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Quantum Mechanics
A colleague of mine, Anne Broadbent, just published a fascinating piece of work in Science. The story has been picked up by the BBC as well! Their were television crews in the building all morning interviewing Anne about her work.
Here is the IQC's press release regarding the experiment.
This coming March I am going to be explaining some the intricacies of Quantum Mechanics using Lindy Hop. To pull this off, I need your help.
The goal is to get as many scenes as possible to film themselves performing the routine. The footage will then be spliced together and be incorporated into a larger performance.
A documentary by Karol Jalochowski that profiles a number of physicists working at the Centre for Quantum Technologies1 in Singapore. It is great to hear fellow physicists talk about why they love science and the things that attract them to quantum mechanics.
From the Vimeo description:
THE MECHANICS is a short documentary project about the crazy world of quantum mechanics. The mechanics - all based in the Centre for Quantum Technologies in Singapore - are: Stephanie Wehner, Dagomir Kaszlikowski, Elisabeth Rieper, Kwek Leong Chuan, Pawel Kurzynski, Artur Ekert, and Momo Lu Yin.
Captivating one hour lecture by Brian Cox on Quantum Mechanics. This is one of the best public science lectures I have ever seen. Using one of the largest uncut diamonds ever discovered, Brian delves into the structure of the universe and explains how diamonds bigger than our Sun can be formed.
Special celebrity volunteers, like Simon Pegg, help Brian convey the physics. I love how he offset the technical parts of the talk with humour. Brian Cox is, in many ways, the next iteration of Carl Sagan.
I wish the Canadian Broadcasting Corporation (CBC) created more programs like this.
(via scienceisbeauty)
Wow. Our double-slit experiment published earlier this year in Science has been voted as the top Physics breakthrough of 2011 by Physics World! We are in some good company considering all of the things that have happened this year. Congratulations to Aephraim, Sacha, Boris, Sylvain, Marty, Rich.
But after much debate among the Physics World editorial team, this year's honour goes to Aephraim Steinberg and colleagues from the University of Toronto in Canada for their experimental work on the fundamentals of quantum mechanics. Using an emerging technique called "weak measurement", the team is the first to track the average paths of single photons passing through a Young's double-slit experiment – something that Steinberg says physicists had been "brainwashed" into thinking is impossible.
Honorable mention goes to Jeff Lundeen whose work on a similar experiment comes in second.
Here is a link to some of the coverage about our experiment.
Speaking of Scott Aaronson, here is his entertaining, as always, take on the recent quantum foundations paper by Matthew Pusey, Jonathan Barrett, and Terry Rudolph. Scott ends with the following (after taking a jab at Luboš Motl):
There’s an important lesson here for mathematicians, theoretical computer scientists, and analytic philosophers. You want the kind of public interest in your work that the physicists enjoy? Then stop being so goddamned precise with words! The taxpayers who fund us—those who pay attention at all, that is—want a riveting show, a grand Einsteinian dispute about what is or isn’t real. Who wants some mathematical spoilsport telling them: “Look, it all depends what you mean by ‘real.’ If you mean, uniquely determined by the complete state of the universe, and if you’re only talking about pure states, then…”
Scott Aaronson provocatively lays out the importance of quantum computing research without resorting to hyperbole and fluff. Often, when quantum computing is explained to the public, the focus is on the razzle-dazzle promise of future computing power. What are left out are the advances in our understanding of nature that have happened as a result of physics using techniques from computer science.
Scott writes:
Quantum computing really is one of the most exciting things happening in science right now. Just not for the reasons you usually hear. [...]
And yet, even though useful quantum computers might still be decades away, many of their payoffs are already arriving. For example, the mere possibility of quantum computers has all but overthrown a conception of the universe that scientists like Stephen Wolfram have championed. That conception holds that, as in the “Matrix” movies, the universe itself is basically a giant computer, twiddling an array of 1’s and 0’s in essentially the same way any desktop PC does.[...]
But the biggest payoff so far may have been an improvement in the way quantum mechanics itself is taught and understood. Since its beginnings in the 1920s, quantum mechanics has been considered the prototype of an abstruse, complicated theory: something beyond the grasp of all but a few physicists. Today, though, I and others regularly explain its underlying logic to students by focusing on the simplest imaginable system to which that logic applies: the qubits that make up a quantum computer.
Is the universe deterministic? This is something I have spent many hours thinking about and debating with other physicists. Sean Carroll, in a response to a post by Massimo Pigliucci, provides a good introduction to some of the different view points taken in this debate. Much of it hinges on which interpretation of quantum mechanics you choose to hang your hat.
