Monthly Archives: December 2021

A quantum-steampunk photo shoot

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Shortly after becoming a Fellow of QuICS, the Joint Center for Quantum Information and Computer Science, I received an email from a university communications office. The office wanted to take professional photos of my students and postdocs and me. You’ve probably seen similar photos, in which theoretical physicists are writing equations, pointing at whiteboards, and thinking deep thoughts. No surprise there. 

A big surprise followed: Tom Ventsias, the director of communications at the University of Maryland Institute for Advanced Computer Studies (UMIACS), added, “I wanted to hear your thoughts about possibly doing a dual photo shoot for you—one more ‘traditional,’ one ‘quantum steampunk’ style.”

Steampunk, as Quantum Frontiers regulars know, is a genre of science fiction. It combines futuristic technologies, such as time machines and automata, with Victorian settings. I call my research “quantum steampunk,” as it combines the cutting-edge technology of quantum information science with the thermodynamics—the science of energy—developed during the 1800s. I’ve written a thesis called “Quantum steampunk”; authored a trade nonfiction book with the same title; and presented enough talks about quantum steampunk that, strung together, they’d give one laryngitis. But I don’t own goggles, hoop skirts, or petticoats. The most steampunk garb I’d ever donned before this autumn, I wore for a few minutes at age six or so, for dress-up photos at a theme park. I don’t even like costumes.

But I earned my PhD under the auspices of fellow Quantum Frontiers blogger John Preskill,1 whose career suggests a principle to live by: While unravelling the universe’s nature and helping to shape humanity’s intellectual future, you mustn’t take yourself too seriously. This blog has exhibited a photo of John sitting in Caltech’s information-sciences building, exuding all the gravitas of a Princeton degree, a Harvard degree, and world-impacting career—sporting a baseball glove you’d find in a high-school gym class, as though it were a Tag Heuer watch. John adores baseball, and the photographer who documented Caltech’s Institute for Quantum Information and Matter brought out the touch of whimsy like the ghost of a smile.

Let’s try it, I told Tom.

One rust-colored November afternoon, I climbed to the top of UMIACS headquarters—the Iribe Center—whose panoramic view of campus begs for photographs. Two students were talking in front of a whiteboard, and others were lunching on the sandwiches, fruit salad, and cheesecake ordered by Tom’s team. We took turns brandishing markers, gesturing meaningfully, and looking contemplative.

Then, the rest of my team dispersed, and the clock rewound 150 years.

The professionalism and creativity of Tom’s team impressed me. First, they’d purchased a steampunk hat, complete with goggles and silver wires. Recalling the baseball-glove photo, I suggested that I wear the hat while sitting at a table, writing calculations as I ordinarily would.

What hat? Quit bothering me while I’m working.

Then, the team upped the stakes. Earlier that week, Maria Herd, a member of the communications office, had driven me to the University of Maryland performing-arts center. We’d sifted through the costume repository until finding skirts, vests, and a poofy white shirt reminiscent of the 1800s. I swapped clothes near the photo-shoot area, while the communications team beamed a London street in from the past. Not really, but they nearly did: They’d found a backdrop suitable for the 2020 Victorian-era Netflix hit Enola Holmes and projected the backdrop onto a screen. I stood in front of the screen, and a sheet of glass stood in front of me. I wrote equations on the glass while the photographer, John Consoli, snapped away.

The final setup, I would never have dreamed of. Days earlier, the communications team had located an elevator lined, inside, with metal links. They’d brought colorful, neon-lit rods into the elevator and experimented with creating futuristic backdrops. On photo-shoot day, they positioned me in the back of the elevator and held the light-saber-like rods up. 

But we couldn’t stop anyone from calling the elevator. We’d ride up to the third or fourth floor, and the door would open. A student would begin to step in; halt; and stare my floor-length skirt, the neon lights, and the photographer’s back.

“Feel free to get in.” John’s assistant, Gail Marie Rupert, would wave them inside. The student would shuffle inside—in most cases—and the door would close.

“What floor?” John would ask.

“Um…one.”

John would twist around, press the appropriate button, and then turn back to his camera.

Once, when the door opened, the woman who entered complimented me on my outfit. Another time, the student asked if he was really in the Iribe Center. I regard that question as evidence of success.

John Consoli took 654 photos. I found the process fascinating, as a physicist. I have a domain of expertise; and I know the feeling of searching for—working toward—pushing for—a theorem or a conceptual understanding that satisfies me, in that domain. John’s area of expertise differs from mine, so I couldn’t say what he was searching for. But I recognized his intent and concentration, as Gail warned him that time had run out and he then made an irritated noise, inched sideways, and stole a few more snapshots. I felt like I was seeing myself in a reflection—not in the glass I was writing on, but in another sphere of the creative life.

The communications team’s eagerness to engage in quantum steampunk—to experiment with it, to introduce it into photography, to make it their own—bowled me over. Quantum steampunk isn’t just a stack of papers by one research group; it’s a movement. Seeing a team invest its time, energy, and imagination in that movement felt like receiving a deep bow or curtsy. Thanks to the UMIACS communications office for bringing quantum steampunk to life.

The Quantum-Steampunk Lab. Not pictured: Shayan Majidy.

