Serge Haroche's Talk At NUS

French physicist Professor Serge Haroche came to the new NUS Alumni House last Wednesday to give a public talk entitled "Power and Strangeness of the Quantum".

I think that quantum physics is one of the most misunderstood fields of science in the public perception, so I decided to go to the lecture to learn more about it directly from an expert in this area.

Since it was going to be a public talk, hopefully there won't be too much difficult maths!















As you can see, the turnout for the talk was excellent. This was my first visit to the Alumni House - they have a nice big lecture theatre, which was about three-quarters full on that day.

The crowd was quite varied; there were political dignitaries (I assume from the French Embassy), French-speaking scientists, school kids in uniform and even a Sister in religious dress.















Here's the MC for the evening starting off the event by introducing the Dean of Science, Professor Andrew Wee, who would be giving the welcome address.















In his address, Prof. Wee said jokingly that he was glad that so many people turned up for the talk, even though it was April Fool's Day!

He noted that this talk was part of the 80th anniversary celebrations of the Faculty of Science, which would include many other activities, such as science busking.

He also revealed that the Ambassador of France was in attendance in the audience, which indicates that the invited speaker is a highly respected academic indeed.















Next, Prof. Wee called upon Christian Miniatura, who is a visiting professor at the Centre for Quantum Technologies, to give an introduction about Prof. Haroche's research career.















Here's a quick overview of Prof. Haroche's many academic accomplishments. Note that he has taught in American universities for a number of years - I'll come back to that later.















Next, a photo of the research group where Prof. Haroche was a graduate student. His supervisor Prof. Claude Cohen-Tannoudji would later share the Physics Nobel Prize in 1997.

Prof. Miniatura remarked that Prof. Haroche looked pretty casual at that time, with his hands in his pockets...















Another photo of Prof. Student Haroche at that time, not looking very prominent amongst a big stack of research equipment.

Prof. Miniatura noted that those machines may look antiquated, but our instruments today would also look old-fashioned to our grandchildren.

I should also add that scientific equipment may become faster and better, but one thing will never change - troubleshooting.

Remember kids, if there isn't any troubleshooting, it ain't science!















After the brief introduction, Prof. Haroche was welcomed onto the stage...















... and there was a lolcat right there waiting for him.

But of course.

What did you expect?

Did you really think that you can sit through a lecture on quantum physics without seeing a lolcat?!??

Think inside the box, my friend!















Prof. Haroche began by remarking that seeing those old photos again gave him a bittersweet feeling, because it reminded him of how fast time flies.

I think that the years that he spend in the USA has affected his accent; he sounds less French than Prof. Miniatura.

(I also noticed that French people who have spent too many years in Singapore pick up an amazingly authentic Singlish accent, far more accurate than Americans or Brits. But that's a topic for another time...)

He then pointed out that the famed Richard Feynman quote - "nobody understands quantum mechanics" - should be taken with a grain of salt.

"But just in case you don't learn anything from my talk, at least you're in good company," he joked.

Nice.















Though quantum physics is usually associated with microscopic phenomena, it actually deals with more than 60 orders of magnitude!

As mentioned in the previous slide, quantum law appears at all scales, but at the macroscopic level, it is generally "veiled".

This is an important point that he'll explain in detail later.















As usual, with these sort of scale charts, biological scales are often represented by the DNA double-helix, but never the collagen triple-helix.

It always makes me smirk. Oh well, I'm not a biochemist anyway.

And biologists always appear "sandwiched" between particle physicists and astronomers.

That's fine to me too; it's the stuff in the "middle" that determines the flavour of a sandwich...















This is a public talk where the audience may be more interested in tangible benefits, thus Prof. Haroche spent some time emphasizing the importance of quantum physics to everyday technologies, such as computers...















... lasers...















... atomic clocks (less than one second error over 10 million years!) and GPS systems that depend on them...















... and the quintessential marvel of modern technology - the MRI, which is actually a combination of three quantum technologies.















Now for the maths... time to run and hide!

Not so fast, Prof. Haroche is simply stating that the behaviour of an electron in a hydrogen atom can be described using a wavefunction - a mathematical tool that gives probabilistic results.

Instead of a particle moving in a fixed orbit, the electron is considered to be in a superposition of an infinite number of possible positions.

He noted that Nature has a "wavy" structure. In quantum physics, determinism is replaced by randomness and particles are replaced by wavefunctions.

Apparently Einstein disliked the random aspect of the wavefunction so much that he uttered his famous "God doesn't play dice" quote.















Wavefunctions may sound like mere mathematical constructs, but Prof. Haroche showed us that modern instruments can produce real images of wavefunctions.















Once again, he emphasized that quantum theory is a probabilistic theory.















The essence of quantum strangeness is exemplified by the bizarre phenomenon of quantum interference, which is often demonstrated using Young's double-slit experiment.

When individual particles (eg. electrons) are fired one-by-one through the setup, they hit the target screen at random positions.

As more and more particles pass through, a predictable interference pattern builds up progressively.

But how can there be "interference" if there was only one particle passing through at any one time?















In quantum physics, the wave equation accurately predicts the appearance of the interference pattern.

But Prof. Haroche remarked that classical physicists are not satisfied with that sort of "explanation"...















... they want to know exactly what happened to the particle...















... but the very act of observing the particle disrupts the interference pattern on the target screen!

