Paul Erdős (as quoted by Graham and Spencer, 1990, hat tip: Lamaze Tishallishmi)

“Suppose aliens invade the earth and threaten to obliterate it in a year’s time unless human beings can find the Ramsey number for red five and blue five. We could marshal the world’s best minds and fastest computers, and within a year we could probably calculate the value. If the aliens demanded the Ramsey number for red six and blue six, however, we would have no choice but to launch a preemptive attack.“

In a Nature paper published this week, a group of researchers from John Martinis’s lab at Google announced arguably the first demonstration of “quantum supremacy” – a computational task carried out by a 53 qubit quantum computer that would require a prohibitive amount of time to simulate classically.

Google’s calculations of the “classical computation time” might have been overly pessimistic (from the classical point of view), and there has been work from IBM as well as some work of Johnnie Gray suggesting that there are significant savings to be made. Indeed, given the lessons that we learned from private key cryptography, where techniques such as linear and differential cryptanalysis were used to “shave factors from exponents”, we know that even if a problem requires exponential time in general, this does not mean that by being very clever we can’t make significant savings over the naive brute force algorithm. This holds doubly so in this case, where, unlike the designers of block ciphers, the Google researchers were severely constrained by factors of geometry and the kind of gates they can reliably implement.

I would not be terribly surprised if we will see more savings and even an actual classical simulation of the same sampling task that Google achieved. In fact, I very much hope this happens, since it will allow us to independently verify the reliability of Google’s chip and whether it actually did in fact sample from the distribution it is supposed to have sampled from (or at least rule out some “null hypothesis”). But this would not change the main point that the resources for classical simulation, as far as we know, scale exponentially with the number of qubits and their quality. While we could perhaps with great effort simulate a 53 qubit depth 20 circuit classically, once we reach something like 100 qubits and depth then all current approaches will be hopelessly behind.

In the language of my essay on quantum skepticism, I think this latest result, and the rest of the significant experimental progress that has been going on, all but rules out the possibility of “Skepticland” where there would be some fundamental physical reason why it is not possible to build quantum computers that offer exponential advantage in the amount of resources to achieve certain tasks over classical computers.

While the worlds of “Popscitopia” (quantum computers can do everything) and “Classicatopia” (there is an efficient classical algorithm to simulate BQP) remain mathematical possiblities (just as P=NP is), most likely we live in **“Superiorita”** where quantum computers do offer exponential advantage for *some* computational problems.

Some people question whether these kind of “special purpose” devices that might be very expensive to build are worth the investment. First of all (and most importantly for me), as I argued in my essay, exploring the limits of physically realizable computation is a grand scientific goal in its own right worthy of investment regardless of applications. Second, technology is now a 3.8 trillion dollar per year industry, and quantum computers are in a very real sense the first qualitatively different computing devices since the days of Babbage and Turing. Spending a fraction of a percent of the industry’s worth to the economy on exploring the potential for quantum computing seems like a good investment, even if there will be no practical application in the next decade or two. (By the same token, spending a fraction of a percent on exploring algorithm design and the limitations of *classical *algorithms is a very good investment as well.)

Of course I can’t help but posting again the fake nytimes headline I produced for my 2016 crypto course when I wanted to motivate the study of so called “quantum-resistant cryptography”:

]]>Deal friends,

We are happy to announce the birth of a new conference on Information-Theoretic Cryptography (ITC). Information-theoretic cryptography studies security in the presence of computationally unbounded adversaries and covers a wide array of topics at the intersection of cryptography, coding theory, information-theory and theory of computation. Notable examples include randomness extraction and privacy amplification, secret sharing, secure multiparty computation and proof systems, private-information retrieval and locally decodable codes, authentication codes and non-malleable codes, differential privacy, quantum information processing, and information-theoretic foundations of physical-layer security. See https://itcrypto.github.io for more information.

