Reporting from the ‘Frontiers of Quantum Information Science’

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What am I referring to with this title? It is similar to the name of this blog–but that’s not where this particular title comes from–although there is a common denominator. Frontiers of Quantum Information Science was the theme for the 31st Jerusalem winter school in theoretical physics, which takes place annually at the Israeli Institute for Advanced Studies located on the Givat Ram campus of the Hebrew University of Jerusalem. The school took place from December 30, 2013 through January 9, 2014, but some of the attendees are still trickling back to their home institutions. The common denominator is that our very own John Preskill was the director of this school; co-directed by Michael Ben-Or and Patrick Hayden. John mentioned during a previous post and reiterated during his opening remarks that this is the first time the IIAS has chosen quantum information to be the topic for its prestigious advanced school–another sign of quantum information’s emergence as an important sub-field of physics. In this blog post, I’m going to do my best to recount these festivities while John protects his home from forest fires, prepares a talk for the Simons Institute’s workshop on Hamiltonian complexity, teaches his quantum information course and celebrates his birthday 60+1.

The school was mainly targeted at physicists, but it was diversely represented. Proof of the value of this diversity came in an interaction between a computer scientist and a physicist, which led to one of the school’s most memorable moments. Both of my most memorable moments started with the talent show (I was surprised that so many talents were on display at a physics conference…) Anyways, towards the end of the show, Mateus Araújo Santos, a PhD student in Vienna, entered the stage and mentioned that he could channel “the ghost of Feynman” to serve as an oracle for NP-complete decision problems. After making this claim, people obviously turned to Scott Aaronson, hoping that he’d be able to break the oracle. However, in order for this to happen, we had to wait until Scott’s third lecture about linear optics and boson sampling the next day. You can watch Scott bombard the oracle with decision problems from 1:00-2:15 during the video from his third lecture.

oracle_aaronson

Scott Aaronson grilling the oracle with a string of NP-complete decision problems! From 1:00-2:15 during this video.

The other most memorable moment was when John briefly danced Gangnam style during Soonwon Choi‘s talent show performance. Unfortunately, I thought I had this on video, but the video didn’t record. If anyone has video evidence of this, then please share!
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Of sensors and science students

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Click click.

Once the clasps unfastened, the tubular black case opened like a yard-long mussel. It might have held a bazooka, a collapsible pole tent, or enough shellfish for three plates of paella.

“This,” said Rob Young, for certain types of light, “is the most efficient detector in the world.”
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Building a Computer: Part I

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During my senior year in high school, I was fortunate enough to participate in the Intel International Science and Engineering Fair. At the awards banquet I was seated with fourteen others and we each had the choice of ordering either salmon or steak for our respective entrées. I noticed that while taking our fifteen different orders, our waiter did not write anything down. How on Earth was he going to remember what each of us had requested?!

It turns out the answer is intimately related to Problems 2 and 5 in my last post. Did you realize you always save at least 999 people on the game show? Here’s how:

The person at the back of the line will look at all 999 hats in front of him. If the number of black hats is odd, he will shout “Black!” If the number of black hats is even, he will shout “White!” From this information, the second person in line can deduce from the hats in front of him what the color of his own hat is! For example, if Contestant 1 shouts “Black!” and Contestant 2 sees an even number of black hats in front of him, he can deduce that his own hat is black because the total number of black hats Contestant 1 sees is odd. From information given in Contestant 1’s and Contestant 2’s answers, Contestant 3 can determine his hat’s color via a similar parity argument, and so on. At least $999 will be donated to charity.

How about Problem 5? One solution requires knowledge of how to represent numbers in binary. Let’s say you owe your friend $3,761.50, and want to pay him using pennies and dimes, as well as $1, $10, $100, and hypothetical $1,000 bills. How would you pay him using the least number of monetary tokens? The answer to this is easy – we all learned about the hundredths’ place, the tenths’ place, ones’ place, the tens’ place, the hundreds’ place, and so on in elementary school. The digit in the ones’ place tells us how many $1 bills we need to give our friend, the digit in the tens’ place tells us how many $10 bills we need to give our friend, and so on. Written more suggestively,

3,761 = 3*103 + 7*102 + 6*101 + 1*100 + 5*10-1 + 0*10-2

Why does the number 10 appear so significant in the above equation? In the above equation, 10 is called the “base.” In base 10, we write every number as the sum of whole multiples of powers of 10. Notice that none of the bold numbers – the digits – can be greater than or equal to the base (10); they must be between 0 and 9. If one of the bold digits was greater than 9, we could just use a monetary token of higher value to reduce the total number of bills and coins we need to repay our friend. This leads to:

Rule #1: The value of each digit must be less than the base.

