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Physics

Schrödinger's lunch

While visiting the University of Vienna for a conference, I came across Erwin Schrödinger's old desk set up in the lunch room. Sitting down at the desk to eat my lunch I stumbled upon a new quantum "paradox". Schrodinger's lunch

The Minute Physics Interactive Periodic Table of Awesome

Interactive Periodic Table

Henry Reich and Jasper Palfree have created an amazing interactive version of the Periodic Table. As you change temperature, you can see the elements transition between different states of magnetism. You can also see at what temperatures an element changes state from solid to liquid to gas. There is even an option to display temperatures in Fahrenheit for the heathens among you. If that isn't awesome enough, Henry makes clever use of Youtube, HTML5, and the interactive periodic table to explain how to destroy a magnet. You can also click on any element to see a clip, courtesy of Periodic Videos, about it. This is a great educational tool. I can't wait to see what Henry and Jasper come up with next.

A levitating Eiffel Tower

Julien Bobroff, a French physicist who is heavily involved in science outreach, has been coming up with clever ways of exploring the boundary between art and science using superconductivity. Check out his outreach site for some clever videos, craft projects, and animations that deal with a range of quantum behaviour.

I particularly like his collaboration with designer François Azambourg to convey some of the surprising properties of superconductivity. These include levitating jewellery, a no-contact line of clothing, a superconductivity circus, and a delightful superconducting Rube Goldberg machine breakfast maker.

He has also produced this page, Quantum made simple, which has some stunning animations of quantum tunnelling, lasers, and the double slit.

The blackhole firewall paradox

Excellent overview by Jennifer Ouellette of a new paradox that is taking the physics world by fire. I first heard about this a month ago from Patrick Hayden. It looks like this could turn into one of the great thought experiments that tackles the difficulties merging quantum mechanics and general relativity.

Paradoxes in physics have a way of clarifying key issues. At the heart of this particular puzzle lies a conflict between three fundamental postulates beloved by many physicists. The first, based on the equivalence principle of general relativity, leads to the No Drama scenario: Because Alice is in free fall as she crosses the horizon, and there is no difference between free fall and inertial motion, she shouldn’t feel extreme effects of gravity. The second postulate is unitarity, the assumption, in keeping with a fundamental tenet of quantum mechanics, that information that falls into a black hole is not irretrievably lost. Lastly, there is what might be best described as “normality,” namely, that physics works as expected far away from a black hole even if it breaks down at some point within the black hole — either at the singularity or at the event horizon.

Together, these concepts make up what Bousso ruefully calls “the menu from hell.” To resolve the paradox, one of the three must be sacrificed, and nobody can agree on which one should get the ax.

Physicists don’t lightly abandon time-honored postulates. That’s why so many find the notion of a wall of fire downright noxious. “It is odious,” John Preskill of the California Institute of Technology declared earlier this month at an informal workshop organized by Stanford University’s Leonard Susskind. For two days, 50 or so physicists engaged in a spirited brainstorming session, tossing out all manner of crazy ideas to try to resolve the paradox, punctuated by the rapid-fire tap-tap-tap of equations being scrawled on a blackboard. But despite the collective angst, even the firewall’s fiercest detractors have yet to find a satisfactory solution to the conundrum.

Joe Polchinski, one of the authors who published the paper on the blackhole firewall paradox, has a more technical write up of the subject over on Cosmic Variance.

Earlier this year, with my students Ahmed Almheiri and Jamie Sully, we set out to sharpen the meaning of black hole complementarity, starting with some simple `bit models’ of black holes that had been developed by Samir Mathur and Steve Giddings. But we quickly found a problem. Susskind had nicely laid out a set of postulates, and we were finding that they could not all be true at once. The postulates are (a) Purity: the black hole information is carried out by the Hawking radiation, (b) Effective Field Theory (EFT): semiclassical gravity is valid outside the horizon, and (c) No Drama: an observer falling into the black hole sees no high energy particles at the horizon. EFT and No Drama are based on the fact that the spacetime curvature is small near and outside the horizon, so there is no way that strong quantum gravity effects should occur. Postulate (b) also has another implication, that the external observer interprets the information as being radiated from an effective membrane at (or microscopically close to) the horizon. This fits with earlier observations that the horizon has effective dynamical properties like viscosity and conductivity.

