The Journal of Quantum Information Science will not be getting any of my papers starting today, because today is when I learned that they recently published the following gem: A Resolution of Cosmic Dark Energy via a Quantum Entanglement Relativity Theory, by M. El Naschie.
Upon closer inspection, it isn’t hard to see why they published this paper. It’s because “El Naschie is very highly regarded in the community” and is “always spoken of as a possible Nobel prize candidate”. And as the great man himself has said, “Senior people are above this childish, vain practice of peer review”, so there was no need for that.
Oh, but despite the apparent lack of peer review, they do have a $600 article processing charge for open access. I wonder what costs these charges are meant to offset if the “submit” button just puts the article straight into the publication? Hmmm, I hope that the journal didn’t simply accept money in exchange for publishing the paper under the pretense of “open access”! Golly, that would be unethical.
Test your intuition
The name of this post was shamelessly stolen from Gil Kalai’s popular series Test Your Intuition. But today’s post will be testing our physics intuition, rather than our mathematical intuition. Although this is a quantum blog, we’ll look at the behavior of a classical fluid.
The question is: what happens when you soak a washcloth with water and then ring it out… in zero gravity?
Think about it for a few minutes before watching the result of the actual experiment below.
Sydney Postdoctoral Fellowships
The University of Sydney is now accepting applications for the Sydney Postdoctoral Fellowships. These are very competitive and prestigious university-wide fellowships, with terrific salary and benefits: a 3 year appointment with a A$99,000 annual salary and a A$25,000 discretionary research fund for travel, visitors, or equipment.
Because they are so competitive, you have to arrange for a faculty sponsor before applying. If you are interested in applying and joining the quantum physics group, then read the Sydney Postdoctoral Fellowship guidelines here:http://bit.ly/ZZ2r26. If you qualify, send me an email (sflammia at physics.usyd.edu.au) with a cover letter that briefly describes your qualifications and a short CV. In particular, please specify how you see yourself fitting in and complementing work within the rest of the quantum physics group at Sydney.
There are a few relevant deadlines: the deadline to secure a faculty sponsor is Friday 3 May, but the actual application deadline is 31 May, so you will have plenty of time to finish the application. However, because of the initial deadline, I will only consider applications before Tuesday the 30th of April.
Q-Tube
This is a rare gem: Four lectures on quantum mechanics by Paul Dirac… on YouTube! Here’s the first one.
Also, the Q+ online lecture series continues to go strong, bringing in a steady stream of high-quality speakers. This month constitutes the “Nobel lecture”, and will be given by Dietrich Leibfried of NIST Boulder, in lieu of Dave Wineland, on April 23rd at 5pm UK time. The title is “Towards scalable quantum information processing and quantum simulation with trapped ions”, and it’s sure to be a great talk. Though the number of live video streams will be limited, you can go to the Q+ website to reserve a spot, or wait until after the lecture and watch a recording.
Reflections on the Discord Bubble
The following is a guest post by Marco Piani.
A couple of months ago Steve wrote a post on “the discord bubble“. Let me try to provide a summary of his post and of his thoughts.
There have been too many works, too often of insufficient quality either technically or conceptually (“pointless” works in Steve’s words) about a property of quantum systems and correlations—the so-called quantum discord—that has not been proven yet to be key in our understanding of nature or of the `inner workings’ of quantum information processing. That is, such flurry of activity does not appear to be justified and is rather due to “hype”; most importantly, the product of such activity is way too often of questionable quality. Steve goes on to suggest that the bubble needs to be put under control, so that we would go down to a reasonable rate of publications on the subject, hopefully of higher average quality. In order to assess such quality, Steve proposes some rules of thumb—check them out in Steve’s post—to be applied hopefully by the authors themselves. In his words, Steve’s intention was
“not to trash the subject as intrinsically uninteresting; rather, [he wanted] to highlight the epidemic of pointless papers that constitute the discord bubble. [He hoped] that thinning the herd will increase the quality of the results in the field and decrease the hype surrounding it, because it has really gotten completely out of control.”
While I found Steve’s post essentially to the point and I furthermore highly appreciated his invitation to highlight in the comments good research on quantum discord—because there is good research on the topic—I feel that there is room for more reflection and discussion, in particular within—but of course not limited to—the community working on discord-related problems. To start it, I would like to express some of my own opinions.
Is there a bubble? What is it at its origin?
Yes, there is a bubble. Yes, there is too much hype. Yes, there are too many papers on the subject that are of questionable quality.
