A Public Lecture on Quantum Information

Sooner or later, most scientists are asked to deliver a public lecture about their research specialties. When successful, lecturing about science to the lay public can give one a feeling of deep satisfaction. But preparing the lecture is a lot of work!

Caltech sponsors the Earnest C. Watson lecture series (named after the same Earnest Watson mentioned in my post about Jane Werner Watson), which attracts very enthusiastic audiences to Beckman Auditorium nine times a year. I gave a Watson lecture on April 3 about Quantum Entanglement and Quantum Computing, which is now available from iTunes U and also on YouTube:


I did a Watson lecture once before, in 1997. That occasion precipitated some big changes in my presentation style. To prepare for the lecture, I acquired my first laptop computer and learned to use PowerPoint. This was still the era when a typical physics talk was handwritten on transparencies and displayed using an overhead projector, so I was sort of a pioneer. And I had many anxious moments in the late 1990s worrying about whether my laptop would be able to communicate with the projector — that can still be a problem even today, but was a more common problem then.

I invested an enormous amount of time in preparing that 1997 lecture, an investment still yielding dividends today. Aside from figuring out what computer to buy (an IBM ThinkPad) and how to do animation in PowerPoint, I also learned to draw using Adobe Illustrator under the tutelage of Caltech’s digital media expert Wayne Waller. And apart from all that technical preparation, I had to figure out the content of the lecture!

That was when I first decided to represent a qubit as a box with two doors, which contains a ball that can be either red or green, and I still use some of the drawings I made then.

Entanglement, illustrated with balls in boxes.

Entanglement, illustrated with balls in boxes.

This choice of colors was unfortunate, because people with red-green color blindness cannot tell the difference. I still feel bad about that, but I don’t have editable versions of the drawings anymore, so fixing it would be a big job …

I also asked my nephew Ben Preskill (then 10 years old, now a math PhD candidate at UC Berkeley), to make a drawing for me illustrating weirdness.

The desire to put weirdness to work has driven the emergence of quantum information science.

The desire to put weirdness to work has driven the emergence of quantum information science.

I still use that, for sentimental reasons, even though it would be easier to update.

The turnout at the lecture was gratifying (you can’t really see the audience with the spotlight shining in your eyes, but I sensed that the main floor of the Auditorium was mostly full), and I have gotten a lot of positive feedback (including from the people who came up to ask questions afterward — we might have been there all night if the audio-visual staff had not forced us to go home).

I did make a few decisions about which I have had second thoughts. I was told I had the option of giving a 45 minute talk with a public question period following, or a 55 minute talk with only a private question period, and I opted for the longer talk. Maybe I should have pushed back and insisted on allowing some public questions even after the longer talk — I like answering questions. And I was told that I should stay in the spotlight, to ensure good video quality, so I decided to stand behind the podium the whole time to curb my tendency to pace across the stage. But maybe I would have seemed more dynamic if I had done some pacing.

I got some gentle criticism from my wife, Roberta, who suggested I could modulate my voice more. I have heard that before, particularly in teaching evaluations that complain about my “soporific” tone. I recall that Mike Freedman once commented after watching a video of a public lecture I did at the KITP in Santa Barbara — he praised its professionalism and “newscaster quality”. But that cuts two ways, doesn’t it? Paul Ginsparg listened to a podcast of that same lecture while doing yardwork, and then sent me a compliment by email, with a characteristic Ginspargian twist. Noting that my sentences were clear, precise, and grammatical, Paul asked: “is this something that just came naturally at some early age, or something that you were able to acquire at some later stage by conscious design (perhaps out of necessity, talks on quantum computing might not go over as well without the reassuring smoothness)?”

Another criticism stung more. To illustrate the monogamy of entanglement, I used a slide describing the frustration of Bob, who wants to entangle with both Alice and Carrie, but finds that he can increase his entanglement with Carrie only my sacrificing some of his entanglement with Alice.

Entanglement is monogamous. Bob is frustrated to find that he cannot be fully entangled with both Alice and Carrie.

Entanglement is monogamous. Bob is frustrated to find that he cannot be fully entangled with both Alice and Carrie.

This got a big laugh. But I used the same slide in a talk at the APS Denver meeting the following week (at a session celebrating the 100th anniversary of Niels Bohr’s atomic model), and a young woman came up to me after that talk to complain. She suggested that my monogamy metaphor was offensive and might discourage women from entering the field!

