# 2016 goals in review

It is widely accepted that 2016 was a terrible year. I agree, although it had its good moments, like Colombia finally signing a peace treaty to end the armed conflict with the FARC.

I had essentially no influence or control over the elections, deaths, and conflicts that have marked this last orbit around the sun, but I do have control over my own life. 2016 was the first year that I set myself quantitative goals, making it possible to look back and evaluate my performance with at least some degree of precision.  I set ambitious goals that I knew would be difficult to achieve: that’s the way to improve!

Below, I review these goals and my accomplishments in reaching them. I do this not only as a form of reflection, but also in the hope that it may inspire others to do something similar in the upcoming year  🙂

Goal #1: Obtain a total of 100 citations to my articles

As a young postdoc, I am in the stage of my scientific career where the stakes are high. Permanent positions are scarce and the competition is fierce: I have to perform at the highest level. At the end of 2015, I had 45 citations to my articles, so my goal was to essentially double that amount. Looking at my colleagues in quantum information who have been researchers longer than me, I have found that getting to ~1000 citations is a good indication of having reached the level of impact in a field that may merit a tenure-track position in respected research institutions. Hence, my goal is to aim at doubling my total citations every year until I reach that point: 50, 100, 200, 400, and so on. In that case, I would be on track to being competitive in my applications to permanent positions by the time I finish a second postdoc.

At the time of writing, I have a total of 81 citations to my papers, which is a non-negligible amount below my goal. Of course, I cannot really control how many times my papers are cited. All I can do is publish good research and work hard to make it visible to the community. Also, we should never forget that citations are not an accurate method of assessing scientific merit. However, it is important that I objectively analyze my competitiveness as I look to making important career decisions in the future.

Goal #2: Publish at least 5 papers.

What the community thinks of my work is ultimately not up to me, but it is in my power to be a productive scientist. As opposed to my days in grad school, as a postdoc I can work exclusively on research, most of which is related to topics that I have already mastered. This is truly the best time to shine as a researcher. I published six papers during the four years it took me to complete a PhD, so my goal was to effectively reach that level of productivity in only one year.

Indeed, I have accomplished this goal with five papers:

However, I think it is fair to say that I have actually exceeded this goal, as I have an additional review paper on satellite quantum key distribution which is almost finished, and I have several projects which will be close to completion in the first month of 2017. Yey!

Goal #3: 150 sessions of exercise.

I have reached a point in my life when I have to work hard to maintain my health and well-being. My reasoning in setting 150 sessions as my goals was that I would have roughly three sessions per week. In fact, I was disciplined with exercise, which I have smoothly incorporated into my routine: gym on Tuesday and Thursday, table tennis on Friday. In 2016, I tallied a total of 116 sessions, and I am very satisfied with my body and strength.

So why only 116 sessions if I was disciplined? Well, it turns out that I exercised practically every time I could exercise, but there were too many moments when I could not: facility closures, travels, and sicknesses prevented me from going even when I wanted to. Overall, 150 hours was ambitious and I am satisfied with my progress towards this goal.

Goal #4: Play 5 complete songs in the guitar

I have been playing the guitar for many years now, but only as a very casual hobby. Music is something that I don’t want to do seriously — quite the contrary — it is a respite from everything that is serious in life. As such, when I would grab my guitar, I would play only excerpts of songs, not really putting in the effort to master them in their entirety. Again, this is fine, but I still wanted to at least have a small repertoire that I could play to completion. This was a relatively easy goal to achieve, and I can now fully play

• Hey There Delilah – Plain White T’s
• Lazy Eye – Silversun Pickups
• Hotel California – The Eagles
• Better Man – Robbie Williams
• Sleepwalk – Johhny and Santo (this one is getting a bit rusty)
• Good Riddance – Green Day

Goal #5: Read 5 books on investment

As a postdoc in Singapore I have finally reached the point in my life where, together with my wife Aleks, we earn more than we spend. As such, it is crucial to me to be responsible and knowledgeable about how to handle our savings, however modest. Throughout my life, I have received indirect advice from my parents and friends, but I am always more comfortable making decisions based on my own knowledge and understanding.

This year I read 3 books on finance, while deciding to stop there around the middle of the year. The reason is that I already learnt quite a lot from these books and I did not find any others than seemed to both interesting and different enough to merit a commitment to read. What I realize now is more useful is to read financial news and to start learning through practice and experience. The books I read are

• A Random Walk Down Wall Street, Burton Malkiel
• The Essays of Warren Buffet, Warren Buffet
• Irrational Exuberance, Robert Schiller

Goal #6: Donate 1% of my income to charity

I don’t only care about improving my own life, but about making the entire world a better place. I try to do this with my actions every day, but another meaningful way of achieving this is to donate money directly to people who need it.

My only problem with donations is that I don’t have confidence in most charities making proper use of the donations they receive. That is why I love the approach of Raising for Effective Giving (REG), a meta-charity founded by professional poker players that works to allocate donations to the most effective charities. In their own words: “We rely on scientific thinking and cooperate with researchers, think tanks, and charity evaluators to find the interventions most effective at reducing suffering in the world and to provide members with the best information on the most effective giving opportunities.”

Even though it took me until the last month of the year, I have indeed donated 1% of my income to REG. I hope I can continue to increase this percentage for may years to come.

Happy 2017 everyone!

# Anyone can understand quantum mechanics — Part 3

Before, we begin, HAVE YOU WATCHED THE VIDEO “ANYONE CAN QUANTUM”??? Paul Rudd, Keanu Reeves, Stephen Hawking, Quantum Chess, Quantum Physics for Babies, and even tardigrades: this video has it all!

Made by our colleagues from the Institute for Quantum Information and Matter in Caltech, this clip has masterfully shared with almost two million people all around the world the same message that I have been trying to spread with these blog posts: anyone can understand quantum mechanics! In their video, Keanu Reeves tells us that “Paul Rudd changed the world by showing the world that anyone can grapple with the concepts of quantum mechanics. It sparked an era of invention and ingenuity the likes of which humanity had never seen.” There is a lot of truth in that: when everyone believes they can understand nature at its most fundamental level, we can accomplish amazing things.

Of course, it’s one thing to claim that people can understand quantum mechanics, but it’s something else entirely to help people actually do it. That’s the job I started with my previous posts and that I am going to continue today. Let’s go!

In the previous installment of this series, we learnt the basic postulates of quantum mechanics. In other words, we learnt what quantum mechanics is. In this final part of the series, we are going to shift gears and study what quantum mechanics implies about our universe. What is possible in a quantum world that can’t be done in a classical one? What is new, what is different? These are important questions and today we’ll learn some of the answers!

My job, for instance, could be loosely described as studying the implications of quantum mechanics for communication, cryptography and thermodynamics. In particular, in this lesson we’ll learn about two important aspects of quantum mechanics that are not present in classical theories: Heisenberg’s uncertainty principle and entanglement.