On one hand, the subfield of the `general quantumness of correlations’—as I like to think of discord and related concepts—still lacks a killer application to justify the present level of activity. The explosion of interest in the subfield was in a good part due to hints that such quantumness could help explain the quantum advantage in some noisy models of (limited) quantum computation. Such hints, to my knowledge, remain just hints; that is, too little to justify so many papers. We are still searching for a task/protocol that convincingly highlights discord or similar related properties as `resources’ or `the key’ in a general enough scenario—see this related post by Valerio Scarani. On the other hand, as Steve pointed out, many papers on discord are characterized by a low scientific merit, technically and/or conceptually.
I believe that the “discord bubble” is due to a combination of several factors, which have all come together to create the `perfect bubble’. Some are:
1) we live in a “publish or perish” (academic) world: if hype starts to be generated regarding a topic, many researchers will flock to that topic in the hope to score well in the number and kind of publications—high-impact journals—and the corresponding citations they are bound to get;
2) when there is a `new’ topic (like `discord’ with respect to the good ol’ `entanglement’) the technical and conceptual threshold to contribute new results is lower; on the other hand, quantum information is by now a mature field and new exciting results in `traditional’ theoretical topics—quantum Shannon theory, quantum error correction, quantum computation, … —require a high level of expertise and skills;
3) some form of `confirmation bias’: positive statements on the value and significance of new and old results on the topic are easily accepted and perpetuated, especially in light of 1) and 2).
Let me stress that these factors are mostly independent of the topic itself—discord. I am pretty sure that other fields of science have their own bubbles.
Is it worth working on discord and related issues?
Quantum information processing aims at exploiting quantum features to provide us with new, powerful means to manipulate information. Reaching this goal requires the best possible understanding of such features.
More specifically for our case, there are quantum features that 1) are proper of bi- and multi-partite systems (i.e., they do not have a real correspondent for single systems) and 2) do not reduce to entanglement, e.g, they can be present also in the absence of entanglement. For example, one of these properties is related to the celebrated no-cloning theorem; another one is the unavoidable disturbance introduced by local measurements. In this sense there is a `general quantumness of correlations’, which, for the above reasons, I believe is worth investigating.
Of course, an argument like “[PROPERTY] could be useful, so we should study it” is not enough, if not substantiated. There should be some concrete evidence and some convincing perspective of such usefulness in order to motivate the related investment of resources. I think that what we know about the general quantumness of correlations, although not enough to justify the number of papers dealing with it, satisfies these requirements, at least partially. More clearly:
We have concrete evidence that the general quantumness of correlations is a useful concept to consider.
Such usefulness goes from foundations—e.g., addressing the measurement problem and the emergence of classicality—to the alternative take on the no-cloning theorem mentioned above, to the study of quantum effects in the `locking’ of classical correlations in quantum information theory.
On the other hand:
We have not yet found a way to think about and exploit the general quantumness of correlations that makes such quantumness worthy of the central stage of quantum information processing, or of the title of `resource’.
As mentioned above, the protocols so far designed that pinpoint discord as the relevant `resource’ at play can be considered contrived. More generally, I doubt that discord will ever achieve a status of resource similar to entanglement. I rather believe that, for example, discord is—with the risk of sounding like I am trying to be witty—something that makes it possible to make something else impossible. For example, discord makes it impossible to access `in a classical way’ part of the information content of correlations.
All in all, I do believe that the general quantumness of correlations will further prove its usefulness, both as a conceptual tool and as concrete property present in distributed systems. What we have to remember is that such usefulness is not well established and that most of the work on the subject should still go in the direction of clarifying the value and applicability of the concept rather than, e.g., calculating discord in all sorts of physical systems.
Let me add that I consider the study of the general quantumness of correlations also as an attempt to think about the quantum from a different/larger perspective—different/larger with respect to what was previously done. In my case, thinking in terms of the `general quantumness of correlations’ has helped me, for example, to better understand entanglement itself.
What should people who work or consider working on discord do? What about the rest of the quantum information community?
The effort worth investing—as individual researchers, as a scientific (in particular, quantum information) community, and as a society (e.g., in terms of funding)—in the study of the general quantumness of correlations is not easy to determine. This actually holds in general, for essentially any research subject. What is worrisome about a bubble, is that it can reduce the efficiency of the procedures in place—in particular the peer-review process—to shape the activity of the community, to reallocate its resources, and to induce researchers to adopt a good practice. [We actually know that the peer-review process, in particular in the standard form associated to publication in journals, does not work perfectly in general.] As personal experience goes, I have often rejected low-quality papers on discord only to see them published in another journal. So it is important to recognize the presence of a bubble and bring the problem to the attention of the community, so that extra care can be taken in assessing the value of papers, both in terms of correctness and relevance. While I endorse Steve’s rules of thumb to assess the quality of papers related to discord, I would like to address the problem of the discord bubble with a list of suggestions mostly comprising general good practices.
