I am an atheist

I believe in seeking truthful answers to the most fundamental questions regarding human existence, questions such as:

Where does the Universe come from?

Is there life after death?

How should we treat the people around us?

What is the path towards true happiness?

I do not want to be wrong in my answers to these questions, and frankly, I do not think anyone wants to be mistaken. How we answer these central questions determines, to a great extent, how we live our lives.

Historically, however, they have been often condensed into a single question, arguably the most fundamental of all:

Is there a God?

Even as a child I could recognize the importance of this question, because I could easily see how much was at stake with the answer. For as long as I can remember, I approached this question with the utmost seriousness. I have thought about it for years, objectively hearing arguments from both sides, debating them in my head and with other people. I have also read many books and essays on the subject, and I have collected evidence in favour and against God’s existence, which I analysed carefully.  After this investigation, my firm verdict is that there is no God. By definition, this makes me an atheist.

But this post is not about why I am an atheist, it is about who I am as an atheist. I think that it is not an exaggeration to state that the majority opinion across the world is that atheists are despicable people: immoral, dangerous and untrustworthy. The wikipedia page on discrimination against atheists provides a thorough collection of historical and contemporary examples, but as an illustration, I provide a few here as well.

There are 13 countries where atheism is punishable by death.

Atheists are the most hated demographic in Brazil.

There are seven states in the USA that ban atheists from holding public office.

In view of facts like this, it should come as no surprise that many atheists are closeted: they internally hold the belief that God does not exist, but are unwilling to state it publicly and openly. See this reddit post for striking examples. Admitting to being an atheist usually sparks rejection from family and friends, it can lead to persecution and insult, and it may have negative consequences for a person’s career. Being openly atheist is frightening and difficult, but it doesn’t have to be. There is nothing shameful or reproachable about believing that there is no God, specially when that belief is held after a process of careful and objective consideration.

As an atheist, I treat people around me with respect, compassion and kindness, not because I am instructed to do so by a figure of authority, but because I understand that this makes my life better, as well as the lives of those around me.

As an atheist, I listen carefully to people’s opinions and arguments because I am interested in knowledge and truth. If I am proven wrong, I will gladly admit it, even if this requires me to abandon a cherished belief I have held for many years.

As an atheist, I do not discriminate others based on their gender, race, sexual orientation, country of origin or religion, because I know that these differences are historical and mostly accidental. All human beings are capable of enjoyment as well as suffering, and I believe it is best when we strive to increase everyone’s happiness and minimize their misery.

As an atheist, I am convinced that what awaits us after death is exactly the same as what we experienced before birth: absolute nothingness. This makes our finite existence even more valuable and precious, and makes it urgent that we appreciate every second we are alive while allowing others to do so as well.

As an atheist, I recognize that many of the events that occur on Earth are due directly to human activity, and are not the consequence of intervention from a supernatural agent. This means that human beings have the ability to achieve extraordinary feats, which we should continue to perform, but we also have the responsibility of  preventing  awful ones from happening.

As an atheist, I see the striking similarities between all living organisms on the planet, and I think that they deserve the same treatment, respect and protection that human beings do.

As an atheist, I am marvelled by the vastness and beauty of the cosmos, but mostly I am amazed by our ability to comprehend it. I find more awe and allure in the properties of neutron stars, the neural pathways that control emotions, and the rules of quantum mechanics, than I have ever found in religious mythology and mysticism.

As an atheist, I know that we can have goodness, fairness, respect, love and understanding without invoking the existence of an omniscient and almighty being.

As an atheist, I admit that I have many flaws, many of which are hard to overcome: I am forgetful, I can be very messy as well as irresponsible, I don’t always manage to speak clearly, I can sometimes be insulting and harsh, and I often fail to be helpful when I have the chance.

Overall, I am just another human trying hard to become a better person each day, to be happy and to have a positive impact on the world. I also happen to believe that God does not exist.

Does being an atheist make me a bad person?

Is being an atheist something I should be ashamed of?

Is being an atheist something I should be afraid of admitting?

Absolutely not.


I thank my Aleks for helping me obtain the strength that I was lacking during most of my life.


Let Colombia’s scientific history begin

I used to think that, in order to be a scientist, one also needed to be a rebel. I used to think that people who dreamt of becoming scientists also needed to be brave and, above all, have the strength to go against the thousands of voices who, wrongfully, keep advising them to take different paths. I used to think that becoming a scientist meant driving in the opposite direction, accelerating as fast as possible, with the conviction that everyone else was headed the wrong way. But now I understand that this is only true in places like Colombia.

A few years ago, I was having lunch with a few PhD students from the Centre for Theoretical Physics in the ETH in Zürich, Switzerland. Innocently, I commented that I had always thought it weird that none of the scientists I knew had parents who were also scientists.  As soon as I finished my sentence, two of the students immediately reacted:

– Then, I’m the first one. My dad’s a physicist!

– Hey, mine too!

Amongst the five people sitting at that table, 40% had at least one parent who was a scientist. Incredible. After thinking about it for a few minutes, I realized that I only knew the professions of my friends’ parents in Colombia. They were medical doctors, engineers, architects… But none of them were scientists.

In fact, the majority of scientists my age come from families of scientists. For example, my officemate’s father is a biology professor at the University of Alberta, the father of a friend in the office next door is the director of the Institute for Quantum Science and Technology in the University of Calgary, and the list goes on. In the world of research, Colombia’s case is the exception, not the rule.

During my undergrad in physics in Bogota, I would constantly hear the following questions being frequently asked to any aspiring scientist:

– What are you planning to do after graduation?

– Pure physics or engineering physics (sic)? Seriously? Pure physics? (As if physics could somehow be impure)

– Are you crazy?

– And what are you going to do with this?

Juan Manuel Pedraza, Professor at the University of the Andes, said the following in an interview:

Juan Manuel Pedraza

Juan Manuel Pedraza

“When I said I was going to study physics, my parents told me: ‘No way, you’ll die of hunger! What are you going to do as a physicist?’ So I told them: ‘OK, I’ll study civil engineering too, so I can live off something later on’.”