Could we use a number other than 10 as our base? Let’s try using 2! I can think of at least one way to write 3,761.50 as the sum of multiples of powers of two:

3,761.50 = 1*211 + 0*210 + 0*29 + 0*28 + 0*27 + 0*26 + 53*25 + 1*24 + 0*23 + 0*22 + 0*21 + 1*20 + 1*2-1

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The Navajo connection

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A few months ago, Prof. Keith Schwab brought visiting students and teachers from Navajo Preparatory School to tour some of the IQIM labs, listen to some quick lectures on optics, and talk to scientists. Since this opportunity was only allowed to the one carload that made the 11.5 hour drive from Farmington, NM, everyone involved agreed that we could reach far more students if the IQIM sent Caltech students there. Ana Brown and I both enjoyed speaking with the visiting students and teachers, and responded enthusiastically when Prof. Schwab offered to send us.  My enthusiasm momentarily dimmed when I realized our trip would be occurring in the dead of winter and it was projected to snow while we were there (having only lived in northern and southern California, let’s say I have a heightened sensitivity to weather), but I excitedly spent thanksgiving putting together demonstrations with supplies I found in my closet and garage. I’ve always enjoyed talking about applied math, science, and engineering to anyone, especially anyone young enough to have only heard “math is boring” or “science is too hard” few enough times I can convince them otherwise.  Navajo Prep seemed ideal for this, since the school prepares the students well and sends over 95% of the students to college, and is working to increase student interest in math, science, and engineering.

it's colder than it looks, I swear

Panorama from the center of Navajo Prep

With a suitcase half full of clothes and half full of tools and hacked-together electronics, I was picked up from the airport, and arrived at the school in the afternoon the Monday after Thanksgiving weekend. While Monday was spent arranging which classes I would attend, and what topics I would discuss, my second day involved a trip with the school’s outreach coordinator and Cody, one of the two students who visited Caltech, taking a tour of some of the local highlights, including a traditional Navajo lunch (steam corn stew, roast mutton, and I even tried ach’ii”) and toured the remnants of the cliff dwellings at Mesa Verde, about half an hour from the school. Exploring a region with such a rich history and discussing it with my hosts, who are descendants in part from that history was an incredible experience.

yup, some 70 rooms built in a recess carved into the canyon wall almost a thousand years ago.

Rooms at the Oak Tree House at Mesa Verde

On Wednesday, I began talking to the freshman physics classes about optics, intending to discuss the properties of light, like frequency, speed, wavelength, velocity, energy, and momentum, but to give some context I began with a historical summary of discoveries in optics. I know I was surprised when I was preparing, so you might enjoy answering the same questions that I asked the class. Take a second, and guess when you think the first lenses were made and when wearable glasses were first used. (After you think you have a guess, scroll to the bottom to see how you did.)  When I realized that the class was more interested in seeing rather than hearing about optics, I skimmed over what I’d prepared in order to spend more time on the demonstrations where I showed refraction in glass and explained how that can be derived from assuming a different speed of light in the material. We found lenses for the students to manipulate/play with, and even though historically there were about 300 years between invention of glasses (and the proliferation of lens-making) and the invention of the telescope, some of the students unintentionally built telescopes after taking a second lens from their friends and were shocked to hear that what they had just made was better than the one Galileo used to first discover the four largest moons of Jupiter.

I promise this shot is not advertising for Under Armour.

Measuring focal lengths and observing lensing with a drop of water on a glass slide

We also demonstrated double slit diffraction and calculated light’s wavelength for three different laser pointers to within 5% accuracy using only a tape measure, a post-it, and a knife. I decided not to bring a demonstration to measure the speed of light with a laser, a few mirrors, a computer fan, and a reverse-biased photodiode hooked up to an old speaker, because I couldn’t get the fan to spin fast enough to get a reasonably short delay length. (From that can you guess what my set-up was?) On Thursday, Ana and I gave a similar lecture to a different pair of 90 minute freshman physics classes, and spent the other periods talking with math classes. In calculus, I described the different kinds of math classes offered in college, their applications, and their connections to each other in an attempt to give more meaning to the course titles they would no doubt be reading next fall. In geometry and trigonometry I answered the perennial high school math question: “when will we ever use this?” by talking about some applications in geometric optics.