So, to the people working/interested in working on discord:
a) re-evaluate why you are working on the topic. A useful exercise it that of imagining explaining to someone who is NOT already working on discord why he should be interested in investigating the subject. If whatever reason you provide is based on previous results in the field, make sure that you have checked the source at a sufficient level of detail to be sure that those results—and in particular any related strong claim—would be convincing for him, and, most importantly, that they are convincing for you;
b) be aware of the large body of work that already exists in quantum information processing: what you think is new and exciting may well be already known (either published, or easy to see and part of the `folklore’);
c) analyze critically your work and that of the others, both as author and as referee: cite only literature that is significant and relevant to your paper and reject papers that do not provide substantial advance in neither understanding nor applications;
d) focus on providing more—and possibly conclusive—evidence that the study of the quantumness of correlations is justified: we need `killer applications’ and `killer concepts’;
e) entanglement theory has been a very fruitful field of study because entanglement is a fundamental concept and it can be understood/analyzed as a resource in a reasonable, operationally justified framework—that of distant labs, where the quantum operations allowed are only local, at most coordinated by classical communication. Trying to mimic successful stories might be a good idea, but there are dangers involved. Let us avoid creating the Bizzarro version of entanglement.
To the rest of the quantum information community:
Be critical and open-minded at the same time.
While complaining about the existence of a discord bubble is more than reasonable and, from my point of view, quite welcome, attacking the study of discord per se is unjustified. Please challenge whoever makes claims that are too strong, question observations and calculations that you judge irrelevant, push people who work on discord to meet the highest standards in international research, reject papers when they do not meet such standards. But please do not dismiss a talk or a paper just because it deals with discord; evaluate it only on the basis of its specific scientific merit. Furthermore, if you feel like it, you can ponder for some minutes on questions like “Is there anything quantum about a distributed quantum state that is not solely due to entanglement?”, and “Can we make use of it?”.
On the fractal nature of bubbles
The best results of recognizing that there is a `discord bubble’ and of taking corresponding action—maybe on the lines suggested above—would be, on one hand, to improve the research activity on discord, and, on the other hand, to avoid the risk that the subject and the people working on it acquire a bad reputation.
Let me mention that there are scientists who think that research on quantum computation is itself a bubble—see this post by Scott Aaronson. Is this further proof that bubbles can have a fractal structure? Of course the `accusation’ of being bubbles is at different levels for discord and quantum information, and not just in the sense of the `fractal level’. The criticism towards quantum computing is mostly about its realizability, while discord, although a useful conceptual tool, has not convincingly been proven to be a `resource’, even in theory. Nonetheless, there is something in common about the two accusations of being a bubble: hype—again. Indeed, Scott writes about the accusations of the quantum computing skeptic M. I. Dyakonov:
“Dyakonov fumes about how popular articles, funding agency reports, and so forth have overhyped progress in quantum computing, leaving the conditions out of theorems and presenting incremental advances as breakthroughs. Here I sadly agree.”
So, let me add a point to the above list of suggestions:
f) try to reduce—or at least do not contribute to—the hype.
This will have the effect of making the topic of discord less attractive for people whose work will not actually improve the standing of the topic, and improve its reputation within the quantum information community, potentially attracting good researchers.
The above-mentioned post by Scott is also notable for having started a high-quality discussion in the comments section on whether quantum computing deserves the accusation of being a bubble. It would be great to have a similar discussion on discord in the comments below. I expressed already my personal opinion: we are in front of a discord bubble, but there is merit in studying the general quantumness of correlations. I would be particularly happy to have a discussion on whether—and why—my opinion is too harsh or too mild, and to receive, as Steve already asked in his post, motivated suggestions about works that should survive a `pop’ of the discord bubble.
