LWP: Quantum memory with a single two-level atom in a half cavity

by Y. Wang, J. Minar, G. Hetet, and V. Scarani.
Physical Review A 85, 013823 (2012)

Wang and collaborators show that it is possible to store a single-photon pulse in a two-level atom within a half cavity setup where the decay rate between the atom and the light is controlled by motion of the one mirror in the half cavity.

A dipole-field interaction leading to optical Bloch equations from Heisenberg picture is used; the effects of the half-cavity are encoded in a term accounting for decay  into the half-cavity (pulse) mode, decay and noise introduced by the environment are also taken into account. Assumptions include: Markov approximation (long half-life times compared to light's round-trip between atom and mirror), small mirror motion (of the order of a wavelength) leading to neglect amplitude changes in time scales smaller or equal to a round-trip time—but this cannot be assumed in the phases due to the importance of interferences in the sysme— 

The probability of the two-level system absorbing a single-photon wave packet is found and a suitable decay function is given that maximizes such probability. Storage is achieved by placing the atom at a node of the half-cavity system. Then, the emission efficiency is calculated and a decay rate is defined which controls the temporal shape of the outgoing single-photon pulse. The authors present simulations for a sampling of time-bin single-photon pulses and their respective control decay-rate leading to high fidelity storage and possible implementations of their protocol.

The article is didactic in its presentation and the topic is quite interesting. I was not familiar with half-cavity schemes and this manuscript presents a nice survey of references in the topic. I hope experiments using their protocol follow soon.

The Black Swan by Nassim Nicholas Taleb

The Black Swan written by Nassim Nicholas Taleb deals with the impact of the highly improbable—the actual subtitle of the book—in the real world. The title comes from the fact that one single event is enough to prove a theory wrong; in this case the European theory that all swans were white previous to the discovery of Australia and black swans.

I really hated/loved the book. The mean reason for the first was the introduction of an example in the person of a writer—which I couldn't find in Google—that made me believe that Dr. Taleb was some kind of literary conman creating a fake narrative to advance his ideas. I felt betrayed. I like confidence games but I don't like being conned by an author while dealing with a serious topic. Good thing is that later, in a footnote, it is made clear that the author/example was mere fiction, a gedankenexperiment. Then, I came to love the book: It is an anecdotal narrative denouncing our weakness and inclination for anecdotal, causal narratives that blinds us from the skeptical, empirical analysis of events in economics, history, sociology and other human endeavors to understand our  non-ideal selves, societies and surroundings. I think I can construct another paradoxical phrase like the latter: In parts, t is a name dropping exposition denouncing name dropping expositions. 

I found many things to like from the manuscript—a flowing prose filled with real and imaginary examples, an ample reference and bibliographical section (almost one third of the electronic version)—and just one to dislike: I felt the first two parts became repetitive.

The ideas are sound, our actual knowledge does not allow us to simulate realistic scenarios to provide accurate predictions and, most probably, you and I will be long dead when, if, such an exercise becomes feasible—think about Assimov's psychohistory in Foundation *wink*.

Is there a way to predict the future when it comes to phenomena that belong to the so-called Extremistan (most of the modern real world)? No.

Then, what's the use of knowing that? Awareness, there are infinitely many things we don't know that could affect us, but one we can try to control: our actions and, thus, our exposure to those unknown.

It's a great book, try it. I even see it as a kind of philosophy of life. I am really thankful to my brother Andre for suggesting it to me. I think that I would not have picked it up by myself.

I, the media consumer...

The life and times of a starving vagabond is many things and nothing at all. It is an attempt to practice English, which allegedly is my second language. Sometimes it is a conduct to free my shoulders through cathartic ranting or disjointed—but therapeutic—narrative. Most of the time, it is just about post-consumption impressions.

While the starving part of the blog's title comes from a story of two close-friends (cousin Shaggy and I) driving through Mexico without much money and eating boiled potatoes and eggs, cheese and hard bread for one week, it also reflects my urge for consumerism and consumption of narratives in any given media format. I hunger for stories presenting diverse points of view that may—or, most probably, not due to my intrinsic stupidity—widen my perspective on the condition of being human.

Being human is so amazing, so different: there's almost 7 billion different ways of being human in the present; plus some three or four billion death ways of being human since the beginning of homo sapiens. Can a single individual experience the whole spectra of humanity? My answer is no, being human is a conjunction of the person, his/her ideas and actions, people interacting with him/her (with their ideas and actions), surroundings and the succession of random events that, all together, I come to call life.