Another example? Ana María Rey, Professor at the University of Boulder in Colorado, who was recently awarded a MacArthur Fellowship, also had to fight against her parents’ wishes.

Ana María Rey

Ana María Rey

“I went to the University of the Andes, I must say, without my parents’ approval, who wanted me to study engineering. So I was lucky because I won a scholarship to study physics and that’s when my career began.”

I was lucky because my parents never opposed my academic decision, but I’m sure it was also an act of courage for them to give me their support.  They were as rebellious as I was, for example, when they had to defend me after hearing one of my relatives say: “It’s such a shame to see that Juan Miguel is wasting his intelligence studying physics.”  I simply can’t imagine any Colombian in my parents’ generation saying something like: “I’m so happy, we’re finally going to have a scientist in our family!”

However, I’m not just trying to complain about this difficult situation; I also want to try to explain it. My hypothesis is the following: The adversity that science has to face in Colombia is due, at least in part, to the fact that there is no history of Colombian science.

Why is there so much uncertainty? Why are there so many questions regarding a scientists’ career?  Because almost no one knows of any successful Colombian scientist! There are no precedents; no one is familiar with it. Why are these questions so recurring? How can they be explained? Perhaps in the following way:

What are you planning to do after graduation? Explanation: I have no idea what a scientist does because I don’t know a single one.  I know what a lawyer, an engineer or a medical doctor does; but a physicist… no clue.

Pure physics or engineering physics (sic)? Seriously? Pure physics? Explanation: I’ve only heard of pure physics as a concept, not as a profession.  Or, as a job for people who want to become physics teachers. Do you want to be a teacher?

Are you crazy? Explanation: Only a crazy person would study something I’ve never even heard of. Quantum mechanics? Isn’t that a theory by Deepak Chopra?

And what are you planning to do with this? Explanation: I can tell you’re smart, so I want to give you the benefit of the doubt. There must be a reason why you want to become a scientist, even though I can’t think of any way in which this could be useful. Can you make money out of that? Start a company?

How different things would be if we could refer to existing historical examples, prominent figures of science in Colombia, important discoveries and achievements, all of which could help give perspective to the dreams of aspiring scientists. But such a thing does not exist.

Someone in England can dream of becoming the next Newton. Someone in the United States can dream of becoming the next Feynman. Someone in Serbia can dream of becoming the next Tesla. Someone in India can dream of becoming the next Bose. Someone in Poland can dream of becoming the next Marie Curie. Someone in Argentina can dream of becoming the next Maldacena. Someone in Colombia can dream of becoming the next… who? Actually, no one.

The next Garavito? Give me a break.

The next Garavito? Give me a break.

 The history of science in Colombia must start some day, preferably soon.

Why do I insist on science? Why is science so special compared to the many other academic fields? Because science gives us the tools to understand and manipulate nature, and this knowledge is the starting point of technological and economic development. 

It’s a simple formula: scientific research leads to discoveries, which are transformed into new technologies. Then, these new technologies result in economic growth. And all this comes with the added benefit of providing us with a better understanding of the universe and our place in it. Wonderful.

Investing in research is one of the smartest decisions a government can make. You don’t believe me? Take a look at the following chart:

Ranking of countries in terms of investment in research and development, as a percentage of GDP.

Colombia: 0.16%

And now let’s compare it with these countries’ ranking in terms of GDP per capita:

  • Israel: $34.770 (ranked 25th in the world)
  • Finland: $35.617 (ranked 24th in the world)
  • Sweden: $41.188 (ranked 13th in the world)
  • South Korea: $33.189 (ranked 27th in the world)
  • Japan: $36.899 (ranked 22nd in the world)
  • Denmark: $37.900 (ranked 19th in the world)
  • Switzerland: $46.430 (ranked 7th in the world)
  • Taiwan: $39.767 (ranked 16th in the world)
  • United States: $53.101 (ranked 6th in the world)
  • Germany: $40.007 (ranked 15th in the world)
  • Colombia: $11.189 (ranked 85th in the world)

Investing in research generally leads to economic prosperity and social well-being. It’s really that simple.

As for my own area of research, quantum information, the Canadian government invested millions of dollars in the Institute for Quantum Computing – where I work – with the goal of placing it as the leading research centre of its kind in North America. Recently, the government of Great Britain announced a 270-million-pound-investment in quantum technologies. Other countries, such as Singapore, China, and Australia, have made similar investments over the years.  If the technologies that may arise from these endeavours (quantum computers, quantum sensors, and quantum cryptography) manage to have a strong economic impact, these countries will benefit immensely. Colombia will not.

A few weeks ago, when the world cup ended, millions of people dressed in yellow jerseys were screaming that Colombia had made history because it had reached the quarterfinals of the tournament for the first time.  But now that the party is over, it’s easy to realize how little impact a sport has in changing the course of a country. Colombia is a place with a rich history in politics, sports, culture and the arts. But it doesn’t have any scientific history.

My friend Juan Diego Soler says that: “Someone with a PhD in Colombia is like a dog who can drive the Transmilenio (i.e. Bogota’s ironically-named bus system)… no one knows how he achieved it and no one knows what to do with him.” This has to change. It’s time to ask the Colombian government to invest in science. It’s time to support all aspiring scientists. It’s time to read and learn about the great achievements of science. It’s time to leave the past behind, learn from uncountable mistakes and transform the country. It’s time to start making history, the type of history that really matters.


This post was brilliantly translated and greatly improved with the help and talent of my loving spouse, Aleksandra Ignjatovic. She continues to improve my life in ways I never anticipated.


