A Second Way to Build a Topological Qubit, and It Runs on Hardware Already Available

Chapter 10 of Quantum from the Ground Up tells one story about topological qubits: Microsoft growing an exotic nanowire material to host a particle called a Majorana zero mode. That approach needs new physics and new materials, and it has been slow going. A team at Quantinuum, working with researchers at Harvard, UChicago, and Stony Brook University, just showed a different way to get the same protection against errors. They published the result in Nature.

Here is the paper describing a universal topological gate set built from braiding and fusing exotic particles called anyons. They did not grow anything new. They took an ordinary trapped-ion quantum computer, Quantinuum's H2, and used 54 of its regular qubits to build a state of matter that behaves the way the exotic Majorana material is supposed to behave.

Start with what an anyon is. In everyday physics, particles come in two types: fermions, like electrons, and bosons, like photons. Anyons are not fundamental particles. They only show up inside certain engineered quantum systems, as patterns in how a group of qubits is entangled together. The interesting kind here are called non-Abelian anyons. If you take two of them and swap their positions, then swap two more in a different order, you get a different final result depending on which order you did the swapping in.

That sounds like a technicality, but it is the whole point. Because the result depends on the order of the swaps and not on small local wobbles or noise, information stored this way is naturally protected. Physicists call the swapping process braiding, since tracking two anyons moving around each other looks like braiding two strands of hair. In the diagram below, a1 passes in front of a2, shown by the small break in a2's line where it crosses behind. Swap them the other way, with a2 in front instead, and the anyons end up in a different state. Which one passes in front is not a drawing choice. It is the physical information the braid records.

Braiding by itself has a known gap. Researchers proved back in a 2003 proposal from physicist Carlos Mochon that for the simplest type of non-Abelian anyons, braiding alone cannot give you every operation a computer needs. You can protect information this way, but you cannot fully compute with it. Something was missing.

The Quantinuum team's answer was to add a second move: fusion. Instead of only moving anyons around each other, they also merge two anyons together and measure what comes out. Braiding plus fusion turns out to supply the missing operations, creating a mathematically complete set of gates capable of running any algorithm.

They built a 54-qubit state based on a mathematical structure called S₃—the smallest group that produces non-Abelian anyons—then stored information in the combined fusion outcomes of many anyons taken together rather than in any single qubit. Each unit of stored information could hold three states instead of the usual two (a qutrit rather than a qubit), since these anyons naturally support three possible fusion outcomes. Using braiding and fusion together, the team ran a computationally universal set of operations and read out the result correctly.

As a real test, they used the setup to build what is called a magic state, a specific resource that most fault-tolerant quantum computing schemes need. Normally, generating that resource requires an expensive extra process called magic state distillation, which eats up huge numbers of physical qubits just to produce one clean logical one. This approach made the same resource directly via topological operations without that extra step.

What This Changes in the Book

Chapter 10 needs a second section. Microsoft and Quantinuum are both chasing the same goal—a qubit that resists errors because of its shape rather than because of constant correction—but they are getting there in different ways. Microsoft is trying to grow a new material that hosts the right kind of particle directly. Quantinuum instead uses software and precise control to make an ordinary quantum computer behave as if that exotic material were there.

Chapter 6 gets an update too. The H2 processor was already in the book because of its record for entangling 56 qubits at once. Now it has a second claim to fame: it is a working testbed for this kind of engineered, error-resistant state of matter.

Neither team has built an actively error-corrected logical qubit that outperforms physical hardware yet. Both just found a more believable road toward one—and it turns out you do not need exotic new hardware to try.

This post will roll into the next edition, due September 1. The current edition is free at gordostuff.com/p/quantum-from-ground-up-hardware.html

Why Quantum Computing Matters, Even If You Never Touch One

I logged into my bank app last week to move some money to pay some bills. A padlock icon appeared next to the address bar. Secure connection. I didn't think about it again. Somewhere, someone already has a copy of that session, sitting on a hard drive, waiting.

That padlock runs on a math problem: factor a huge number into its two prime components. A classical computer needs longer than the age of the universe to do that. A large enough quantum computer, running an algorithm built for exactly this job, does it in hours. That computer does not exist yet. It is being built right now, funded by billions of dollars, and no government or company controlling that funding will announce the day it works.

You do not get to wait for that announcement. Security researchers call the attack already underway harvest now, decrypt later. Think about what you have touched on the web this year: your bank, your medical portal, your voter registration, your immigration or legal filings, your tax return, your cloud photo backup. State-backed intelligence services and criminal groups are copying that same traffic from millions of other people today, and storing it cheaply. Almost none of it needs to be cracked now. It needs to still exist, on somebody's drive, the day a quantum computer catches up. Then all of it becomes readable at once.