In recent years, I have become a consumer of other people's points of view and have got it with mine. Curiously, I have started to find more and more taxing—and kind of useless—to be in social gatherings where there are so many people that makes it impossible to have a true dialogue leading to the exchange of opinions. I find myself leaving parties with small pieces of information from this or that person and end up reconstructing a story that has my point of view inherently embedded. I want to learn what you think about love, honesty, ethics, vengeance, religion, death and whatnot. I don't want to reconstruct your ideas through dilute and disjoint one minute burst of conversation and end up creating what I think is your narrative from my point of view. I rather read, listen or watch them whole in media. Thus, my consumerism—my desire to gather and collect enormous quantities of information—is born.

Trying to turn my consumption of media for the better, I use it to practice my English and synthesis skill. I'm not trained in aesthetics nor semantics, thus my reports on the consumed works are nothing but online dumps of impressions left on me by them—and a sorry excuse to use English in a non-scientific context—. Anyway, I hope the Last Weekend Movies or Last Month Book series of posts help you choosing a film, tv-series or book to kill time with.

Last weekend movies (4th week 2012)...

This was a nice long weekend that I'm sure is gonna remain unchallenged in my personal annals of laziness for years to come. It also was a weekend of independent cinema...

1. Fright Night, ****
   It has been ages without a vampire movie! This is a reboot of a 80's film with the same name. A vampire comes to town and its teenage neighbor has to fight it to protect his loved ones. One star is pure euphoria for finding a horror movie that involves mythological creatures and not a human serial killer.
   
   
2. Beginners, ****
   A man's life after the death of his father trying to construct a relationship— fighting his impulses to always run away—while dealing with the past; his father came out the day his mother died and his take on the family makes him evade relationships. This is a great and dramatic romantic comedy. The characters are so fresh and lovable. And the pace is just perfect to get soaked with the photography and the music.
   
   
3. Our Idiot Brother, ****
   Ned is a naive, honest, kind and idealist man who always tries to empathize with the neighbor (I like the Spanish word "prójimo" more but there exist no English equivalent) but manages to always screw things up, or so it seems like. The topic, honesty and idealism, really got me. It is a fresh and elegant comedy of situations with a big human factor on it. 
   
   
4. Lucky, ***
   A newbie serial killer inherits a winning lottery ticket from one of his victims and his newly won money gets the attention of his childhood love. They get married and manage not to kill each other for a few weeks. It has been ages since I watched a dark comedy and this one really got me smiling, it lacks a great script but it is morbid and funny enough.
   
   
5. Texas killing fields, ***
   There's a serial killer on the loose in rural Texas and two cops get emotionally involved in the case. This crime drama is loosely based on a real case. The story is so dark that the film doesn't manage to show it most of the time, nevertheless the photography is good and the takes of the Texas bayou managed to give me the chills.
   
   
6. The Art of Getting by,  ***
   A lonely teen has to find himself or flunk high-school. I liked the opening: "you are born alone, you will die alone" which is a chopped paraphrase of Orson Welles'  "We are born alone, we live alone, we die alone. Only through our love and friendship we can  create the illusion for the moment that we are not alone." The rest of the movie can be considered an audio-visual rendition of the rest of Mr. Welles' phrase.
   
   
7. The Son of No One, *
   A young cop is haunted and hunted by ghosts of his past when he killed two men. The crimes of past and present intertwine in this not so much of a thriller with the background of 9-11. It's a good idea but I guess you need to have some context that I lack to really appreciate the movie.
   
   
8. Lone Wolf and Cub 6, *
   This film should have a three or four stars rating but I watched the first five parts in the last two weekends and the memory of them are too fresh in my mind. The lone wolf finally faces his rival the Ura-Yagyu and nothing happens. C'mon! Give me an ending! I read somewhere that they are planning a new movie for the series with possible release date in 2014.

What is happening with the television series, I have never followed a season in the past and it is very annoying that during this month some of them have been going in and out...

1. Last Man Standing S01-E14, ****
   Mike screws it big time with the neighbors thanks to his honesty, leading to troubles with his socially active wife. In the end, well, Mike's proven right.
   
   
2. Castle S04-E12, ****
   The shadows behind power reappear to keep the mayor of New York from running for governor and keep Beckett out of her mothers case.
   