Que comience la historia científica de Colombia

Yo solía pensar que para poder ser un científico, se necesitaba también ser un rebelde. Solía creer que para cualquier joven con el sueño de hacer ciencia, era necesario tener coraje y sobre todo, tener la fortaleza de ir en contra de las miles de voces que perjudicialmente aconsejan tomar caminos diferentes. Solía pensar que para ser un científico había que marchar en contravía, con el pedal a fondo, con la firmeza de que son todos los demás los que andaban en la dirección equivocada. Pero ahora entiendo que esto sólo es cierto en lugares como Colombia.

Hace un par de años estaba almorzando con varios estudiantes de doctorado en el Centro de Física Teórica del ETH en Zürich, Suiza. Inocentemente comenté que siempre me había parecido curioso que ninguno de los jóvenes científicos que conocía tenía padres científicos. Al terminar mi frase, dos de los estudiantes inmediatamente comentaron: “¡Entonces yo soy el primero, mi papá es físico!”, “¡El mío también!” En una mesa de cinco personas, el 40% tenía un padre científico. Increíble. Después de un par de minutos de reflexión entendí que sólo conocía la profesión de los padres de mis amigos en Colombia: médicos, ingenieros, arquitectos, pero nunca científicos.

Por el contrario, ahora que presto más atención, me doy cuenta que el caso de Colombia es la excepción, no la regla. La mayoría de científicos de mi edad vienen de familias de científicos. Por ejemplo, el padre de mi compañero de oficina es un profesor de biología en la Universidad de Alberta, el padre de un amigo en una oficina contigua es el director del Centro de Ciencia y Tecnología Cuántica en la Universidad de Calgary, y la lista continúa. En el mundo de la investigación, el caso de Colombia es la excepción, no la regla.

Durante mis años de pregrado en física en Bogotá, escuchaba constantemente las siguientes preguntas frecuentes para cualquier aspirante a científico:

– ¿Qué va a hacer después de que se gradúe?

– ¿Física pura o ingeniería física? ¿En serio física pura? (Como si la física puediese ser impura)

– ¿Está loco?

– ¿Y eso para qué sirve?

Ese tipo de preguntas son las voces a las que me refería, la corriente contra la cual la rebeldía debe luchar. Y no piensen que fue sólo mi experiencia. En una entrevista a Juan Manuel Pedraza, profesor de la Universidad de los Andes, él nos cuenta lo siguiente:

Un ingeniero menos.

Juan Manuel Pedraza.

Cuando dije que iba a estudiar física mis padres me dijeron “¡no! se va a morir de hambre, ¿qué va a hacer usted de físico?”… entonces yo dije “bueno, hago ingeniería civil también, como para vivir de algo después”.

¿Otro ejemplo? Ana María Rey, profesora de la Universidad de Boulder en Colorado, quien recientemente fue galardonada con una beca MacArthur, también tuvo que luchar contra los deseos de sus padres.

Ana María Rey.

Ana María Rey.

Fui a la Universidad de Los Andes, puedo decir que sin la aprobación de mis papás, que querían que estudiara ingeniería, así que estuve de buenas porque me gané una beca para estudiar Física y ahí comenzó mi carrera

Yo he sido  afortunado porque mis padres jamás se opusieron a mi decisión académica, pero estoy seguro que para ellos también fue un acto de valentía  darme su apoyo. Han sido ellos tan rebeldes como lo he sido yo, por ejemplo, al defenderme luego de escuchar a uno de mis familiares decir “Qué lástima que Juan Miguel desperdicie su inteligencia estudiando física”. Simplemente no me imagino a ningún Colombiano en la generación de mis padres diciendo “¡Qué alegría, por fin vamos a tener un cientíco en la familia!”

Mi objetivo, sin embargo, no es sólo reclamar esta penosa situación, sino tratar de explicarla. Mi hipótesis es la siguiente: La adversidad hacia la ciencia en Colombia se debe, al menos en parte, a que la historia científica de Colombia no existe. 

¿Por qué tanta incertidumbre, tantas preguntas con respecto a la carrera de un científico? ¡Porque casi nadie conoce el caso de un científico Colombiano exitoso! No hay precedentes, no hay entendimiento, no hay familiaridad. Por ejemplo, ¿cómo explicar la frecuencia de las preguntas anteriores? De la siguiente forma:

– ¿Qué va a hacer después de que se gradúe? Explicación: No tengo idea qué hace un científico porque no conozco niguno y nunca he oído hablar de ellos. Yo sé qué hace un abogado, un ingeniero, un médico – pero un físico, ni idea.

¿Física pura o ingeniería física? ¿En serio física pura? Explicación: Yo sólo he escuchado de ‘física pura’ como un concepto, pero no como una carrera. O bueno, una carrera para quienes quieren enseñar física en un colegio. ¿Usted quiere ser profesor?

¿Está loco? Explicación: Solamente un loco podría estudiar algo de lo que jamás he oído hablar. ¿Mecánica cuántica, eso no es una teoría de Deepak Chopra?

¿Y eso para qué sirve? Explicación: Bueno, usted es una persona inteligente, así que le doy el beneficio de la duda. Alguna razón debe tener para querer ser un científico, porque a mi de verdad no se me ocurre para qué puede ser útil. ¿Se puede montar un negocio de eso?

Qué diferente sería si exisitiesen ejemplos históricos, grandes figuras de la ciencia Colombiana, importantes hallazgos y logros que pudiesen poner en perspectiva los deseos de cada joven que soñase con ser parte de la rica historia científica de Colombia. Pero tal cosa no existe. Un inglés puede soñar con ser el próximo Newton, un estadounidense con ser el próximo Feynman, un serbio con ser el próximo Tesla, un joven en la India con ser aún mejor que Bose, un profesor y un estudiante en China con seguir los pasos de Yang y Lee, una niña en Polonia con ser la siguiente Marie Curie, un argentino con superar a Maldacena, y un padre e hijo en Australia pueden soñar con ser como la familia Bragg. Un estudiante en Colombia, por su parte, sólo puede aspirar a seguir los pasos de … ¿quién? No hay nadie en realidad.

¿El próximo Garavito? Deja mucho que desear.