1Who hasn’t blogged in a while. How about it, John?

Balancing the tradeoff

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So much to do, so little time. Tending to one task is inevitably at the cost of another, so how does one decide how to spend their time? In the first few years of my PhD, I balanced problem sets, literature reviews, and group meetings, but at the detriment to my hobbies. I have played drums my entire life, but I largely fell out of practice in graduate school. Recently, I made time to play with a group of musicians, even landing a couple gigs in downtown Austin, Texas, “live music capital of the world.” I have found attending to my non-physics interests makes my research hours more productive and less taxing. Finding the right balance of on- versus off-time has been key to my success as my PhD enters its final year.

Of course, life within physics is also full of tradeoffs. My day job is as an experimentalist. I use tightly focused laser beams, known as optical tweezers, to levitate micrometer-sized glass spheres. I monitor a single microsphere’s motion as it undergoes collisions with air molecules, and I study the system as an environmental sensor of temperature, fluid flow, and acoustic waves; however, by night I am a computational physicist. I code simulations of interacting qubits subject to kinetic constraints, so-called quantum cellular automata (QCA). My QCA work started a few years ago for my Master’s degree, but my interest in the subject persists. I recently co-authored one paper summarizing the work so far and another detailing an experimental implementation.

The author doing his part to “keep Austin weird” by playing the drums dressed as grackle (note the beak), the central-Texas bird notorious for overrunning grocery store parking lots.
Balancing research interests: Trapping a glass microsphere with optical tweezers.
Balancing research interests: Visualizing the time evolution of four different QCA rules.

QCA, the subject of this post, are themselves tradeoff-aware systems. To see what I mean, first consider their classical counterparts cellular automata. In their simplest construction, the system is a one-dimensional string of bits. Each bit takes a value of 0 or 1 (white or black). The bitstring changes in discrete time steps based on a simultaneously-applied local update rule: Each bit, along with its two nearest-neighbors, determine the next state of the central bit. Put another way, a bit either flips, i.e., changes 0 to 1 or 1 to 0, or remains unchanged over a timestep depending on the state of that bit’s local neighborhood. Thus, by choosing a particular rule, one encodes a trade off between activity (bit flips) and inactivity (bit remains unchanged). Despite their simple construction, cellular automata dynamics are diverse; they can produce fractals and encryption-quality random numbers. One rule even has the ability to run arbitrary computer algorithms, a property known as universal computation.

Classical cellular automata. Left: rule 90 producing the fractal Sierpiński’s triangle. Middle: rule 30 can be used to generate random numbers. Right: rule 110 is capable of universal computation.

In QCA, bits are promoted to qubits. Instead of being just 0 or 1 like a bit, a qubit can be a continuous mixture of both 0 and 1, a property called superposition. In QCA, a qubit’s two neighbors being 0 or 1 determine whether or not it changes. For example, when in an active neighborhood configuration, a qubit can be coded to change from 0 to “0 plus 1” or from 1 to “0 minus 1”. This is already a head-scratcher, but things get even weirder. If a qubit’s neighbors are in a superposition, then the center qubit can become entangled with those neighbors. Entanglement correlates qubits in a way that is not possible with classical bits.

Do QCA support the emergent complexity observed in their classical cousins? What are the effects of a continuous state space, superposition, and entanglement? My colleagues and I attacked these questions by re-examining many-body physics tools through the lens of complexity science. Singing the lead, we have a workhorse of quantum and solid-state physics: two-point correlations. Singing harmony we have the bread-and-butter of network analysis: complex-network measures. The duet between the two tells the story of structured correlations in QCA dynamics.

In a bit more detail, at each QCA timestep we calculate the mutual information between all qubits i and all other qubits j. Doing so reveals how much there is to learn about one qubit by measuring another, including effects of quantum entanglement. Visualizing each qubit as a node, the mutual information can be depicted as weighted links between nodes: the more correlated two qubits are, the more strongly they are linked. The collection of nodes and links makes a network. Some QCA form unstructured, randomly-linked networks while others are highly structured. 

Complex-network measures are designed to highlight certain structural patterns within a network. Historically, these measures have been used to study diverse networked-systems like friend groups on Facebook, biomolecule pathways in metabolism, and functional-connectivity in the brain. Remarkably, the most structured QCA networks we observed quantitatively resemble those of the complex systems just mentioned despite their simple construction and quantum unitary dynamics. 

Visualizing mutual information networks. Left: A Goldilocks-QCA generated network. Right: a random network.

What’s more, the particular QCA that generate the most complex networks are those that balance the activity-inactivity trade-off. From this observation, we formulate what we call the Goldilocks principle: QCA that generate the most complexity are those that change a qubit if and only if the qubit’s neighbors contain an equal number of 1’s and 0’s. The Goldilocks rules are neither too inactive nor too active, balancing the tradeoff to be “just right.”  We demonstrated the Goldilocks principle for QCA with nearest-neighbor constraints as well as QCA with nearest-and-next-nearest-neighbor constraints.

To my delight, the scientific conclusions of my QCA research resonate with broader lessons-learned from my time as a PhD student: Life is full of trade-offs, and finding the right balance is key to achieving that “just right” feeling.