Since I figure you readers like thinking about this sort of thing, I’ll elaborate: I started with the fact that a light beam’s incident angle (measured from the perpendicular of a surface) is equal to its reflected angle. This means that light propagation, like much of (but not all of) physics, is reversible in all but a few specific cases. As a result, light generated at or passing through the center of a circle is reflected off the circle back to the center. An ellipse has a similar property where light through one focus is all reflected to the other. Try deriving that from the fact that an ellipse is defined to be the set of all points where the sum of the distances to the two foci equals some fixed constant. In the lecture, I then used the fact that a parabola is the set of all points equidistant from a point (the focus) and a line (the directrix) to show that light from the focus is reflected off the parabola and collimated (focused at infinity).

Ana brought some IQIM hats and shirts, which the freshman physics classes seemed to definitely enjoy when we met with each class for 40 minutes on Friday.

We probably tripled the number of high school varsity football players who've worn IQIM gear in that one picture

One of the four freshman physics classes we got to spend time with

I tried to give them an impression of what we do in the IQIM, but I had a hard time giving a satisfactory explanation of the significance of quantum information, and Ana easily convinced me that it would be more engaging to use the 90 minute introduction I had already given them on optics to explain and describe solar energy, since many buildings deep in the Navajo reservation are off the power grid.  There are also plans to construct a large solar power plant on the reservation that will be much cleaner than the three local coal power plants in the region.

I think I made a joke and Ana might have been the only one to laugh. Still, it's proof I can be funny.

Action shot during the lecture on solar

Ana and I also spoke to the senior seminar, which contained the entire graduating class, where she talked about the difficulties transitioning to college experienced by some of her friends in college who were from the Navajo reservation. She gave such great advice on applying to schools, applying for fellowships, and developing a healthy work/life balance, that the only thing I felt like I could contribute was some advice on picking a major (since I’ve picked about 4 different majors), where I described the difference between science and engineering, and talked about different fields within each. I loved how truly helpful I felt when so many of the students told us that they either found certain pieces of advice to be useful, thanked us for introducing them to an idea they hadn’t heard of, or asked us to come back soon.

Occasionally a student asked what I personally do, and their curiosity was rewarded with an explanation that lasted as long as they were interested.  The shortest lasted two sentences and the longest explanation (given to a calculus class of 5 people) involved 30 minutes with my laptop out showing all the steps I take to fabricate nanoscale devices to trap light in almost a cubic-wavelength volume in proximity to an “optically interesting” rare earth ion which my advisor and I hope will provide a viable quantum optical memory.  (Here‘s a little more about our work.)

In the evenings we cheered for the school’s basketball team, had dinner with some of the students and teachers, and discussed the school’s science curriculum and science fair projects. Ana and I consulted on a solar water heating project some of the students were working on, and, after the students all went home for the weekend, I even spent 2 hours in 17ºF weather the last night calibrating an 8″ diameter Schmidt-Cassegrain telescope that had been donated to the school. Compared to Pasadena the viewing was spectacular, and I could easily spot galaxies, nebulae, and discern stripes on Jupiter and the four Galilean moons. I can only expect that some of the students I met will be as excited as I was.

From wikipedia: “The earliest known lenses were made from polished crystal, often quartz, and have been dated as early as 700 BC for Assyrian lenses” and “Around 1284 in Italy, Salvino D’Armate is credited with inventing the first wearable eye glasses.” For anyone who’s interested in the history of science, I’d suggest you check it out.

More Brainteasers

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As promised, I’m back to tell you more about myself and tickle your brain! I’m terribly sorry for giving such a short description of my background in my last post. If I had to describe myself in another \leq 5 words, I’d write: “Breakdancing, bodybuilding physicist… Ladies: single.”

Problem 1: A thousand balloons numbered 1, 2, … , 1000 are arranged in a circle. Starting with balloon 1, every alternating balloon is popped. So balloon 1 is popped, balloon 3 is popped, balloon 5 is popped, and so on until balloon 999 is popped. But the process does not stop here! We keep going around the circle with the remaining balloons and pop every other one. So next balloon 2 is popped, balloon 4 is skipped, balloon 6 is popped, and so on. This process continues until only one balloon is left remaining; which is the last balloon standing?

