His research has been supervised by Alberto Morpurgo, who has been in Delft for quite some time, has made much important research here, but has left for a better position in Geneve about a year and half ago. They say he did not fit well. They did not want to promote him to a full professor. Although the story is rather old, I still feel a pity – not that much for Alberto, rather for my colleagues and Dutch society in general that has an apparent difficulty in appreciating unusual, ambitious and not-always-agreeable personalities.
Due to this, Hangxing Xie has been working in Delft as wel in Geneve, Huub Salemink was his promotor from the Delft side. His defence performance was very tough and to the point. Beside scientific question I have addressed one of his propositions: that went about online shopping and women. I was astonished by his serious studies of the question and brisk manner of presenting every detail of this subject.
Producing entanglement
Modern theoretical physics of condensed matter is sufficiently developed to compute all physical quantities of interest. Perhaps this signals that we shall proceed to the next challenge, and compute unphysical ones.
Most interesting unphysical quantities are related to information, especially quantum aspects of it. They characterize things like entanglement of quantum states and their informational content. The "unphysical" aspect is that these quantities are not linear in density matrix, and therefore can not be regarded as common quantum observables. Non-linearity makes the computation of these quantities rather challenging from the technical point of view.
There is a flourishing community dealing with these quantities in condensed matter. I am not exactly a part of it, but these things interest me, and I’d like to be. I have decided to attend their workshop in Dresden in June.
For this workshop, I’d like to make a small exercise, so to say, to produce some entanglement by myself. I’ve got an interesting starting idea, and elaborated on this. Naturally, I’d like to compare my findings with the results of previous research. In particular, I wanted to undrestand the correspondence with poineering results of Carlo Beenakker and Leonid Levitov.
Well, it turned out that the gentlemen have produced entanglement of a different sort, that I failed to understand from the beginning. This is the danger to work with unphysical values: they are subjective so small differences in interpretation and taste generate great differences in final answers. So I have to learn more and understand more. The exercise took most part of the week past.
Depression
It was wonderful in Grenoble, I came to Delft full of energy and new ideas: and has been hit by a wave of depression in very first day. Depressive feelings are not alien to me, they are well-known but still dangerous enemy. I guess many in my environment are having depression from time to time, but do not discuss this and try to deny it. When depressed, I don’t do things scheduled and/or those I have to do. Rather, I’m busy with things completely unnecessary and sometimes even damaging for me and others. The pain from not doing things I have to do or not doing them in a proper way is sharp, overwhelming and pleasant in masochistic way, and it drives me to further depression. The feeling of miserability, despair and apathy persists. I become increasingly asocial and even rude while demanding and needing more attention from people around.
The danger of depression is easy to understand in physical terms. It arises spontaneously, like an instability, and sustains itself by a sort of negative feedback: apathy and relation damage caused by depression brings more despair and therefore more apathy and damage. If I try to compile a list of all things that would drive me to a depression, it’ll cover 80% of my working and family duties. It is especially bad to have a depression in the fasting period: yelding to despair is a sin, and the despair is a fertile soil for almost all other sins, and failure to fast does produce more and more depression. This is why the depression tries to hit us in this particular time.
Being human, I can do very little against instabilities and negative feedback loops of my tainted soul. I have to bring the topic to Him, though initially this seems both unnecessary or blasphermic. There’s an old prayer:
- O Lord and Master of my life,
the spirit of emptiness, despair (that is, depression), domination or idle talk
do not let me have it. - But give rather a spirit of purity, humility, patience and love, give me to Thy servant.
- Yea, O Lord and King,
grant me to see mine own faults and not to judge my brother,
for blessed art Thou unto the ages of ages. Amen.
Pilgrims of Brodsky
there’s a lazy sunday far from home, so I’ve found an English translation of another Brodsky’s poem. This poem I’ve first heard in the age of twenty, and given the circumstances of epouche, it was an underground song, a manifestation of forbidden culture. For Brodsky in the time of writting, the poem was most probably post-christian. Yet what’s Brodsky: he’s just a magical mirrow that shows our souls rather than faces. For me of that age, the poem was a kind of pre-christian, that drove me think of things beyond earthy world. Here it goes:
PILGRIMS
Past arenas and temples,
past churches and taverns,
past elegant graveyards,
past thundering markets,
past the world, and past sorrow,
past Rome, and past Mecca –
scorched by the sun’s blueness,
the pilgrims are trekking.
They are hunchbacked, they hobble.
They are hungry, half-noked –
with eyes full of sunset
and hearts full of sunrise.
The wastes sing behind them,
heat-lightning flares feebly,
the stars sweep above them,
birds screech to them hoarsely:
"The world has not altered."
