# Local operations and Chinese communications

The workshop spotlighted entanglement. It began in Shanghai, paused as participants hopped the Taiwan Strait, and resumed in Taipei. We discussed quantum operations and chaos, thermodynamics and field theory.1 I planned to return from Taipei to Shanghai to Los Angeles.

Quantum thermodynamicist Nelly Ng and I drove to the Taipei airport early. News from Air China curtailed our self-congratulations: China’s military was running an operation near Shanghai. Commercial planes couldn’t land. I’d miss my flight to LA.

Two quantum thermodynamicists in Shanghai

An operation?

Quantum information theorists use a mindset called operationalism. We envision experimentalists in separate labs. Call the experimentalists Alice, Bob, and Eve (ABE). We tell stories about ABE to formulate and analyze problems. Which quantum states do ABE prepare? How do ABE evolve, or manipulate, the states? Which measurements do ABE perform? Do they communicate about the measurements’ outcomes?

Operationalism concretizes ideas. The outlook checks us from drifting into philosophy and into abstractions difficult to apply physics tools to.2 Operationalism infuses our language, our framing of problems, and our mathematical proofs.

Experimentalists can perform some operations more easily than others. Suppose that Alice controls the magnets, lasers, and photodetectors in her lab; Bob controls the equipment in his; and Eve controls the equipment in hers. Each experimentalist can perform local operations (LO). Suppose that Alice, Bob, and Eve can talk on the phone and send emails. They exchange classical communications (CC).

You can’t generate entanglement using LOCC. Entanglement consists of strong correlations that quantum systems can share and that classical systems can’t. A quantum system in Alice’s lab can hold more information about a quantum system of Bob’s than any classical system could. We must create and control entanglement to operate quantum computers. Creating and controlling entanglement poses challenges. Hence quantum information scientists often model easy-to-perform operations with LOCC.

Suppose that some experimentalist Charlie loans entangled quantum systems to Alice, Bob, and Eve. How efficiently can ABE compute some quantity, exchange quantum messages, or perform other information-processing tasks, using that entanglement? Such questions underlie quantum information theory.

Taipei’s night market. Or Caltech’s neighborhood?

Local operations.

Nelly and I performed those, trying to finagle me to LA. I inquired at Air China’s check-in desk in English. Nelly inquired in Mandarin. An employee smiled sadly at each of us.

We branched out into classical communications. I called Expedia (“No, I do not want to fly to Manila”), United Airlines (“No flights for two days?”), my credit-card company, Air China’s American reservations office, Air China’s Chinese reservations office, and Air China’s Taipei reservations office. I called AT&T to ascertain why I couldn’t reach Air China (“Yes, please connect me to the airline. Could you tell me the number first? I’ll need to dial it after you connect me and the call is then dropped”).

As I called, Nelly emailed. She alerted Bob, aka Janet (Ling-Yan) Hung, who hosted half the workshop at Fudan University in Shanghai. Nelly emailed Eve, aka Feng-Li Lin, who hosted half the workshop at National Taiwan University in Taipei. Janet twiddled the magnets in her lab (investigated travel funding), and Feng-Li cooled a refrigerator in his.

ABE can process information only so efficiently, using LOCC. The time crept from 1:00 PM to 3:30.

Nelly Ng uses classical communications.

What could we have accomplished with quantum communication? Using LOCC, Alice can manipulate quantum states (like an electron’s orientation) in her lab. She can send nonquantum messages (like “My flight is delayed”) to Bob. She can’t send quantum information (like an electron’s orientation).

Alice and Bob can ape quantum communication, given entanglement. Suppose that Charlie strongly correlates two electrons. Suppose that Charlie gives Alice one electron and gives Bob the other. Alice can send one qubit–one unit of quantum information–to Bob. We call that sending quantum teleportation.

Suppose that air-traffic control had loaned entanglement to Janet, Feng-Li, and me. Could we have finagled me to LA quickly?

Quantum teleportation differs from human teleportation.

xkcd.com/465

We didn’t need teleportation. Feng-Li arranged for me to visit Taiwan’s National Center for Theoretical Sciences (NCTS) for two days. Air China agreed to return me to Shanghai afterward. United would fly me to LA, thanks to help from Janet. Nelly rescued my luggage from leaving on the wrong flight.

Would I rather have teleported? I would have avoided a bushel of stress. But I wouldn’t have learned from Janet about Chinese science funding, wouldn’t have heard Feng-Li’s views about gravitational waves, wouldn’t have glimpsed Taiwanese countryside flitting past the train we rode to the NCTS.

According to some metrics, classical resources outperform quantum.

At Taiwan’s National Center for Theoretical Sciences

The workshop organizers have generously released videos of the lectures. My lecture about quantum chaos and fluctuation relations appears here and here. More talks appear here.

With gratitude to Janet Hung, Feng-Li Lin, and Nelly Ng; to Fudan University, National Taiwan University, and Taiwan’s National Center for Theoretical Sciences for their hospitality; and to Xiao Yu for administrative support.

Glossary and other clarifications:

1Field theory describes subatomic particles and light.

2Physics and philosophy enrich each other. But I haven’t trained in philosophy. I benefit from differentiating physics problems that I’ve equipped to solve from philosophy problems that I haven’t.

# What is Water 2.0

Before I arrived in Los Angeles, I thought I might need to hit the brakes a bit with some of the radical physics theories I’d encountered during my preliminary research. After all, these were scientists I was meeting: people who “engage in a systematic activity to acquire knowledge that describes and predicts the natural world”, according to Wikipedia. It turns out I wasn’t hardly as far-out as they were.

I could recount numerous anecdotes that exemplify my encounter with the frighteningly intelligent and vivid imagination of the people at LIGO with whom I had the great pleasure of working – Prof. Rana X. Adhikari, Maria Okounkova, Eric Quintero, Maximiliano Isi, Sarah Gossan, and Jameson Graef Rollins – but in the end it all boils down to a parable about fish.