To me, the easiest way of bending my brainz around this is to think of "observation" here as an active process that can perturb the behaviour of the particle.

Something like how people look away when you shine a bright light in their faces!

More on this later.















Quantum interferences don't just occur spatially, but temporally as well. Interference patterns that appear in time are called "quantum beats".















I'm not going to pretend that I understand the maths behind quantum entanglement.

Suffice to say that once again Einstein didn't like this, calling it "spooky action at a distance", but John Bell found a way to experimentally test it and prove him wrong.















Another strange feature of quantum mechanics has to do with particle identity.

At macroscopic scales, "identical" particles can still be differentiated from one another.















But in quantum systems, identical particles cannot be distinguished from each other. They have no "colours".

Particles can be divided into two categories, based on their interactions with one another: Fermions and Bosons.















Here's a quick overview of the differences between fermions and bosons.

Particle constituents of matter are fermions while intervening particles (such as photons) are bosons.

Got it.















But atoms that are made up of an even number of fermions behave like bosons.

Er... I'm getting a little lost here.















So, depending on the total number of particles in an isotope (including electrons), an atom can behave either as a fermion or as a boson, thus producing a different interference pattern.

I think I understand this.















Now, to me this is the most important slide in the entire talk, because it addresses a key public misunderstanding of quantum physics that is often exploited by New Age woo-meisters.

Can quantum strangeness occur to macroscopic objects?

Erwin Schrödinger once posed this question as a thought experiment: the infamous Schrödinger's Cat (referenced in the lolcat slide earlier) which has become sort of a mascot for quantum strangeness.

Schrödinger was thinking of a way to transform a superposition inside an atom to a large-scale superposition of a live and dead cat by coupling the cat and atom using a specially constructed device.

He wanted to critique the Copenhagen interpretation of quantum mechanics by illustrating the absurdity of its consequences.

Wikipedia describes this concisely:

A cat, along with a flask containing a poison, is placed in a sealed box shielded against environmentally induced quantum decoherence.

If an internal Geiger counter detects radiation then the flask is shattered, releasing the poison which kills the cat.

Quantum mechanics suggests that after a while the cat is simultaneously alive and dead.

Yet, when we look in the box, we see the cat either alive or dead, not a mixture of alive and dead.

Prof. Haroche explained that quantum strangeness usually does not happen to macroscopic objects precisely because of decoherence: the environment gets entangled with the system and destroys quantum superpositions.

He said that you can consider it as the environment "spying" on the cat.

Decoherence becomes faster as the system size increases, thus macroscopic objects behave in a more intuitive, classical manner.















Schrödinger did not expect anyone to actually test his thought experiment, but today physicists have the tools to fight decoherence and it is now possible to do the imaging of isolated trapped atoms...















... see microwave photons...















... and even set up a photonic version of the Schrödinger's Cat experiment.

Here, the purple feature under the disk corresponds to the "cat state" quantum coherence.















As decoherence effects set in, you can see the purple feature gradually disappear from the field diagram as the quantum system is transformed into a classical system (towards upper right).















Prof. Haroche then proceeded to talk about new quantum technologies on the horizon.

An exciting new field of quantum computing is emerging and has the potential to be much faster than current technology.

However, he cautioned that building a large practical quantum computer is very difficult because of decoherence.

A simpler application of quantum entanglement is in cryptography - used for the purposes of secure communications. This technology is already available on the market.















In his last slide, Prof. Haroche turned to his attention to the question of whether a second "quantum revolution" is approaching.

He speculated that we might see new applications in the future that we can't even dream about today.

As a concluding message, he encouraged young scientists to let their curiosity drive their research and not to be obsessed with the quantum computer, but quickly added "as long as the funding agencies permit it".

He joked: "That is our tragic position in life."

With that, he ended his talk and it was time for the Q&A session!

I asked the first question of the evening, and not surprisingly it was:

"What popular misconception of quantum physics in the public annoys you the most?"

Prof. Haroche replied that he especially disliked the abuse of quantum physics in discussions of consciousness or free will, because those processes operate at an "overwhelmingly classical" level.

Later, a member of the audience stood up and commented: "I'm just a layman but now I know where the term 'quantum leap' comes from!"

Then there was a question about quantum tunneling, and Prof. Haroche proceeded to give a quick overview of that effect.

I think the best question of the evening came from a young man who asked:

"There are now numerous interpretations of quantum mechanics. Which interpretation do you prefer?"

Prof. Haroche conceded that it was a good question - he was aware of physicists who were adamant that quantum mechanics does not "need" interpretations and that the mathematics was all that you needed.

He used to subscribe to that view, but confessed that as he got older, he appreciated interpretations more. Still, he thought that it could be an "endless game" since our intuition is simply unable to understand quantum mechanics.



















After all that heavy intellectual "food" it was time to stuff my face with some real "classical" stuff!

It was Thai food, and you can see that there was a good spread.

As I munched on my dinner, I was thinking about decoherence due to environmental entanglement and how it vastly simplifies the behaviour of macroscopic objects, which fits nicely into my FAMILIAR model.

Maybe I'm really on to something...


Would you like to know more?

Other lectures by prominent academics:
- Bruce Alberts At The Biopolis
- Embryonic Stem Cell Lecture (Prof. Martin Evans)
- Early Detection Is Your Best Bet (Prof. Lee Hartwell)