¿El próximo Garavito? Deja mucho que desear.

La historia científica Colombiana debe comenzar algún día, y mientras más temprano mejor.

 ¿Pero por qué insito tanto en la ciencia, qué tiene de especial en comparación a las muchas áreas de la actividad humana en las que Colombia tampoco tiene historia? Porque la ciencia nos brinda las herramientas para comprender y manipular el mundo natural, y este conocimiento es la cuna del desarrollo tecnológico y económico de cualquier país. Es una fórmula simple: la investigación científica produce resultados que se transforman en nuevas tecnologías, y estas tecnologías generan crecimiento económico. Y todo esto con el beneficio adicional de proporcionarnos una mayor comprensión del universo y nuestro lugar en él. Maravilloso.

Invertir en investigación es una de las decisiones más inteligentes que puede hacer un gobierno. ¿No me creen? Miren la siguiente gráfica (en inglés):

Los países que más invierten en investigación y desarrollo, como porcentaje del PIB.

Ranking de los países que más invierten en investigación y desarrollo, como porcentaje del PIB.

Colombia: 0.16%

Ahora comparen con la posición de cada uno de los países en términos de PIB per capita:

  • Israel: $34,770 (puesto 25 en el mundo).
  • Finlandia: $35,617 (puesto 24 en el mundo).
  • Suecia:  $41,188 (puesto 13 en el mundo).
  • Corea del Sur: $33,189 (puesto 27 en el mundo).
  • Japón:  $36,899 (puesto 22 en el mundo).
  • Dinamarca:  $37,900 (puesto 19 en el mundo).
  • Suiza:  $46,430 (puesto 7 en el mundo).
  • Taiwan:  $39,767 (puesto 16 en el mundo).
  • Estados Unidos:  $53,101 (puesto 6 en el mundo).
  • Alemania:  $40,007 (puesto 15 en el mundo).
  • Colombia: $11,189 (puesto 85 en el mundo).

La inversión en investigación produce riqueza económica y bienestar social. Es así de simple. De hecho, el factor de conversión entre inversión y ganancia puede ser extremadamente alto.


 En mi propia área de investigación, información cuántica, el gobierno canadiense ha invertido cientos de millones de dólares en el lugar en el que yo trabajo, con el objetivo de establecer el centro líder en investigación en norteamérica. Recientemente, el gobierno de Gran Bretaña anunció una inversión de 270 millones de libras, y otros países como Singapur y China por varios años han hecho inversiones similares. Si las tecnologías que pueden surgir de estos esfuerzos – computadores cuánticos, sensores cuánticos y criptografía cuántica – llegan a tener un fuerte impacto económico, son estos países quienes se van a beneficiar enormemente. Colombia, por ejemplo, no lo hará.

Hace pocos días, al finalizar el mundial de fútbol, millones de personas con camisetas amarillas gritaban que Colombia había hecho historia con su paso a los cuartos de final. Pero ahora que la fiesta se acabó, es fácil darse cuenta del poco poder que tiene un deporte para cambiarle el rumbo a un país. Colombia es un lugar del planeta con una rica historia política, deportiva, cultural y artística. Pero no hay historia científica.

Mi amigo Juan Diego Soler dice que “Un PhD en Colombia es como un perro que sabe manejar Transmilenio… nadie sabe como lo logró y nadie sabe que hacer con él.” Esto tiene que cambiar. Es el momento de exigir al gobierno que invierta en la ciencia Colombiana. Es el momento de apoyar a todos los jóvenes que aspiran con ser investigadores. Es el momento de leer y aprender acerca de los grandes logros científicos de la humanidad. Es el momento de dejar el pasado atrás, aprender de incontables errores y transformar el país hacia su verdadero potencial. Es el momento de comenzar a hacer historia, la historia que importa de verdad.


La foto que acompaña este blog es cortesía de la hermosa y maravillosa Aleksandra Ignjatovic.

Quantum Quotes

Whenever I attend a talk, I carry with me a blue notebook and a pen. Not trusting my already saturated memory, I use them to write down anything about the presentation that I want to remember. These annotations are usually scientific and technical, but every once in a while, the presenter will come up with a witty remark that I can’t help but to include in my notes.

In this post, I want to share this collection of quotes, overheard at some of the many quantum talks I have sat down in. Whenever possible– i.e. when I actually wrote it down– I will include the speaker’s name next to the quote. Please keep in mind that the sentences are not a literal translation of the words spoken, but only my best attempt at a faithful reproduction.


“Your career path most likely will not be a straight line.” Crystal Bailey.

“Since I’m mostly talking to experimentalists…”

“Free entanglement is like free love, it changed the world.” Nilanjana Datta.

“Infinite precision is a bad approximation.” Ish Dhand.

“To understand the Hong-Ou-Mandel dip, we should think in terms of singlets and triplets.” Barry Sanders.

“Immanants have relevance to the quantum world.” Barry Sanders.

“Shifting problems is a good strategy. Either problems go away or they become someone else’s problem.” Norbert Lütkenhaus.

“We do a theory experiment, of course.” Norbert Lütkenhaus.

“And now quantum mechanics is only in our heads.” Norbert Lütkenhaus.

“Let’s hope there is enough coffee for that!” Norbert Lütkenhaus.

“The uncertainty relation is the monogamy of entanglement.” Renato Renner.

“We don’t do calculations, we just think.” Norbert Lütkenhaus.

“It’s the typical situation, if you see something you don’t expect in an experiment, you just pretend it didn’t happen.” Norbert Lütkenhaus.

“Don’t think that device-independent gets rid of the problem: there is always modelling involved. We cannot avoid engineering best practices.” Norbert Lütkenhaus.

“Not something someone my age or younger should ignore.” Michele Mosca.

“The case for QKD needs to be studied and articulated credibly and clearly.” Michele Mosca.

“I know that entanglement is not going to solve the world’s problems.” Michele Mosca.