Lesson 1: The uncertainty principle

The uncertainty principle of the Heisenberg on the right.

In our previous lesson, we used a quantum coin as an example of a quantum system, whose state could be $|Heads\rangle$, $|Tails\rangle$ or any superposition of these two states. Today, we are going to be more general and instead we are going to think of a system with two possible configurations which we call $|0\rangle$ and $|1\rangle$. Using this notation is great because it’s shorter to write (which is always appreciated) and because it is more general: we don’t really need to be talking about a quantum coin, it could be any system with two degrees of freedom. The word we use for such an object is a qubit, in analogy with a classical bit, which is any system that can be in states 0 or 1.

Remember that in quantum mechanics we can have superpositions, so we are also going to define two other important states of a qubit

$|+\rangle=\frac{1}{\sqrt{2}}|0\rangle + \frac{1}{\sqrt{2}}|1\rangle$

$|-\rangle=\frac{1}{\sqrt{2}}|0\rangle - \frac{1}{\sqrt{2}}|1\rangle$.

Notice that the states $|+\rangle$ and $|-\rangle$ are both an equal superposition of the states $|0\rangle$ and $|1\rangle$. Notice also that the states $|0\rangle$ and $|1\rangle$ are equal superpositions of $|+\rangle$ and $|-\rangle$ since we can write

$|0\rangle=\frac{1}{\sqrt{2}}|+\rangle + \frac{1}{\sqrt{2}}|-\rangle$

$|1\rangle=\frac{1}{\sqrt{2}}|+\rangle - \frac{1}{\sqrt{2}}|-\rangle$.

Qubits come in many different kinds. This one is a superconducting qubit from the lab of John Martinis.

Do you remember how to define a measurement in quantum mechanics from the previous lesson? The only thing we have to do is to ask systems what states they are in. In this lesson, we are going to focus on two special measurements of a qubit. We’ll call the question

“Are you in state $|0\rangle$ or $|1\rangle$ ?”

a Z measurement. Similarly, we’ll call the question

“Are you in state $|+\rangle$ or $|-\rangle$ ?”

an X measurement. Why do we call them that? Well, there’s a relatively complicated historical reason behind it, but this is the terminology that scientists use and I want you to be familiar with these terms.

Now let’s suppose that we have a qubit in the state $|0\rangle$ and we want to measure it. If we make a Z measurement, we know for sure that the outcome will be “I’m in state $|0\rangle$”. However, because of the laws of quantum mechanics that we learnt last time, if we make an X measurement, half of the time we’ll obtain the outcome “I’m in state $|+\rangle$” and the other half we’ll get the outcome “I’m in state $|-\rangle$”. In other words, for this state, we don’t have any uncertainty about the outcome of a Z measurement, but we have maximum uncertainty about the outcome of an X measurement. See where I’m going?

What happens if instead we start with a qubit in the state $|+\rangle$? You guessed it, the situation is reversed! In this case, we don’t have any uncertainty about the outcome of an X measurement, but we have maximum uncertainty about the outcome of a Z measurement!  It turns out that no matter what state we start with, there will always be some uncertainty in at least one of these two measurements. That is Heisenberg’s uncertainty principle.

More precisely, the uncertainty principle states that for virtually any two measurements we can make on any system – let’s call them measurement A and measurement B – it holds that

Uncertainty(A)+Uncertainty(B)>0.

In other words, no matter what state the system is in, there exist pairs of measurements whose outcomes cannot both be predicted perfectly. This never happens classically! In a classical world, if we know the state of a system perfectly, in principle we can predict everything about its future behaviour, including the results of any two measurements. But in a quantum world, there is a fundamental limitation to our ability to predict the outcomes of measurements: most of the time, there will always be some uncertainty about which outcomes we’ll see. The only exception to this rule occurs when both A and B are said to commute, but most pairs of measurements don’t have that property.

Many of you are probably thinking, “Wait, didn’t the uncertainty principle have something to do with the position and momentum of a particle?” Perhaps some of you have even heard this joke before:

Well, the uncertainty principle applies to measurements of position and momentum as well: we can never predict the outcome of both measurements perfectly. In other words, in our universe, for any measurement X of the position of a particle and any measurement P of its momentum, it holds that

Uncertainty(X)+Uncertainty(P)>0.

The uncertainty principle tells us something very deep about our ability to obtain information from physical systems. In many ways, it sets a fundamental limit to our capability to make predictions and to perform precise measurements. This has HUGE implications. To name a few, the uncertainty principle is the reason why quantum states cannot be cloned, why empty space is not really empty, and why quantum cryptography is possible. That’s the beauty of our quantum world!

Before our next lesson, you can take a break and admire this picture that my wife took of the Gardens by the Bay in Singapore, the city where we now live.

Futuristic nature

Lesson 2: Entanglement

So far in our discussion of quantum mechanics we have focused on single systems: a single quantum coin, a single quantum die, a single qubit. But what happens if we combine systems together? In particular, what happens if we have two qubits instead of one?

The first thing we have to understand is how to represent the states of two qubits. Turns out that all we have to do is to “stick them together”. If one qubit is in state $|0\rangle$ and the other is in state $|1\rangle$, then we represent the joint state of both qubits as $|0\rangle |1\rangle$. Easy! Mathematicians call this operation “taking the tensor product”, I prefer to use the term “sticking them together”: it gets the point across.

Other examples of possible states of two qubits are

$|1\rangle |0\rangle$

$|+\rangle |1\rangle$

$|-\rangle |+\rangle$

$(\frac{3}{5}|0\rangle +\frac{4}{5}|1\rangle) |0\rangle$

You get the idea. Notice that in each of these examples, it is straightforward to identify what state each of the two individual qubits is in. For instance, for the state $|-\rangle |+\rangle$, it is clear that the first qubit is in state $|-\rangle$ and the second qubit is in state $|+\rangle$.

Now comes the interesting part. Remember that in quantum mechanics we can have superpositions of different states. Hopefully many of you are already realizing that much of the magic of the quantum world comes solely from superposition: it is one of the defining properties that makes quantum mechanics such a beautiful and rich theory. For example, in quantum mechanics, a system of two qubits can be in the state

$\frac{1}{\sqrt{2}}(|0\rangle |1\rangle + |1\rangle |0\rangle)$.

Does this state look special to you? If not, then let me ask you a couple of questions: what state is the first qubit in? What state is the second qubit in? Think about it for a while.

Seriously, think about it for a while.

Are you thinking about it? Because you really should…

So, what’s the answer? That’s right: they don’t have a definite state! In fact, if we perform any measurement in either of the two qubits, we will always get a completely random outcome.  Thus, this peculiar state has the intriguing property that even though we know the state of both qubits perfectly, we are completely ignorant of the state of each individual qubit. Mind-blowing isn’t it?