A thousand red balloons numbered from 1 to 1000. Starting at the gold star, we pop every other balloon while traveling clockwise. Which is the last balloon remaining?

A thousand red balloons numbered from 1 to 1000. Starting at the gold star, we pop every other balloon while traveling clockwise. Which is the last balloon remaining?

It is of course easy to solve Problem 1 via brute force, but can you think of a more elegant solution? Do you really need to go around the circle log(n) times? If you get stuck, try working on Problem 2 for a while:

Problem 2: A thousand people stand in single file on a game show. Each person is wearing a hat which is either black or white. Each person can see the hats of all the people in front of them in line but they cannot see their own hat. Starting with the person at the back of the line and progressing forward, the game show host will ask, “What color is your hat?” Each contestant is only permitted to answer “black” or “white.” For each correct answer, the host will donate $1 to charity. If the contestants are allowed to discuss a strategy before they are lined up and given their hats, how much can they guarantee will be donated to charity?

If you managed to solve Problem 2, Problem 3 should be easy.

Problem 3: Now each person is given a hat which is one of n colors, and is allowed to answer the host’s question by giving any of the n colors. How much can the contestants guarantee will be donated to charity?

Problem 4: You are given ten coin-making machines which produce coins weighing 2 grams each. Each coin-maker can produce infinitely many coins. One of the ten machines, however, is defective and produces coins weighing 1 gram each. You are also given a scientific balance (with a numerical output). How many times must you use the balance to determine which machine is defective? What if the weight of the coins produced by the rogue machine is unknown?

I happen to be very good personal friends with Count von Count. One day as we were walking through Splash Castle, the Count told me he had passed his arithmetic class and was throwing a graduation party! Alas, before he could host the get-together, he needed to solve a problem on injective mappings from powersets to subsets of the natural numbers…

Problem 5: The Count has a thousand bottles of apple juice for his party, but one of the bottles contains spoiled juice! This spoiled juice induces tummy aches roughly a day after being consumed, and the Count wants to avoid lawsuits brought on by the innocent patrons of Sesame Place. Luckily, there is just enough time before the party for ten of the Count’s friends to perform exactly one round of taste-testing, during which they can drink from as many bottles as they please. How can the ten friends determine which bottle is both tummy ache- and lawsuit-inducing? You can assume Count’s friends have promised not to sue him if they get sick.

Please let me know what you think of these problems in the comments! Too easy? Too hard? Want more? Tell me so!

Jostling the unreal in Oxford

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Oxford, where the real and the unreal jostle in the streets, where windows open into other worlds…

So wrote Philip Pullman, author of The Golden Compass and its sequels. In the series, a girl wanders from the Oxford in another world to the Oxford in ours.

I’ve been honored to wander Oxford this fall. Visiting Oscar Dahlsten and Jon Barrett, I’ve been moonlighting in Vlatko Vedral’s QI group. We’re interweaving 21st-century knowledge about electrons and information with a Victorian fixation on energy and engines. This research program, quantum thermodynamics, should open a window onto our world.

Radcliffe camera

A new world. At least, a world new to the author.

To study our world from another angle, Oxford researchers are jostling the unreal. Oscar, Jon, Andrew Garner, and others are studying generalized probabilistic theories, or GPTs.

What’s a specific probabilistic theory, let alone a generalized one? In everyday, classical contexts, probabilities combine according to rules you know. Suppose you have a 90% chance of arriving in London-Heathrow Airport at 7:30 AM next Sunday. Suppose that, if you arrive in Heathrow at 7:30 AM, you’ll have a 70% chance of catching the 8:05 AM bus to Oxford. You have a probability 0.9 * 0.7 = 0.63 of arriving in Heathrow at 7:30 and catching the 8:05 bus. Why 0.9 * 0.7? Why not 0.90.7, or 0.9/(2 * 0.7)? How might probabilities combine, GPT researchers ask, and why do they combine as they do?