ITC replaces the International Conference on Information Theoretic Security (ICITS), which was dedicated to the same topic and ran 2005-2017. ITC can be seen as a reboot of ICITS with a new name, a new steering committee and a renewed excitement. (beware: there is a fake website for ICITS 2019 created by a known fraudulent organization)

The conference will have two tracks: a conference track and a “greatest hits” track. The conference track will operate like a traditional conference with the usual review process and published proceedings. The “greatest hits” track consists of invited talks (not included in the proceedings) that highlight the most exciting recent advances in the area. We solicit nominations for “greatest hits” talks from the community.

The first ITC conference will take place in Boston, MA on June 17-19, 2020 (just before STOC). The submission deadline for ITC 2020 is Dec 16, 2019 and the call for papers (including a nomination procedure for the greatest hits track) is available here: https://itcrypto.github.io/2020.html

Please submit your best work to ITC 2020! We hope to see many of you there!

best regards,The Steering Committee: Benny Applebaum (Chair), Ivan Damgård , Yevgeniy Dodis, Yuval Ishai, Ueli Maurer, Kobbi Nissim, Krzysztof Pietrzak, Manoj Prabhakaran, Adam Smith, Yael Tauman Kalai, Stefano Tessaro, Vinod Vaikuntanathan, Hoeteck Wee, Daniel Wichs, Mary Wootters, Chaoping Xing, Moti Yung

]]>The Swiss Winter School on Lower Bounds and Communication Complexity (10-14 February 2020, https://theory.epfl.ch/WinterSchool2020/ ) is the first in a series of annual winter schools in Theoretical Computer Science jointly organized by EPFL and ETH Zurich. The goal of the school is to educate top international theory PhD students about exciting recent developments in the field. The winter school will be held in Zinal, a mountain village in the Swiss Alps that has a long tradition of hosting academic workshops and that allows for nice excursions and stimulating discussions in a relaxed atmosphere.

This year’s installment features an exciting trinity of speakers: Kasper Green Larsen (Data Structure Lower Bounds), Raghu Meka (Communication Complexity) and Amir Shpilka (Algebraic complexity).

The application deadline is November 15th 2019, and acceptance notifications will be sent by December 1st 2019. The application form is available at https://theory.epfl.ch/WinterSchool2020/. Attendance of the winter school is free of charge and includes room and board (shared rooms).

Organizers: Michael Kapralov (EPFL), David Steurer (ETH) , Ola Svennson (EPFL)

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to get .
I’ve blogged about the equation editor before but one pet peeve of mine was that I like to have my math in a different color, but never found a way to do this automatically. I finally decided to invest the time and find out how to do it. After a mere several years of investigation, I am happy to report that it is in fact possible to do so using Visual Basic for Applications (VBA).

You can view the developer tab by following these instructions, and then click on “macros”, type a name such as `All_eqs`

and click on “create” at which point you can add the following code:

Sub All_eqs() Dim oSld As Slide Dim oShp As Shape Dim oShapes As Shapes For Each oSld In ActivePresentation.Slides Set oShapes = oSld.Shapes For Each oShp In oShapes If oShp.HasTextFrame Then If oShp.TextFrame.HasText Then With oShp.TextFrame.TextRange For x = 1 To .Characters.Count If .Characters(x).Font.Name = "Cambria Math" Then .Characters(x).Font.Color.RGB = RGB(0, 112, 192) End If Next x End With End If End If Next oShp Next oSld End Sub]]>

Update and follow-up on the Safe ToC initiative:

Last year, a group of us served on an ad hoc committee to combat harassment and discrimination in the Theory of Computing community. In our report, we suggested a number of measures that the various theory conferences could adopt to help in this effort. At a minimum, we wanted conferences to adopt a code of conduct and to appoint volunteers to serve as ToC Advocates whose role will be to provide support to any individual who has experienced harassment at a conference. Our full final report is now available here:

https://www.ics.uci.edu/~irani/ToC_SH_report.pdf

A small subset of the original committee along with Yuval Rabani in his capacity as IEEE TCMF chair are working on implementing some of the recommendations in the recent report. We have now launched a web site for the SafeToC Initiative: safetoc.org

So far, the support from the broader community has been strong. Quite a few conferences have passed resolutions to adopt the recommended practices in our report. The new web site lists all the participating conferences as well as the names of volunteers who have signed on to be ToC Advocates. The web site also provides information for ToC Advocates, conference organizers, and members of the ToC community.