Rana’s version, which he recounted to me on our first meeting, goes as follows: “There are these two young fish swimming along, and a scientist approaches the aquarium and proclaims, “We’ve finally discovered the true nature of water!” And the two young fish swim on for a bit, and then eventually one of them looks over at the other and goes, “What the hell is water?”” In David Foster Wallace’s more famous version, the scientist is not a scientist but an old fish, who greets them saying, “Morning, boys. How’s the water?”

The difference is not circumstantial. Foster Wallace’s version is an argument against “unconsciousness, the default setting, the rat race, the constant gnawing sense of having had, and lost, some infinite thing” – personified by the young fish – and an urgent call for awareness – personified by the old fish. But in Rana’s version, the matter is more hard-won: as long as they are fish, they haven’t the faintest apprehension of the very concept of water: even a wise old fish would fail to notice. In this adaptation, gaining awareness of that which is “so real and essential, so hidden in plain sight all around us, all the time” as Foster Wallace describes it, demands much more than just an effort in mindfulness. It demands imagining the unimaginable.

Albert Einstein once said that “Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand.” But the question remains of how far our imagination can reach, and where the radius ends for us in “what there ever will be to know and understand”, versus that which happens to be. My earlier remark about LIGO scientists’ being far-out does not at all refer to a speculative disposition, which would characterise amateur anything-goes, and does go over-the-edge pseudo-science. Rather, it refers to the high level of creativity that is demanded of physicists today, and to the untiring curiosity that drives them to expand the limits of that radius, despite all odds.

The possibility of imagination has become an increasingly animating thought within my currently ongoing project:

As an independent curator of contemporary art, I travelled to Caltech for a 6-week period of research, towards developing an exhibition that will invite the public to engage with some of the highly challenging implications around the concept of time in physics. In it, I identify LIGO’s breakthrough detection of gravitational waves as an unparalleled incentive by which to acquire – in broad cultural terms – a new sense of time that departs from the old and now wholly inadequate one. After LIGO’s announcement proved that time fluctuation not only happens, but that it happened here, to us, on a precise date and time, it is finally possible for a broader public to relate, however abstract some of the concepts from the field of physics may remain. More simply put: we can finally sense that the water is moving.[1]

One century after Einstein’s Theory of General Relativity, most people continue to hold a highly impoverished idea of the nature of time, despite it being perhaps the most fundamental element of our existence. For 100 years there was no blame or shame in this. Because within all possible changes to the three main components of the universe – space, time & energy – the fluctuation of time was always the only one that escaped our sensorial capacities, existing exclusively in our minds, and finding its fullest expression in mathematical language. If you don’t speak mathematics, time fluctuation remains impossible to grasp, and painful to imagine.

But on February 11th, 2016, this situation changed dramatically.

On this date, a televised announcement told the world of the first-ever sensory detection of time-fluctuation, made with the aid of the most sensitive machine ever to be built by mankind. Finally, we have sensorial access to variations in all components of the universe as we know it. What is more, we observe the non-static passage of time through sound, thereby connecting it to the most affective of our senses.

Of course, LIGO’s detection is limited to time fluctuation and doesn’t yet make other mind-bending behaviours of time observable. But this is only circumstantial. The key point is that we can take this initial leap, and that it loosens our feet from the cramp of Newtonian fixity. Once in this state, gambolling over to ideas about zero time tunnelling, non-causality, or the future determining the present, for instance, is far more plausible, and no longer painful but rather seductive, at least, perhaps, for the playful at heart.

Taking a slight off-road (to be re-routed in a moment): there is a common misconception about children’s allegedly free-spirited creativity. Watching someone aged between around 4 and 15 draw a figure will demonstrate quite clearly just how taut they really are, and that they apply strict schemes that follow reality as they see and learn to see it. Bodies consistently have eyes, mouths, noses, heads, rumps and limbs, correctly placed and in increasingly realistic colours. Ask them to depart from these conventions – “draw one eye on his forehead”, “make her face green” – like masters such as Pablo Picasso and Henri Matisse have done – and they’ll likely become very upset (young adolescents being particularly conservative, reaching the point of panic when challenged to shed consensus).

This is not to compare the lay public (including myself) to children, but to suggest that there’s no inborn capacity – the unaffected, ‘genius’ naïveté that the modernist movements of Primitivism, Art Brut and Outsider Art exalted – for developing a creativity that is of substance. Arriving at a consequential idea, in both art and physics, entails a great deal of acumen and is far from gratuitous, however whimsical the moment in which it sometimes appears. And it’s also to suggest that there’s a necessary process of acquaintance – the knowledge of something through experience – in taking a cognitive leap away from the seemingly obvious nature of reality. If there’s some truth in this, then LIGO’s expansion of our sensorial access to the fluctuation of time, together with artistic approaches that lift the remaining questions and ambiguities of spacetime onto a relational, experiential plane, lay fertile ground on which to begin to foster a new sense of time – on a broad cultural level – however slowly it unfolds.

The first iteration of this project will be an exhibition, to take place in Berlin, in July 2017. It will feature existing and newly commissioned works by established and upcoming artists from Los Angeles and Berlin, working in sound, installation and video, to stage a series of immersive environments that invite the viewers’ bodily interaction.

Though the full selection cannot be disclosed just yet, I would like here to provide a glimpse of two works-in-progress by artist-duo Evelina Domnitch & Dmitry Gelfand, whom I invited to Los Angeles to collaborate in my research with LIGO, and whose contribution has been of great value to the project.

For more details on the exhibition, please stay tuned, and be warmly welcome to visit Berlin in July!

Text & images: courtesy of the artists.

ORBIHEDRON | 2017

A dark vortex in the middle of a water-filled basin emits prismatic bursts of rotating light. Akin to a radiant ergosphere surrounding a spinning black hole, Orbihedron evokes the relativistic as well as quantum interpretation of gravity – the reconciliation of which is essential for unravelling black hole behaviour and the origins of the cosmos. Descending into the eye of the vortex, a white laser beam reaches an impassible singularity that casts a whirling circular shadow on the basin’s floor. The singularity lies at the bottom of a dimple on the water’s surface, the crown of the vortex, which acts as a concave lens focussing the laser beam along the horizon of the “black hole” shadow. Light is seemingly swallowed by the black hole in accordance with general relativity, yet leaks out as quantum theory predicts.