Not that, in GPTs, probabilities combine as in 0.9/(2 * 0.7). Consider the 0.9/(2 * 0.7) plucked from a daydream inspired by this City of Dreaming Spires. But probabilities do combine in ways we wouldn’t expect. By entangling two particles, separating them, and measuring one, you immediately change the probability that a measurement of Particle 2 yields some outcome. John Bell explored, and experimentalists have checked, statistics generated by entanglement. These statistics disobey rules that govern Heathrow-and-bus statistics. As do entanglement statistics, so do effects of quantum phenomena like discord, negative Wigner functions, and weak measurements. Quantum theory and its contrast with classicality force us to reconsider probability.
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Fundamental Physics Prize Prediction: Green and Schwarz

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Michael Green

Michael Green

John Schwarz

John Schwarz

The big news today is the announcement of the nominees for the 2014 Fundamental Physics Prize: (1) Michael Green and John Schwarz, for pioneering contributions to string theory, (2) Joseph Polchinski, for discovering the central role of D-branes in string theory, and (3) Andrew Strominger and Cumrun Vafa, for discovering (using D-branes) the microscopic origin of black hole entropy in string theory. As in past years, all the nominees are marvelously deserving. The winner of the $3 million prize will be announced in San Francisco on December 12; the others will receive the $300,000 Physics Frontiers Prize.

I wrote about my admiration for Joe Polchinski when he was nominated last year, and I have also greatly admired the work of Strominger and Vafa for many years. But the story of Green and Schwarz is especially compelling. String theory, which was originally proposed as a theory of the strong interaction, had been an active research area from 1968 through the early 70s. But when asymptotic freedom was discovered in 1973, and quantum chromodynamics became clearly established as the right theory of the strong interaction, interest in string theory collapsed. Even the 1974 proposal by Scherk and Schwarz that string theory is really a compelling candidate for a quantum theory of gravity failed to generate much excitement.

A faithful few continued to develop string theory through the late 70s and early 80’s, particularly Green and Schwarz, who began collaborating in 1979. Together they clarified the different variants of the theory, which they named Types I, IIA, and IIB, and which were later recognized as different solutions to a single underlying theory (sometimes called M-theory). In retrospect, Green and Schwarz were making remarkable progress, but were still largely ignored.

In 1983, Luis Alvarez-Gaume and Edward Witten analyzed the gravitational anomalies that afflict higher dimensional “chiral” theories (in which left-handed and right-handed particles behave differently), and discovered a beautiful cancellation of these anomalies in the Type IIB string theory. But anomalies, which render a theory inconsistent, seemed to be a nail in the coffin of Type I theory, at that time the best hope for uniting gravitation with the other fundamental (gauge) interactions.

Then, working together at the Aspen Center for Physics during the summer of 1984, Green and Schwarz discovered an even more miraculous cancellation of anomalies in Type I string theory, which worked for only one possible gauge group: SO(32). (Within days they and others found that anomalies cancel for E8 X E8 as well, which provided the impetus for the invention of the heterotic string theory.) The anomaly cancellation drove a surge of enthusiasm for string theory as a unified theory of fundamental physics. The transformation of string theory from a backwater to the hottest topic in physics occurred virtually overnight. It was an exciting time.

When John turned 60 in 2001, I contributed a poem to a book assembled in his honor, hoping to capture in the poem the transformation that Green and Schwarz fomented (and also to express irritation about the widespread misspelling of “Schwarz”). I have appended the poem below, along with the photo of myself I included at the time to express my appreciation for strings.

I’ll be delighted if Polchinski, or Strominger and Vafa win the prize — they deserve it. But it will be especially satisfying if Green and Schwarz win. They started it all, and refused to give up.

To John Schwarz

Thirty years ago or more
John saw what physics had in store.
He had a vision of a string
And focused on that one big thing.

But then in nineteen-seven-three
Most physicists had to agree
That hadrons blasted to debris
Were well described by QCD.

The string, it seemed, by then was dead.
But John said: “It’s space-time instead!
The string can be revived again.
Give masses twenty powers of ten!”

Then Dr. Green and Dr. Black,
Writing papers by the stack,
Made One, Two-A, and Two-B glisten.
Why is it none of us would listen?

We said, “Who cares if super tricks
Bring D to ten from twenty-six?
Your theory must have fatal flaws.
Anomalies will doom your cause.”

If you weren’t there you couldn’t know
The impact of that mightly blow:
“The Green-Schwarz theory could be true —
It works for S-O-thirty-two!”

Then strings of course became the rage
And young folks of a certain age
Could not resist their siren call:
One theory that explains it all.

Because he never would give in,
Pursued his dream with discipline,
John Schwarz has been a hero to me.
So please, don’t spell it with a “t”!

Expressing my admiration for strings in 2001

Expressing my admiration for strings in 2001.