Simple circuit "factors" arbitrarily large numbers
Last Thursday, at the QIP rump session in Beijing, John Smolin described recent work with Graeme Smith and Alex Vargo [SSV] showing that arbitrarily large numbers $latex N$ can be factored by using this constant-sized quantum circuit
to implement a compiled version of Shor’s algorithm. The key to SSV’s breathtaking improvement is to choose a base for exponentiation, $latex a$, such that the function $latex a^x bmod N$ is periodic with period 2. (This kind of simplification—using a base with a short period such as 2, 3, or 4—has in fact been used in all experimental demonstrations of Shor’s algorithm that we know of). SSV go on to show that an $latex a$ with period 2 exists for every product of distinct primes $latex N=pq$, and therefore that the circuit above can be used to factor any such number, however large. The problem, of course, is that in order to find a 2-periodic base $latex a$, one needs to know the factorization of $latex N$. After pointing this out, and pedantically complaining that any process requiring the answer to be known in advance ought not to be called compilation, the authors forge boldly on and note that their circuit can be simplified even further to a classical fair coin toss, giving a successful factorization whenever it is iterated sufficiently many times to obtain both a Head and a Tail among the outcomes (like having enough kids to have both a girl and a boy). Using a penny and two different US quarters, they successfully factor 15, RSA-768, and a 20,000-bit number of their own invention by this method, and announce plans for implementing the full circuit above on state-of-the art superconducting hardware. When I asked the authors of SSV what led them into this line of research, they said they noticed that the number of qubits used to do Shor demonstrations has been decreasing over time, even as the number being factored increased from 15 to 21, and they wanted to understand why. Alas news travels faster than understanding—there have already been inquiries as to whether SSV might provide a practical way of factoring without the difficulty and expense of building a large-scale quantum computer.
Viacheslav Belavkin
I am sad to report that Viacheslav Belavkin recently passed away. One of the rarified few who made important contributions to quantum information in the 1970’s, Belavkin’s work was and is very significant in both physics and mathematics.
Belavkin won the Main State Prize of Russia (formerly the Lenin prize) in 1996, jointly with Stratanovich, for his contributions to stochastic calculus and the theory of quantum measurement.
I only met Belavkin once, while he was visiting the Perimeter Institute. He was dining alone, and had just finished dinner and was about to pay, so he told the server put the bill on the tab for Belavkin. Overhearing this, I turned to him and said “Oh, you’re Belavkin!” He was clearly pleased that I knew who he was, and over a beer he shared with me some of the very interesting history of the early days of quantum information theory. You can read for yourself Belavkin’s perspective on the early days of the field through his potted autobiography. (The link is to a web cache, since sadly the University of Nottingham has taken down his personal webpage.)
It was clear from my conversation with him that he was the quintessential jaded ex-Soviet scientist who had seen everything done 10 years ahead of its rediscovery in the West. He wasn’t very modest about his own discoveries, either. I distinctly remember him saying the following, “My first paper on quantum information theory was in 1972. And Stratanovich had some in the 60’s.” To his great credit, though, he was essentially correct! Much of his work was rediscovered in the 90’s, often in less generality.
Chris Fuchs told me a classic story about Belavkin, which I’ll recall as best I can. Sometime in the 90’s, Chris was at a conference along with many smart people working on continuous measurement and feedback control of quantum systems. When it was Belavkin’s turn to talk, he calmly took the chalk and began to recap the talks from the morning session where people had been presenting their recent work.
“This morning we heard a talk by Prof. Smith in which he proved the following theorem.” Belavkin calmly scrawled the statement of the theorem on the board, in a formal style,
Theorem 1 [Smith, 1995]. For all $latex x$, there exists a $latex y$ such that…
He continued, “Then we heard a talk by Prof. Jones, where he proved the following.” Once more, he carefully wrote the statement of the theorem on the board, just below the first one. “And finally we heard from Prof. Brown, who demonstrated this theorem.” Again, he patiently wrote the formal statement of the theorem on the board, with the name and date for attribution.
Belavkin paused for dramatic effect, then began writing new dates to the right of the theorems. “In 1972 I proved Theorem 1. In 1976 I proved Theorem 2. And in 1985 I proved Theorem 3. Now we will hear about some new results.”
Here is the notice of his passing from the University of Nottingham. I hope that they will make his old webpage available again.
Who should blog in 2013?
The quantum theory blogosphere has seen some great new additions this year:
- The Caltech IQIM blog, Quantum Frontiers
- Thomas Vidick, MyCQstate
- Miguel Navascues, Schoedinger’s Rat
But this is not enough! Our researchers are legion. And so must it be with our blogs.
There really are a huge number of creative and interesting people in our field, and it would be great if more of them shared their thoughts and opinions online. Therefore, let’s see if the Quantum Pontiff faithful can convince a few people to start blogging in 2013. It doesn’t have to be a lot: let’s say 10 posts for the year.
