A few days ago we posted a new paper.

General Bound on the Rate of Decoherence [arXiv:10045405]

Cesar A. Rodriguez-Rosario, Gen Kimura, Hideki Imai, Alan Aspuru-Guzik

We establish the necessary and sufficient conditions for a quantum system to be stable under any general system-environment interaction. Quantum systems are stable when the time-derivative of their purity is zero. This stability provides a dynamical explanation of the classicality of measurement apparatus. We also propose a protocol to detect global quantum correlations using only local dynamical information. We show how quantum correlations to the environment provide bounds to the purity rate, which in turn can be used to estimate dissipation rates for general non-Markovian open quantum systems.

[SciRate]

The paper could have been alternatively titled: “Necessary and Sufficient Conditions for System Stability Under Any Coupling to the Environment”. In this post, I want to discuss briefly our first result of the paper:

.

We were interested in finding universal decoherence stability criteria that depended on the structure of the system-environment state, but was independent of the particular Hamiltonian dynamics. We focused on the measure of decoherence called “Purity”, in particular the rate of change of purity. We found that there exist system-environment states that preserve the purity of the system independent of the details of the interaction Hamiltonian. These states are given by the commutator in the equation above vanishing, and we call them “Stable System States” or SSS for lack of a better name.

SSS states are sparse topologically and not-dense: they are quite rare. But, at the same time, they include states whose system part looks very classical. On first sight, since they are rare, this would raise the question of why does the world looks classical to us. However, the equation above also implies that these states are stable under decoherence, and thus can be long-lived.

In other words, we can prove how classical states emerge naturally in the world without any assumptions of the dynamics! This provides a non-equilibrium thermodynamical explanation to why our universe looks classical.

Reuter’s ScienceWatch recently posted an interview with Prof. Daniel Lidar from USC where they discuss Daniel’s most important papers, focusing on decoherence free subspaces. Daniel was very kind to mention my own work on Open Quantum Systems with initial correlations during the interview.

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“The theory of its operation is rudimentary and attempts to improve its performance are still made in an almost haphazard way”
-Sadi Carnot on engines

I spent last week in Portland for the APS March meeting. It was one of my favorite APS meetings so far. First, the city has some free public transportation, is walkable, and very fun. I got to see many old friends. And I ended up giving two talks.

The first talk was on our PRL paper Time-Dependent Density Functional Theory for Open Quantum Systems with Unitary Propagation.

The session was very interesting, with many proposals for how to expand the realm of applicability of TD-DFT. My boss was supposed to give this talk, but ended up canceling his trip at the last minute.

The second talk was on our paper Linear assignment maps for correlated system-environment states.

This talk was part of the OQS and Decoherence session. For some reason, this session is always on Friday afternoon, which is always the least attended day at the APS, as many leave the conference early. Can this be changed? Still, I got all the usual questions about negative maps, so people were somewhat interested.

How are the sessions organized? How are the days chosen, how are the talks in the session organized? I don’t know. Hopefully, next year, my talk will be at a reasonable day and time.

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At dawn of day, when you dislike being called, have this thought ready: “I am called to man’s labour; why then do I make a difficulty if I am going out to do what I was born to do and what I was brought into the world for? Is it for this that I am fashioned, to lie in bedclothes and keep myself warm?”  “But this is more pleasant.”  “Were you born then to please yourself; in fact for feeling, not for action? Can’t you see the plants, the birds, the ants, the spiders, the bees each doing his own work, helping for their part to adjust a world? And then you refuse to do a man’s office and don’t make haste to do what is according to your own nature.” “But a man needs rest as well.”
-Marcus Aurelius’ Meditations, on how hard it is for a roman emperor to get up in the morning

It took some time with the printing proofs, but finally, the paper has been published.

Quantum stochastic walks: A generalization of classical random walks and quantum walks

We introduce the quantum stochastic walk (QSW), which determines the evolution of a generalized quantum-mechanical walk on a graph that obeys a quantum stochastic equation of motion. Using an axiomatic approach, we specify the rules for all possible quantum, classical, and quantum-stochastic transitions from a vertex as defined by its connectivity. We show how the family of possible QSWs encompasses both the classical random walk (CRW) and the quantum walk (QW) as special cases but also includes more general probability distributions. As an example, we study the QSW on a line and the glued tree of depth three to observe the behavior of the QW-to-CRW transition.