I love that one of the postulates is called "no drama."

Entangling three photons in energy and time

Entangling three photons in energy and time

Our latest paper, on which I was the lead author, has just been published in Nature Physics. I am working with Jasper Palfree to develop a comprehensive page that explains the work. Unfortunately, that is not ready yet. In the mean time, here is the official press release:

Photon Triplet Counts

Extending Einstein

Researchers at the University of Waterloo and the University of Calgary have carried out an experiment, using the quantum properties of three particles light, that could provide new insights into the philosophical arguments by Einstein about the foundations of quantum mechanics.

In 1935 Albert Einstein, Boris Podolsky, and Nathan Rosen (EPR) published a thought experiment designed to show that quantum mechanics, by itself, is not sufficient to describe reality. Using two entangled particles – particles that share correlations stronger than those allowed by classical physics – EPR tried to demonstrate that there must be some hidden parameters that quantum mechanics does not account for. The ensuing debate led to the pioneering work of John Bell who, in 1964, showed that by following the arguments of EPR to their logical conclusion one arrives at a contradiction with experiments; hidden parameters, like the ones EPR argued for, are incompatible with our observations of nature and the mystery at the heart of quantum mechanics remains intact. This has profoundly shaped our understanding of quantum theory, and today the entanglement between two particles that EPR first proposed is a valuable resource in emerging quantum technologies like quantum computing, quantum cryptography, and quantum precision measurements.

77 years after EPR's landmark work a new paper in Nature Physics, authored by physicists at the Institute for Quantum Computing in Waterloo and at the University of Calgary, has finally experimentally extended the original ideas of Einstein and his colleagues from two to three entangled particles. This new form of three-particle entanglement, based on the position and momentum properties of photons, may prove to be a valuable part of future communications networks that operate on the rules of quantum mechanics, and could lead to new fundamental tests of quantum theory that deepen our understanding of the world around us. According to group leader Thomas Jennewein, "It is exciting, after all this time, to be able to create, control, and entangle quantum particles in this new way. Using these states of light it may be possible to interact with and entangle distant quantum computer memories based on exotic atomic gases."

In the experiment the researchers took a highly energetic blue photon and passed it through a special crystal that caused it to split into a pair of red coloured daughter photons. They then repeated this process with one of the daughter photons to create three entangled photons. The energy of these three photons, through the conservation of energy, must be equal to the energy of the original blue photon. Because the splitting process is instantaneous, the three photons must arrive at the detectors at the same time. It is therefore possible to learn the precise energy (corresponding to their total momentum) of the three photons as well as their arrival times (corresponding to their position). At first this seems to be an apparent contraction with the Heisenberg uncertainty principle which states that it is impossible to simultaneously learn arbitrarily precise information about a particle's position and momentum. However, with entangled particles, it is possible to gain precise information about the sum and differences of their position and momentum in a manner not possible with classical particles. This is in part because each of the particles in an entangled state gives up its own individual identity–the properties of the particles are instead shared collectively. It still remains impossible to gain position and momentum information of any individual particle. Says lead author Krister Shalm, "It is as if you could only discover how many points two teams combined to score in a basketball game, but had no way of knowing how many points each individual team had scored." Co-author Deny Hamel adds, "Because the entangled photons cooperate with one another they can do things that classical particles are unable to."

The next step for the researchers is to try to combine the position and momentum entanglement between their three photons with more traditional types of entanglement based on angular momentum. This will allow the creation of hybrid quantum systems that combine multiple unique properties of light at the same time. According to Christoph Simon from the University of Calgary, "This work opens up a rich area of exploration that combines philosophy, quantum mechanics, and quantum technologies. The powerful insights by Einstein and his co-workers in 1935 are still informing the way we understand the world around us."

2012 Nobel Prize: How Do We See Light?

Henry Reich from Minute Physics explains the science behind Serge Haroche's quantum non-demolition measurements. Since Max Planck and his study of black body radiation, the interaction between light and matter has played a critical role in the development of quantum mechanics.