“Unconditional security, security based on physics: Vadim (Makarov) can break them. Even if Vadim does not exist, realistic implementations might not have security.” Renato Renner.

“In classical cryptography, it is impossible to quantify the probability that a scheme will be broken. This quantity is not computable.” Renato Renner.

“A plane that doesn’t fly, usually doesn’t crash.” Renato Renner.

“Proof by reconstruction.”

“Any printing device a good guy can build, a sufficiently determined bad guy can build too.” Scott Aaronson.

“It is impossible to make anything fool-proof, because fools are so ingenious.” Krister Shalm.

“Everybody wants it, but nobody wants to pay for it.” (In reference to practical QKD systems.)

“Everything is negotiable (if you have leverage).”

“We are trying simultaneously to determine both what the theory predicts and what the theory is. Are we smart enough to do this?” John Preskill.

“The relative entropy appears everywhere in information theory.” David Reeb.

“Can we store a qubit forever?” Mikhail Lukin.

“Enclanglement.” Maris Ozols.

“Quantical Mechanics.” Maris Ozols.

“It is hard to build a quantum machine that can beat my codes.” Matthias Troyer.

“The resolution to Maxwell’s demon paradox is to interpret all probabilities as subjective.” Renato Renner.

“Some problems are better solved if you take a different approach.” Giannicola Sarpa.

“I’m going to start with a really long motivation.” Ivette Fuentes.

“It’s laughable how easy it is.” Ivette Fuentes.




Contra-causal free will.

Do you have any regrets?

I have made many decisions that, in retrospect, where not the best. Many of these decisions were made after very careful consideration and long periods of debate and scrutiny. This raises an obvious question: Could I have done otherwise?

Intuitively, the answer appears to be yes, I truly could have done otherwise. For example, it is easy to imagine a situation like this: “Today I wore a red shirt that didn’t really match my pants and shoes. That was a mistake. But sure, I could have worn the blue shirt instead. I didn’t, but I could have”. In fact, I don’t think this just aligns with our intuitions, I would go as far as to claim that it is the attitude that most people have towards their own and other people’s past actions. “He could have shot that penalty kick just a few centimetres to the right and we would have won the cup!”, “If I hadn’t kissed her that night, we wouldn’t be together today”.

The problem that I have with this intuition is that whenever I attempt to meticulously reconstruct the precise situation that led to a particular decision, I can’t genuinely imagine an outcome that is any different than the one that actually occurred. In the red shirt example, a moment’s reflection may lead to a train of thoughts like the following: “Now that I think about it, I recall that someone at work had claimed that I was a very conservative person, and I didn’t like the comment. The next day, when looking through my clothes, I remembered this remark and felt the need to prove that person wrong. At that point, I wasn’t thinking of matching my clothes well, but of making a statement in the office, so I opted for the more extravagant red shirt. I then took a glance at the time and realizing how late it was, I hurried to get ready, picking the wrong pants and shoes in the process.”

In this thought experiment, it seems very hard to imagine a situation were you would have chosen a blue shirt. Your actions were heavily influenced by prior events and by particularities of the current situation. Given that you were called conservative and that you woke up late that day, could you really have made a better decision? When we take into account all of the complex historical interactions, the chains of events and the current state of affairs moments before our decision was made, the possibility that we could have done otherwise seems to vanish. Think about the actions you regret. Think of everything that had influenced you back then, think of who you were and what you were experiencing.

Do you still genuinely think you could have done things differently?

In philosophical circles, the notion that human beings could have acted differently is known as contra-causal or libertarian free will. I want to distinguish this from the general discussion on free will, which is fascinating, but significantly more complex. For the interested reader, I recommend reading Sam Harris delightfully concise essay ‘Free Will’, as well as his exchange with Daniel Dennett. This blog post is also a nice summary of some common misconceptions regarding free will.

This post is not about free will. It is about contra-causal free will, and about how we don’t have any of it. Why do I claim so? Simple:

Contra-causal free will is not compatible with the fundamental laws of nature as we currently understand them.

More precisely, for any physical system–and humans are no exemption–its future state is completely determined by initial conditions and the outcome of random events over which the system has no control. In other words, given the state of the universe at some point in time and given the outcomes of possibly truly random events, there is only one possibility for the behaviour of any physical system. This includes human beings, no exceptions. In the face of randomness, which may be quantum in origin, our actions may not be determined or predictable, but by definition, we have no control over them either.

When we intuitively believe our actions could have been different, we are simply envisioning a situation that is also compatible with the laws of nature, so we regard it as a real possibility. The mistake we make is to neglect the initial conditions and influences that, when taken into account, yield only one possible series of events. If I hadn’t been thinking about not being conservative, I could have opted for a blue shirt. Except that I was thinking of not being conservative. If I had woken up earlier, I could have chosen different pants and shoes. Except that I did not wake up early. 

Consider the pendulum of the video below as an analogy for the human mind, with its final positions as the analogues of our choices.

Could it have landed on a different final position than it did in the video? Yes. Given that it was released exactly from where it was released, and given the state of the air, table, light and everything in its surroundings, could it have landed in another position? No, it couldn’t have.

How do you feel about the fact that, in your entire life, you could not have behaved any differently than you did?

Facebook survey: Are coherent states of light ‘classical’?

I am fortunate to have many smart and knowledgeable physicist friends on facebook (and in real life). I often take advantage of this by conducting surveys in which I post a provocative question and wait to hear what my friends have to say about it. I do this not because I am looking for a definite answer to the questions, but to have a feeling for how researchers may react when confronted with unusual questions, insights or puzzles.

Since I find these surveys valuable, my guess is that so will the Internet. The poll I am presenting in this post was inspired by a common reaction to our quantum fingerprinting paper (see also this post). People are often suspicious of the claim that a protocol that uses only coherent states of light as information carriers can demonstrate truly quantum features, such as an exponential reduction in communication complexity compared to the classical case.