Sean makes several interesting observations including this one:
My personal suspicion is that the ultimate laws of physics will embody something like the many-worlds philosophy: the underlying laws are perfectly deterministic, but what happens along any specific history is irreducibly probabilistic. (In a better understanding of quantum gravity, our notion of “time” might be altered, and therefore our notion of “determinism” might be affected; but I suspect that there will still be some underlying equations that are rigidly obeyed.) But that’s just a suspicion, not anything worth taking to the bank.
Emphasis added by me. This is an excellent point that I had never considered before. There is a chance that our view of time and determinism our incomplete within the current quantum framework. This would be surprising (at least to me), but I have not spent much time think about issues in quantum gravity.
Sean also makes a good point about arguments concerning free will. Often determinism and free will are conflated with one another:
It matters, of course, how one defines “free will.” The usual strategy in these discussions is to pick your own definition, and then argue on that basis, no matter what definition is being used by the person you’re arguing with. It’s not a strategy that advances human knowledge, but it makes for an endless string of debates.
A better question is, if we choose to think of human beings as collections of atoms and particles evolving according to the laws of physics, is such a description accurate and complete? Or is there something about human consciousness — some strong sense of “free will” — that allows us to deviate from the predictions that such a purely mechanistic model would make?
If that’s your definition of free will, then it doesn’t matter whether the laws of physics are deterministic or not — all that matters is that there are laws. If the atoms and particles that make up human beings obey those laws, there is no free will in this strong sense; if there is such a notion of free will, the laws are violated. […] Quantum mechanics doesn’t say “we don’t know what’s going to happen, but maybe our ineffable spirit energies are secretly making the choices”; it says “the probability of an outcome is the modulus squared of the quantum amplitude,” full stop. Just because there are probabilities doesn’t mean there is room for free will in that sense.
Interesting and thought provoking. I am eager to see how this discussion unfolds.
A new paper in Science claims to have entangled the vibrations of two large1 slabs of diamonds at room temperature! If this is true, it is a really cool result.
Until I have a chance to go through the paper in detail I remain skeptical of the results. At room temperature the entanglement would last for a vanishingly short amount of time. This must be an experiment that uses some form of heavy handed post-selection to see the entanglement. Still, the results are impressive.
Jonathan Mann has been writing a song a day for over 1000 days. According to his Youtube channel he is up to 1061 songs and is still going strong.
I imagine trying to come up with an original song every day is a challenge. One technique is to sing the abstracts of physics papers. On day 264 that is exactly what Jonathan did; he turned the abstract of this paper by Daniel E. Sheehy and Leo Radzihovsky into a song (free version of the paper here).
We study a one-dimensional gas of fermionic atoms interacting via an s-wave molecular Feshbach resonance. At low energies the system is characterized by two Josephson-coupled Luttinger liquids, corresponding to paired atomic and molecular superfluids. We show that, in contrast to higher dimensions, the system exhibits a quantum phase transition from a phase in which the two superfluids are locked together to one in which, at low energies, quantum fluctuations suppress the Feshbach resonance (Josephson) coupling, effectively decoupling the molecular and atomic superfluids. Experimental signatures of this quantum transition include the appearance of an out-of-phase gapless mode (in addition to the standard gapless in-phase mode) in the spectrum of the decoupled superfluid phase and a discontinuous change in the molecular momentum distribution function.
As awesome as I find this, there is a reason the Beatles and Rolling Stones have never tried this approach.
A little poster I made about Bose-Einstein condensates (BEC). When steam turns to water or water turns to ice it is known as a phase-transition. If you were to keep cooling ice it will undergo a number of other transitions into new states of matter.
But how cold can you go?
Using some special techniques, it is possible to cool a cloud of dilute atoms down to a a few billionths of a degree above absolute zero. When these temperatures are reached, the atoms all suddenly enter their lowest energy state (known as the ground state). When this happens, the atoms begin to act collectively. It is even possible to create a laser made out of atoms in a BEC.
In 2001 the Nobel Prize in Physics was awarded to Eric Cornell, Carl Wieman and Wolfgang Ketterle for their work creating the first BECs. I recently came across the Nobel lecture given by Eric Cornell and Carl Wieman; a fascinating read about the history behind the making of the first BEC.
(Image Credit: NIST)
This summer I was asked to give a lecture at the Quantum Cryptography School for Young Students. Some of the brightest high school students from around the world gathered at the Institute for Quantum Computing (where I work) to learn about what we do. I spoke about Bell's Inequalities, one of the fundamental ideas that is the foundation for much of what we do in my field.
The lecture is aimed at a more advanced enthusiasts. I was impressed by how well the students were able to keep up. Bell's inequalities is not easy to explain and the subtleties are even lost on many physicists. I have been searching for a way to convey the critical results of Bell's inequalities to a ten year old, but have so far failed. If anyone knows of a clever explanation, let me know. (I don't think the standard explanations using the colour of ones socks or baking cakes are clear for a general audience.)
