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Quantum physics can make rocket science look like kindergarten circle time. Even experts find it daunting. So imagine the challenges that science writers face, both in understand the physics and conveying it to a general readership. To try to help, Sabine Hosenfelder and I organized a workshop on quantum physics for science journalists, held at the Nordic Institute for Theoretical Physics in Stockholm this past August. Sabine and I got the idea a couple of years ago at a Nordita social event, where the open bar made us so rash as to commit ourselves to doing it.
The workshop gave writers a chance to extricate themselves from the hurly-burly of publishing for a few days, recharge their intellectual batteries, and learn about what's going on in all sorts of important and fun areas, from quantum optics to topological insulators. Some 25 of them came from across Europe to hear seven physicists, including FQXi members Raymond Laflamme, Lárus Thorlacius, and Silke Weinfurtner, as well as Eddy Ardonne, Marie Ericsson, Rainer Kaltenbaek, and Chad Orzel.
The event was modeled on the journalist "bootcamps" held routinely in the U.S., but less commonly in Europe. It amounted to a series of seminars along with evening social events and rambles through historic Stockholm so that people could get to know one another and ask the questions they'd been wondering about for years, but never had the chance or gumption to pose. The speakers enjoyed having an appreciative audience, with no one asking what they needed to know for the exam.
One afternoon, Mohamed Bourennane brought us into his lab at Stockholm University to witness quantum weirdness for ourselves. Afterwards, we had a good discussion about whether physicists and journalists overuse terms such as "quantum weirdness." Does this language help or hinder public understanding of the subject? Sabine has started a discussion about this on her blog.
The image shows Planck's Northern (on the left) and Southern (right) sky projections. Dark blue indicates parts of the sky that are clearer of dust. BICEP2 looked at the region marked by the black box in the Southern projection.
For background, listen to our podcast editions from May, with interviews with Andrei Linde and especially Joao Magueijo (who raised these particular concerns and others), and June, with Alan Guth.
The latest edition of the podcast is up -- and you may notice there's a bit of a quantum animal theme. Listen to it here.
First up, we talk to Andrew Jordan of Rochester University about recent experiments that allow you to track and steer Schrodinger's metaphorical cat (or in this case a superconducting "transmon") between life and death, while it is locked in a box. The technique could be used to create a new kind of quantum control.
Other animals featuring in the main podcast are quantum pigeons. FQXi member Jeff Tollaksen chats about his theoretical analysis that suggests that there is a new type of quantum correlation that's even spookier than those we've come to know and love. We're used to talking about quantum entanglement, which continues to link two or more particles that have been specially prepared together, no matter how far apart they are separated. But Tollaksen and his colleagues have calculated that quantum particles can become united without having to ever have been in contact. And he illustrates this by talking about vanishing pigeons!
Both of these items described by Jordan and Tollaksen are based on pioneering theoretical work on "weak measurements" in the 1960s by FQXi member Yakir Aharonov and colleagues. These allow experimenters to measure some properties of quantum systems, without destroying them. You can read more about that program in the article, "The Destiny of the Universe" by Julie Rehmeyer.
That research program has also lead to the idea that it is possible to create what Tollaksen dubs a "Quantum Cheshire Cat." Just as the cat in Alice in Wonderland managed to slowly vanish leaving behind a grin without a cat, physicists have recently carried out experiments in which a neutron has been separated from its properties. Tollaksen spoke to me about these tests too, and you can hear that as a podcast extra on the website, but note that it is not in the main podcast. (The image above, by Leon Filter, appears in the team's paper in Nature Communications. Thank you to Gina Parry for suggesting a forum post based on this piece of research.)
We have also included some non-animal items too. For cosmology fans, and those hankering for a resolution of the black hole information paradox, check out the interview with FQXi's Carlo Rovelli. His latest analysis with Hal Haggard, based on the theory of Loop Quantum Gravity, predicts that when black holes die, they explode into white holes, spewing all the matter that they swallowed back out again. If he and his colleague are correct, then astronomers may be able to pick up signs of such exploding black holes -- which would also be the first observational support for this model, or indeed any candidate theory of quantum gravity.
But it's not all smooth sailing. Keen podcast listeners may remember an interview from the June 2013 podcast with Jorge Pullin, who carried out a similar analysis also using loop quantum gravity, but got a different answer. Pullin argued that at the center of black holes you will find wormholes that fast track you to other parts of the universe. Listen to the podcast to find out what Rovelli has to say about the conflicting results.
And, if you enjoyed reading Sophie Hebden's profile of Noson Yanofsky and his work using category theory to study whether Occam's Razor is really mathematically valid, then you can also listen to her interview with him.