Haroche's experiment was able to detect, without destroying, the presence of single photons in a cavity cooled to 0.8K. This allowed him to "see" the birth and death of black body radiation photons. Being able to detect single photons without destroying them has important implications for quantum information. I have always been taken by how this experiment connects Planck's work with quantum information, forming a beautiful narrative that spans more than a century of physics. This is only one of several incredible experiments by Haroche that contributed to his selection for the 2012 Nobel Prize in physics.

I am also continually amazed by Henry and the quality, both in presentation and content, of his videos.

A way around Nobel’s 3-person limit

It is rare for a discovery or breakthrough in science to come from a single person or group. Science is a collaborative effort so how do you appropriately give credit for a discovery with something like the Nobel Prize where many people have contributed, but only up to three people can be recognized? Charlie Bennet has a clever solution using randomness.

Quantum Optics Researchers win 2012 Nobel Prize

Quantum Optics Researchers win 2012 Nobel Prize

David Wineland And Serge Haroche
David Wineland And Serge Haroche

From the Nobel Prize Committee:

The Nobel Prize in Physics 2012 was awarded jointly to Serge Haroche and David J. Wineland "for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems"

This is exciting news for people, like myself, who work in the field of quantum optics and quantum information. Both David Wineland and Serge Haroche have spent decades carrying out beautiful experiments that further push and refine our ability to manipulate and control quantum systems.

David Wineland's work with trapped ions has led to important improvements in atomic clocks and served as exciting testbed for quantum computing. Serge Haroche's work with cavity quantum electrodynamics is opening up new techniques for controlling the interaction of light and matter.

The Nobel Prize Committee has a nice, but slightly more technical, background of the research that is worth a read:

The behaviour of the individual constituents that make up our world – atoms (matter) and photons (light) – is described by quantum mechanics. These particles are rarely isolated and usually interact strongly with their environment. The behaviour of an ensemble of particles generally differs from isolated ones and can often be described by classical physics. From the beginning of the field of quantum mechanics, physicists used thought experiments to simplify the situation and to predict single quantum particle behaviour.

During the 1980s and 1990s, methods were invented to cool individual ions captured in a trap and to control their state with the help of laser light. Individual ions can now be manipulated and observed in situ by using photons with only minimal interaction with the environment. In another type of experiment, photons can be trapped in a cavity and manipulated. They can be observed without being destroyed through interactions with atoms in cleverly designed experiments. These techniques have led to pioneering studies that test the basis of quantum mechanics and the transition between the microscopic and macroscopic worlds, not only in thought experiments but in reality. They have advanced the field of quantum computing, as well as led to a new generation of high-precision optical clocks.

Here is an interview with David Wineland that IQC conducted earlier this year when he was visiting.

Congratulations to both research groups and everyone involved.

The CIA and Jeff Bezos Bet on Quantum Computing

A 30 million dollar bet. That's a lot of money for D-Wave.

It's an attitude that seems to have played well with investors, but it still rankles academics. "At an engineering level they've put together a setup that's impressive in various ways," says Scott Aaronson, an MIT professor who studies the limits of quantum computation. "But in terms of the evidence that they're solving problems using quantum mechanics faster than you could classically, I don't think it's there yet." A fierce critic of D-Wave in the years following its 2007 demo, Aaronson softened his stance last year after the company's Nature paper showing quantum effects. "In the past there was an enormous gap between the marketing claims and where the science was and that's come down, but there's still a gap," says Aaronson, who visited the company's labs in February. "The burden of proof is on them and they haven't met the burden yet."

Aaronson's biggest gripe is that the design of D-Wave's system could plausibly solve problems without quantum effects, in which case it would simply be a very weird conventional computer. He and other critics say the company must still prove two things: that its qubits really can enter superpositions and become entangled, and that the chip delivers a significant "quantum speed-up" compared to a classical computer working on the same problem. So far the company has presented proof of neither in a peer-reviewed forum.

If I had to wager today, my money would be on IBM.