This is one of my favourite TED talks. John Bohannon completely blew my mind. In the space of eleven minutes using dancers he talks about laser cooling, super fluids, slow light, and cellular biology. This talk, especially the first half, is a synthesis of all the things I have come to believe about science communication. Incredible choreography and timing.
John also runs the popular Dance your PH.d contest I entered a couple years back. My favourite line from the talk:
I think that bad Powerpoint presentations are a serious threat to the global economy.
My only criticism is that during the second half, when he is making his point about Powerpoint and arts funding, the dancers were distracting. The attention should have been solely on John and what he was saying, not the lazy boy the dancers formed. I think it would have been more powerful to have the dancers leave the stage and then rush back in for the finale. The absence of the dancers would have fit nicely with his point about what would happen if arts funding is cut. Still, this is a very minor quibble. I loved this talk and will be watching it over and over again.
(via Madhur Anand)
If anyone is wondering what to buy me for Christmas, this shirt in either navy, black, or forest green (size=L) is a good place to start.
Quantum Mechanic: Tweaking your reality one atom at a time.
I would also accept a shirt with the Schrödinger cat dead and alive design as well.
This has been going around Facebook. A great use of negative space to convey a deep concept in physics. Kudos to the artist who designed this (I have not been able to track down the original yet).
An interesting take by Matt Leifer on Matthew Pusey, Jonathan Barrett, and Terry Rudolph's recent foundations of quantum mechanics paper:
The question is whether a scientific realist can interpret the quantum state as an epistemic state (state of knowledge) or whether it must be an ontic state (state of reality). It seems to show that only the ontic interpretation is viable, but, in my view, this is a bit too quick. On careful analysis, it does not really rule out any of the positions that are advocated by contemporary researchers in quantum foundations. However, it does answer an important question that was previously open, and confirms an intuition that many of us already held. Before going into more detail, I also want to say that I regard this as the most important result in quantum foundations in the past couple of years, well deserving of a good amount of hype if anything is.
Also, check out Scott Aaronson's analysis of the results.
This is why I love Futurama. In less than two minutes they cite Lorentz invariance, refraction, and Schrödinger's cat. It should come as no surprise how science savvy this show is; the writing staff is stacked with scientists and David Cohen, one of the co-developers, has degrees in physics and computer science. From this 2007 Wired piece:
Futurama was geek-friendly to begin with: Episodes are built around sci-fi staples like parallel universes, spaceship battles, and time travel. But look more closely and you'll spot fleeting jokes that are geekier than a Slashdot comments thread, gags about the Heisenberg Uncertainty Principle, particle physics, and the P=NP problem.
There is also this excellent interview by SEED magazine with the writers of the show.
This could be one of the most exciting result in a generation that has come out about the foundations of quantum mechanics. I have just downloaded the article and started to wade through it. In the meanwhile here is what Nature News has to say about it:
Their theorem effectively says that individual quantum systems must “know” exactly what state they have been prepared in, or the results of measurements on them would lead to results at odds with quantum mechanics. They declined to comment while their preprint is undergoing the journal-submission process, but say in their paper that their finding is similar to the notion that an individual coin being flipped in a biased way — for example, so that it comes up 'heads' six out of ten times — has the intrinsic, physical property of being biased, in contrast to the idea that the bias is simply a statistical property of many coin-flip outcomes.
I can't wait to get back from Ottawa to talk to my colleagues about this. Here is the link to the preprint of the paper by Matthew Pusey, Jonathan Barrett, and Terry Rudolph.
With apologies to William Blake Photon! Photon! Forming Flight, In the lab as dark as night. What nonlinear order Chi Could spring entangled Symmetry?
In what distant laser dyes Sparked thy subtle wave-like guise? What on resonance transpires? On what level lasing fires?
And what calcite, and what part? Could squeeze thy spin with such art? And when thy mode began to lock, What short pulse, and what short clock
What the Amplitude? What the Phase? Of this single-photon craze? What the particle? What dread thought In what paradox are we caught?
When the stars threw down their spears, That travelled for a million years, Did the correlations bunch? Just like Twiss and the other's hunch?
Photon! Photon! Forming Flight, In the lab as dark as night. What nonlinear order Chi Could spring entangled Symmetry?
—Krister Shalm 2010
This is the poem that I wrote for my PhD thesis. I have been meaning to post it for awhile now.
For those of you who missed it in person, the video for the Quantum Physics & Harry Potter is now live. Dan and I had a lot of fun putting this on and are hoping to repeat the show sometime in the winter. A big thanks to Peter Kovacs for shooting and editing the video.