No. It has not altered.
It is what it has been.
It is what it will be.
Its snow-crust still dazzles,
its warmth is still doubtful.
The world will be faithless
and yet everlasting.
Perhaps men can know it
and yet it is endless.
Which means there’s no meaning
in faith in oneself, or
in God; all that’s left is
the Road and the Dreaming.
Yet earth will know sunsets.
And earth will know dawnings.
Dead soldiers will loam it,
live poets affirm it.
p.s. you have noticed "noked" The second letter must be "a". Yet this blog is hosted by an educational organization, and such words are unacceptable in this blog. Seriously: nothing is more dangerous than automated stupidity.
Grenoble
Since Thursday I’m in Grenoble. It’s my first time over here, so I thoroughly enjoy unbelieavbly scenic views the city and its neighbourhoods have to offer. I have had already a good long hike yesterday.
But for science have I come, and that they have in abundance too. There are two large scientific centers in the city where, among other things, nanoscience activities take place. Both are thoroughly fenced off any external disturbance: the heritage of cold-war era or something else. I am visiting CEA, and have to exchange my passport for a badge with ever-worst photo of mine: the price for gaining access to their latest scientific results. On Friday my curiosity has extended to CNRS. Phyisically, it’s 200 m away. Yet there are fences too high to jump over. My host directed me to an automated gate that would let me out: naturally enough, I would not be able to get back. Yet the host was too high of opinion about my general intellegence. Finally, he had to come along and personally push all necessary buttons. It is a wonderful integrating power of science that makes the scientists of both centers aware of their mutual presence: they know each other names and, reportedly, even meet in Grenoble (by the gate?) to discuss the research, not restricting personal communications to international conferences. To finish with the topic: we’ve no (visible) fences in Delft, but surprisingly much personal communication with my colleagues takes place during international conferences.
I have talked to Julia Meyer, Manuel Houzet, Xavier Waintal – energetic, talented scientists of younger generation, and to my old friend Frank Hekking. I will remain in Grenoble for ten more days.
Thanks for 128,000 views!
It is my pleasure to report another doubling of number of views. It took 45 days to achieve this, while my bet was 90 days. Thank you very much for your attention, this is very encouraging.
If I extrapolate (see http://mrkwr.wordpress.com/2006/11/08/mark-twain-on-the-perils-of-extrapolation/), I understand that I reach 10^11 views in 3 years, so every inhabitant of the planet will read each of my posts at least once.
Disentangling the effects
of spin-orbit and hyperfine interactions on spin blockade is another long title. This is an experimental work where Jeroen Danon and me have been involved. It analyses spin blockade in double quantum dots made in a semiconducting nanowire. This is the first submission of Stevan Nadj-Perge. For quite a time, he entertained us with colorful pictures showing current throught the dots versus magnetic field and detuning. He has seen distinct and unusual patterns in these pictures that he named "aircraft", "Mickey Mouse", "deep peak", etc. We have finally sorted out the interplay of competing factors producing the patterns, that is, "disentagled" these factors.
I am not very happy with the title since that may sound as a challenge to quantum information community: they want to entangle things rather than disentangle them. Yet the only alternative was "Measurements…" and that sounded dull.
The paper is available on cond-mat, http://arxiv.org/abs/1002.2120
Ted Chiang
is an American sci-fi author who writes really very little but is famous in circles since he harvests a noticeable fraction of prestigious sci-fi awards. I read most his stories, they seemed well-crafted and entertainingly bizzar but I could not say they had touched me.
Recently I have read his "Exhalation" and this get to my soul. It is a story where there is no word about God and faith while everything speaks of God and faith. I recommend it to everybody who is interested in the relation between science and religion, and …
No, you’d better read it yourself. By kind permission of the author, you can find the story at
http://www.nightshadebooks.com/Downloads/Exhalation%20-%20Ted%20Chiang.html
and it IS short.
Kees Harmans
has given today a talk at Quantum Transport group meeting. He’s promised a "colourful" one, and he gave one. Main topic was an original project of making a superposition of two photons in two different oscillators, that is, of two different colours. It is both doable and interesting project. Actually, I believe the resulting state will be entangled: just if one defines entanglement properly.
Kees has struck us with suggestion that this may well be his last talk at the group meeting: he will retire in the end of the year. So in the last part of his talk, instead of sketching the prospects of research, he told us about his plans for retirement. He has listed many interesting activities, and physics of noise (produced by aircraft) took a part in the list.
Thanks, Kees, I’ve enjoyed both parts of the talk as well as the combination of the two. May God help me to give my last talk as you did: remaining inspired and inspiring.