Phys. Rev. A 81, 022323 (2010)

Previously: video abstract

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Man, you come right out of a comic book. -Enter the Dragon

Friends have asked me many questions about Obama’s nuclear plan. Although, I am not a nuclear physicists, I did get trained, have been around and/or managed radioactive material while at a Oak Ridge National Lab and University of Texas.

What surprised me was that although I tried to explain each of the different risks, trying to distinguish between radiation exposure and material toxicity, my friends demanded, begged, for apocalyptic scenarios of devastation. This is very much like discussing air travel safety by discussing TWA Flight 800 only, ignoring statistics, ignoring how cars are much more dangerous, and only focusing on what is relevant for a bad blockbuster movie.

Let me be clear, I am not defending nuclear plants disasters, I am not dismissing all the risks of nuclear powered plants. I am surprised how it is impossible to discuss the risks. Any risks involves understanding the different kinds of dangers multiplied by the possibilities of those happening. Without this, benefit, cost and risks analysis are impossible. Without this analysis, public policy cannot be discussed. Why are we so afraid of the dangers of nuclear power, but we are never worried about all the dangers of coal-powered plants? Why, cognitively, these dangers feel so different in our heads? Why in the public eye, nuclear power isn’t about environmental science and economics, but about the apocalypse? This raises many questions about the nature of fear in society, questions I have no answers to.

For example, Nuclear Magnetic Resonance is a standard medical (and general science) technique. It doesn’t have to do with atomic energy, just with the fact that each of the atoms we are made up has a nucleus that consists of protons and neutrons. However, the ‘nuclear’ name had such negative connotations that the name was changed to “Magnetic Resonance Imaging”. Why is this?

My dad has gone through several medical techniques in the past years, including MRI (Nuclear Magnetic Resonance), PET Scan (Positron Emission Tomography) and Radioactive Iodine treatment. He is concerned about the effects of all those nuclear things. I tried explaining how the techniques are very different, containing no radiation, or different kinds of radiation, emphasizing that there is no heavy-metal toxicity in each of these, discussing what does the half-life of iodine really mean to his body by considering that iodine is water soluble, explaining that microwave ovens aren’t dangerous or nuclear, nor are TVs, nor cellphone radiation is of nuclear origins. I did spend significant time talking to my family about this, and maybe it was my fault, maybe I talked over the heads. I was unable to dispel irrational fears in my family, fears that weakened their spirits while my dad was going through an already difficult medical process.

Maybe I was unable to reach them because we meant different things. Maybe there is a very significant difference in the meaning of nuclear to them and to me, a difference in meaning I wasn’t able to overcome with all my explanations.

Why is it so hard for the general public to discuss these issues? Why is discussing nuclear power a taboo? I propose to blame cognition, an image in the mind. After the end of World War II, after the cold war, after The Hulk, the term “nuclear” started carrying a lot of overhead, a lot of imagery and meaning beyond its semantic nucleus of the word [pun].

Bruce Banner, Physicist, demonstrating the effects of Nucular Power

My proposal is the following. There are two different kinds of ‘nuclear’ in the public mind:

1. nuclear as in nuclear family, nucleus as in “the core”
2. nuclear, as in atomic bombs, as in neon glowing toxic rods, as in mutated turtles that learn ninjitsu, as in Cold War, as in nucular.

However, there is only one nuclear in the physicists’ mind, which refers to the core of the atom, which refers to protons and neutrons, which refers to the forces that keep the nucleus stable and make the existence of matter possible, a meaning which is closer to nuclear family than to nucular. It has nothing to do with mutagen, or Homer Simpson and is as far from a nuclear wasteland as Bernoulli’s principle is from crash landing. The same applies to the word “atomic”, that to the general public feels more like “ka-BOOM” than “a tiny piece of anything”.

Is this why there are many public figures that mispronounce nuclear in favor of nucular? Is it that their minds want to distinguish between these two definitions? A linguist at Berkeley suggests this as he explains ‘nucular’ as a folk etymology, not as mispronunciation.

Phonetically, in fact, nuclear is pretty much the same as likelier, and nobody ever gets that one wrong. (”The first outcome was likular than the second”? )

Maybe there are two different meanings of nuclear in the public mind, maybe the nuclear taboo and the word nucular are signs of this. Maybe this is why discussing the dangers and possibilities of nuclear power is so difficult.