Anyway, please tune in and listen to all the latest weird and wonderful experiments and models. As Alice would say, things are getting curiouser and curiouser.
The judges have made their decisions…and we can now (almost) reveal the winners of this year's essay contest, which asked: "How Should Humanity Steer the Future?" We had 155 entries this year and we're awarding 16 prizes. Thank you to everyone who entered, read the entries, commented, and voted for their favourites.
This year, we're doing something a bit different with the announcement of the big winners. We're inviting you to tune in to a live webcast of the award ceremony, where you can join FQXi directors Max Tegmark and Anthony Aguirre as they reveal the top 3 prize winners. Our first prize winner will walk away with $10,000, and our two second prize winners will each take home $5,000.
The event: The FQXi Essay Contest Award Ceremony 2014
The time: Thursday 21st August, 1pm EDT
The place: Here
This is also your chance to quiz the winners, so please post your burning questions below. To aid you in framing your questions, I have permission to reveal the panellists…but I cannot yet tell you which of them has won first prize, and which two are runners-up. You'll find out -- as will they -- tomorrow at the ceremony!
So congratulations to our panellists, who between them have won the top 3 prizes. They are listed here in alphabetical order:
Please post your questions and comments below (or tweet them to @FQXi).
We've also been busy announcing the names of our six 3rd place winners ($2,000), five 4th place winners ($1,000) and two special prize winners ($1,000) on twitter and Facebook. You can check out the list of the winners who have been revealed so far here. Congratulations to each of them for providing some thought-provoking reading matter.
When a ballerina does a pirouette she must escape the friction of the ground in order to get the freedom to move. (Figure 1: Photo by Michael Garner, courtesy of English National Ballet.) She does this by restricting her contact with the ground to a point. In a recent paper I and my collaborators Andrew Garner and FQXi's Vlatko Vedral show that quantum theory in a very similar way escapes a fundamental constraint on movement by accepting uncertainty.
Quantum systems are associated with states which encode the statistics of future possible measurements. The collection of such states may be represented as a geometric shape. In the smallest possible quantum systems, single qubits (quantum bits), this shape is a sphere, called the Bloch sphere.
For example, think about a property of a qubit, such as its position: the qubit could be associated with two possible positions, A and B, say, or it can be in a fuzzy superposition where it exists in both of these mutually incompatible states simultaneously, before being observed. If it's in a superposition then although experimenters cannot know with certainty what position they will find it in when they make a measurement, they will have some sense of the probability of getting a certain outcome. The Bloch sphere helps to visualise this odd feature and the probabilistic nature of quantum mechanics. In the example, a vector pointing to the north pole of the sphere could represent position A, while the south pole represents position B. (In a classical system, this would represent the only two options available for a binary digit, or bit, to access). However, a qubit can also be represented by a vector pointing elsewhere on the surface of the sphere, corresponding to the fuzzy in-between states.
The maximal state space conceivable would actually be the cube outside of the sphere, as shown in figure 2. The quantum state space is the sphere, but if there were no uncertainty principle all states in the outer cube could be allowed. In this case certain measurements could all have predictable outcomes at the same time, in violation of the quantum uncertainty principle.
One may ask why quantum theory is restricted to the sphere, and accordingly to having the uncertainty principle.
We came across an intriguing answer when thinking about how the cube state space would handle an interferometer. In an interferometer the particle or photon is firstly placed in a superposition of being in two places and then operations are done on each site. Now when you have two different sites fundamental locality restrictions come into play. In particular, we point out that if a system has 0 probability of being found on site B, then an operation on site B must leave the state of the system invariant. Otherwise we could do action at a distance. Contrary to some popular science depictions, quantum theory does not allow action at a distance. The universe would be almost inconceivably odd and complicated if action at a distance were possible. We would not be able to make a statement about an individual system without taking into account what happens everywhere else in the world.
On the Bloch diagram, state transformations move points around, e.g. by rotating the shape. So, if one accepts that this locality restriction holds, it turns out that operations on site B must leave all points (states) on the lower plane of the cube invariant. It is like the points are stuck by total friction between the shape and the lower plane. As a result the cube has a big disadvantage over the sphere because if the entire square face touching the ground is restricted, then the whole cube gets stuck and no states can change.
But now imagine metamorphosing the cube into a sphere, or indeed something else with only one point on the lower plane, like how the ballerina goes up on one toe. Then the shape, with all the quantum states in it, can move. The quantum sphere has the advantage over the cube that it can rotate even if there is full friction with the lower (and/or upper) plane, just as the ballerina accepts the uncertainty of only having a point in contact with the ground in return for the ability to pirouette.
One may say that uncertainty, rather than being just limiting, liberates quantum states to change.
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