Mind=blown

Any state that cannot be written in the form $|state_1\rangle|state_2\rangle$ is called entangled, where $|state_1\rangle$ is some state of the first qubit and $|state_2\rangle$ is some state of the second qubit. You can check for yourself that indeed the state

$\frac{1}{\sqrt{2}}(|0\rangle |1\rangle + |1\rangle |0\rangle)$,

which from now on we’ll call $|\Psi\rangle$, cannot be written in this form and is therefore an entangled state.

The Centre for Quantum Technologies, where I now work as a research fellow, organized a mini-competition last year to coin a new way of referring to entanglement to replace the popular “spooky action at a distance”, which I dislike (more on that in a few minutes). The winner entry was “Mutual existence”, which was chosen by writer George Musser and CQT professor Christian Kurtsiefer. You can read more about it and other entries here. In Musser’s words “I like ‘mutual existence’ because it captures the principle that entangled particles behave as a single unified system, with global properties that do not reside on either particle, or even derive from them.” Now you know what he means! The joint state of two entangled systems is perfectly defined, but in such a way that their individual states are not. Beautiful!

Now what happens if we measure one of the qubits in an entangled state? Well, we know we’ll get some outcome, but as you might have guessed, because the state of each individual qubit is not well defined, no matter what measurement we make, we’ll always obtain a random answer. If we measured the first qubit of state $|\Psi\rangle$ by asking “are you in state $|0\rangle$ or in state $|1\rangle$?” we’ll obtain each possible answer with 50% probability. But notice something amazing: because quantum mechanics always gives consistent answers, if we then measure the second qubit we know what outcome we’ll obtain! If the outcome of the measurement of qubit 1 was “I’m in state $|0\rangle$” then for sure we’ll obtain outcome  “I’m in state $|1\rangle$” when we measure qubit 2, since $|\Psi\rangle$ was an equal superposition of $|0\rangle|1\rangle$ and $|1\rangle|0\rangle$. Moreover, this is true no matter how far apart the qubits are from each other.

Many people were frightened by this realization: the state of qubit 2 is initially not well-defined, but as soon as we measure qubit 1, we immediately know the state of qubit 2. This is what led Einstein to call this effect “spooky action at a distance”. But as you’ll see, it’s not spooky and it’s not action at a distance.

Following the argument of the great John Stewart Bell, imagine there is a person that always wears socks of different colours. In Bell’s case, this was his friend, Reinhold Bertlmann. On a given day, it was impossible to predict what sock he would wear on each foot. However, if you got a glimpse at one of his socks then you immediately knew that the other sock must be of a different colour. Sounds familiar?

The colour of Bertlmann’s socks is uncertain, but as soon as we see that one of them is pink, we immediately know the other isn’t.

So you see, there is nothing quantum about objects being correlated in this way: even if their states are uncertain, their shared properties may allow us to make inferences about one of them from knowledge of the other. Here’s what’s quantum about entangled states: this powerful correlation remains no matter what measurements we make!

Once again, in quantum mechanics, we have superpositions, so we can ask a richer class of questions. In the case of the entangled state $|\Psi\rangle$ , we could ask the first qubit “Are you in state $|+\rangle$ or in state $|-\rangle$.” You can check for yourselves (or trust me on this) that we can equivalently write $|\Psi\rangle$ as $|\Psi\rangle=\frac{1}{\sqrt{2}}(|+\rangle |+\rangle - |-\rangle |-\rangle)$ so now we know that the outcome of the same measurement on qubit 2 will always be the same as for qubit 1. This correlation between several different measurements is not possible to achieve classically: entangled states have much stronger correlations. That’s the reason that my personal entry for the mini competition was this:

Quantum correlations are stronger than classical ones and they lead to a myriad of applications, like randomness generation, quantum cryptography, and quantum teleportation. Perhaps most importantly, as shown by Bell in the 1970’s, the properties of entangled states have taught us that we cannot understand the world as being one in which the outcomes of all events have been pre-established and where signals cannot travel faster than light: at least one of these two principles does not hold in our universe.

I hope you have enjoyed this trip across the quantum world. My honest hope is to have given you an understanding of the basic concepts of quantum mechanics and, most importantly, to have ignited a desire to learn more about this most beautiful of theories.

# Anyone can understand quantum mechanics — Part 2

In Part 1 of this series I made the bold claim that, unlike what famous figures in science seemed to suggest, quantum mechanics is a beautiful and simple theory that is accessible to anyone who is enthusiastic about learning it. In Part 2, I am going to put my money where my mouth is and teach you the basics of quantum mechanics in four short lessons. Sounds good?

Before we begin, there are two important points I need to clarify.

1. I need your help! It would be great if we could learn new things passively and without any effort, like Neo in the first Matrix movie.

Unfortunately, the technology for instant learning is not currently available, so we’ll have to rely on old-school methods like reading, thinking, and discussing. For best results, I recommend that you find time during a quiet afternoon, make yourself a coffee or tea, sit down in a comfy chair and go through the material with patience. If you do it together with a friend or loved one, even better. The ideas I will present are not really complicated, but they will be unfamiliar and unlikely to sink in if you don’t help me with your full attention and enthusiasm.

1. There will be math! I know that the fear of mathematics is a widespread malady that would normally make many of you run away from this post as quickly as possible. My wife, for example, automatically starts yawning when she hears the word “probability”.

There’s math in the post? Noooooo!

I can assure you, there is nothing to fear. Many science writers choose to get completely rid of math when discussing quantum mechanics, probably hoping to increase the sales of their books. This leads to a tragic state of affairs where any explanation of the subject is either full of technical jargon – as in standard university textbooks – or it is carried out with imprecise analogies and hand-wavy arguments. This would be understandable if the mathematics were actually hard – like in general relativity – but in quantum mechanics, we don’t really need to do much more than add and multiply numbers. I won’t insult the intelligence of my students by pretending they will run away just because we’ll use the same type of math they already use when they need to figure out how much money to take on their next vacation. Just stick with me and you’ll be fine.

Lesson 1: What is quantum mechanics?

Surprisingly, quantum mechanics is not a physical theory. It is a framework that is used to build physical theories. In learning and understanding quantum mechanics, we will be learning something that actually doesn’t look like physics at all, but more like a set of abstract rules. My favourite statement of this fact is one that Scott Aaronson, a professor at MIT, makes in his book, Quantum Computing since Democritus:

“Basically, quantum mechanics is the operating system that other physical theories must run on as application software […]. But if quantum mechanics isn’t physics in the usual sense – if it’s not about matter, or energy, or waves, or particles – then what is it about? From my perspective, it’s about information and probabilities and observables, and how they relate to each other.”

This quote is so good, it is even used to sell printers in Australia, as seen in the short ad below.

When physicists talk about a quantum theory, they are referring to a physical theory that follows the framework of quantum mechanics. For example, quantum optics is a theory about the behaviour of light that is constructed according to the rules of quantum mechanics. This is also why it makes sense to talk about quantum computation: it is simply a theory of computation where computers follow the rules of quantum mechanics. Therefore, from now on, instead of talking about electrons and atoms, we will discuss a set of abstract rules that we can later apply to the context of interest.

