In recent years noted string theorist and blogger Lubos Motl has increasingly turned his attention to the foundations of quantum theory. Those of us who study quantum foundations for a living have tended to find his commentary mildly annoying, as he consistently calls those of us who disagree with his views “anti-quantum zealots”, crackpots, and worse.

I have recently come to the realization that Lubos’ views on this subject are completely correct. Specifically, I now believe the following:

- The Copenhagen founders of quantum theory—Bohr, Heisenberg, Pauli, Born et. al.—had things essentially right. They were only missing the details of decoherence theory in order to properly understand the classical limit.
- The decoherent histories formalism as proposed by Gell-Mann and Hartle, gives a completely consistent account of these minor details and is the correct way to understand physical properties and probabilities in quantum theory.
- People who work on high energy physics, and especially string theory, are the ultimate arbiters of truth about the nature of quantum theory. Only they have the background needed to make meaningful statements on the subject. This is especially true of theorists who are or ever have been employed at Harvard. Any idea that has not been discussed by these physicists is probably wrong. No insight is to be gained by actually studying the foundations of quantum theory for several years, rather than working on proper fundamental physics.
- And finally, in the face of any other views on quantum theory, the correct response is always, “It’s quantum stupid!”

Having adopted this new credo, I now realize that my previous view that quantum theory should be founded on a realist ontology that gives a clear picture of what is going on in reality independently of the observer was wrong-headed. Lubos’ blog posts on the subject make a compelling argument that my view was guided more by religious zealotry and communist ideology than by empirical data and rational argument. It therefore seems appropriate that I should enter into a period of repentance by adopting a garb of sackcloth and ashes for a while before emerging cleansed of my previous religious views.

Given the impracticality of wearing sackcloth and ashes in modern life, I have instead decided to wear a t-shirt that identifies me as the anti-quantum zealot that I am. You can see a picture of me wearing this t-shirt at the top of this post. Before embarking on a career in string theory, or more likely quitting academia to become an accountant because I do not have the intelligence to understand real physics, I still have several engagements where I shall have to speak about my previous bigoted research. I therefore promise that I will wear my anti-quantum zealot t-shirt at all such speaking engagements for the next year.

At this point, I would like to urge my colleagues who have also been denounced by Lubos’, and those who hold similar views but have so far flown under Lubos’ radar, to reconsider their views and join me in repentance. If each of us wears an anti-quantum zealot t-shirt publicly then we may be able to prevent others from following us down the path of ideologically motivated nonsense.

Fortunately, I have made it easy for you to purchase your own anti-quantum zealot apparel and merchandise, from the Spreadshirt shop at this link. It is available in any colour, so long as it is communist red. I receive a commission of 2CAD for every purchase from this shop (the rest goes to Spreadshirt, so complain to them about their overpriced t-shirts rather than me). I would dearly love to keep that commission money because I will be short of income for a while as I retrain as a string theorist or accountant. However, that would greatly complicate my tax situation, so I have decided to donate it to a charity that will protect future generations of physicists from adopting anti-quantum ideas. For this purpose, my commission will be donated to the Next Einstein Initiative of the African Institute for Mathematical Sciences (AIMS), which seeks to establish centres of excellence in mathematical science across Africa. AIMS does cover fundamental physics, but I note with approval that they do not currently have programmes in quantum foundations, so they will not be teaching wrong-headed ideas to the next generation of African physicists.

You might be tempted to consider your purchase of anti-quantum zealot merchandise as a charitable contribution, but if you really want to support AIMS you should forget about the t-shirt and just donate all of the money your would have spent to them directly. Anti-quantum zealot merchandise is only intended for those who want to seriously repent for their anti-quantum beliefs.

In order to encourage donations, either through merchandise purchases or direct contributions to AIMS, I will be offering a special prize to whoever makes the largest donation in response to this post by the end of this month (April). You simply have to let me know how much you have donated, either by email, or by leaving a comment if you want to boast about how generous you are (I will be asking the winner to verify their donation by sending copies of their receipts).

What is this special prize you ask? Well, it is a collection of schwag that I stole from my absolute favourite academic publisher—Elsevier—at the recent APS March meeting.

As you can see, it consists of two pens advertising the exciting new journal “Reviews in Physics”, which I assume will soon surpass Reviews in Modern Physics as the premier physics review journal. I believe this because of the extremely rigorous editorial oversight that Elsevier applies to all of its journals.

In addition to this, you get a luggage tag advertising Elsevier’s offerings in Optics, which is filled with some mysterious blue liquid, because everything is better with blue stuff in it. If your luggage accidentally ends up at the Elsevier offices because the baggage handlers read the side of the label displayed in the photo rather than the address written on the back, I am assured that Elsevier will apply their open access policy to your bags and charge you $80 for their return.

]]>Date/time: Wed. 26th Nov. 2014 10pm GMT/UTC

Speaker: Howard Wiseman (Griffith University)

Title: After 50 years, Bell’s Theorem Still Reverberates

Abstract:

Fifty years ago this month, Belfast-born physicist John Bell submitted for publication a paper [1] which has been described as “the most profound discovery in science” [2]. However, its significance is still much disputed by physicists and philosophers [3, 4].