What is the solution? I see only two options:

1. invent an euphemism for the word “nuclear” in nuclear power. Call it “freedom power”, “awesome fuel” or “funky style”,
   
2. start calling everything nucular, trying to reunite both misleading diverging meanings. Like, “the nuculus of the cell contains the DNA” and “nucular families are the basis of society”
   

I don’t see any other option that could allow having a public discussion of the pros/cons of nuclear power as public policy, instead of nuclear disaster as a Nostradamus predictions. An apocalyptic image, even if unfounded, has a lot more power than statistics, power that brings out pure fear, preventing all rational discussion. Remember when the news focused on the dangers of black hole creation when the LHC started, instead of actually explaining what the particle accelerator actually does?

Nucular is fear.

If there are any social psychologists around there, can you contact me with references about the origin, nature and effects of fear in society?

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Vamos a seguir bailando!
Vamos a seguir contento!
y sigamos vacilando!
Vamos a seguir en esto,
porque un dia de estos.
Que tu veras que va llegar un demonio atomico.
y atracata acangana! y nos va limpiar.
Despues de muerto no se puede gozar!
-El Gran Combo

2010 has been awesome so far. I’m having a hard time keeping up with blogging all the good news.

Talks

I was in invited The Winter Meeting on Statistical Mechanics in Taxco, Mexico. What a fantastic conference! I learned a lot about many different areas in Statistical Physics, got to meet many awesome researchers, and the keynote talks were in a natural amphitheater inside the Cacahuamilpa caves. Stunning! This was one of the best conferences I’ve been to.

I was also invited to give a talk at Reed College last week. This was my first time ever in Portland, Oregon, and I fell in love with the city. It felt like a mixture of Austin, Northern California and Seattle that I really liked. The academic culture at Reed is something that should be emulated everywhere: students honestly don’t care about grades, just about learning. One thing is to hear it, and another is to witness how true it is! The physics department at Reed has the most motivated and energetic physicists I’ve ever met. Wow.

Papers:

Finally, the paper that I had mentioned before appeared in PRL:

Time-Dependent Density Functional Theory for Open Quantum Systems with Unitary Propagation

Also, the PRA on assignment maps is out in the published wild.

Linear assignment maps for correlated system-environment states

Writing for the general public about science news is hard. ArsTech has an article where they accuse many news organizations of deliberately lying in their science coverage, and discuss how they can get away with it do to double standards.

As a scientist with interest in informing the public of my research, are there any guidelines to follow when talking to the press? I want them to see them as allies, but most of the science news are so bad I can’t help but hating them.

I’ve thought much about how to describe my research to family and friends, and haven’t found any good and concise way to do it. More specifically, can any one suggest any good, simple, cocktail-party style one-liners to explain what is quantum mechanics and quantum computing, but that doesn’t make me feel like I’m lying? If I read again the phrase “what Einstein called spooky action at a distance” I might vomit.

Any ideas?

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When Men fly from danger, it is natural for them to run farther than they need.
-The Mischiefs that ought justly to be apprehended from a Whig-goverment

World’s Physicists Complete Study Of Physics

Ladies and gentlemen, our job is done.

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“The Universe is nothing without the things that live in it, and everything that lives, eats.”
-Brillat-Savarin’s The Physiology of Taste

I’m back.

After a long, tough, wintery and busy month, I’m back.

Progress report follows.

Alright, first, I went to SQuInT. The Southwestern Quantum Information and Technology conference isn’t true to its name. It was held in the Northwest, Seattle, where beautiful weather seemed to tunnel through the mountains’ potential just for us. The conference itself was very productive and I had the opportunity to see family, friends and collaborators.

In other news, we submitted a paper on Open Quantum Systems and Time Dependent Current Density Functional Theory titled Time-dependent current-density functional theory for generalized open quantum systems to the journal Physical Chemistry, Chemical Physics (PCCP). It has been accepted for publication and might appear in a special issue on Time Dependent Density Functional Theory.

We also submitted a related paper to another journal, paper titled Time-Dependent Density Functional Theory for Open Quantum Systems using Closed Systems. You can read it in the arXiv.

Finally, I went to the APS March Meeting, where 7,000 physicists took over the city of Pittsburgh, where I was able to find bars decorated with Roberto Clemente posters, where a restaurant served Carrucho (Conch). Sometimes I feel the APS March meeting is too big, too overwhelming, talks are too short, and there is too much going on simultaneously. But then I’m surprised by meeting people I hadn’t seen in almost 10 years now, and by how APS March meeting always lead to new collaborations.

Exciting times these are.

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“I have wept three times in my life. Once when my first opera failed. Once again, the first time I heard Paganini play the violin. And once when a truffled turkey fell overboard at a boating picnic.”
-Gioachino Rossini