ER = EPR | 2017

Two co-rotating vortices, joined together via a slender vortical bridge, lethargically drift through a body of water. Light hitting the water’s surface transforms the vortex pair into a dynamic lens, projecting two entangled black holes encircled by shimmering halos. As soon as the “wormhole” link between the black holes rips apart, the vortices immediately dissipate, analogously to the collapse of a wave function. Connecting distant black holes or two sides of the same black hole, might wormholes be an example of cosmic-scale quantum entanglement? This mind-bending conjecture of Juan Maldacena and Leonard Susskind can be traced back to two iconoclastic papers from 1935. Previously thought to be unrelated (both by their authors and numerous generations of readers), one article, the legendary EPR (penned by Einstein, Podolsky and Rosen) engendered the concept of quantum entanglement or “spooky action at a distance”; and the second text theorised Einstein-Rosen (ER) bridges, later known as wormholes. Although the widely read EPR paper has led to the second quantum revolution, currently paving the way to quantum simulation and computation, ER has enjoyed very little readership. By equating ER to EPR, the formerly irreconcilable paradigms of physics have the potential to converge: the phenomenon of gravity is imagined in a quantum mechanical context. The theory further implies, according to Maldacena, that the undivided, “reliable structure of space-time is due to the ghostly features of entanglement”.

[1] I am here extending our capacity to sense to that of the technology itself, which indeed measured the warping of spacetime. However, in interpreting gravitational waves from a human frame of reference (moving nowhere near the speed of light at which gravitational waves travel), they would seem to be spatial. In fact, the elongation of space (a longer wavelength) directly implies that time slows down (a longer wave-period), so that the two are indistinguishable.

Isabel de Sena

# It’s CHAOS!

My brother and I played the video game Sonic the Hedgehog on a Sega Dreamcast. The hero has spiky electric-blue fur and can run at the speed of sound.1 One of us, then the other, would battle monsters. Monster number one oozes onto a dark city street as an aquamarine puddle. The puddle spreads, then surges upward to form limbs and claws.2 The limbs splatter when Sonic attacks: Aqua globs rain onto the street.

The monster’s master, Dr. Eggman, has ginger mustachios and a body redolent of his name. He scoffs as the heroes congratulate themselves.

“Fools!” he cries, the pauses in his speech heightening the drama. “[That monster is] CHAOS…the GOD…of DE-STRUC-TION!” His cackle could put a Disney villain to shame.

Dr. Eggman’s outburst comes to mind when anyone asks what topic I’m working on.

“Chaos! And the flow of time, quantum theory, and the loss of information.”

Alexei Kitaev, a Caltech physicist, hooked me on chaos. I TAed his spring-2016 course. The registrar calls the course Ph 219c: Quantum Computation. I call the course Topics that Interest Alexei Kitaev.

“What do you plan to cover?” I asked at the end of winter term.

Topological quantum computation, Alexei replied. How you simulate Hamiltonians with quantum circuits. Or maybe…well, he was thinking of discussing black holes, information, and chaos.

If I’d had a tail, it would have wagged.

“What would you say about black holes?” I asked.

Sonic’s best friend, Tails the fox.

I fwumped down on the couch in Alexei’s office, and Alexei walked to his whiteboard. Scientists first noticed chaos in classical systems. Consider a double pendulum—a pendulum that hangs from the bottom of a pendulum that hangs from, say, a clock face. Imagine pulling the bottom pendulum far to one side, then releasing. The double pendulum will swing, bend, and loop-the-loop like a trapeze artist. Imagine freezing the trapeze artist after an amount $t$ of time.

What if you pulled another double pendulum a hair’s breadth less far? You could let the pendulum swing, wait for a time $t$, and freeze this pendulum. This pendulum would probably lie far from its brother. This pendulum would probably have been moving with a different speed than its brother, in a different direction, just before the freeze. The double pendulum’s motion changes loads if the initial conditions change slightly. This sensitivity to initial conditions characterizes classical chaos.

A mathematical object $F(t)$ reflects quantum systems’ sensitivities to initial conditions. [Experts: $F(t)$ can evolve as an exponential governed by a Lyapunov-type exponent: $\sim 1 - ({\rm const.})e^{\lambda_{\rm L} t}$.] $F(t)$ encodes a hypothetical process that snakes back and forth through time. This snaking earned $F(t)$ the name “the out-of-time-ordered correlator” (OTOC). The snaking prevents experimentalists from measuring quantum systems’ OTOCs easily. But experimentalists are trying, because $F(t)$ reveals how quantum information spreads via entanglement. Such entanglement distinguishes black holes, cold atoms, and specially prepared light from everyday, classical systems.

Alexei illustrated, on his whiteboard, the sensitivity to initial conditions.

“In case you’re taking votes about what to cover this spring,” I said, “I vote for chaos.”

We covered chaos. A guest attended one lecture: Beni Yoshida, a former IQIM postdoc. Beni and colleagues had devised quantum error-correcting codes for black holes.3 Beni’s foray into black-hole physics had led him to $F(t)$. He’d written an OTOC paper that Alexei presented about. Beni presented about a follow-up paper. If I’d had another tail, it would have wagged.

Sonic’s friend has two tails.

Alexei’s course ended. My research shifted to many-body localization (MBL), a quantum phenomenon that stymies the spread of information. OTOC talk burbled beyond my office door.

At the end of the summer, IQIM postdoc Yichen Huang posted on Facebook, “In the past week, five papers (one of which is ours) appeared . . . studying out-of-time-ordered correlators in many-body localized systems.”

I looked down at the MBL calculation I was performing. I looked at my computer screen. I set down my pencil.

“Fine.”

I marched to John Preskill’s office.

The bosses. Of different sorts, of course.

The OTOC kept flaring on my radar, I reported. Maybe the time had come for me to try contributing to the discussion. What might I contribute? What would be interesting?

