Monday, November 24, 2014

Quantum computing with Majorana fermions is science fiction fantasy

Someone has to say it.
I said it publicly today. Several people told me they were glad to hear it.

Majorana fermions are fascinating from a fundamental science point of view. They are worth investigating by a few theoretical and experimental groups. However, they are the latest fashion that is taking the solid state and quantum information communities by storm. It is the latest exotica. Much of the justification for all this research investment is that Majorana fermions could be used for "fault tolerant" quantum computing.

Lets get real. Lets not kid ourselves. First, as far as I am aware, no one has even demonstrated yet that the relevant solid state "realisations" even exhibit Majorana statistics. Suppose they do. Maybe in a few years someone will have 2 qubits. Looking at the complicated nanoscale devices and fabrication needed I fail to see how on any reasonable time scale (decades?) one is going to produce say 6-8 qubits. Yet even that is just a quantum "abacus", a toy.

The cartoon is taking from Gil Kalai's blog.

Sunday, November 23, 2014

An introduction to emergent quantum matter

Here are the slides for my talk, "An introduction to emergent quantum matter" that I am giving tomorrow at the Australasian Workshop on Emergent Quantum Matter.

A good discussion of some of the issues is Laughlin and Pines article The Theory of Everything and Piers Coleman's article Many-body Physics: Unfinished Revolution.

A more extensive and introductory discussion by Pines is at Physics for the 21st Century.

I welcome any comments.

Saturday, November 22, 2014

Investing in soft matter

I really enjoyed my visit to the TIFR Centre for Interdisciplinary Sciences (TCIS) of the Tata Institute for Fundamental Research in Hyderabad. This is an ambitious and exciting new venture. Higher education and basic research is expanding rapidly in India, with many new IITs, IISERs, and Central Universities. These are all hiring and so it is wonderful time to be looking for a science faculty job in India.

The initial focus of hiring of the new campus of TIFR (India's premier research institution in Mumbai) has been on soft condensed matter (broadly defined) with connections in biology and chemistry. There are many good reasons for this focus. Foremost, is that there excellent Indian's working in this area. However, I see many other reasons why choosing this area is a much better idea than quantum condensed matter, ultra cold atoms, quantum information, cosmology, elementary particle physics, string theory (yuk!), ...

Other reasons why I think investing in soft matter is wise and strategic include:
  • this is exciting and important inter-disciplinary research
  • there are real world applications ranging from to foams to medicine to polymer turbulence drag reduction [used in oil pipelines and in fire fighter hoses]
  • these types of applications are particularly important in Majority World countries
  • in public outreach one can talk about flocking and do simple and impressive demonstrations such the Briggs-Rauscher oscillating chemical reaction or sand flowing through channels.
  • the experimental infrastructure and start up costs are relatively small. most experiments are "table top" and at room temperature. this allows a new institution to get some momentum and "runs on the board" as quickly as possible.
Having said that I think there are significant obstacles and challenges with such interdisciplinary initiatives. These challenges are scientific, intellectual, and cultural (in the disciplinary sense).
Excellent inter-disciplinary teaching and research is a just plain hard work and slow. Getting people to put in the time and keep sticking at is difficult. It requires special individuals (both faculty and students) to build bridges, learn each others languages, respect, and persevere.

The TCIS Director, Sriram Ramaswamy is co-author of a nice RMP article, Hydrodynamics of soft active matter.

I am looking forward to seeing how this exciting new adventure develops over the years. India is leading the way.

Friday, November 21, 2014

Broken symmetry, rigidity, and dissipative structures

On monday I am giving the opening talk at the Australasian Workshop on Emergent Quantum Matter. Since it is a broad audience with a range of backgrounds I am going to give a tutorial talk, building on the UQ colloquium I gave earlier this year.  Later I will post my draft slides.

One concept I want to expand on is the concept of rigidity, associated with broken symmetry. To do this I am reading a nice article "Some general thoughts about broken symmetry," written by Phil Anderson in 1981. It is reprinted in A Career in Theoretical Physics, and here is a scanned copy of the article. It contains the figure above.

What is the connection between the "rigidity" of  solids and broken symmetry? A liquid is invariant under continuous translations and rotations. When it becomes a solid it is only invariant under discrete rotations and translations. Symmetry is broken. Unlike a liquid, a solid can "sustain/resist" a shear stress. Solids are rigid.

I also want to say something about non-equilibrium. Anderson has something critical to say about "dissipative structures" such as Bernard cells associated with self-organisation and hydrodynamic instabilities.

Thursday, November 20, 2014

A dream graduation speech

While in India, I enjoyed reading Chetan Bhagat's best selling novel,  Five Point Someone:  What Not to do at IIT. The novel was made into a commercially successful movie, 3 idiots. The latter is only based loosely on the novel, and I think is better. I loved it.

In the novel, the villainous Professor Cherian undergoes a transformation. At the end of the novel he departs from his usual graduation speech and says the following profound words.
 Anyway, this is my message to all you students as you find your future. One, believe in yourself, and don’t let a GPA, performance review or promotion in a job define you. There is more to life than these things - your family, your friends, your internal desires and goals. And the grades you get in dealing with each of these areas will define you as a person.  
Two, don’t judge others too quickly. I thought my son was useless because he didnt get into IIT. I tell you, I was a useless father. It is great to get into IIT, but it is not the end of the world if you don’t. All of you should be proud to have the IIT tag, but never every judge anyone who is not from this institute - that alone can define the greatness of this institute.
This receives thunderous applause.
The only problem is then Hari, the protagonist, wakes up from his dream. He has overslept and missed his graduation.

I too dream of such graduation speeches.

Wednesday, November 19, 2014

How important is my graduate class cohort?

Very important. You will learn a lot from them.

Recently, when I visited TIFR-Hyderabad I was asked to meet with a group of graduate students for a question and answer session on career issues. This was actually the first time I have actually done something like that. That had many excellent questions. Some I may later blog about. Here I will just focus on this one question.

Getting a Ph.D is not just about writing a thesis or even going to classes, doing experiments, talking to your advisor, and passing exams.
At every stage of a program you can learn an immense amount from informal interactions with your peers [your class cohort]. Each has different background, interests, expertise, strengths, and weaknesses. Talking with them and sometimes working together on joint projects can be immensely valuable. Just the art of learning to talk to each other, asking questions, and crossing specialist boundaries [theory vs. experiment, chemistry vs. physics, field theory vs. condensed matter, soft vs. hard condensed matter] can be a rewarding but slow process.
Peers can also provide significant feedback and emotional support.

For some of us this may mean taking risks, overcoming shyness, and not making comparisons.

In reality, you may actually learn more from your peers than from the formal part of the program. Some people also develop  lifetime friends and/or collaborators from their cohort.

 If I had my time over again I would have interacted a lot more with my peers. At the time I just did not realise how valuable it could be.

This is why I think you are much better off in a Ph.D program that
-is highly ranked
-has a reasonable size cohort [10 plus new students per year]
-has a significant course work component
-provides on campus shared accomodation
-encourages informal interactions including shared offices that mix up research groups
-encourages interactions across groups and departments.

Sunday, November 16, 2014

Should you be concerned about nuclear weapons?

It is amazing how since the end of the cold war the issue of the nuclear weapons stockpiles of the USA and Russia attract little political attention and concern.
In his usual inimitable style John Oliver highlights why we should be concerned.