I’ve been traveling a lot lately, you might have noticed how I have been unable to update the blog frequently. Here is a quick update of where science has taken me.

November

Dresden – There I visited the group of Wanter Strunz. They are experts in open quantum systems and quantum optics, and we had much to discuss about open systems with initial system-environment correlations. Dresden has some stunning architecture.

Ulm – Susana Huelga invited me to the beautiful city of Ulm. I’m friends with many people in her group, and this was a great opportunity to catch up, and discuss some new research ideas.

December

Hong Kong – GuanHua Chen invited to Hong Kong University where we worked together on open quantum systems, master equations and quantum transport. Also, during these days, I was able to participate in the CECAM Workshop on Simulating and Modeling Emerging Electronics. This was a fantastic conference where I learned about the challenges of nano-electronics. This was a fun and intense visit. Fun, because Hong Kong is a very fun city to explore, and has amazing food. Intense, because the conference was very productive, with a lot of ideas flying around.

My paper on Non-Markovian Open Quantum systems has been published in the Special Issue of International Journal of Quantum Information (IJQI):

Non-Markovian Open Quantum Systems: System-Environment Correlations in Dynamical Maps

We construct a non-Markovian dynamical map that accounts for systems correlated to the environment. We refer to it as a canonical dynamical map, which forms an evolution family. The relationship between inverse maps and correlations with the environment is established. The mathematical properties of complete positivity is related to classical correlations, according to quantum discord, between the system and the environment. A generalized non-Markovian master equation is derived from the canonical dynamical map.

This paper is an updated version of my 2008 preprint.

Last week, here at the BCCMS we hosted the CECAM conference titled “Perspectives and Challenges of Many-Particle Methods”. This was a very good conference, bringing together leaders from all sorts of ab initio and many-body methods. The program is here.

I had written before about the concept of Lazy States.  Questions in non-equilibrium thermodynamics are usually said to be intractable, due to how much they depend on the details of the dynamical equations. We discovered that in quantum non-equilibrium thermodynamics, there was a simple way to separate the role of system-environment states and of the details of their Hamiltonian coupling. For a class of states, , Lazy States, the entropy rate is always zero independent of the interaction Hamiltonian. These Lazy States are rare, which opens the question of how come thermodynamic equilibrium is so common in the universe?

On a new paper in the arXiv titled Almost all states are pretty lazy, Adrian Hutter and Stephanie Wehner, from the Centre for Quantum Technologies in Singapore, tackled exactly this problem. They were able to show that even if states aren’t lazy, almost all states lead to dynamics which is very close to the ones generated by lazy states. Thus, even if systems are away from equilibrium, they cannot be too far away from it. This leads them to conclude that “Almost all states are pretty lazy”.

I’m very happy to announce that I have started a new position in Universität Bremen, Bremen Center for Computational Materials Science.

Charlie Marcus gave a very nice and accessible TEDx talk about what is quantum computing.

Highly recommended!

[via Computacion Cuantica]

I become an associate editor for the Journal of Universal Rejection, and have now rejected my first paper! I would like to thank CleverBot for making this rejection possible.

A news feature in the journal Nature discusses how Quantum Discord is related to Quantum Computation. They interviewed several of my collaborators, Kavan Modi and Animesh Datta, and have a very nice summary of why it has become so fashionable lately.

Quantum Discord was first proposed by Wojciech Zurek as a measure of bipartite quantum correlations different from entanglement. As Wojciech described it to me, he presented this at a conference, and many people did not understand its significance at the time, mainly because it wasn’t clear how it related to entanglement. Meanwhile, Vlatko Vedral independently proposed a similar measure of quantum correlations. These results were both published around 2001, but Zurek’s name stuck.

A few years later, while I was in graduate school, I heard Zurek was coming to visit us in the Sudarshan group. Zurek had been a student of our department decades before, and I was very excited to meet him. I studied some of his papers, and we had a discussion that ended up on the topic of quantum discord. Although at the time I was not thinking too much about measures of quantum correlations, I was interested in the problem of initial system-environment correlations in open quantum systems.

A few months later, while walking around town lake in Austin Tx, I proposed to Kavan Modi (then a graduate student like me) and Prof. Sudarshan that the concept of classical correlations (as defined by quantum discord), might help us understand some of the issues in open quantum systems with initial correlations. That winter, Kavan and I decided to go on a road trip to New Mexico, where we visited our friend Anil Shaji, now a postdoc in Prof. Caves group. We then also met Animesh Datta. During this road trip we also visited Zurek in Los Alamos, and we had further discussions about quantum discord.

Kavan and Cesar on their way to visit Zurek to discuss Quantum Discord

All these conversations led to the first paper to use quantum discord, which connected it to the mathematical properties of complete positivity of dynamical maps.

Animesh and Anil took a different direction that ultimate proved to be very useful: they noted that quantum discord was an important resource for some quantum algorithms. It was this result that has led to so many recent publications in the field.

More recently, some of us have shown how quantum discord is a fundamental dynamical characteristic of non-equilibrium thermodynamical systems.

Quantum Discord has led to advances that can be grouped into two areas: as what could become another resource in quantum computation, and as some fundamental property of the dynamics of bipartite states. Could there be a relationship between these?

The Department of Energy is having an online contest of submissions of videos from all its Energy Frontier Research Center. You can see them all here.

Since I am part of the Center for Excitonics, I am partial to thinking that the video titled Excited about Excitons should get your vote. Vote for it by clicking here.