I will explain what is so puzzling about the types of correlations Bell introduced, by a specific example based on [5]. (For those well-versed in Bell inequalities this may still be of pedagogical interest.)

But what exactly do these Bell-type correlations violate? Bell’s original answer [1] was the joint assumptions of determinism and locality. His later answer [6] was the single assumption of local causality (which, confusingly, he sometimes also called locality). Different ‘camps’ of physicists – operationalists and realists respectively – prefer the different versions of Bell’s theorem.

Which of Bell’s notions, locality or local causality, expresses the causal structure of Einstein’s theory of relativity? I will argue for the answer: neither [3,4]. Both notions require an additional causal assumption, and the one required for local causality is a stronger one. I will discuss how the different assumptions fit with the ideologies of the two camps, and how they can best be reconciled.

[1] J. S. Bell, “On the Einstein-Podolsky-Rosen paradox”, Physics 1, 195-200 (1964).

[2] H. P. Stapp, “Are superluminal connections necessary?”, Nuovo Cim. 40B, 191 (1977).

[3] H. M. Wiseman, “The two Bell’s theorems of John Bell”, J. Phys. A 47, 424001 (2014) (Invited Review for Special Issue, 50 years of Bell’s theorem)

[4] H. M. Wiseman, “Bell’s theorem still reverberates”, Nature 510, 467-9 (2014).

[5] P. K. Aravind, “Bell’s theorem without inequalities and only two distant observers”, Found. Phys. Lett. 15, 397 (2002).

[6] J. S. Bell, “The Theory of Local Beables”, Epistemological Lett. 9, 11-24 (1976).

To watch the talk live, visit the event page at the appointed hour.

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]]>Date: Monday 27th October 2pm GMT/UTC

Spekaer: Marco Piani (University of Strathclyde)

Title: Usefulness of entanglement and steering in the discrimination of physical processes

Abstract: Not all entangled states are created equal: they are all special, but some are more special than others. In particular, this is true in an operational characterization of quantum correlations based on their usefulness in the discrimination of physical processes. We will discuss how every entangled state of a probe-ancilla composite system is useful as a resource for the problem of minimum-error channel discrimination. We will then focus on the subset of entangled states that exhibit steering. The latter is the entanglement-based quantum effect that embodies the “spooky action at a distance” disliked by Einstein and scrutinized by Einstein, Podolsky, and Rosen. We prove that, for any fixed steerable state, there are instances of a generalization of the channel discrimination problem, which we dub quantum subchannel discrimination, where such a state allows a correct discrimination with strictly higher probability than in absence of entanglement, even when measurements are restricted to local measurements aided by one-way communication. On the other hand, unsteerable states are useless under such a restriction, even when entangled. We also prove that the above steering advantage can be exactly quantified in terms of the steering robustness, which is a natural measure of the steerability exhibited by the state.

This talk is based on joint work with J. Watrous, arXiv:1406.0530.

To watch live, visit the hangout page at the appointed hour.

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]]>Date/time: Tue. May 20th 2014 2pm BST/UTC+1

Speaker: Daniel Gottesman (Perimeter Institute)

Title: Fault-tolerant quantum computation with constant overhead

Abstract: The threshold theorem for fault tolerance tells us that it is possible to build arbitrarily large reliable quantum computers provided the error rate per physical gate or time step is below some threshold value. Most research on the threshold theorem so far has gone into optimizing the tolerable error rate under various assumptions, with other considerations being secondary. However, for the foreseeable future, the number of qubits may be an even greater restriction than error rates. The overhead, the ratio of physical qubits to logical qubits, determines how expensive (in qubits) a fault-tolerant computation is. Earlier results on fault tolerance used a large overhead which grows even larger (albeit slowly) with the size of the computation. I show that it is possible in principle to do fault-tolerant quantum computation with the overhead constant in the size of the computation, and with a low constant at that. The result depends on recent progress on quantum low-density parity check codes.

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]]>Date/time: 22nd April 2014 2pm BST/UTC+1

Speaker: Chris Richardson (University of Liege)

Title: On the Uncertainty of the Ordering of Nonlocal Wavefunction Collapse when Relativity is Considered

Abstract: The temporal measurement order and therefore the originator of the instantaneous collapse of the wavefunction of a spatiality entangled particle pair can change depending on the reference frame of an observer. This can lead to a paradox in which its seems that both measurements collapsed the wavefunction before the other. We resolve this paradox by demonstrating how attempting to determine the order of measurement of the entangled pair introduces uncertainty which makes the measurement order impossible to know.

To watch the talk live, go to the event page at the appointed hour.

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or visit our website.