Lesson 2: Ket notation. An essential starting point in quantum mechanics is the concept of the state of a system, which simply corresponds to one of its possible configurations. For example, when studying a Canadian one dollar coin, we assign one state to the coin showing the face of the queen (Heads) and another state to the coin showing a loonie (Tails). If the coin is in the configuration shown on the left in the image below, we say that it is in state “Tails”.

We can do the same for any system of interest. For example, we can assign a state to each of the faces of a dice, to the balance of your savings account, or to the energy of an electron in a hydrogen atom. Essentially, all we are really doing is assigning a label to the possible configurations we are considering.

In quantum mechanics we have a particular notation for the state of a system, which we call a “ket”. Although it may seem strange and pointless, it comes in handy when doing advanced calculations and it is a great way of making clear that we are referring to a quantum state. The way this works is that instead of writing a state in quotation marks – like I have done so far – we write inside of an uneven bracket. For example, instead of writing “Heads” or “Tails”, we write $|Heads\rangle$ and $|Tails\rangle$. Similarly, when listing all the states of a dice we write:

$|1\rangle, |2\rangle, |3\rangle, |4\rangle, |5\rangle, |6\rangle.$

A possible state of your savings account would be written as $|+1,203\rangle$. A cat could be in the state $|Alive\rangle$ or the state $|Dead\rangle$. You get the idea.

I have introduced this notation for two reasons. First, I want to use the notation that cutting-edge researchers employ every day. Second, I want you to be able to recognize, just by glimpsing, that the equation written in a whiteboard has something to do with quantum mechanics.

Lesson 3: Superposition. In the previous lesson, you were perhaps wondering what was so quantum anyway about writing |Heads> instead of “Heads”. If that crossed your mind, you are right! There’s nothing quantum about that, it’s just notation. Now I am going to tell you one of the two main features that makes quantum mechanics different. In the quantum world, there are more possibilities for the kinds of states that a system can be in. For example, the state:

$|Heads\rangle + |Tails\rangle$

is also a valid quantum state of a coin. We refer to such a state as being in a superposition of both states. In fact, the state:

$|Heads\rangle - |Tails\rangle$

is also a valid quantum state, although in a different kind of superposition. We’ll discuss this difference in another lesson. Similarly, the state:

$|1\rangle + |2\rangle -|3\rangle -|4\rangle + |5\rangle + |6\rangle$

is also a valid state of a quantum dice. In general, we can add and even subtract any set of states in any way we want, or even multiply them by any number, and end up with another valid state[1]. There are as many valid states as there are ways of combing them together by adding and multiplying by a number! For example, the following are also valid states of a quantum coin and a quantum dice, respectively:

$-4 |Heads\rangle - 2|Tails\rangle$

$|2\rangle + 2|3\rangle -|4\rangle +0.5 |5\rangle$

In quantum mechanics, there are so many more possibilities. Can you write down other interesting states of a quantum dice or coin?

In lesson 4, you’ll learn that we have to make an important adjustment to this rule, but for now, the important point is that there is an added richness in quantum mechanics in terms of the possible configurations of physical systems, since it is now possible for them to be in superposition.

What does it mean for a coin to be in the state $|Heads\rangle + |Tails\rangle$? That is a great question. The answer is… we don’t really know. People have come up with different proposals, from multiple universes to subjective views of reality, but none of them is entirely satisfactory. This is precisely the kind of situation that led Feynman to believe that no one understands quantum mechanics. But of course we understand! Quantum mechanics tells us that we can have superpositions, which are just sums of different states. This is not hard to grasp, is it? The difficulty comes when we ask questions regarding a connection of the theory with the natural world. These are very important and interesting questions that we should ask and try to answer and that I am personally very interested in. But strictly speaking, they are not questions about the theory. Remember, quantum mechanics is a framework, a set of rules that any physical theory must obey. Are these rules hard to understand? I don’t think so!

While the message of this lesson sinks in, take some time to admire this beautiful picture of the Milky Way galaxy.

Lesson 4: Measurements. Speaking of questions, what happens when we ask a quantum system what state it is in? In other words, what happens when we measure a system to determine its state? To provide an answer, we first have to make an adjustment to lesson 3. Remember I claimed that we could add up states in any way we wanted? Strictly speaking, this isn’t true: the state that we end up with must satisfy an additional property. It’s easiest to illustrate with an example. In quantum mechanics, instead of writing:

$|Heads\rangle + |Tails\rangle$

We must actually write:

$\frac{1}{\sqrt{2}}|Heads\rangle + \frac{1}{\sqrt{2}}|Tails\rangle$

The numbers $\frac{1}{\sqrt{2}}$ are referred to as the coefficients of the state. For example, what are the coefficients of the state:

$\frac{3}{5}|Heads\rangle + \frac{4}{\sqrt{5}}|Tails\rangle$?

That’s right, the coefficients are $\frac{3}{5}$ and $\frac{4}{5}$. Quantum mechanics requires that, when we square the coefficients and add them together, the result must always equal $$1$$. In this case, we say that the state is normalized. For example, since:

$(\frac{1}{\sqrt{2}})^2+(\frac{1}{\sqrt{2}})^2 = \frac{1}{2}+\frac{1}{2}=1$

then our new state satisfies the rule. Similarly, the state:

is normalized because:

$(\frac{3}{5})^2+(\frac{4}{5})^2=\frac{9}{25}+\frac{16}{25}=1$.

Fortunately, we can always normalize a state by simply re-scaling its coefficients appropriately, which is why I didn’t bother doing it in the previous lesson.

Good news for all the students who don’t like math: that’s the hardest math we’ll have to use learning quantum mechanics!

Now, suppose that we have a quantum coin in a given state and we want to measure it. In quantum mechanics, a measurement is equivalent to asking a system: “In which of the following states are you in?” For example, in the case of a quantum coin, a valid measurement is to ask: “Are you in state $|Heads\rangle$ or in state $|Tails\rangle$?” Quantum mechanics then tells us that the outcome of the measurement – i.e. the answer to our question – will definitely be either $|Heads\rangle$ or $|Tails\rangle$ and the probability that each outcome occurs is equal to the square of the corresponding coefficient.

Let’s look at some examples. Suppose that we have a quantum coin in the state:

$\frac{1}{\sqrt{2}}|Heads\rangle + \frac{1}{\sqrt{2}}|Tails\rangle$

and we ask: “Are you in state $|Heads\rangle$ or in state $|Tails\rangle$?”

Then with probability $(\frac{1}{\sqrt{2}})^2=\frac{1}{2}$ the outcome will be $|Heads\rangle$ and with probability $(\frac{1}{\sqrt{2}})^2=\frac{1}{2}$ the outcome will be $|Tails\rangle$.