We kicked around ideas.

“Well,” John ventured, “you’re interested in fluctuation relations, right?”

Something clicked like the “power” button on a video-game console.

Fluctuation relations are equations derived in nonequilibrium statistical mechanics. They describe systems driven far from equilibrium, like a DNA strand whose ends you’ve yanked apart. Experimentalists use fluctuation theorems to infer a difficult-to-measure quantity, a difference $\Delta F$ between free energies. Fluctuation relations imply the Second Law of Thermodynamics. The Second Law relates to the flow of time and the loss of information.

Time…loss of information…Fluctuation relations smelled like the OTOC. The two had to join together.

I spent the next four days sitting, writing, obsessed. I’d read a paper, three years earlier, that casts a fluctuation relation in terms of a correlator. I unearthed the paper and redid the proof. Could I deform the proof until the paper’s correlator became the out-of-time-ordered correlator?

Apparently. I presented my argument to my research group. John encouraged me to clarify a point: I’d defined a mathematical object $A$, a probability amplitude. Did $A$ have physical significance? Could anyone measure it? I consulted measurement experts. One identified $A$ as a quasiprobability, a quantum generalization of a probability, used to model light in quantum optics. With the experts’ assistance, I devised two schemes for measuring the quasiprobability.

The result is a fluctuation-like relation that contains the OTOC. The OTOC, the theorem reveals, is a combination of quasiprobabilities. Experimentalists can measure quasiprobabilities with weak measurements, gentle probings that barely disturb the probed system. The theorem suggests two experimental protocols for inferring the difficult-to-measure OTOC, just as fluctuation relations suggest protocols for inferring the difficult-to-measure $\Delta F$. Just as fluctuation relations cast $\Delta F$ in terms of a characteristic function of a probability distribution, this relation casts $F(t)$ in terms of a characteristic function of a (summed) quasiprobability distribution. Quasiprobabilities reflect entanglement, as the OTOC does.

Collaborators and I are extending this work theoretically and experimentally. How does the quasiprobability look? How does it behave? What mathematical properties does it have? The OTOC is motivating questions not only about our quasiprobability, but also about quasiprobability and weak measurements. We’re pushing toward measuring the OTOC quasiprobability with superconducting qubits or cold atoms.

Chaos has evolved from an enemy to a curiosity, from a god of destruction to an inspiration. I no longer play the electric-blue hedgehog. But I remain electrified.

1I hadn’t started studying physics, ok?

2Don’t ask me how the liquid’s surface tension rises enough to maintain the limbs’ shapes.

3Black holes obey quantum mechanics. Quantum systems can solve certain problems more quickly than ordinary (classical) computers. Computers make mistakes. We fix mistakes using error-correcting codes. The codes required by quantum computers differ from the codes required by ordinary computers. Systems that contain black holes, we can regard as performing quantum computations. Black-hole systems’ mistakes admit of correction via the code constructed by Beni & co.

# Ten finalists selected for film festival “Quantum Shorts”

“Crazy enough”, “visually very exciting”, “compelling from the start”, “beautiful cinematography”: this is what members of the Quantum Shorts festival shortlisting panel had to say about films selected for screening. As a member of the panel, and as someone who has experienced the power of visual storytelling firsthand (Anyone Can Quantum, Quantum Is Calling), I was excited to see filmmakers and students from around the world try their hand at interpreting the weirdness of the quantum realm in fresh ways.

The ten shortlisted films were chosen from a total of 203 submissions received during the festival’s 2016 call for entries. Some of the finalists are dramatic, some funny, some abstract. Some are live-action film, some animation. Each is under five minutes long. Find the titles and synopses of the shortlisted films below.

Screenings of the films start February 23 with confirmed events in Waterloo (23 February) and Vancouver (23 February), Canada; Singapore (25-28 February); Glasgow, UK (17 March); and Brisbane, Australia (24 March).

More details can be found at shorts.quantumlah.org, where viewers can also watch the films online
and vote for their favorite to help decide a ‘People’s Choice’ prize. The website also hosts interviews with the filmmakers.

The Quantum Shorts festival is run by the Centre for Quantum Technologies at the National University of Singapore with a constellation of prestigious partners including Scientific American magazine and the journal Nature. The festival’s media partners, scientific partners and screening partners span five countries. The Institute for Quantum Information and Matter at Caltech is a proud sponsor.

For making the shortlist, the filmmakers receive a $250 award, a one-year digital subscription to Scientific American and certificates. The festival’s top prize of US$1500 and runner-up prize of US $1000 will now be decided by a panel of eminent judges. The additional People’s Choice prize of$500 will be decided by public vote on the shortlist, with voting open on the festival website until March 26th. Prizes will be announced by the end of March.

Quantum Shorts 2016: FINALISTS

Ampersand

What unites everything on Earth? That we are all ultimately composed of something that is both matter & wave

Submitted by Erin Shea, United States

Approaching Reality

Dancing cats, a watchful observer and a strange co-existence. It’s all you need to understand the essence of quantum mechanics

Submitted by Simone De Liberato, United Kingdom

Bolero

The coin is held fast, but is it heads or tails? As long as the fist remains closed, you are a winner – and a loser

Submitted by Ivan D’Antonio, Italy

Novae

What happens when a massive star reaches the end of its life? Something that goes way beyond the spectacular, according to this cosmic poem about the infinite beauty of a black hole’s birth

Submitted by Thomas Vanz, France

The Guardian

A quantum love triangle, where uncertainty is the only winner

Submitted by Chetan Kotabage, India

The Real Thing

Picking up a beverage shouldn’t be this hard. And it definitely shouldn’t take you through the multiverse…

Submitted by Adam Welch, United States

Together – Parallel Universe

It’s a tale as old as time: boy meets girl, girl is not as interested as boy hoped. So boy builds spaceship and travels through multi-dimensional reality to find the one universe where they can be together

Submitted by Michael Robertson, South Africa

Tom’s Breakfast

This is one of those days when Tom’s morning routine doesn’t go to plan – far from it, in fact. The only question is, can he be philosophical about it?