So leave the name of someone that you’d like to see blogging in the comments section. When we see these people at QIP we can bug them, “Have you started blogging yet?”
I’ll start things off by naming a few people off the top of my head that I wish would blog: David Poulin, Dorit Aharonov, Patrick Hayden. Perhaps we can even goad some weedy unkempt blogs to till their fields again. Matt Leifer and Tobias Osborne, I’m looking at you. 🙂
Cirac and Zoller win the Wolf Prize for physics
Ignacio Cirac and Peter Zoller were just announced as winners of the 2013 Wolf Prize for physics. I’m not sure if this is the official citation, but the Jerusalem Post is saying the prize is:
for groundbreaking theoretical contributions to quantum information processing, quantum optics and the physics of quantum gases.
If that isn’t the official citation, then it is certainly an accurate assessment of their work.
Cirac and Zoller are in very good company: the list of previous Wolf Prize winners have all made exceptional contributions to physics, and many of them have gone on to win Nobel prizes.
It’s great to see these two giants of the field get the recognition that they richly deserve. Congratulations to both!
Pop goes the discord bubble
Well, the rat is out of the bag; Schroedinger’s Rat, that is. That’s the new quantum blog by Miguel Navascues and boy is it snarky! I was keeping it under my hat for a while so I could enjoy it privately, but the time has come to announce it to the world. Miguel is fearless about shouting his colorful opinions from the rooftops, and I can respect that, even if I don’t agree with everything he says.
Miguel’s second post is all about quantum discord. As anyone who reads quant-ph knows, there are around two or three papers per week about discord for years now. Unfortunately, a huge number of these are nearly worthless! Quoth the Rat:
The quantum discord of a bipartite state was first defined by Ollivier and Zurek as the difference between its original quantum mutual information and the same quantity after we perform a rank-1 projective measurement on one part.
Now, what does that mean? Probably, nothing. But lack of motivation has never prevented investigation at international scale. And so we ended up with one more research topic that clearly goes nowhere, in the line of entanglement sudden death…
If you thought he was exaggerating, here is a paper that has been cited 263 times since May 2009: Robustness of quantum discord to sudden death. Wow, discord is immortal! And in case you want more, you can just go to quantumdiscord.org and find a list of discord papers and see for yourself.
Before we can treat the patient we have to understand the disease, and this is exemplified by a typically test case: Quantum discord for two-qubit X-states (cited 256 times). The authors compute the quantum discord and a few other entanglement measures for a family of two-qubit states and conclude that there is no obvious relationship between the various measures. Why did they do this? “Because it’s there” might have been a good reason to scale Everest, but this feels more like a homework assignment for a graduate course. Wait, I take that back: Scott’s students’ homework is much more interesting and relevant.
But Steve! What about all the good discord papers? You can’t just trash the entire field!
You’re absolutely right, there are good discord papers. I can even name about 5 of them, and I’m willing to bet there are as many as 12 or 15 total. My intention is definitely not to trash the subject as intrinsically uninteresting; rather, I want to highlight the epidemic of pointless papers that constitute the discord bubble. I hope that thinning the herd will increase the quality of the results in the field and decrease the hype surrounding it, because it has really gotten completely out of control.
Here are some good rules of thumb for those moments when you find yourself writing a discord paper. If you are calculating something and you don’t know why you are calculating it, then close your latex editor. You do not have one of the good discord papers. If the discord you calculated is not related to a resource (physical, computational, etc.) in a quantifiable way, you probably don’t have a good discord paper. If it is related to a resource, but you had to concoct that relationship in a totally ad hoc way that doesn’t generalize, then you do not have a good discord paper. Ditto if the relationship is via a protocol that literally nobody cares about. If you only have two qubits, you almost certainly don’t have a good discord paper. Good theory papers usually have $latex n$ qubits. And if your weak theory result suffers from one or more of the above but you add in some equally unimpressive experimental results to cover up that fact, then you absolutely, unequivocally do not have a good discord paper. I don’t care what journal it’s published in, it is not a good paper and you should be ashamed of yourself for inflating the bubble even further.
As bad as the authors are, this bubble is also the fault of the referees. Simply being correct is not enough to warrant publication. It also has to be new, non-trivial, and interesting. Please referees, “Just Say No” to papers that don’t meet this standard!
Enough of this bad medicine. In the comments, feel free to mention some of the actually good discord papers, and why they deserve to keep their value after the bubble bursts.