Participating conferences all have codes of conduct and are ensuring that participants agree to abide by the code as part of their registration process. In addition, some of these conferences are adopting new mechanisms for author-declared conflicts of interests. This is especially important if an author feels that he or she may receive an unfair review due to a previous harassment-related incident.

Of course, the work is not done, and this important effort needs to continue. What can everyone do from here?

- First, we are in need of trained ToC Advocates, to spread this important service around! An advocate would be a designated conference attendee who would be available to provide support and information to anyone who has observed or experienced harassment at the conference The work is not difficult. Right now the training consists of an hour-long webinar sponsored by the ACM. We are envisioning one or two group Skype meetings per year to share experiences and best practices. If you are interested in serving as a ToC Advocate for a conference, you can contact someone on the steering committee for that conference.

- Second, even if you are not serving as an Advocate, please familiarize yourself with the various codes of conduct, and perhaps even listen to a training video! A larger community of invested bystanders who are aware of these issues and prepared to support and/or intervene as needed is critical. This does not have to mean formal reporting – even helping to diffuse a problematic situation or checking in on a colleague to be sure they are ok after a difficult conversation can make a big difference to someone involved in an incident.

We will continue to update the web page as participation in this effort grows. Thank you to everyone for helping to make our community a safe and welcoming place for everyone.

Erin Chambers

Martin Farach-Colton

Sandy Irani

Yuval Rabani

List of Resources:

- ACM training webinar (https://webinars.on24.com/acm/harassment)
*No Means No: Respond to Harassment in the Moment,*Webinar sponsored by the Association for Women in Science. (https://vimeo.com/163581972/6b1f96fb72)*Spot and Stop It: How To End Harassment at Professional Meetings,*Webinar sponsored by the Association for Women in Science. (https://vimeo.com/166410162/8dc250e79a)- Sexual Harassment Resources from the CRA-W (https://cra.org/cra-w/sexual-harassment)

In a recent breakthrough, Hao Huang gave a 6 page paper proving the longstanding sensitivity conjecture. (Hat tip, Scott Aaronson and Gil Kalai. See this stackexchange post and this paper of Avishai for some links to the literature on this.)

The proof is beautiful and simple. I will write a few words here, but it is probably easier for you to just read the paper. The sensitivity conjecture was known to follow from the following statement: let be the *Boolean Cube* which is the degree graph on vertices identified with such that for every , if their Hamming distance is one. Then, the maximum degree of every subgraph of of size is at least .

Hao proves the above statement by showing that there is a *signing* of the adjacency matrix of that turns it into a matrix with eigenvalues equaling and eigenvalues equaling . That is, he shows (using a simple but clever inductive argument, see the 5 line proof of his Lemma 2.2) that there is an matrix with entries in whose nonzero entries correspond to the edges of the Boolean cube, and such that all the eigenvalues of are and they sum up to zero. (Note that this makes sense since should have the same *Frobenius norm* as the adjacency matrix of . The Frobenius norm squared is both the sum of squares of entries, which is for which is a degree graph, and also equal to the sum of squares of the eigenvalues, which is if all eigenvalues are .)

Once you have such a signing, the result follows from Cauchy’s Interlace Theorem that says that for every matrix and any matrix that is a principle sub-matrix of ,

where are the eigenvalues of and is the maximum eigenvalue of . A corollary of this (which is the only fact we need) is that if has its top eigenvalue with multiplicity (i.e., ), then every principle sub-matrix of order larger than will satisfy . (In fact, we only need .)

