Discord on Nature

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
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?

Quantum Crypto School for High School Students

Are you a High School Students interested in Quantum Mechanics and Cryptography? You should attend to this summer school in Waterloo!

The Quantum Cryptography School for Young Students (QCSYS) is an exciting week-long program offered to students in Grades 10-12. This year the program will run through August 8-12, 2011. The program is run by the Institute for Quantum Computing in conjunction with the University of Waterloo.

Students will be given a first-hand look into one of the most exciting topics in contemporary science – quantum cryptography. Not only will students be exposed to cutting-edge topics like quantum physics and cryptography – they will have the opportunity to meet some of the most renowned researchers the field has to offer. In addition, students will get a tour of quantum computing and quantum cryptography experiments.


“It is thermodynamics gone mad,” by Lord Kelvin, one of the founders of thermodynamics, commenting on Boltzmann’s derivation of Stefan’s law.

‘Lazy States’ accepted in PRL

Our latest paper Lazy states: sufficient and necessary condition for zero quantum entropy rates under any coupling to the environment has been accepted for publication in Physical Review Letters. Woohoo!

Lazy states: sufficient and necessary condition for zero quantum entropy rates under any coupling to the environment

We find the necessary and sufficient conditions for the entropy rate of the system to be zero under any system-environment Hamiltonian interaction. We call the class of system-environment states that satisfy this condition lazy states. They are a generalization of classically correlated states defined by quantum discord, but based on projective measurements of any rank. The concept of lazy states permits the construction of a protocol for detecting global quantum correlations using only  local dynamical information. We show how quantum correlations to the environment provide bounds to the entropy rate, and how to estimate dissipation rates for general non-Markovian open quantum systems.

I had the feeling that, through the surface of atomic phenomena, I was looking at a strangely beautiful interior, and felt almost giddy at the thought that I now had to probe this wealth of mathematical structure nature had so generously spread out before me.
-Heisenberg

International Journal of Quantum Information Call for Papers: Quantum Correlations: entanglement and beyond

Kavan Modi has asked me to share this call for papers for a special issue. It looks very exciting indeed.

CALL for PAPERS (Special Issue)
INTERNATIONAL JOURNAL of QUANTUM INFORMATION
Quantum Correlations: entanglement and beyond

GUEST EDITORS
Shunlong Luo (Chinese Academy of Sciences, CN)
Sabrina Maniscalco (Heriot-Watt University, Edinburgh, UK)
Kavan Modi (National University of Singapore, SG)
G. Massimo Palma (University of Palermo, IT)
Matteo G. A. Paris (University of Milano, IT)

Quantum correlations have been the subject of intensive studies in the last two decades, mainly due to the general belief that they are fundamental resources for quantum information processing and other
tasks in quantum technology. The first rigorous attempt to address the classification of quantum correlations was put forward by Werner, who formalized the elusive concept of quantum entanglement. More recently, other quantities, as such quantum discord, have been proposed to capture different aspects of the quantumness of correlations. In parallel, several applications where quantum, classical, hybrid correlations play a role have been suggested and implemented. Among them we mention quantum imaging, interferometry, state engineering, computing and entanglement-assisted quantum measurements.

This special issue is aimed to collect papers addressing both fundamental problems and applications, thus offering to readers comprehensive and up-to-date overview on the characterization and use
of quantum correlations.  We welcome papers that address fundamental aspects of quantum and classical correlations in discrete and continuous variable systems, propose implementations to make
quantitative measurements of quantum correlations, or describe experiments that exploit quantum correlations as a resource for quantum technology.

Possible topics include, but are in no way limited to: characterization and measurement of entanglement and quantum discord, discrimination of classical and quantum correlations in quantum systems, applications of quantum correlations to quantum technology, dynamics of quantum correlations in open systems, decoherence, metrology, error correction.

Manuscripts should be submitted to matteo.paris@fisica.unimi.it with subject “[QCSPE] and must meet the normal refereeing standards of IJQI.

LaTeX is the exceedingly preferred format, IJQI macros are available at
http://www.worldscinet.com/style_files/ijqi/187-readme_2e.shtml
Deadline for submission is May 15th 2011. Publication is expected within 2011.

Sincerely,

Kavan Modi, PhD
Centre for Quantum Technologies
National University of Singapore


“It is thermodynamics gone mad,” by Lord Kelvin, one of the founders of thermodynamics, commenting on Boltzmann’s derivation of Stefan’s law.

Royal Society Podcast

The Royal Society has a podcast! Both in Audio and Video versions.

Each podcast is well produced and features a famous scientist or popularizer giving a short but entertaining lecture, or a scholar discussing the history behind some famous member of the Society. I love them!

it comes first to fluidity, then to orbiculation, then fixation, so to angulization, then crystallization, from thence to germination or ebullition, then vegetation, then plantanimation, perfect animation, sensation local motion, and the like
-Gimcrack, making fun of Robert Hooke

Yakawow! Deconstructing science-news articles

This hilarious meta-article deconstructs everything that is bad about science writting in news-sites.

it comes first to fluidity, then to orbiculation, then fixation, so to angulization, then crystallization, from thence to germination or ebullition, then vegetation, then plantanimation, perfect animation, sensation local motion, and the like
-Gimcrack, making fun of Robert Hooke