In order to address that suspicion, I asked my friends whether they thought that coherent states of light were classical. I was trying to understand how physicists are used to thinking about coherent states. The contributions I received strongly support the claim that many physicists have memorized the statement that coherent states are ‘classical’. However, as you will see, the conversation quickly turned from an informal discussion into a fruitful source of important insights. I hope you will enjoy the exchange of these bright minds as much as I have.

Original post:

Juan Miguel Arrazola: A survey for my physicist friends: Are coherent states of light ‘classical’?


Vadym Kliuchnikov: I guess they are classical because their Wigner function is positive.

Nicolas Quesada: So are squeezed states which are not classical.

Andres Garcia Escovar: How about quasi classical?

JMA: So far only Vadym has given a definite answer! Are they classical or not?

AGE: http://galileo.phys.virginia.edu/…/CoherentStates.htm

Torsten Scholak: Yes, because they do not fulfil any of the established criteria that would make them qualitatively nonclassical.

JMA: If coherent states are classical, how come they are widely used in quantum cryptography?

Erika Janitz: Coherent states have a non-zero expectation value for the electric field, and have a mean photon number and variance of |alpha|^2, which is what you would expect from a classical field in the limit of large alpha @_@

Varun Narasimhachar: They achieve minimum uncertainty, so in this sense, they are as classical as anything can be. But turns out, the extent to which they are quantum is enough to enable Eve-busting, which is why they are useful in cryptography.

Oleg Gittsovich: Yes.

Evan Meyer-Scott: Coherent states are not widely used in quantum cryptography. Phase-randomized coherent states (or Poissonian mixtures of Fock states) are! Are they classical?

Marco Piani: I think you should distinguish between classicality of the single state and classicality of the set of states that are involved in whatever protocol you are considering. In general, there might be conflicting notions of classicality. Any single coherent state is the most classical possible with respect to certain criteria of classicality that have little to do with information and a lot to do with physics. When you start to consider instead sets of coherent states and the relevant feature Is something information-theoretic as distinguishability, things are different. Does your question mean that you have heard back from the journal?

OG: Evan, well here I think they are not. Just because if you say mixtures, you out of a sudden jump to convex sets.. Classical states do not form a convex set, if I am not mistaken.. So you can find non-classical examples of those mixtures..

JMA: Thanks everyone for your replies. I was trying to have a feel for just how engraved in physicists minds is the idea that coherent states are ‘classical’. For me, it is clear that coherent-states can exhibit properties with no classical analog, like non-orthogonality (would everyone in this thread also jump to say that a coherent state with alpha=1 or alpha=0 is ‘classical’?) However, most people’s impression seems to be that there can’t be anything quantum about a protocol that uses coherent states, which isn’t quite right! Of course, this just goes to show how ill-defined the conceptions of classical and quantum are in the average physicist’s mind, but it helps me understand how to best explain some aspects of our recent work.

JMA: Marco, we haven’t heard back from the journal but from the QIP commitee. Nevertheless, the reactions “there is nothing quantum about that protocol” and “you are using too many modes” are extremely popular amongst anyone that first encounters the results. I’m trying to best understand how to address or prevent these reactions.

OG: uhm… “However, most people’s impression seems to be that there can’t be anything quantum about a protocol that uses coherent states, which isn’t quite right!”

This is totally true.. I believe Mr. Glauber explains in which sense coherent states are understood to be classical quite well.

OG: “there is nothing quantum about that protocol”… ask referee for truly quantum protocols… this is not a scientific answer… I am sorry

Juan Bermejo-Vega: Woa, my favorite topic!: what is quantum and what is not? Ok, ultimately, I have no idea of whether they are quantum or not, but IF you give me one coherent state I will give you a quantum algorithm to do a hybrid phase estimation quantum algorithm: which something quite quantum in the same sense that Shor’s algorithm is something quite quantum http://arxiv.org/abs/quant-ph/0008057

JBV: Also, I was under the impression that coherent states + Gaussian unitaries + local measurements are enough to enable universal (measurement-based) quantum computation. If that holds, there should be at least one quantum ingredient there that makes the computation quantum. So… which one do you wanna pick?

MP: I have not really read it, but you might be interested in having a look at http://arxiv.org/abs/1203.2661, at least just to have an idea/example of how different definitions of classicality can conflict.

As the rebuttal or at least the discussion of the criticism goes:

1) I suggest that you check the literature (in particular, the quantum optics literature) and check why coherent states are considered “classical”. If I am not wrong you will find that the reasons why they are considered classical apply anyway best when the amplitude is very high. I.e., coherent states are the closest possible approximation to classical states of light, but even that best approximation is only really good in absolute terms when the amplitude is big

2) Add to that the issue of orthogonality and distinguishability for sets of states

3) As the number of modes goes, you must be very careful, and explain why, from your perspective, it is not the right thing to look at and such.

The point in the discussions about quantum vs classical is that one often tries to compare apples and pears. The taste of some apples might be more similar to that of pears, even if the shape of those apples is less similar to that of pears than the shape of other apples that in turn may taste very different from pears. So, the answer to the question of which apples are more similar to pears depends on what you care about. In this sense, you must first of all address the issue of what are the relevant properties. I think you have increasingly done so in subsequent presentations/explanations, and that is good. Unfortunately you can only do so much, simply because, to complicate the issue, different people care about different aspects of quantum vs classical. What I can suggest is that you may want to avoid (strong) claims that may trigger a very skeptical attitude. It is a difficult balance, because then you also water down your result, or at least the selling of your results. I can only wish you good luck and remain available in case you want to discuss in person. Cheers.

Deny Hamel: I guess one way you can think about is whether or not you can explain your scheme without quantizing the light field and with some kind of threshold detector.

JMA: Evan: What about an implementation of B92 with two non-orthogonal coherent states?

JMA: Deny: Help me out: Would two classical fields of very low amplitude entering a beam-splitter interfere in the same way as two coherent states?