Indeed, suppose that is a subgraph of the Boolean cube of size . Then the principle submatrix of corresponding to the vertices of satisfies (since and the first eigenvalues of are ). But it’s easy to show that for every matrix the maximum eigenvalue of is upper bounded by the maximum norm of its rows, which in our case is the maximum degree of the graph .

]]>Dear all,

The TCS Women 2019 program is finalized: https://sigact.org/tcswomen/tcs-women-2019/. Here are some details:

On June 23rd, we have our TCS Women Spotlight workshop from 2 pm to 5 pm. This will feature an inspirational talk by Ronitt Rubinfeld (MIT & Tel Aviv University)–“Comedy of Errors”, and rising stars talks by Naama Ben-David (CMU), Debarati Das (Charles University), Andrea Lincoln (MIT) and Oxana Poburinnaya (Boston University). The workshop is open to all and we would love to see you all there.

On June 24th, we have the TCS Women lunch and panel of distinguished researchers from academia and industries. This year’s panelists include Shuchi Chawla (University of Wisconsin), Julia Chuzhoy (TTIC), Edith Cohen (Google), Faith Ellen (University of Toronto), Rachel Lin (University of Washington) and Nutan Limaye (Indian Institute of Technology, Mumbai). The event is open to all women participants of FCRC.

In addition to these, there will be a TCS Women poster session held jointly with the STOC poster session on June 24th. Fourteen women researchers will be presenting posters on their research. More information is available on our website. All are welcome.

We are providing travel scholarships to more than forty women students this year to attend STOC and FCRC. We secured funding from the NSF, Akamai, Amazon, Google and Microsoft. Thank you!

Looking forward to seeing you soon!

Best wishes,

The TCS Women organizers

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Specifically, in the previous version of the book I used *programming languages *as the main computational models. While I still think this is the right way if we were to “start from scratch”, these idiosyncratic models made it harder for students to use other resources such as textbooks and lecture notes. They also make it more difficult for instructors to use individual chapters in their courses without committing to using the full book.

Hence in the new revision the standard models of **Turing Machines** and **Boolean Circuits** are front and center. We do talk about the programming-language equivalents as well, since I think they are important for the connection to practice and some concepts such as the duality of code and data are better explained in these terms. I also use the programming-language variants to demonstrate concepts to students in code including compilers from circuits to straightline programs, various “syntactic sugar” transformations, and the Cook-Levin Theorem and NP reductions.

One thing did not change – we still start with *Boolean Circuits *rather than automata as the initial computational model. Boolean circuits are closer to actual implementations of computing, are a finite (and hence simpler) model, but one that is non-trivial enough to allow showing some important theorems early in the course including existence of a circuit for computing every finite function, the existence of a circuit to evaluate other circuits, and the counting lower bound as well as the counting lower bound.

Circuits are also crucial for later material in the course since they make the proof of the Cook-Levin Theorem much simpler and cleaner, allow talking about results such as and Sipser-Gacs, and are crucial to be even able to state results in advanced topics such as derandomization, cryptography, and quantum computing.

We do cover automata as well, including the equivalence of regular expressions and deterministic finite automata. We also cover context-free grammars (though not pushdown automata) and the λ calculus, including its equivalence with Turing Machines and the Y combinator (see also this notebook)

I have also done some work on the technical side of producing the book. The book is written in markdown. Markdown has many advantages but it wasn’t designed for 600-page technical books full of equations and cross-references so I did need to use some extensions to it. I am using pandoc (and my own filter) to produce both the HTML and LaTeX/PDF versions of the book.

There is still more work to do. I plan to add a chapter on space complexity and on proofs and computation (including both interactive and zero knowledge proofs, as well as the “propositions as types” correspondence between proofs and programs). I need to add more examples and exercises. There are also still several chapters where the text is “rough around the edges”.

As usual, the latest version of the book is available on https://introtcs.org . If you see any typo, problem, etc.., please post an issue on the GitHub repository (you can also make a pull request for small typo fixes if you prefer)

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