Submitted by Ben Garfield, United Kingdom

Triangulation

Only imagination can show us the hidden world inside of fundamental particles

Submitted by Vladimir Vlasenko, Ukraine

Whitecap

Dr. David Long has discovered how to turn matter into waveforms. So why shouldn’t he experiment with his own existence?

Submitted by Bernard Ong, United States

# How do you hear electronic oscillations with light

For decades, understanding the origin of high temperature superconductivity has been regarded as the Holy Grail by physicists in the condensed matter community. The importance of high temperature superconductivity resides not only in its technological promises, but also in the dazzling number of exotic phases and elementary excitations it puts on display for physicists. These myriad phases and excitations give physicists new dimensions and building bricks for understanding and exploiting the world of collective phenomena. The pseudogap, charge-density-wave, nematic and spin liquid phases, for examples, are a few exotica that are found in cuprate high temperature superconductors. Understanding these phases is important for understanding the mechanism behind high temperature superconductivity, but they are also interesting in and of themselves.

The charge-density-wave (CDW) phase in the cuprates – a spontaneous emergence of a periodic modulation of charge density in real space – has particularly garnered a lot of attention. It emerges upon the destruction of the parent antiferromagnetic Mott insulating phase with doping and it appears to directly compete with superconductivity. Whether or not these features are generic, or maybe even necessary, for high temperature superconductivty is an important question. Unfortunately, currently there exists no other comparable high temperature superconducting materials family that enables such questions to be answered.

Recently, the iridates have emerged as a possible analog to the cuprates. The single layer variant Sr2IrO4, for example, exhibits signatures of both a pseudogap phase and a high temperature superconducting phase. However, with an increasing parallel being drawn between the iridates and the cuprates in terms of their electronic phases, CDW has so far eluded detection in any iridate, calling into question the validity of this comparison. Rather than studying the single layer variant, we decided to look at the bilayer iridate Sr3Ir2O7 in which a clear Mott insulator to metal transition has been reported with doping.

While CDW has been observed in many materials, what made it elusive in cuprates for many years is its spatially short-ranged (it extends only a few lattice spacings long) and often temporally short-ranged (it blinks in and out of existence quickly) nature. To get a good view of this order, experimentalists had to literally pin it down using external influences like magnetic fields or chemical dopants to suppress the temporal fluctuations and then use very sensitive diffraction or scanning tunneling based probes to observe them.

But rather than looking in real space for signatures of the CDW order, an alternative approach is to look for them in the time domain. Works by the Gedik group at MIT and the Orenstein group at U.C. Berkeley have shown that one can use ultrafast time-resolved optical reflectivity to “listen” for the tone of a CDW to infer its presence in the cuprates. In these experiments, one impulsively excites a coherent mode of the CDW using a femtosecond laser pulse, much like one would excite the vibrational mode of a tuning fork by impulsively banging it. One then stroboscopically looks for these CDW oscillations via temporally periodic modulations in its optical reflectivity, much like one would listen for the tone produced by the tuning fork. If you manage to hear the tone of the CDW, then you have established its existence!

We applied a similar approach to Sr3Ir2O7 and its doped versions [hear our experiment]. To our delight, the ringing of a CDW mode sounded immediately upon doping across its Mott insulator to metal transition, implying that the electronic liquid born from the doped Mott insulator is unstable to CDW formation, very similar to the case in cuprates. Also like the case of cuprates, this charge-density-wave is of a special nature: it is either very short-ranged, or temporally fluctuating. Whether or not there is a superconducting phase that competes with the CDW in Sr3Ir2O7 remains to be seen. If so, the phenomenology of the cuprates may really be quite generic. If not, the interesting question of why not is worth pursuing. And who knows, maybe the fact that we have a system that can be controllably tuned between the antiferromagnetic order and the CDW order may find use in technology some day.

# Hamiltonian: An American Musical (without Americana or music)

Author’s note: I intended to post this article three months ago. Other developments delayed the release. Thanks in advance for pardoning the untimeliness.

Critics are raving about it. Barak Obama gave a speech about it. It’s propelled two books onto bestseller lists. Committees have showered more awards on it than clouds have showered rain on California this past decade.

What is it? The Hamiltonian, represented by $\hat{H}$. It’s an operator (a mathematical object) that basically represents a system’s energy. Hamiltonians characterize systems classical and quantum, from a brick in a Broadway theater to the photons that form a spotlight. $\hat{H}$ determines how a system evolves, or changes in time.

I lied: Obama didn’t give a speech about the Hamiltonian. He gave a speech about Hamilton. Hamilton: An American Musical spotlights 18th-century revolutionary Alexander Hamilton. Hamilton conceived the United States’s national bank. He nurtured the economy as our first Secretary of the Treasury. The year after Alexander Hamilton died, William Rowan Hamilton was born. Rowan Hamilton conceived four-dimensional numbers called quaternions. He nurtured the style of physics, Hamiltonian mechanics, used to model quantum systems today.