Similarly, if we have a quantum coin in the state:

$\frac{1}{2}|Heads\rangle + \frac{\sqrt{3}}{2}|Tails\rangle$

and ask the same question, with probability $(\frac{1}{2})^2=\frac{1}{4}$ the outcome will be $|Heads\rangle$ and with probability $(\frac{\sqrt{3}}{2})^2=\frac{3}{4}$ the outcome will be $|Tails\rangle$.

Moreover, if we ask two questions in a row, then quantum mechanics tells us that we always get the same answer. In other words, the theory doesn’t contradict itself. We would be in trouble otherwise! In our first example, it was equally likely to obtain either of the outcomes. But after an outcome has occurred, let’s say $|Heads\rangle$, if we ask the same question we’ll always obtain $|Heads\rangle$ as the answer, no matter how many times we ask.

This is a good place for a break, so before taking a look at some examples, let’s take a quick break to admire the beautiful building that hosts IQC and from which I wrote these words.

You may be wondering: how is this quantum coin any different than a regular coin? That’s an excellent question! Remember how quantum mechanics tells us that we can have a richer class of states thanks to superpositions? Well, in quantum mechanics we also have a richer class of measurements! For example, the question:

“Are you in state $\frac{1}{\sqrt{2}}|Heads\rangle + \frac{1}{\sqrt{2}}|Tails\rangle$ or in state $\frac{1}{\sqrt{2}}|Heads\rangle -\frac{1}{\sqrt{2}}|Tails\rangle$?”

is a valid measurement in quantum mechanics. This allows something truly unique to happen: A quantum coin in a given state can give probabilistic outcomes with respect to one measurement and deterministic outcomes with respect to another measurement. No regular coin can do this! For example, what happens if we have a coin in the state:

$\frac{1}{\sqrt{2}}|Heads\rangle + \frac{1}{\sqrt{2}}|Tails\rangle$

and we ask the question:

“Are you in state $\frac{1}{\sqrt{2}}|Heads\rangle + \frac{1}{\sqrt{2}}|Tails\rangle$ or in state $\frac{1}{\sqrt{2}}|Heads\rangle -\frac{1}{\sqrt{2}}|Tails\rangle$?”

Well, with certainty, we are going to get $\frac{1}{\sqrt{2}}|Heads\rangle + \frac{1}{\sqrt{2}}|Tails\rangle$ as the answer! This is completely different from what happened with our other question, where we obtained a completely random outcome. John Preskill, a professor at Caltech in the United States, refers to this ability to make different possible measurements by saying that “in the quantum case, there is more than one way to open the box.” Amazing, isn’t it?

The richer class of quantum states and the richer class of quantum measurements that arise because of superposition gives rise to many unique quantum properties – such as the uncertainty principle and entanglement – as well as important implications to the ways in which we can manipulate information, leading to exciting research fields such as quantum computing and quantum cryptography. This will be the topic of the last part of this series, in which we’ll use our new understanding of the rules of quantum mechanics to unravel their implications and potential technological applications.

Thank you for staying until the end of the lesson, I hope it was as much fun for you as it was for me!

[1] In fact, quantum mechanics allows us to use complex numbers in the superposition.

# Anyone can understand quantum mechanics — Part 1

Pixar’s delightful movie Ratatouille – an animated film inspired by the world of French haute cuisine – features two characters with opposing views on cooking. On one hand we have Gusteau, a jolly and chubby chef with an optimistic message that he constantly repeats in his books and TV shows:

On the other hand there is Anton Ego, a famous food critic who doesn’t just like food, he loves it. And if he doesn’t love it, he doesn’t eat it (hence his skinny figure). Mr. Ego is of a very different opinion than chef Gusteau:

At the end of the movie (spoiler alert!), Anton Ego has a change of heart, which he expresses beautifully in one of the greatest reviews ever.

To me, the answer to their dilemma is obvious: of course anyone can cook, cooking is easy – even I can do it! It definitely takes practice, with a few burnt dishes along the way, but it’s not like there is an insurmountable barrier only a few chosen ones can overcome. In fact, out of plain necessity, billions of people around the world cook their own food every day. However, it is also clear that we all cook with different degrees of skill and not anyone can do it as well as the best chefs in the world. For instance, I doubt that I could ever prepare this dish, “Lily bulbs, distillation of finger lime and lily and apple blossoms” from the restaurant Alinea in Chicago:

Looks amazing! How do they do this?

So what does all of this have to do with quantum mechanics?

Simple: I believe that the Anton Egos of the scientific world have been spreading the message that quantum mechanics is a mind-boggling, counter-intuitive, and spooky theory that not even the greatest geniuses can understand. The truth, however, is that quantum mechanics is as easy to grasp as any other theory in science and its basic principles are something that anyone can understand; just like cooking.

Why would anyone spread the message that quantum mechanics is so difficult to understand?

A hundred years ago, when quantum mechanics was first emerging as a physical theory, everyone was extremely confused. Researchers had been trained following a scientific tradition that had been brilliantly successful at explaining the natural world and which gave a very compelling picture of what the universe was really like. In particular, scientists had been taught to view the universe as composed of elementary particles whose properties could be known and whose behaviour could, in principle, be predicted perfectly. Just try and imagine how difficult it was for them to deal with a new theory that was turning this picture of the universe upside down, a theory which claimed that the properties of physical systems couldn’t always be known perfectly and their behaviour could only be predicted probabilistically! The situation was not unlike what happened during Dagen H, the day when Sweden changed from driving on the left-hand side of the road to the right. Chaos, confusion, and disputes were inevitable.

Kungsgatan in Stockholm on Dagen H, September 3, 1967

As a consequence of this clash with pre-existing views came the first examples of renowned physicists boasting about the difficulty of understanding quantum mechanics. In fact, at the time, there were many scientists who were manifestly arguing that the theory had to be wrong or incomplete. In retrospect, this comes as no surprise; it is to be as expected as traffic jams in Stockholm on September 3, 1967. The issue is that this confusion continues to propagate in many introductory courses and most tragically, in countless books and articles for the general public. As an example, the following is a recurring quote by Niels Bohr which I find to be the most irritating:

If Bohr is right, then either we’ll be shocked when learning one of the most important and fundamental truths about the universe – as opposed to enlightened and happy – or if we aren’t shocked, we’ll have to come to terms with the fact that we are not smart enough to comprehend it. A no-win situation. Thanks Niels.

This was the first generation of quantum physicists, people who were around at the time when the theory was actually proposed and built from scratch. With them came the first wave of confusion, caused by the clash between their pre-existing worldview and the basic principles of quantum mechanics. Their bewilderment is understandable and to be expected, but not something we should be teaching in the 21st century. Think about it, why would anyone keep bringing up this quote by Bohr? What are they trying to achieve? Nothing good in my opinion.