Polarizer: Rise of the Efficiency

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How should a visitor to Zürich spend her weekend?

Launch this question at a Swiss lunchtable, and you split diners into two camps. To take advantage of Zürich, some say, visit Geneva, Lucerne, or another spot outside Zürich. Other locals suggest museums, the lake, and the 19th-century ETH building.

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The 19th-century ETH building

ETH, short for a German name I’ve never pronounced, is the polytechnic from which Einstein graduated. The polytechnic houses a quantum-information (QI) theory group that’s pioneering ideas I’ve blogged about: single-shot information, epsilonification, and small-scale thermodynamics. While visiting the group this August, I triggered an avalanche of tourism advice. Caught between two camps, I chose Option Three: Contemplate polar codes.

Polar codes compress information into the smallest space possible. Imagine you write a message (say, a Zürich travel guide) and want to encode it in the fewest possible symbols (so it fits in my camera bag). The longer the message, the fewer encoding symbols you need per encoded symbol: The more punch each code letter can pack. As the message grows, the encoding-to-encoded ratio decreases. The lowest possible ratio is a number, represented by H, called the Shannon entropy.

So established Claude E. Shannon in 1948. But Shannon didn’t know how to code at efficiency H. Not for 51 years did we know.

I learned how, just before that weekend. ETH student David Sutter walked me through polar codes as though down Zürich’s Banhofstrasse.

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The Banhofstrasse, one of Zürich’s trendiest streets, early on a Sunday.

Say you’re encoding n copies of a random variable. When I say, “random variable,” think, “character in the travel guide.” Just as each character is one of 26 letters, each variable has one of many possible values.

Suppose the variables are independent and identically distributed. Even if you know some variables’ values, you can’t guess others’. Cryptoquote players might object that we can infer unknown from known letters. For example, a three-letter word that begins with “th” likely ends with “e.” But our message lacks patterns.

Think of the variables as diners at my lunchtable. Asking how to fill a weekend in Zürich—splitting the diners—I resembled the polarizer.

The polarizer is a mathematical object that sounds like an Arnold Schwarzenegger film and acts on the variables. Just as some diners pointed me outside Zürich, the polarizer gives some variables one property. Just some diners pointed me to within Zürich, the polarizer gives some variables another property. Just as I pointed myself at polar codes, the polarizer gives some variables a third property.

These properties involve entropy. Entropy quantifies uncertainty about a variable’s value—about which of the 26 letters a character represents. Even if you know the early variables’ values, you can’t guess the later variables’. But we can guess some polarized variables’ values. Call the first polarized variable u1, the second u2, etc. If we can guess the value of some ui, that ui has low entropy. If we can’t guess the value, ui has high entropy. The Nicole-esque variables have entropies like the earnings of Terminator Salvation: noteworthy but not chart-topping.

To recap: We want to squeeze a message into the tiniest space possible. Even if we know early variables’ values, we can’t infer later variables’. Applying the polarizer, we split the variables into low-, high-, and middling-entropy flocks. We can guess the value of each low-entropy ui, if we know the foregoing uh’s.

Almost finished!

In your camera-size travel guide, transcribe the high-entropy ui’s. These ui’s suggest the values of the low-entropy ui’s. When you want to decode the guide, guess the low-entropy ui’s. Then reverse the polarizer to reconstruct much of the original text.

The longer the original travel guide, the fewer errors you make while decoding, and the smaller the ratio of the encoded guide’s length to the original guide’s length. That ratio shrinks–as the guide’s length grows–to H. You’ve compressed a message maximally efficiently. As the Swiss say: Glückwünsche.

How does compression relate to QI? Quantum states form messages. Polar codes, ETH scientists have shown, compress quantum messages maximally efficiently. Researchers are exploring decoding strategies and relationships among (quantum) polar codes. With their help, Shannon-coded travel guides might fit not only in my camera bag, but also on the tip of my water bottle.

Should you need a Zürich travel guide, I recommend Grossmünster Church. Not only does the name fulfill your daily dose of umlauts. Not only did Ulrich Zwingli channel the Protestant Reformation into Switzerland there. Climbing a church tower affords a panorama of Zürich. After oohing over the hills and ahhing over the lake, you can shift your gaze toward ETH. The worldview being built there bewitches as much as the vista from any tower.

P1040476

A tower with a view.

With gratitude to ETH’s QI-theory group (particularly to Renato Renner) for its hospitality. And for its travel advice. With gratitude to David Sutter for his explanations and patience.