Hamilton has enchanted audiences and critics. Ticket sell out despite costing over $1,000. Tonys, Grammys, and Pulitzers have piled up. Lawmakers, one newspaper reported, ridicule colleagues who haven’t seen the show. One political staff member confessed that “dodging ‘Hamilton’ barbs has affected her work—so much so that she hasn’t returned certain phone calls ‘because I couldn’t handle the anxiety’ of being harangued for her continued failure to see the show.” Musical-theater fans across the country are applauding Alexander. Hamilton forbid that William Rowan should envy him. Let’s celebrate Hamiltonians. I’ve been pondering the Hamiltonian It describes a chain of $L$ sites. $L$ ranges from 10 to 30 in most computer simulations. The cast consists of quantum particles. Each site houses one particle or none. $\hat{n}_j$ represents the number of particles at site $j$. $c_j$ represents the removal of a particle from site $j$, and $c_j^\dag$ represents the adding of a particle. The last term in $\hat{H}$ represents the repulsion between particles that border each other. The “nn” in “$E_{\rm nn}$” stands for “nearest-neighbor.” The $J$ term encodes particles’ hopping between sites. $\hat{c}_j^\dag \hat{c}_{j+1}$ means, “A particle jumps from site $j+1$ to site $j$.” The first term in $\hat{H}$, we call disorder. Imagine a landscape of random dips and hills. Imagine, for instance, crouching on the dirt and snow in Valley Forge. Boots and hooves have scuffed the ground. Zoom in; crouch lower. Imagine transplanting the row of sites into this landscape. $h_j$ denotes the height of site $j$. Say that the dips sink low and the hills rise high. The disorder traps particles like soldiers behind enemy lines. Particles have trouble hopping. We call this system many-body localized. Imagine flattening the landscape abruptly, as by stamping on the snow. This flattening triggers a phase transition. Phase transitions are drastic changes, as from colony to country. The flattening frees particles to hop from site to site. The particles spread out, in accordance with the Hamiltonian’s $J$ term. The particles come to obey thermodynamics, a branch of physics that I’ve effused about. The Hamiltonian encodes repulsion, hopping, localization, thermalization, and more behaviors. A richer biography you’ll not find amongst the Founding Fathers. As Hamiltonians constrain particles, politics constrain humans. A play has primed politicians to smile upon the name “Hamilton.” Physicists study Hamiltonians and petition politicians for funding. Would politicians fund us more if we emphasized the Hamiltonians in our science? Gold star for whoever composes the most rousing lyrics about many-body localization. Or, rather, fifty white stars. # Zoe Saldana Answers the Quantum Call Stephen Hawking & Zoe Saldana try to save Simon Pegg’s cat Watch Quantum Is Calling with Zoe Saldana, Stephen Hawking, Keanu Reeves, Paul Rudd, Simon Pegg, and John Cho. We are on the verge of a quantum revolution. Like in the days of the space race, technology has brought an impossibly distant frontier to our doorstep. Just over 17 years ago Michael Crichton wrote a parallel universe-hopping adventure, Timeline, whose fundamental transportation technology required the advent of quantum computing – a concept that was still only theoretical at the time. Today, IBM’s five-quantum bit (or qubit) array is at the fingertips of anyone within reach of the cloud. Google is building a fifty-qubit array. Microsoft is bankrolling a brain trust that will build a quantum computer based on topological qubits. Intel is investing$50 million on spin qubit technology. The UK has announced a £270 million program, and the EU a €1 billion program, to develop quantum technologies. And even more quantum circuits are on the way; the equivalent of competing classes of space shuttles. Only these crafts aren’t meant to travel through space, or even time. They travel through the complete unknown. Qubits fluctuate between the infinite universes of possibility, their quantum states based inherently on uncertainty. And the best way to harness that seemingly unlimited computing power, and take the first steps into the quantum frontier, is through the elusive concept of entanglement.

So then, the quantum crafts are ready; the standby lights on their consoles blinking in a steady yellow cadence. What we’re missing are the curiosity-driven pilots willing to grapple with the uncertain and unpredictable.

The quantum mechanics property of entanglement was discovered by Albert Einstein, Boris Podolsky, and Nathan Rosen and soon after described in a famous 1935 paper. Einstein called it “spooky action at a distance.” Virtually all of his contemporaries, including Edwin Schrödinger who coined the term “entanglement”, and the entire subsequent generation of physicists would struggle with this paradox. Although their struggles would be necessary to arrive at this particular moment in time, this precipice, their collective and prodigious minds were, and remain to be, handcuffed by training and experiences rooted in a classical understanding of the laws of nature – derived from phenomena that can be seen or felt, either directly or indirectly. Quantum entanglement, on the other hand, presents a puzzle of a fundamentally abstract nature.

Paul Rudd & Stephen Hawking chatting it up

When Paul Rudd defeated Stephen Hawking in a game of quantum chess – a game built from the ground up with a quantum mechanical set of moves leveraging superposition and entanglement – our intent was to suggest that an entirely new generation of physicists can emerge with an intuitive understanding of entanglement, even before having to dip their toes in mathematics.

Following up on Anyone Can Quantum, the challenges were to (1) further introduce and elaborate on quantum entanglement and (2) reach a wider audience, particularly women. Coming from a writer’s perspective, my primary concern was to make the abstract concept of entanglement somehow relatable. Popular stories, at their most basic, are told through interactions between people in relationships. Only through relational interactions can characters be challenged enough to affect a change in behavior, and as a result support a theme. Early story concepts evolved from the idea that any interaction with entanglement would result in a primary problem of miscommunication. Entanglement, in any form approaching personification, would be fully alien and incomprehensible. Language then, I decided, would become the fabric by which we could create a set of interactions between a human and entanglement.

Dr. Louise Banks (Amy Adams) & Ian Donnelly (Jeremy Renner) in Arrival

This particular dynamic was tackled in the recent movie Arrival. There, the fictional linguist Dr. Louise Banks is tasked with translating the coffee-ring-stain sign language of a visiting alien civilization before one of the world’s many nervous armies attacks them and causes an intergalactic incident. In the process of decoding the dense script, the controversial Sapir-Whorf theory is brought up introducing the idea that language shapes the way people think. While this theory may or may not hold snow, I am still impressed with the notion that a shared, specific, and descriptive language is necessary to collaborate and innovate. This impression is supported by my own experience in molecular and cell biology research in which communicating new findings always requires expending a tremendous amount of energy crafting a new and appropriate set of terms, or in other words, an expansion of the language.

Marvel To The Rescue

The Tesseract & Groot in Guardians of the Galaxy

To drive their building, multi-threaded Infinity Stones storyline, the Marvel Cinematic Universe (MCU) has been fortuitously bold in broaching quantum physics concepts and attempting to ground them in real science, taking advantage of the contacts available through the Science & Entertainment Exchange. Through these consultations, movies like Thor and Ant-Man have already delivered to a wide and diverse audience complex concepts such as Einstein-Rosen bridges (wormholes) and the Quantum Realm.