After quantum mechanics was developed into a complete and well-defined mathematical theory, it quickly begun to be successfully applied to many areas of physics. This lead to new technologies such as lasers and transistors, as well as to a deeper understanding of the properties of matter and elementary particles. This was the second generation of quantum physicists, the people that grew up with the theory and learnt about it in university, people who even had textbooks to follow with exercises and solutions in the back. With them came the second wave of confusion. Their generation did not have doubts concerning the validity of the theory, which had passed every single empirical test with flying colours. The issue was that nobody could pin down what kind of universe is ruled by the laws of quantum mechanics! They knew the rules, but could not provide a coherent picture of the world to go with it. To no surprise, once again came famous figures in science telling us that the quest for understanding quantum mechanics was destined for failure, for not even the greatest geniuses could emerge victorious. The most annoying of such claims is this quote by Feynman:

So, the person who won a Nobel Prize for developing quantum electrodynamics and wrote a best-selling series of physics textbooks is saying that nobody understands quantum mechanics? No way! Why did they give him a prize then? Why are people buying his textbooks? What Feynman meant was that there remained some profound foundational questions about quantum mechanics for which nobody had been able to provide satisfactory answers. To him, this meant that the theory was not completely understood. But of course it was understood, he was teaching it to hundreds of students!

Why do we keep quoting Feynman on this? How are we supposed to get people excited about learning quantum mechanics when we tell them from the start that nobody can understand it?

Thankfully, like Bob Dylan said, “the times they are a changin.” Now it’s time for us, the third generation of quantum scientists, to give quantum mechanics the reputation it deserves: that of a beautiful and simple theory that should be understood by as many people as possible. For example, at the Institute for Quantum Computing (where I did my PhD), they are making great efforts to share our research and teach quantum theory to the world. Every year they host around 40 high school students from Canada and the world and teach them the basics of quantum mechanics in the Quantum Cryptography School for Young Students. IQC has also recently started a training program called Teaching Quantum Technology, aimed for teachers who are interested in introducing the ideas behind quantum mechanics and their application to technology in their classrooms. Recently, they even created a video game: Quantum Cats! (I helped 0.1% to develop it.) This is only an example of a worldwide trend to spread our knowledge of quantum mechanics, a movement that is guided by the conviction that Bohr and Feynman were wrong: anyone can understand quantum mechanics.

If you are interested in being one of the growing number of people that have added quantum theory to their database of knowledge, please join me for part 2 of this series, where I will teach you the basics of this most splendid theory. No matter your age, your background or your preferences, I am sure that these are ideas that you can grasp and that you will enjoy learning. I will be expecting you!

# Our Quantum World

I haven’t been blogging for a while, largely because I am busy trying to get a PhD, but also because I have re-directed my blogging efforts into helping create a new blog for the Institute for Quantum Computing! The blog is called “Our Quantum World” and if you haven’t seen it yet, I invite you to go check it out by visiting

https://uwaterloo.ca/institute-for-quantum-computing/blog

We’ve had several great posts already by students, postdocs and faculty. The blog updates every two weeks and we have a lot of new content coming. I even wrote a post myself about academic publishing! Here is the link if you want to read it:

https://uwaterloo.ca/institute-for-quantum-computing/blog/post/i-have-dream

I feel a great sense of fulfillment to have taken part in this project and I genuinely hope that it will grow to be a window to share the brilliant ideas of researchers at IQC. Welcome to our quantum world! 🙂

# Eating as little meat as I can

When I first moved to Canada in 2010, it didn’t take me long to realize that vegetarianism was a big thing here, certainly more than in Colombia. Most restaurants have clear indications of a wide-range of dishes that do not contain meat or animal products, not to mention the numerous restaurants that specialized in vegetarian cuisine. The residence were I was staying, had many options for vegetarians in its meal plan. Similarly, of the dozens of people I met, a surprisingly large fraction of them were excluding meat from their diets. At the time, this struck me as something unique to Canada, but I understand now that the shift away from animal products is actually a global trend, specially in the developed world.

As a scientist, my instinctive reaction to this phenomenon was genuine curiosity. Why are all these people not eating meat? Embarrassingly, I did not have an answer to that question, so I started to investigate. This is a general strategy of mine: Whenever I am faced with an important question whose answer will have a direct impact on my life, I make an honest effort to research the topic and think about it as objectively as possible. See this post for an example. Only through unbiased inquiry can you unravel truths that your instincts and prejudices would have prevented you from discovering.

What did my investigations lead me to? To the truth: Eating meat is really bad for your health, it is terrible for the environment, and it is specially horrific for the animals we farm and kill for food. This is an ugly, inconvenient, and harsh truth, but it is the truth nonetheless.

To make this point clearer, here are a few facts about eating meat. Unless otherwise stated, they are taken from the meticulously researched book Eating Animals by Jonathan Safran Foer:

– In the United States, 83% of all chicken meat (including organic and antibiotic free brands) is infected with either campylobacter or salmonella at the time of purchase. This is a major cause of food-borne illnesses.

– 76 million Americans become ill from their food annually, mostly due to animal products.

– In the United States, about 3 million pounds of antibiotics are given to humans each year, but at least 17.8 million pounds are fed to livestock.

– One-third of the land surface of the planet is dedicated to livestock.

– Farmed animals in the United States produce 130 times more waste than the human populations, roughly 87,000 pounds of manure per second.

– The UN special envoy on food called it a “crime against humanity” to funnel 100 million tons of grain and corn to ethanol while almost a billion people are starving. But animal agriculture uses 756 million tons of grain and corn per year, not to mention the fact that 98% of the 225 million tonnes of globally produced soy crop is fed to farm animals.

– Per weight, raising beef requires about one hundred times more water than most vegetables.

– American farmers are four times more likely to commit suicide than the general population.

– Slaughterhouse workers have the highest injury rate of any job, 27% annually.

– The United Nations Food and Agriculture Organization reports that current production levels of meat contribute between 14 and 22 percent of the 36 billion tons of “CO2-equivalent” greenhouse gases the world produces every year. This is more than the whole of the transportation industry combined. (Reference: Scientific American)

– There are at least 40 different diseases that can be transferred from animal waste to humans. (Reference: Rolling Stone)

– Yearly slaughter numbers for the United States: 9 billion broiler chickens, 113 million pigs, 33 million cows, 250 million turkeys. (Reference: Rolling Stone)

– The majority of the mass of land mammals on the planet is taken up by our livestock and pets. (Reference: xkcd)

– Reducing the consumption of farmed animals will help prevent deforestation, curb global warming, reduce pollution, save oil reserves, decrease human rights abuses, improve public health, and help eliminate the most systematic animal abuse in world history.

If you are skeptical of the facts I have listed, I invite you to check the links I have provided and the references therein. As far as I can tell after examination and cross-checking, the numbers I have provided are accurate. Most of the data refers to the United States, but there is very little reason to think that the situation is significantly different anywhere else in the world where meat is easily affordable.