]]>Date/time: Tuesday 25th March 2014 2pm GMT/UTC

Speaker: Tobias Fritz (Perimeter Institute)

Title: A Combinatorial Approach to Nonlocality and Contextuality

Abstract:

Most work on contextuality so far has focused on specific examples and concrete proofs of the Kochen-Specker theorem, while general definitions and theorems about contextuality are sparse. For example, it is commonly believed that nonlocality is a special case of contextuality, but what exactly does this mean? After a brief discussion of previous work, I will introduce our “device-independent” approach to contextuality based on the mathematics of test spaces and explain how nonlocality is indeed a special case of contextuality. This work builds on the graph-theoretic approach of Cabello, Severini and Winter by improving on several of its shortcomings and merging it with the work of Foulis and Randall on test spaces. Our results include:

(1) various relationships to graph invariants, similar to CSW;

(2) a proof that our set of quantum models cannot be characterized by a graph invariant;

(3) a proof that the set of all models satisfying the Consistent Exclusivity principle at any number of copies is not convex;

(4) new results on the Shannon capacity of graphs;

(5) an “inverse sandwich conjecture” with ramifications for C*-algebra theory and quantum logic.

This talk is based on arXiv:1212.4084.

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or visit our website.

]]>Date/time: Tue. 25th Feb. at 4pm GMT/UTC

Speaker: Nicholas Brunner (University of Geneva)

Title: Dimension of Physical Systems

Abstract: The dimension of a physical system refers loosely speaking to the number of degrees of freedom relevant to describe it. Here we ask how quantum theory compares to more general models (such as Generalized Probabilistic Theories) from the point of view of dimension. This gives insight to information processing and thermodynamics in GPTs.

To watch the talk live, visit the event page at the appointed hour.

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or visit our website http://qplus.burgarth.de

]]>Date: 28th January 2014

Time: 2pm UTC/GMT

Speaker: Troels Frimodt Rønnow (ETH Zurich)

Title: Quantum annealing on 503 qubits

Abastract: Quantum speedup refers to the advantage of quantum devices can over classical ones in solving classes of computational problems. In this talk we show how to correctly define and measure quantum speedup in experimental devices. We show how to avoid issues that might mask or fake quantum speedup. As illustration we will compare the performance of a D-Wave Two quantum annealing device on random spin glass instances to simulated classical and quantum annealers, and other classical solvers.

To watch the talk live go to http://gplus.to/qplus at the appointed hour.

To keep up to date on the latest news about Q+ hangouts you can follow us on:

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or visit our website at http://qplus.burgarth.de

]]>Date/time: Tue. 26th Nov. 3pm GMT/UTC

Speaker: Mark Wilde (Louisiana State University)

Title: Strong Converse Theorems in Quantum Information Theory

Abstract: One of the main goals in quantum information theory is to establish the capacity of a quantum channel for communicating various kinds of information, whether it be bits or qubits. While several communication capacities of quantum channels are now known, the characterization of capacity in many of these cases is often limited to it being a threshold that determines the rates at which reliable communication is or is not possible. While this characterization might be satisfactory for some purposes, it leaves open the possibility for a trade-off between communication rate and error probability (that is, one might think that it would be possible to send data at a higher rate by allowing for errors to occur some of the time). However, we now know that such a trade-off is not possible for many channels and capacities of interest. That is, many researchers have now established that a strong converse theorem holds for several channels and capacities, so that as soon as the communication rate exceeds capacity, it is guaranteed that the error probability converges to one in the limit of large blocklength, no matter what strategy the sender and receiver employ. These strong converse theorems strengthen the interpretation and our understanding of capacity as a very sharp dividing line between rates for which asymptotically perfect communication is possible and rates for which an error is guaranteed to occur (analogous to a phase transition in statistical physics). This Q+ talk will review much of the progress in establishing strong converse theorems for several channels and their communication capacities in quantum information theory.

Joint work with Bhaskar Roy Bardhan (LSU Baton Rouge), Manish K. Gupta (LSU Baton Rouge), Naresh Sharma (TIFR Mumbai), Dong Yang (UAB Barcelona), and Andreas Winter (UAB Barcelona).

To watch the talk live, go to http://gplus.to/qplus at the appointed hour. To stay up to date on the latest news about Q+ hangouts you can follow us on:

- Google+: http://gplus.to/qplus
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or visit our website http://qplus.burgarth.de

]]>Date/Time: 29th October 2013 2pm GMT

Speaker: Renato Renner (ETH Zurich)

Title: Does freedom of choice imply that the wave function is real?

Abstract:

The question whether the quantum-mechanical wave function is “real” has recently attracted considerable interest. More precisely, the question is whether the wave function of a system is uniquely determined by any complete description of its “physical state”. In this talk I will present a simple and self-contained proof that this is indeed the case, under an assumption that one may term “freedom of choice”. It demands that arbitrary measurements can be applied to the system, and that these can be chosen independently of all parameters available at the time of measurement (with respect to any relativistic frame). A possible interpretation of this result is that the wave function of a system is as “objective or “real as any other complete description of the system’s state.

(This is based on unpublished work in collaboration with Roger Colbeck.)

To watch the talk live go to http://gplus.to/qplus at the appointed hour.

Note that the change from daylight savings time to standard time will have happened in the UK, but not some other countries like the US and Canada. Therefore, your usual timezone calculation may be out by an hour, e.g. the talk is at 10am in East Coast US and Canada. Please check the time conversion for your location.

To keep up to date with the latest news on Q+ hangouts, you can follow us on:

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or visit our website http://qplus.burgarth.de

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