   
3. Hawaii Five O, (no episode?)
   
   
   
4. Big Bang Theory, (no episode?)
   
   
   
   
5. Psych, (not yet back?)
   
   
   
   
6. Phineas and Ferb S01-E01-46,  *****
   
   This is a simple, ten minute long cartoon, about two creative and industrious kids trying to spend summer at their best and their teenage sister trying to bust their plans. It's so innocent and creative and full of stories in just 10 minutes. I really liked it, it just made me laugh again and again.
   
   
7. Game of Thrones S01-E01-10, (mini-series)  ****
   
   Winter is coming! A land where winter brings shadows and horrors is involved in incestuous political intrigue and in the verge of an all out war. Stage and wardrobe design are awesome, the characters have personality and deepness. I only didn't like the slow pace at the beginning but then the epic scale of the plot may need such a pace to develop.
   
   
8. Falling Skies S01-E01-10, (mini-series) ****
   
   An alien vanguard has taken over the earth and a ten percent of the original population survives. Some of these survivors have organized in a resistance trying to figure a way to bring the fight back to the aliens. Great effects, great alien designs, good episode progression, crappy season finale.
   
   
9. The Borgias S01-E01-09,  (mini-series)  **
   
   Rodrigo Borgia has been elected pope Alexander VI and the Borgia family reaches the apex of their political station which is gonna last just a few decades. A free take on the historical Borgia family and its influence in the geopolitics of the Papal States and Mediterranean Europe during the Renaissance. Jeremy Irons plays the role of Rodrigo Borgia! Awesome wardrobe and locations. I was not so happy with the episode design, it didn't manage to get me interested long enough but good to remember the old history lessons from high-school.
   
   

Sadly, we didn't have any Audrey Hepburn due to the fact that my cousin got married and Lyx went to the wedding but we are already planning next weekend. 

LWP:Absence of vacuum induced Berry phases without the rotating wave approximation in cavity QED

by Jonas Larson
Physics Review Letters 108, 033601 (2012)

Some ten years ago, Berry phase was studied in the Jaynes-Cummings model. In this paper, Larson focuses on proving that such a geometric phase arises from the use of the rotating wave approximation.

First, Larson reviews the results fro the Jaynes-Cummings model, that is, under the rotating wave approximation, and derives the accumulated Berry phases by exact diagonalization of the Hamiltonian. Then, he presents a semiclassical approximation derivation by using canonical operators for the field and Born-Oppenheimer approximation to obtain a pair of adiabatic potentials that lead to semiclassical conical energy surfaces giving a Berry phase which is identical to that given by the exact calculation for large photon number. 

Once the validity of this semiclassical approximation is provided by this example, Larson uses the same method to find the semiclassical energy surfaces for the case without the rotating wave approximation, that is, Rabi Hamiltonian, and shows that these surfaces lack the conical intersection that gives a non zero Berry phase. Actually, the semiclassical energy surfaces for this case intersect along the line given by x=0 instead of just a point. It is noted that the author carried a numerical diagonalization of the Hamiltonian and the results were confirmed.

Furthermore, Larson revisits a lambda-atom configuration where a Raman coupling scheme is used and shows that by assuming far detuned driving fields such that adiabatic elimination can be carried on, without any rotating wave approximation, the semiclassical energy surfaces for the system do not intersect at a single point and Berry phase must be zero all the time.

He also discusses the case of a single atom in a bichromatic cavity and shows that within the used semiclassical formalism there are no vacuum induced Berry phases. A trio of other systems are presented with the same result: no Berry phase when the rotating wave approximation is not used.    

It concludes, that the presence of a Berry phase in the Rabi model and other models discussed (adiabatic elimination, bichromatic cavities, etc) in the paper is a result of introducing the rotating wave approximation and not inherent to the models. Thus, a flag is raised: whenever Berry phase is the subject of study one has to be mindful of the approximations used independently of the coupling regime at hand. It may be even possible that this result may change if a multi-level approximation is taken instead of the typical two-level restriction of the Rabi model. It also points the interest of studying vacuum induced Berry phase in nonadiabatic processes. 

This is a very nice paper to read, it presents a concrete, straight to the fact introduction of geometrical phases in cavity-QED and the results are presented in a clear manner. If you are a fan of the Jaynes-Cummings model, you cannot leave this article unread.