Tuesday, May 17, 2016

News about entropy



Did you know that you have been calculating entropy incorrectly during your whole life!   This is at least what I claim to be true in a recently published paper titled: "A consistent flow of entropy."

A common approach to evaluate entropy in quantum systems is to solve a master-Bloch equation to determine density matrix and substitute it in entropy definition. However, this method has been recently understood to lack many energy correlators. The new correlators make entropy evaluation to be different from the substitution method described above. The reason for such complexity lies in the nonlinearity of entropy. In this paper we present a pedagogical approach to evaluate the new correlators and explain their contribution in the analysis. We show that the inherent nonlinearity in entropy makes the second law of thermodynamics to carry new terms associated to the new correlators. Our results show important new remarks on quantum black holes. Our formalism reveals that the notion of degeneracy of states at the event horizon makes an indispensable deviation from black hole entropy in the leading order.

This is a my contribution to special issue in Fortschritte der Physik for the Frontiers of Quantum and Mesoscopic Thermodynamics Conference. Link: arXiv:1605.04620

By: Mohammad H. Ansari

Thursday, February 11, 2016

Hearing a sound from a billion years ago!


Today is a day for cheering. After many years gravitational waves have been finally reported to have been detected. In two separate detectors, in west and east coasts of the US, almost simultaneously it was detected that earth got shrunk a tiny bit from a gravitational curving pulse. Many researchers have been sweating for decades to make these detectors happen.

Let me explain what has been discovered. An early approval for the theory of general relativity in 60's was based on the following fact: the presence of a heavy object, like our sun, will causes its surrounding spacetime to be curved. This has been observed from the following experiment: the straight path on which light travels in the universe from A to B, if passes adjacent to a heavy object, will bend a bit toward the object, thus the path will not remain a straight path anymore.

Now, consider two heavy objects crazily rotate around one another with a crazy speed (a half of speed of light). Right before they merge they make a lot of ups and downs in the spacetime in between. This turbulence in the very spacetime fibres propagate to others places, similar to how tsunami waves propagate in the ocean. In other words, gravitational field is self-interacting; this means that it sources itself. It curves the space around itself because it carries mass/energy by itself much like a star does.

If the objects are many light years away, the waves passing through the Earth today makes a bit of stretches and squeezes in the radius of earth, something of the size of less than the radius of proton! This has been detected last year at LIGO detectors and today was reported, and peer reviewed already in the PRL.

From what they received we assume that the waves came from two 30-solar-mass black holes curling up around one another in a death spiral, a billion light-years away from us. This is a better-than-expected source for LIGO and sometimes the universe is nice to us!  In fact a billion years ago two heavy stars fell in love with one another and played hand in hand like kids, and today we got a bit of their happy sound!  Doing such an amazing science is similar walking a tightrope between surly curmudgeon and starry-eyed cheerleader. 
  
The last thing to notice: If you are sad you do not get cited more often, apparently Einstein’s prediction of gravitational waves has been cited only a few times!

By: Mohammad H. Ansari

Monday, January 25, 2016

APS March Meeting 2016


I'll be chairing a session in the upcoming American Physics Society March Meeting 2016 in Baltimore, USA. The session is focused on Quantum Information and Thermodynamics.

Below you can find the session information. I invited some notable young scientists whose contribution to quantum physics have been impressive in the last year.

Looking forward to run an impressive focus session!

  http://meetings.aps.org/Meeting/MAR16/Session/R44

 Mohammad H Ansari

Thursday, December 24, 2015

Abdolali Ansari 1931-2015


My father passed away yesterday 22 Dec 2015 after a rather short period of age-related illness. He was 84. My father, Abdolali, was a college president and teacher in Kermanshah. He spent most of his efforts to boost up the education quality of the college Daneshsaraa-ye Aali of Kermanshah (college for teacher training). Sometimes, only for joy of it, he contributed to teach geometry, mathematics, and literature. He loved to share his knowledge with his pupils.

Before joining the college he has experienced many other activities such as the business of Giveh, a traditional type of footwear woven by silk and cotton for daily use in western Iran. Nowadays this business is in the hand of my uncles. At age 20, not satisfying from business, he passed an exam and was accepted to enter medical school in Tehran. After a short time he decided to change the field into science educational school for which he and his family of wife and two daughters moved to Tehran.  Four years later he received the degree from one of the best universities in tehran and moved back to Kermanshah to help establishing a modern college named Daneshsaraa-ye Aali of Kermanshah, he was president of the college for more than 20 years.

On weekends of my intermediate school days, one of my best hobbies was to go beyond the geometry of school books. I had a wonderful teacher at home playing with the roses and other flowers of our house yard. I was going to him asking whether he likes to teach me and his response was always with a flame of joy in his eyes. Sometimes we were working more than 5 hours together on different aspects of mathematics, I was sitting next to him working on paper with compass, set square, protractor, drawing lines and curves for proving theorems he was assigning to me. On top of methods, such as how to partition an angle into three with compass, the joy of discovery was what I learned the most  from him.

After retiring from the college, he started a new career at  Razi University in Kermanshah shortly before our entire family move to Tehran. In Tehran, he started another careers in finance, working everyday until the age of 75, not that he needed, only because he loved to work. At this age he started to reduce his activities and stayed mostly at home, yet he was still the source of hope for us. In all ups and downs when I was sharing what is in my chest to him, he could sparkle my mind with the burst of a wise word. This was what I needed to be cheered up.

Abdolali Ansari left behind thousands of students some of whom are nowadays the most influential people in their profession.

God bless you daddy. I am happy that you are eternally home. God bless you...

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Tuesday, September 15, 2015

Let's move to physical quantities: Keldysh Green functions!


Yuli Nazarov: [I] remember a talk given by a high-class theorist with a taste for abstract models, young experimentalists being his primary audience. Somewhere in the middle of the talk he said: "Now let us move to physical quantities, namely, Keldysh Green functions". A burst of laugh lasted for more than five minutes!

For many years Keldysh formalism was considered too much complicated for a practical researcher and hardly applied beyond several specific fields. "Keldysh approach" sounded as a synonym of unnecessary theorization and an antonym to clear physical reasoning.

Excerpts from:

Keldysh formalism for multiple parallel worlds
Abstract:
We present here a compact and self-contained review of recently developed Keldysh formalism for multiple parallel worlds. The formalism has been applied to consistent quantum evaluation of the flows of informational quantities, in particular, to evaluation of Renyi and Shannon entropy flows. We start with the formulation of standard and extended Keldysh technique in single world in a form convenient for our presentation. We explain the use of Keldysh contours encompassing multiple parallel worlds In the end, we shortly summarize the concrete results obtained with the method.

Mohammad Ansari and Yuli V. Nazarov
arXiv/1509.04253

(Submitted on 14 Sep 2015)

It is a big honour for us to present these results in a special issue celebrating numerous scientific merits of Leonid Veniaminovich Keldysh. We gladly appreciate his pioneering research that provided a powerful and indispensable tool for many generations of quantum physicists, us including, and wish him many happy returns of the day.