DH: Yes it’s essentially the same. If I recall correctly for your protocal you just want the field to exit the BS one way if the phases are the same and the other way if they are opposite; classical waves will do that.

Actually, in a completly classical case, woudn’t it be always possible to measure the intensity of every pusle no matter how attenuated they are? In that case you could always just send the whole strings. I would say that the “constant energy” critetion only makes sense once you have some discretization, or at lease a minimum measurable energy.

JMA: Deny, I think you nailed it. My argument so far has been to say that you just can’t go to arbitrarily low amplitudes without encountering quantum effects. But you make me realize that this is crucial: If the energy of the electromagnetic field were continuous, you could always tell whether each output port of the beam splitter had light there or not. However, in our universe, you cannot! The discrete properties of light limit the amount of information that can be gained from a measurement of a very weak pulse. In fact this is intimately related to the non-orthogonality of the incoming coherent states, which is arguably the important quantum property at play.

MP: Let me say that classical information processing with continuous variables is a dangerous business, and always requires taking into account imperfections. Otherwise one ends up claiming that infinite data can be stored in the position of an infinitesimal dent on a ruler, and with all powerful analog computers.

EMS: I didn’t know the B92 protocol was originally for coherent states! Cool. I’ve never heard of an implementation though. Also I really like how Bennett’s optical circuits are done in ASCII art!

Regarding your response to Deny’s comment: what if you measure in the coherent state basis? Then you can get information even from arbitrarily small pulses (barring imperfections Marco). So the quantum nature doesn’t arise until you use single photon detectors. I would argue it is the discrete properties of single photon detectors that limit the information, not of light (in this case).

MP: Notice that as energy goes, you might always go down with the frequency, and I do not think frequency directly enters into your calculations. But with lower frequency should come probably longer pulses (larger time bins). There should be a trade-off somewhere.

JMA: Yes Marco, the ‘constant-energy’ adjective can be deceiving, as it really implies ‘constant mean photon number’, but it sounds nicer! Having said that, the trade-off between photon number and number of modes in quantum is something I would like to quantify and understand better. For example, in principle it is possible to communicate any number of bits with just one time-bin mode: just encode information in the number of photons in the mode!

JMA: Evan: the problem with measuring in the (overcomplete) coherent state basis is that you could not distinguish perfectly between the vacuum and a state of low amplitude, since they are not orthogonal. Thus, you could not tell reliably what output port of the beam splitter was a vacuum and which one was a low amplitude state. So you still have limited information.

JMA: I also just have to say that no matter what impact this work has, it has proved to be a catalyst for amazing discussions.

MP: You might be onto (or dealing with) something important and fundamental. People have tried to come up with information principles for quantum mechanics (or, sometimes, just for correlations in quantum mechanics). Maybe as relativity comes form a limit on the speed at which information can be transferred, similarly quantum mechanics can be deduced by postulating that there is some finite maximal rate (per unit of time x unit of energy) for the transmission of information? Probably people have already thought in this direction but one never knows (btw we are doing science in the open, which is quite nice 🙂 )

JMA: I think Seth Lloyd made a connection between general relativity and quantum mechanics by postulating a minimum unit of information per discrete unit of spacetime (or something like this). It was a talk he gave at QCMC 2012, so indeed there might be something fundamental at play, in the sense that there is a limit to the information-carrying capacity of physical systems. Once I’m done with the QFT assignment, I will think about this a bit more!

JMA: If someone accuses me of procrastination for being on facebook I will reply: Hey, I’m working on open science!

EMS: Re non-orthoganality: yeah, of course! I understand now and agree.

Note: Featured image is a sample of Kim Keever’s abstract liquid art (which I found thanks to my love Aleksandra Ignjatovic.)

QIP 2014

I have around 5 hours to spare in Frankfurt coming back from Barcelona on my way back home to Toronto. I was in Barcelona for QIP 2014: a fantastic conference in an even more extraordinary city. The entire conference experience was enriching and stimulating, so I thought I could spend my time in Germany writing about it.


Conference Group Picture

I heard a few people mentioning that this was the largest instalment of QIP, which seems reasonable when you take a look at the conference picture. I like to think that this is due not only to the convenient and attractive location, but because our field keeps attracting more people and continues to have an influence in increasingly more areas. Daniel Gottesman told me over dinner that when he started working in quantum information, there were conferences organized where basically the entire field would attend, both theorists and experimentalists. Together they would encompass around 20 people. The attendees of QIP 2014 were estimated to be around 400. It is exciting to wonder just how the field will look like in a couple of decades.

Barcelona is an ideal place to host a medium-sized conference like this one. The venue for the talks (AXA Auditorium), the rump session (Centre de Cultura Contemporània de Barcelona) and the conference dinner (Museu Marítim de Barcelona) were all plain gorgeous. I guess this is not hard to achieve in a city where basically every other building is a standing work of art; not something you can say about Waterloo, for example. You could also feel the desire of everyone to explore the city during lunch and after each day’s session. This, combined with the apparent Catalan tradition of taking hours to eat (seriously, it was nearly impossible to have dinner in under 3 hours), was a great formula to have attendees spend time together discussing and exchanging ideas. I most definitely benefited from meeting many people and having very interesting conversations.

Barcelona as seen from atop Parc Güell.

Barcelona as seen from atop Parc Güell.

There were many great talks on a wide range of subjects: very impressive progress keeps being made in the field. Initially, I had expected the content of the talks to be heavily biased towards subjects in computer science and mathematics, and I was concerned that perhaps I would have trouble understanding or being interested in them. I’m glad to say that my experience was quite the contrary: I found myself being able to follow most of the talks and was surprised by how fascinated I was with topics I hadn’t previously encountered in enough detail. I imagine this is a consequence of the exposure I get to the mathematical aspects of quantum information as a student in the Institute for Quantum Computing.  Having said that, I would like to offer a ranking of my personally favourite talks, which is heavily subjective as I am counting mostly how compelling I considered them to be.