The Ant-Man consultation, in particular, resulted in a relationship between IQIM’s own Spyridon Michalakis (aka Spiros) and Ant-Man himself, Paul Rudd. This relationship was not only responsible for Anyone Can Quantum, but it was also the reason why Spiros was invited to be a panelist at the Silicon Valley Comic Con earlier this year, where he was interviewed by science journalist Zuberoa “Zube” Marcos of the global press outfit, El Pais, a woman who would end up playing a central role in getting Quantum Is Calling off the ground.

So the language of quantum physics was being slowly introduced to a wider, global population thanks to the Marvel films. It occurred to us that we had the opportunity to explain some of the physics concepts brought up by the MCU through the lens of quantum physics, and entanglement in particular. The one element of the MCU storylines that was most attractive to us was the Tesseract and its encased Space Stone. It was the first of the Infinity Stones introduced (in Captain America: The First Avenger) and the one that drove the plot of The Avengers, culminating in the creation of a wormhole over Manhattan. For Spiros, the solution was simple: In order to create wormholes, the exotic matter comprising the Space Stone would likely have to exploit entanglement, as described in a conjecture, dubbed “ER=EPR”, published by Leonard Susskind and Juan Maldacena in 2013.

The USS Enterprise (NCC-1701) in the Star Trek TOS episode “The Immunity Syndrome”

Finding Our Star

The remaining challenge was to find the right actress to deliver the new story. The earliest version of our story (back in June, 2016) was based on the crew of the Starship Enterprise encountering an alien creature that was the embodiment of entanglement (a.k.a The Flying Spaghetti Monster), a creature that attempted communication with Earthlings by reciting sound bytes originating from past Earth radio transmissions. In this story iteration, Chief communications officer Uhura would have used her skills to translate the monster’s message amidst rising tension (just like in Arrival).

Zoe Saldana as Lt. Nyota Uhura

In the subsequent revisions to the story we had to simplify the script and winnow down the cast. We opted to lean on Zoe Saldana’s Uhura. Her character could take on the role of captain, communications officer, and engineer. Zoe was already widely known across multiple sci-fi franchises featuring aliens (namely Star Trek, Guardians of the Galaxy, and Avatar) and her characters have had to speak in or translate those languages.

Zoe = Script

But before approaching Zoe Saldana – and at that point in time, we had no idea how to go about that – we needed to complete a script. Two other incredible resources were available to us: the voices of Dr. Hawking and Keanu Reeves; and we had to make all three work together in a unique comedy – one that did not squander the involvement of either voice, but also served to elevate the role of Zoe.

Even in the first version of the story it was my intent to have Keanu Reeves provide the voice for entanglement, expressed through the most alien sounding languages I could imagine. To compress the story to fit our budget we were forced to narrow the list of languages to two, and I chose Dothraki and Navajo. The role of Keanu’s character was to test, recruit, and ultimately invite Zoe Saldana to enter and experience entanglement in the Quantum Realm. Dr. Stephen Hawking would be the reluctant guide that helps Zoe interpret the confusing clues embedded within the Dothraki and Navajo to arrive at the ER=EPR conjecture.

As for the riddle itself, I chose to use two poems from Through the Looking Glass (and What Alice Found There), The Walrus and The Carpenter as well as Haddock’s Eyes, as the reference material, so that those savvy enough to solve even half the riddle on their own would have a further clue pointing them to the final answer.

Simon Pegg’s cat, Schrodinger (not his actual cat)

The disappearance of Simon’s cat, Schrödinger, had a tripartite function of (a) presenting an inciting incident that urged Zoe to subject herself to the puzzle-solving trial, which we called the Riddle of the Tesseract, (b) to demonstrate the risk of touching the Tesseract and the gravity of her climactic choice, and (c) invoking Schrödinger’s famous thought experiment to present the idea that, in the Quantum Realm, the cat and Zoe are both dead and alive, an uncertainty.

The story was done. And it looked good on paper. But the script was just a piece of paper unless we got Zoe Saldana to sign on.

Zuberoa Marcos

Zoe = Zube

For weeks, Spiros worked all of his connections only to come up empty. It wasn’t until he mentioned our holy quest to Zube (from El Pais and Silicon Valley Comic Con) during an unrelated Skype session that he had the first glimmer of hope, even kismet. Zube had been working on arranging an interview with Zoe for months, an interview that would be taking place three days later in Atlanta. Without even a second thought, Spiros purchased a plane ticket and was on his way to Atlanta two days later. Watching the interview take place, he heard Zoe answer one of Zube’s question about what kind of technology interested her the most. It was the transporter, the teleportation machine used by the crew of the Enterprise to shift matter to and from surfaces of alien planets. This was precisely the kind of technology we were interested in describing at a quantum level! Realizing this was the opening we needed, Zube nodded over to Spiros and made the introductions.

It turns out Zoe had been fascinated by science fiction since her early childhood, being particularly obsessed with Frank Herbert’s Dune. Moreover, she was interested in playing the role of our lead character. In the weeks that followed, communication proceeded through managers in an attempt to nail down a filming date.

Mariel, Zoe, and Cicely Saldana

The Dangers of Miscommunication

I probably don’t need to remind you that Zoe Saldana is a core component of three gigantic franchises. That means tight schedules, press conferences, and international travel. Ultimately Zoe said that her travel commitments wouldn’t allow her to film our short. It was back to square one. We were dead in the water. The script was just a piece of paper.

However, for some reason, Spiros and Zube were not willing to concede. Zube found out about Zoe Saldana’s production company Cinestar and got in contact with coordinator Diego Gonzalez, to set up a lunch meeting. At lunch, Diego informed Zube and Spiros that Zoe really wanted to do this, but her team was under the impression that filming for our short video had to take place the week Star Trek: Beyond was to be released (Zoe was arguably busier than the POTUS during that week). Spiros informed Cinestar that we would accommodate whatever date Zoe could be available. Having that hurdle removed paved the way for a concrete film date to be set, October 25th. And now the real work began.