P1040411

The author and her neue Freunde.

The 10 biggest breakthroughs in physics over the past 25 years, according to us.

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Making your way to the cutting edge of any field is a daunting challenge. But especially when the edge of the field is expanding; and even harder still when the rate of expansion is accelerating. John recently helped Physics World create a special 25th anniversary issue where they identified the five biggest breakthroughs in physics over the past 25 years, and also the five biggest open questions. In pure John fashion, at his group meeting on Wednesday night, he made us work before revealing the answers. The photo below shows our guesses, where the asterisks denote Physics World‘s selections. This is the blog post I wish I had when I was a fifteen year-old aspiring physicist–this is an attempt to survey and provide a tiny toehold on the edge (from my biased, incredibly naive, and still developing perspective.)

The IQI's

The IQI’s quantum information-biased guesses of Physics World’s 5 biggest breakthroughs over the past 25 years, and 5 biggest open problems. X’s denote Physics World’s selections. Somehow we ended up with 10 selections in each category…

The biggest breakthroughs of the past 25 years:

*Neutrino Mass: surprisingly, neutrinos have a nonzero mass, which provides a window into particle physics beyond the standard model. THE STANDARD MODEL has been getting a lot of attention recently. This is well deserved in my opinion, considering that the vast majority of its predictions have come true, most of which were made by the end of the 1960s. Last year’s discovery of the Higgs Boson is the feather in its cap. However, it’s boring when things work too perfectly, because then we don’t know what path to continue on. That’s where the neutrino mass comes in. First, what are neutrinos? Neutrinos are a fundamental particle that have the special property that they barely interact with other particles. There are four fundamental forces in nature: electromagnetism, gravity, strong (holds quarks together to create neutrons and protons), and weak (responsible for radioactivity and nuclear fusion.) We can design experiments which allow us to observe neutrinos. We have learned that they are electrically neutral, so they aren’t affected by electromagnetism. They are barely affected by the strong force, if at all. They have an extremely small mass, so gravity acts on them only subtly. The main way in which they interact with their environment is through the weak force. Here’s the amazing thing: only really clunky versions of the standard model can allow for a nonzero neutrino mass! Hence, when a small but nonzero mass was experimentally established in 1998, we gained one of our first toeholds into particle physics beyond the standard model. This is particularly important today, because to the best of my knowledge, the LHC hasn’t yet discovered any other new physics beyond the standard model. The mechanism behind the neutrino mass is not yet understood. Moreover, neutrinos have a bunch of other bizarre properties which we understand empirically, but not their theoretical origins. The strangest of which goes by the name neutrino oscillations. In one sentence: there are three different kinds of neutrinos, and they can spontaneously transmute themselves from one type to another. This happens because physics is formulated in the language of mathematics, and the math says that the eigenstates corresponding to ‘flavors’ are not the same as the eigenstates corresponding to ‘mass.’ Words, words, words. Maybe the Caltech particle theory people should have a blog?

Shor’s Algorithm: a quantum computer can factor N=1433301577 into 37811*37907 exponentially faster than a classical computer. This result from Peter Shor in 1994 is near and dear to our quantum hearts. It opened the floodgates showing that there are tasks a quantum computer could perform exponentially faster than a classical computer, and therefore that we should get BIG$$$ from the world over in order to advance our field!! The task here is factoring large numbers into their prime factors; the difficulty of which has been the basis for many cryptographic protocols. In one sentence, Shor’s algorithm achieves this exponential speed-up because there is a step in the factoring algorithm (period finding) which can be performed in parallel via the quantum Fourier transform.
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Can a game teach kids quantum mechanics?

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Five months ago, I received an email and then a phone call from Google’s Creative Lab Executive Producer, Lorraine Yurshansky. Lo, as she prefers to be called, is not your average thirty year-old. She has produced award-winning short films like Peter at the End (starring Napoleon Dynamite, aka Jon Heder), launched the wildly popular Maker Camp on Google+ and had time to run a couple of New York marathons as a warm-up to all of that. So why was she interested in talking to a quantum physicist?