After discussing the issue with Roberta, I decided to address the problem by swapping the gender roles. The next day, during the question period following Stephen Hawking’s Public Lecture, I spoke about Betty’s frustration over her inability to entangle fully with both Adam and Charlie. But is that really an improvement, or does it reflect negatively on Betty’s morals? I would appreciate advice about this quandary in the comments.

In case you watch the video, there are a couple of things you should know. First, in his introduction, Tom Soifer quotes from a poem about me, but neglects to name the poet. It is former Caltech postdoc Patrick Hayden. And second, toward the end of the lecture I talk about some IQIM outreach activities, but neglect to name our Outreach Director Spiros Michalakis, without whose visionary leadership these things would not have happened.

The most touching feedback I received came from my Caltech colleague Oskar Painter. I joked in the lecture about how mild mannered IQIM scientists can unleash the superpower of quantum information at a moment’s notice.

Mild mannered professor unleashes the super power of quantum information.

Mild mannered professor unleashes the superpower of quantum information.

After watching the video, Oskar shot me an email:

“I sent a link to my son [Ewan, age 11] and daughter [Quinn, age 9], and they each watched it from beginning to end on their iPads, without interruption.  Afterwards, they had a huge number of questions for me, and were dreaming of all sorts of “quantum super powers” they imagined for the future.”

2017-01-13T10:05:54+00:00 April 29th, 2013|The expert's corner, Theoretical highlights|12 Comments


  1. Steph April 29, 2013 at 1:47 pm - Reply

    One might argue that a question regarding Bettys morals but not Bob’s is itself questionable 😉

    But on a more serious note, I dont see an issue. Then again I also didn’t see one with Bob, so even though I’m a woman I’m maybe not an authority on things offensive to women 🙂 well there is a scenario where both things are deemed offensive but I think in such a scenario very many things could be classified as offensive (which in my view they aren’t)

  2. Ann April 29, 2013 at 2:34 pm - Reply

    John, as an aside–a campus programs staffer told me 800 people attended your Watson lecture. That’s almost capacity! I was there, and felt very thankful for the lengths you went to to teach us, entertain us, and give us a window into the IQIM’s work and potential.

  3. avgorshkov April 29, 2013 at 3:37 pm - Reply

    Politically timely and (possibly) politically correct solutions to the monogamy problem:
    – Bob choosing between Adam and Charlie
    – Betty choosing between Alice and Carrie
    – Bob choosing between Adam and Carrie
    – Betty choosing between Alice and Charlie

    • avgorshkov April 29, 2013 at 11:47 pm - Reply

      Thinking about it again, these would probably get John into more trouble…

  4. Deborah Castleman April 29, 2013 at 7:41 pm - Reply

    The Watson Lecture, both in person and with a second viewing on iTunes, was and is EXCELLENT. But, since you asked, let’s address the monogamy entanglement question. I think that putting it in those terms is clever, adds humor and makes the subject clearer (so please don’t shy away from using it). As a woman, I was a little offended that Bob is “frustrated” (why does he want to play around on nice Alice?) — but it occurred to me that you could build on Roberta’s suggestion and add another link, from Alice to Jason, that Alice is not allowed to have due to her entangled state. Then I, for one, am okay with you saying that Alice is “frustrated” in that she can’t link up with Jason. Besides, why would she want to be monogamous with that jerk Bob, anyway.

  5. Paul Ginsparg April 29, 2013 at 8:11 pm - Reply

    Charles Bennett has long used a version of the monogamy slide in his lectures, but sets it up by recalling the period of free love in the ’60s — then no one gets offended because it’s taken for granted people were less sensitive then.
    (In that regard you missed the obvious opportunity to use Bob and Carol and Alice…)
    The spotlight explains that deer-in-the-headlights look in the cover jpg, but I’ve ingested only audio on ipod, can’t wait to listen next fall while raking leaves (now that I have much better metrics to assess style).

    • preskill April 29, 2013 at 8:57 pm - Reply

      Thanks for mentioning Bennett, as I should have. Barbara Terhal gives due credit to Charlie for the monogamy metaphor in this paper.

  6. rrtucci May 1, 2013 at 12:01 pm - Reply

    I posted a politically correct “monogamy for dogs” at my blog. I also give an interpretation of quantum mechanics that is purely dog based

  7. Leo Radzihovsky May 3, 2013 at 10:12 pm - Reply

    Does quantum computing solves the P vs NP problem?

    • spiros May 5, 2013 at 12:20 am - Reply

      The short answer is no. The long answer is probably not.

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