5. Purifications of multipartite states: limitations and constructive methods. Speaker: Gemma de las Cuevas.

A very clear exposure of the problem of finding efficient tensor-network representations of multipartite mixed states. It made me think that a solid knowledge of tensor networks may be a powerful tool to add to the arsenal of a quantum information theorist. This is especially true since, according to the speaker, they may find applications in quantum communication complexity.

4. Robust protocols for securely expanding randomness and distributing keys using untrusted quantum devices.  Speaker: Carl Miller.

Even though I disliked how much advertising was involved in this talk (he was already referring to his own protocol as the Miller-Shi protocol!), the results presented are impressive. I have found randomness to be interesting for as long as I can remember, and the prospect of using fundamental aspects of quantum mechanics to generate reliable random numbers is an exciting one for me. The work presented has gone a long way in elucidating how an ideal random number generator may be constructed.

3. What is the overhead required for fault-tolerant quantum computation? Speaker: Daniel Gottesman.

The essential message of Daniel’s talk was this: we should not be satisfied with the overhead required in current fault-tolerant schemes. As he eloquently stated, we may dream of a quantum computer with one thousand physical qubits, but we would not have gained much if we can only operate on ten logical qubits. To back up his message, he provided a theorem that guarantees that the overhead can be made arbitrarily small in principle. *Restrictions may apply.

2. Classification of the complexity of local Hamiltonian problems. Speaker: Ashley Montanaro.

There had been previously a lot of interest in determining the complexity of several versions of the local Hamiltonian problem. These guys classified an enormous class of problems in one single paper. Amazing. Bonus awarded for using the face of Toby Cubitt to denote a qubit (how many Cubitt-Qubit puns must he have experienced?).

1. Universal fault-tolerant quantum computation with only transversal gates and error correction. Speaker: Adam Paetznick.

I am obviously biased since Adam is a good friend of mine, but I love the result he presented. My favourite kinds of breakthroughs are those that look incredibly simple in hindsight, but that no one had been able to come up with before. Transversality is a highly desired property of the implementation of fault-tolerance schemes for quantum computation, but there was a long-held belief that this was impossible due to a no-go theorem by Eastin and Knill. Adam and his supervisor Ben Reichardt circumvented this fake barrier by simply adding the already existing ingredient of error correction into the mix. His explanation of the basic idea was brilliantly done, and I am sure he had many people in the audience wondering why they hadn’t thought of that before.

I didn’t include any plenary talks into my ranking because I consider them to be closer to a colloquium than to the presentation of new results. Nevertheless, I enjoyed plenary talks greatly, and my favourite was the talk by Matthias Troyer on the classical simulation of complex quantum systems, largely because of how much I learnt. He did an amazing job at showcasing the competition that future quantum computers must face: extremely fast classical supercomputers. As he put it, “it is hard to build a quantum machine that can beat my codes.” Using Quantum Monte Carlo Methods, we are currently able to simulate the equilibrium properties of millions of bosons, a tough task for a quantum computer to surpass. My understanding is that only systems of interacting fermions with a sign problem are hard to simulate classically, so perhaps that’s where quantum computers can really shine. However, Matthias also pointed out that something classical simulators cannot do well is to simulate dynamics: “If I kick a quantum system, no one knows how to simulate what happens.”

He also included a list of the most cited papers in physics, with the vast majority being papers that described methods to solve a particular problem or carry out a simulation. This leads me to the conjecture that the best way to produce a highly cited paper is to find a tool that a large community of working scientists will use.

The poster sessions were, unfortunately, an extremely ineffective way of showcasing research.  The two sessions included around a hundred posters each, in a small crowded room where it was nearly impossible to hear someone who was further than 30cms from your face. During the presentation of my own poster, I had many people stop over, which was great, but literally prevented me from even glimpsing half of the posters presented. If I had to pick my favourite poster, I would probably choose one by Valerio Scarani and his students on the tree complexity of quantum states, but only because it was very relevant to my research in quantum communication complexity.

As this was my first QIP, it was also my first rump session. The evening was a combination of hilariousness, surrealism and schadenfreude. The highlights of the night were the appearance of the Schroedinger’s rat, the Zurich toast protocol (which was largely implemented during the conference dinner) and John Smolin’s talk demolishing D-Wave. I am proud to confess that I was the one who ironically shouted “Go D-Wave!” during the beginning of the talk. Hearing him say “Did someone seriously just say ‘Go D-Wave!’” was priceless. I also laughed intensely when, asking for champagne (in Spanish) to one of the waiters, he took the opportunity to ask me: “Hey, just what the hell is going on here?” I guess that from an external perspective, it all must have seemed incredibly bizarre. Finally, my advice to anyone planning to speak at future rump sessions: Do not talk about your research in any level of seriousness! You will only achieve people ignoring you in a very painful manner.

John Smolin during the Rump Session.

John Smolin during the Rump Session.

On a different note, I was happy to see how good the community looked. Barring a few exceptions, we were a well-dressed, classy-looking group of people, largely destroying the prejudice of scientists as beings who wear t-shirts, non-matching pants and ugly sneakers. I believe we should look as smartly as we actually are.

Sadly, the conference provided a great way of estimating the number of women doing research in quantum information, with the numbers being embarrassingly small. Out of 40 speakers, only three were women (7.5%) and out of the 23 members of the programme committee, only two were women (8.6%). These numbers roughly match what one could estimate by looking at the audience as well. In my opinion, it is worrisome that such a small percentage of the members of our community are women and I truly hope this figure will change significantly in the near future.

A conference like QIP is a great place to put your research into perspective. It is very easy to get lost in obsession with a particular problem and easy to lose grasp of what the rest of the world is worrying about. Part of being a good researcher is asking the correct questions, and this is easier to do when you are aware of all the questions everyone else is asking. Additionally, it allows you to realize how much your own results may impact the community. Overall, QIP 2014 was a wonderful experience and I am already looking forward to the possibility of being in Sydney for QIP 2015.

I love the sea.

I love the sea.