Our paper:

Vanishing quantum discord is not necessary for completely positive maps

The description of the dynamics of a system that may be correlated with its environment is only meaningful within the context of a specific framework. Different frameworks rely upon different assumptions about the initial system-environment state. We reexamine the connections between complete positivity and quantum discord within two different sets of assumptions about the relevant family of initial states. We present an example of a system-environment state with nonvanishing quantum discord that leads to a completely positive map. This invalidates an earlier claim about the necessity of vanishing quantum discord for completely positive maps. In our final remarks, we discuss the physical validity of each approach.

has been published in Physical Review A! This paper challenges some of the main claims of one of the most cited papers in the quantum discord community. We hope this will lead to fruitful discussion on the subject.

I am one of the organizers for the CECAM Workshop on Nanophononics.

It will take place here in Bremen this August, and promises to have all the most important researchers working on the control of phonon transport in the nanoscale. This is going to be an amazing conference. You can register here.

Our paper Positivity in the presence of initial system-environment correlation has been published in Physical Review A!

The constraints imposed by the initial system-environment correlation can lead to nonpositive dynamical maps. We find the conditions for positivity and complete positivity of such dynamical maps by using the concept of an assignment map. Any initial system-environment correlations make the assignment map nonpositive, while the positivity of the dynamical map depends on the interplay between the assignment map and the system-environment coupling. We show how this interplay can reveal or hide the nonpositivity of the assignment map. We discuss the role of this interplay in Markovian models.

Theoretical physicists rely on their blackboards like priests on their pulpits, or like news anchors on their desks. We have very strong opinions about them. Markers vs Chalk? If you like markers, what brand of markers, and how thick? And then, do you write on the whiteboard, the glass window, or just simply, special wall paint? If you like chalk, what kind of chalk? Different brands crumble in different ways. Do you like colored chalk? Do you prefer to write on green or black board?

I am old fashioned about this. I like white chalk on black boards. But, I found that I'm allergic to chalk dust, and I've been forced to use markers on white boards now.

There is a photographic art exhibit about the Blackboards of Quantum Physicists. Some pictures are cool. In some others, I feel that the physicists tried to ruin how authentic the writing were, either by making them too nice, or by trying to sabotage them. Either way, I think this kind of works as a way to convince the public to not be scared by our crazy equations.

I have just come back from Hong Kong, where I was collaborating with the group of Prof. GuanHua Chen. We are interested in studying mathematical properties of the Hierarchical Equations of Motion from a Master Equation point of view. This was a very productive visit.

I also had a wonderful time exploring the city, and finding great food everywhere.

The Bremen Center for Computational Materials Science was host to the International CECAM-Workshop
Graphene: From band structure to many-body physics. See the workshop program here. This was a fantastic conference, with many of the leaders in the field.

Here is one of the Workshop pictures in front of the Bremen Townhall

I just came back from a delightful vacation where I reread The Baroque Cycle. The Baroque Cycle is a series of novels published in three volumes Quicksilver, The Confusion, and The System of the World in the genre of historical fiction about the rise of natural philosophy, important developments in economics and politics during the enlightenment. It is insanely ambitious, imitating literary styles from the era. It is insanely detailed. One of its major characters is Isaac Newton, both in his roles of the greatest natural philosopher ever, and as the master of the Mint, reforming the financial system in England.

Through out the books, references are made to a list of sins that Isaac Newton kept. In this list, he detailed every sin he ever committed. Curiously, the real documents including this list has been found by historians, and published on the internet. Check out the real list of Isaac Newton's sins here.

Our paper Unification of witnessing initial system-environment correlations and witnessing non-Markovianity has appeared in Europhysics Letters. Previously mentioned here.

Our other related paper, titled Dynamical role of system-environment correlations in non-Markovian dynamics has been published as a Physical Review A: Rapid Communitcation. Paper previously mentioned here.

From Saturday Morning Breakfast Cereal.

Our paper Unification of witnessing initial system-environment correlations and witnessing non-Markovianity has been accepted for publication in Europhysics Letters!

Related post about this paper can be found here.