Simon Pegg in Shaun of the Dead

Finding Common Language

We had set the story inside Simon Pegg’s house and the script included voice-over dialogue for the superstar, but we had yet to even contact Simon. We had written in a part with Paul Rudd on a voicemail message. And we had also included a sixth character that would knock on the door and force Zoe to make her big decision. On top of that I had incorporated Dothraki and Navajo versions of century-old poems that had yet to be translated into those two languages. While Spiros worked on chasing down the talent, I nervously attempted to make contact with experts in the two languages.

David J. Peterson

I remember watching a video of Prof. David J. Peterson, creator of the Dothraki language for HBO’s Game of Thrones, speaking at Google about the process of crafting the language. Some unknown courage surfaced and I hunted down contact information for the famous linguist. I found an old website of his, an email address, and sent and inquiry at about midnight pacific standard time on October 14th, the day before my birthday. Within 45 minutes David had responded with interest in helping out. I was floored. And I couldn’t help geeking out. But more importantly this meant we would have the most accurate translation humanly possible. And when one is working on behalf of Caltech you definitely feel the pressure to be above reproach, or unsullied ;).

Keanu Reeves, Jennifer Wheeler, a pumpkin, a highlighter & my left arm

Finding a Navajo translator was comparatively difficult. A couple days after receiving Dr. Peterson’s email, I was in Scottsdale, AZ with my brother. I had previously scheduled the trip so that I could be in attendance at a book-signing featuring two of my favorite authors, as a birthday gift to myself. The event was held at the Poisoned Pen bookstore where many other local authors would regularly hold book-signings. While I was geeking out over meeting my favorite writing duo, as well as over my recent interaction with David Peterson, I was also stressed by the pressure to come through on an authentic Navajo translation. My brother urged me to ask the proprietors of the Poisoned Pen for any leads. And wouldn’t you know it, they had recently hosted a book-signing for the author of a Code Talkers book, and she was local. A morning of emails led to Jennifer Wheeler. We had struck gold. Jennifer had recently overseen Navajo translations of Star Wars: A New Hope and Finding Nemo, complete with voice-overs. There was probably nobody more qualified in the world.

Keanu Reeves as Ted “Theodore” Logan in Bill & Ted’s Excellent Adventure

So it turns out that Navajo is a much more difficult language to translate and speak than I had anticipated. For instance, there are over a hundred vowel sounds. So even though the translation was in good hands, I would be imposing on Keanu Reeves one of the greatest vocal challenges he would ever undertake. Eventually I arranged to have Jennifer on hand during Keanu’s voice recording. Here’s what he had to record (phonetically):

Tsee /da / a / ko / ho / di / say / tsaa, / a / nee / di

aɫ / tso / n’ / shay / ch’aa / go

Echo Papa Romeo / do / do / chxih / da

Bi / nee / yay / bi / zhay / ho / lo / nee / bay / do / bish / go.

Alex Winter & Zoe Saldana hard at work

Filming Day

After months of planning and weeks of script revisions, filming finally happened at an opulent, palatial residence in the Hollywood Hills (big props to Shaun Maguire and Liana Kadisha for securing the location). Six cats. Three trainers. Lights. Cameras. Zube. Zoe Saldana actually showed up! Along with her sisters, Cinestar, and even John Cho! Spiros had gotten assurances from Simon Pegg that he would lend his name and golden voice so we were able to use the ridiculous “Simon’s Peggs” wood sign that we had crafted just for the shoot. Within a few busy hours we were wrapped. All the cats and props were packed and back in LA traffic, where we all seem to exist more often than not. Now the story was left to the fate of editing and post-production.

In Post

Unlike the circumstances involved with Anyone Can Quantum, for which there was a fast approaching debut date, Spiros and myself actually had time to be an active part of the post-production process. Alex Winter, Trouper Productions, and STITCH graciously involved us through virtually every step.

One thing that became quite apparent through the edits was the lack of a strong conclusion. Zoe’s story was designed to be somewhat open-ended. Although her character arc was meant to reach a conclusion with the decision to enter the Quantum Realm, it was clear that the short still needed a clear resolution.

What Seraph looks like as code in the Matrix Reloaded

Through much debate and workshopping, Spiros and I finally arrived at bookend scenes that took advantage of Keanu Reeve’s emblematic representation of, and inescapable entanglement with, The Matrix. Our ultimate goal is to create stories that reflect the quantum nature of the universe, the underlying quantum code that is the fabric from which all things emerge, exist, and interact. So, in a way, The Matrix wasn’t that far off.

Language Is Fluid

LIQUi|> (“liquid”), or Language-Integrated Quantum Operations, is an architecture, programming language, and tools suite designed for quantum computing that is being developed by the Microsoft team at Quantum Architectures and Computation Group (or QuArC). Admittedly taking a few liberties, on Spiros’s advice I used actual LIQUi|> commands to create a short script that established a gate (or data structure) that I called Alice (which is meant to represent Zoe and her location), created an entanglement between Alice and the Tesseract, then teleported the Tesseract to Alice. You’ll notice that the visual and sound effects are ripped right from The Matrix.

This set up the possibility of adapting Neo’s famous monologue (from the end of the original Matrix) so we could hint that Zoe was somewhere adrift within the quantum code that defines the Quantum Realm. Yes, both Spiros and I were in the studio when Keanu recorded those lines (along with his lines in Dothraki and Navajo). Have I mentioned geeking out yet? An accompanying sequence of matrix code, or digital rain, had to be constructed that could accommodate examples of entanglement-related formulas. As you might have guessed, the equations highlighted in the digital rain at the end of the short are real, most of which came from this paper on emergent space (of which Spiros is a co-author).

Keanu Reeves & Keanu

Listen To Your Friend Keanu Reeves. He’s A Cool Dude.

With only a few days left before our debut date, Simon Pegg, Stephen Hawking and Paul Rudd all came through with their voice-over samples. Everything was then stitched together and the color correction, sound balancing, and visual effects were baked into the final video and phew. Finally, and impossibly, through the collaboration of a small army of unique individuals, the script had become a short movie. And hopefully it has become something unique, funny, and inspiring, especially to any young women (and men) who may be harboring an interest in, or a doubt preventing them from, delving into the quantum realm.