You may remember reading about Google’s recent collaboration with NASA and D-Wave, on using NASA’s supercomputing facilities along with a D-Wave Two machine to solve optimization problems relevant to both Google (Glass, for example) and NASA (analysis of massive data sets). It was natural for Google, then, to want to promote this new collaboration through a short video about quantum computers. The video appeared last week on Google’s YouTube channel:

This is a very exciting collaboration in my view. Google has opened its doors to quantum computation and this has some powerful consequences. And it is all because of D-Wave. But, let me put my perspective in context, before Scott Aaronson unleashes the hounds of BQP on me.

Two years ago, together with Science magazine’s 2010 Breakthrough of the Year winner, Aaron O’ Connell, we decided to ask Google Ventures for $10,000,000 dollars to start a quantum computing company based on technology Aaron had developed as a graduate student at John Martini’s group at UCSB. The idea we pitched was that a hand-picked team of top experimentalists and theorists from around the world, would prototype new designs to achieve longer coherence times and greater connectivity between superconducting qubits, faster than in any academic environment. Google didn’t bite. At the time, I thought the reason behind the rejection was this: Google wants a real quantum computer now, not just a 10 year plan of how to make one based on superconducting X-mon qubits that may or may not work.

I was partially wrong. The reason for the rejection was not a lack of proof that our efforts would pay off eventually – it was a lack of any prototype on which Google could run algorithms relevant to their work. In other words, Aaron and I didn’t have something that Google could use right-away. But D-Wave did and Google was already dating D-Wave One for at least three years, before marrying D-Wave Two this May. Quantum computation has much to offer Google, so I am excited to see this relationship blossom (whether it be D-Wave or Pivit Inc that builds the first quantum computer). Which brings me back to that phone call five months ago…

Lorraine: Hi Spiro. Have you heard of Google’s collaboration with NASA on the new Quantum Artificial Intelligence Lab?

Me: Yes. It is all over the news!

Lo: Indeed. Can you help us design a mod for Minecraft to get kids excited about quantum mechanics and quantum computers?

Me: Minecraft? What is Minecraft? Is it like Warcraft or Starcraft?

Lo: (Omg, he doesn’t know Minecraft!?! How old is this guy?) Ahh, yeah, it is a game where you build cool structures by mining different kinds of blocks in this sandbox world. It is popular with kids.

Me: Oh, okay. Let me check out the game and see what I can come up with.

After looking at the game I realized three things:
1. The game has a fan base in the tens of millions.
2. There is an annual convention (Minecon) devoted to this game alone.
3. I had no idea how to incorporate quantum mechanics within Minecraft.

Lo and I decided that it would be better to bring some outside help, if we were to design a new mod for Minecraft. Enter E-Line Media and TeacherGaming, two companies dedicated to making games which focus on balancing the educational aspect with gameplay (which influences how addictive the game is). Over the next three months, producers, writers, game designers and coder-extraordinaire Dan200, came together to create a mod for Minecraft. But, we quickly came to a crossroads: Make a quantum simulator based on Dan200’s popular ComputerCraft mod, or focus on gameplay and a high-level representation of quantum mechanics within Minecraft?

The answer was not so easy at first, especially because I kept pushing for more authenticity (I asked Dan200 to create Hadamard and CNOT gates, but thankfully he and Scot Bayless – a legend in the gaming world – ignored me.) In the end, I would like to think that we went with the best of both worlds, given the time constraints we were operating under (a group of us are attending Minecon 2013 to showcase the new mod in two weeks) and the young audience we are trying to engage. For example, we decided that to prepare a pair of entangled qubits within Minecraft, you would use the Essence of Entanglement, an object crafted using the Essence of Superposition (Hadamard gate, yay!) and Quantum Dust placed in a CNOT configuration on a crafting table (don’t ask for more details). And when it came to Quantum Teleportation within the game, two entangled quantum computers would need to be placed at different parts of the world, each one with four surrounding pylons representing an encoding/decoding mechanism. Of course, on top of each pylon made of obsidian (and its far-away partner), you would need to place a crystal, as the required classical side-channel. As an authorized quantum mechanic, I allowed myself to bend quantum mechanics, but I could not bring myself to mess with Special Relativity.

As the mod launched two days ago, I am not sure how successful it will be. All I know is that the team behind its development is full of superstars, dedicated to making sure that John Preskill wins this bet (50 years from now):

The plan for the future is to upload a variety of posts and educational resources on qcraft.org discussing the science behind the high-level concepts presented within the game, at a level that middle-schoolers can appreciate. So, if you play Minecraft (or you have kids over the age of 10), download qCraft now and start building. It’s a free addition to Minecraft.