Do you know what I asked myself after learning this information? What do I do now? I didn’t want to stop eating meat — meat was an essential part of my diet! Also, I knew that vegetarianism can be a huge inconvenience, specially when travelling, because very often there are either limited or no vegetarian options available. Moreover, completely cutting meat out from my diet would mean missing out from special moments that I enjoy with my friends and family. For example, the favourite restaurant of my partner’s parents is “Le Relais de Venise“, which serves a single main dish: steak frites. We have a tradition of going there for special occasions, like when we visit them in Paris. If I stopped eating meat, I would never go there again.

So I was faced with the following fundamental dilemma:

I understand that the problems with eating meat are severe and undeniable but, at the same time, I love eating meat and it would be a great inconvenience for me to never do it again. What should I do?

I have seen essentially two answers to this question: denial and vegetarianism. People that opt for denial are those who choose to ignore the awful truth about eating meat and continue with their lives in exactly the same way as before. For them, it is just not worthwhile to give up chicken, pork, and beef, so they don’t do it, regardless of the consequences. They toss the facts to the bin and make an effort to ignore them in the future. Since the food industry is a specialist of hiding all these problems, these people have an easy time forgetting that there are any issues at all. Denial is, after all, a very natural reaction when faced with facts that are hard to assimilate.

Alternatively, people will find a way to rationalize their decision to not make any changes to their diet. They will say things like: “But meat is so delicious!”, or: “I buy my meat in Whole Foods so it’s OK”, or even: “Those things you are saying only apply to fast food chains like KFC and McDonald’s, which I don’t go to anyway”. I don’t believe they do this because they do not care about animals, their health or the environment, but because it is the only way of feeling good about eating meat: fool yourself into thinking there is nothing wrong with it.

The vegetarians take the other extreme position — they make a conscious decision to never eat meat again. Some of them continue being vegetarians for the rest of their lives, while many others go back to eating meat at some point in the future. For them, the decision is clear: eating meat is a terrible thing, therefore I should not ever do it. In fact, it seems that unless we pretend that the problems aren’t there, vegetarianism is the only ethical choice. After all, what moral justification can we provide to eating meat even, in small quantities, when every time we do so we are contributing to major problem? Thus, it really appears to be that our only choices are vegetarianism or denial, nothing else. In fact, I believe this is how the dilemma is most often presented to people: Are you going to become a vegetarian or not?

The problem with this line of thinking is that it makes for an extremely ineffective strategy. Morally, I agree with the vegetarians — we should stop eating meat as long as it causes all these horrible problems. But at the same time, I cannot deny that when faced with vegetarianism as the only possibility, the vast majority of people, myself included, will not go down that road — we have too much to lose. This results in a situation in which the efforts everyone who is trying to raise awareness on this issue lead only to converting a small percentage of the population into vegetarians. I think this is an atrociously ineffective way of helping ourselves, our environment, and the billions of animals suffering in factory farms. It is utterly ineffective.

If the goal is to reduce meat consumption, it is more effective to make an effort to eat as little meat as possible. If you want to be a vegetarian, awesome. If you are only going to eat meat during the holidays when you visit your grandma, that’s OK too. If your local cafeteria doesn’t offer good vegetarian options, so you will eat meat there but nowhere else, that’s fine. If you love meat too much, but will make an effort to cut your consumption by 50% (and save money in the process), that’s a great.

The reason that this is a more effective strategy boils down to a simple inequality. Suppose that when people are presented with the truth about eating meat, X% of them will decide to become vegetarians. Alternatively, suppose that on average, each person will reduce their meat consumption by Y%. Then as long as Y>X, it is a better strategy to encourage people to eat as little meat as possible than to encourage them to become vegetarians.

From experience, I would estimate that no more than 10% of people will become vegetarians, even after being strongly persuaded with hard facts. On the other hand, let’s consider a conservative scenario in which the average person changes only three meals per week to dishes without meat. If the person has 21 meals per week, those three meals constitute a 14% reduction in meat consumption. My actual guess is that most people will easily go much higher than that, basically eating meat only on special occasions or when it is otherwise too inconvenient for them. My estimate is that, after being persuaded by evidence, people will reduce their consumption of meat by at least 30%. Graham Hill, who encourages people to become ‘weekday vegetarians’ in his 5 min TED-talk, appears to be largely motivated by the same premise: asking people to eat as little meat as possible is a more effective way of making a positive change in the world.

Notice how this black or white picture that is often painted with respect to meat consumption is not present in other issues. For example, when we learn about climate change, we don’t encourage others to never again use fossil fuels. We don’t offer a binary choice, we expect people to try to minimize their carbon footprint. Both climate change and meat-eating are situations where an argument could be made that an absolute minimization is the best scenario: No fossil fuels, no meat. The reason we don’t insist on a complete eradication is that we understand the drawbacks of never using fossil fuels again. All I am saying we should do the same with respect to meat.

Personally, I have done an immense effort to reduce the amount of meat I eat to an absolute minimum. Aleks, my partner, and I never buy meat beef, pork or chicken in our groceries, with the exception of salami that she can’t resist using on pizzas and calzones. We occasionally buy salmon and even more rarely, shrimp. Outside of home, I will buy meat whenever there are no good vegetarian alternatives, or when the people around me want to go to a place were there are no vegetarian options. Every now and then, I confess that I give into temptation and order a meal with meat, even with a delicious vegetarian dish on the menu.  Overall, it has been surprisingly easy for me to greatly reduce the amount of meat I consume — I always eat things that I love and I completely avoid going through difficulties.

Along the way, I have learnt many valuable things. First, I have realized that most of the time, the meat in a dish is either of bad quality or the flavour of the meat is dominated by the taste of all the other ingredients. For both of these cases, which constitute most meals I was previously having, removing the meat altogether or replacing it with a vegetarian alternative is an almost unnoticeable change. This is true for example in most of Italian, Indian and Mexican food. Second, I have learnt that some vegetarian alternatives are even better than the meat ones! For example, Aleks and I both prefer veggie ground beef, veggie burger patties, and veggie chicken nuggets to their meat counterparts. They are delicious, easy to cook and cheaper! Finally, I have noticed that my health has improved significantly because of this change in my diet.

Since I set myself the goal of eating as little meat as possible, I have reduced my meat consumption by around 90% compared to five years ago when I was living in Colombia. For very little effort, my life has improved immensely, and I have the great satisfaction that I am doing something significant to help our planet and to end the unnecessary and horrendous suffering of animals in factory farms around the world.

So here is my final advice to you: Try your best to eat as little meat as you can. Your body will thank you for it. Planet Earth will thank you for it. The suffering animals will thank you for it. You won’t regret it.

———————————————————

The featured image comes from the Instagram feed of Esther the Wonder Pig. It’s a beautiful example of humans and animals coexisting in harmony.

# QCMC 2014

I am back after a week in Hefei, China, were I was attending the 12th International Conference on Quantum Communication, Measurement and Computing (QCMC). This is probably my favourite conference because it attracts researchers from the entire quantum information community: theorists, experimentalists, computers scientists and engineers. It is also a great way of catching up with the results of the field in the past two years, specially given that many of the talks are informative rather than technical.

On this occasion, the venue was the Institute for Advanced Technology, which is part of the University of Science and Technology of China. The building is impressive in size, dwarfing the dimensions of IQC’s headquarters: the Mike and Ophelia Lazaridis Quantum-Nano Centre. However, perhaps owing to its enormity, it is eerily empty, with most of its floors unoccupied. I venture to speculate that the institute, as well as its surrounding infrastructure, was planned as a long-term investment, and it will take time to have all the facilities running at full capacity. China has grown at a formidable rate in recent decades, and it seems that it is not stopping any time soon. I am genuinely excited and curious to see what this very peculiar and intriguing country will be like in the future.

Since the conference venue was in an unoccupied part of the city which is very hard to access, the organizers had planned for a collection of shuttle buses to take the attendees back and forth from the spectacular Jingling Grand Hotel to the institute. Breakfast and dinner were provided at the hotel, and the evening events were all happening in there as well, which made it basically mandatory for everyone to stay in the hotel. This situation gave the whole conference a very strange ‘school-trip’ feel to it: wake up, have breakfast, take the bus, attend talks, have lunch in the cafeteria, attend more talks, go back in the bus, have dinner, repeat. I disliked this greatly.

Institute for Advanced Technology

QCMC is not a technical, highly specialized conference, but instead it is closer to a summary of the results of the field. As such, close to half of the talks were ‘invited talks’, given by well-known PIs who were selected by the conference committee to talk about the research in their groups. Most of the talks were thus simply an overview of the activities that are taking place in several groups around the world. Overall, I enjoyed the majority of the talks and learnt significantly from them.

I can’t really comment on all the talks, so I have selected my favourite five instead. Note that this is a highly biased selection, as I tend to favour talks that are closest to my research interests.

Eugene Polzik: Beyond the Heisenberg uncertainty. I loved this talk because it introduced me to an entire field I was completely unaware of. This guy and his team are studying — read this carefully — the trajectory of oscillating systems with a negative mass in a quantized reference frame which is entangled with the oscillator. Extremely interesting stuff, with practical applications to magnetometry.

Stephanie Wehner: Quantum cryptography beyond QKD: As I become increasingly interested in quantum cryptography, it is very helpful to hear someone carefully articulate recent advances in the field and new research directions. This talk also convinced me of the power of moving away from information-theoretic security and instead opting for a framework to bounding the quantum capabilities of adversaries.

Nathan Killoran: Identical particles: an accessible source of entanglement: I admit I have a weak spot for elegant, simple and yet profound results. To understand Nathan’s result one needs only to read the title of his talk and carry out a simple calculation, and yet the result is enlightening and apparently settles a long-standing debate on the significance of entanglement in systems of identical particles.

Quantum cryptography using practical photonic systems, Eleni Diamanti: A very helpful overview of current research in quantum cryptography. It was very useful to hear the status, advantages, and disadvantages of continuous-variable QKD being stated clearly and eloquently. It also made me very curious about the challenges of improving quantum coin-flipping protocols and of performing cryptographic tasks in integrated photonic systems.

Steering many-body quantum dynamics, Tommaso Calarco: This has to be the best conference talk I have ever seen. It had it all: comedy, intrigue, theatrics, animations, eloquence and good science. Kudos to Tommaso for showing the rest of us how it’s done.

Unfortunately, the poster session was quite disappointing. The talks in the morning took longer than planned (more on this later), and this led to less time allocated for the poster session. Moreover, we were not given materials to hang the posters, so most of us had to rely on other people who had brought tape or blu-tack. Since there were so many posters and such little time, I had no chance to actually take a look at other posters, but spend the session presenting mine. I was fortunate to have many people interested in my results, and I managed to have very fruitful discussion with several researchers.

Pretending to discuss our posters with Jean-Daniel Bancal. Photo courtesy of Valerio Scarani.

The conference started on a Sunday — I’m still not sure why — and on Monday night, in the hotel, there was an extremely interesting series of lectures given by the editors of PRL and Nature, discussing general aspects of the editorial process, problems with journal metrics and guidelines for submissions. The issues and polemics surrounding scientific publishing, specially with prestigious journals such as PRL and Nature, are close to the heart (brain?) of any scientist, so this session was obviously going to generate some reactions. Before I comment on this further, let me say that I find that the editors of these journals are actually doing a great job, and that most of the problems are not attributable to them but to the entire scientific community, as well as granting agencies and selection committees.

In case you were wondering.

Of course, I wasn’t the only one with an opinion on the matter. The day after, Reinhard Werner, during his award talk, took the opportunity to state his view. He planned to do so as a bonus to his talk on uncertainty relations, but it really was the thing to remember about his presentation. To give you an idea, one of the questions from the audience, after he finished his talk when he run out of time to continue was: “This is a question for the chairman: Can we give Prof. Werner extra time to continue talking about scientific publishing?”. The crowd applauded loudly and so the talk went on, beyond the schedule. Hence the shorter poster session.

Werner’s main point, which many of us are well aware of, is that the incessant focus on the impact factor — which Robert Garisto cleverly pointed out most scientists can’t even define — is extremely detrimental to science. In his words, “when we are judged by idiotic criteria, we all waste a lot of time behaving like idiots.” Carl Caves recently wrote a very timely and accurate column on making essentially this same point, which I highly recommend.

I want to dwell further on Werner’s talk. His first point was that judging the quality of a paper based on number of citations and journal of appearance is simply flawed. I already wrote an entire blog post about it more than a year ago.

Science is not just a competitive sport.

He went on to illustrate this further by pointing out that none of what he considers to be his best 10 papers are PRLs, and neither are any of the papers for which he was receiving the award. Nicolas Gisin also explained in his subsequent talk that his best paper was actually rejected by PRL and appeared instead in an obscure swiss journal. Werner also pointed out something we all know but are very good at forgetting: citation statistics are not an adequate method of assessing the quality of a paper.

Why do YOU cite papers?

Overall, Reinhard Werner made a great service to the quantum information community by reminding us that cleverness to solve scientific problems doesn’t give us a free license to behave like imbeciles.

The talk that followed was the other award talk by Nicolas Gisin. It was inspiring to see him literally share his award with all the students and postdocs that had contributed to his research career. Something else worth remembering: science is collaborative and highly social.

I want to add that this conference left me wondering about the future of the field. I am still fairly new to research, but I didn’t really see much novelty and certainly no breakthroughs, at least not compared to what I saw during QCMC 2012. The field has matured significantly and any ground-breaking results will not be easy to predict nor to attain. Maybe I am making a good bet by looking for new protocols in quantum communication? I guess we’ll have to wait for QCMC 2106 in Singapore!

Hefei skyline.