NIST finalized three new encryption standards built to resist this and set 2035 as the deadline to retire the vulnerable ones. Cloudflare and Google are not waiting until then; they have committed to migrating by 2029. Banks, hospitals, and government agencies holding decades-long records are moving faster still, because for them the clock already ran out on some of what they are protecting.

The fix is not a patch on the old method. It replaces the math underneath it. Government researchers finalized a new set of encryption methods built to survive a quantum computer, the same way today's methods survive an ordinary one. Companies are not waiting to switch over all at once, either. Cloudflare, Google, and Apple already run two locks on the same connection at the same time: the old one and the new one. If someone finds a weakness in the new lock, the old one still holds. If a quantum computer breaks the old lock, the new one still holds. Traffic protected this way stops being worth harvesting, because breaking one lock alone gets an attacker nothing.

Getting every bank, hospital, and government agency onto the new locks is the slow part. It means finding every place the old encryption sits inside a system and replacing it without breaking what depends on it. The federal government has published a shared plan for doing exactly that, across every agency and industry. None of it requires anything from you. It happens inside the apps and websites you already use.

The fix only protects what gets encrypted after it is installed, though. Anything copied under the old lock before that happens is already sitting on somebody's drive, and nothing reverses that. New encryption prevents future harvesting. It does not undo what has already been taken.

Diagram claude.ai generated

Nothing solves the data that is already sitting on somebody's drive. There is no way to reach into another party's storage, revoke a copy, or make it unreadable again. The new locks protect what gets encrypted after they are installed. They have no effect on a copy that left your device years earlier.

How much that matters depends on what kind of data it is. A password can be changed after the fact, so a stolen password loses most of its value once you reset it. A medical record, a Social Security number, or a biometric scan cannot be changed. Whatever gets exposed on that front stays exposed for good. It also depends on how long the data needed to stay private in the first place. Something that only mattered for a few years is probably already safe by the time a quantum computer shows up. Something that needed to stay private for decades, a government file, a company's trade secrets, a hospital's records, is running on a clock that started the day it was copied, not the day the quantum computer arrives.

Most people are not personally worth the effort. A patient attacker spends storage on high-value targets: government communications, corporate research, hospital systems, banks. If you end up exposed, it is more likely through one of those institutions holding your data than through anyone singling you out.

There is not much a consumer can do about data that is already gone. A few things still help:

•   Rotate what can be rotated. Change passwords regularly. A password manager makes it cheap enough to do more than once.

•   Turn on two-factor authentication. It stops a harvested password from being enough to log in on its own, since an attacker also needs your phone, an authenticator app, or a security key. It does not protect the data itself. A hospital record, a legal filing, or an old email that already left your device is untouched by it, because it only fires at login, not on the traffic that carries the data.

•   Not every two-factor method is equal. A text message code can be intercepted or rerouted if someone tricks your phone carrier into moving your number to a new SIM. An authenticator app is safer, since the code generates on your phone instead of traveling over the phone network. A hardware security key is safer still, a small physical device that checks a site's real address before it responds, so it does not work on a convincing fake login page. Use one for your email, your bank, and your password manager itself.

•   Assume what cannot be rotated is already out. Watch for misuse instead of trying to prevent something that may have already happened. A credit freeze and fraud alerts catch someone using a stolen Social Security number long before you would otherwise notice.

•   Keep your software current. The new locks only work if your browser, phone, and apps are recent enough to use them. An old browser is still running the old lock alone.

•   Think twice about what you put online today. Anything sent through email, cloud storage, or a messaging app now can still be harvested under the old lock until your provider finishes switching over.

•   Ask the institutions holding your data. A bank or hospital's own migration timeline affects your exposure more than anything you do personally, and it is a fair question to put to them directly.

None of it undoes what has already been copied. It limits what is still worth harvesting and reduces the damage from what is not.

The padlock on my banking app will look exactly the same through all of this. Behind it, the locks are being swapped one at a time: bank by bank, cloud provider by cloud provider. The question left is not whether the new lock exists. It is how much of your data got copied before it arrived.

Quantum Keys Move Onto Production Routers

Quantum Keys Move Onto Production Routers

I led the telecommunications curriculum for Verizon's Next Step New England program and directed National Science Foundation, or NSF, funded Centers of Excellence at Springfield Technical Community College and the University of Central Florida through the transition from my Dad's Plain Old Telephone Service, or POTS, landlines to Internet Protocol, or IP, based voice, video, and data over copper, fiber and wireless. Our center worked closely with Cisco through that transition. The physics and the protocols changed rapidly snd it was a wild ride. What made the transition real was not the standards documents. It was carriers running the new transport on switches and routers in the central office, and technicians who did not need an advanced degree to keep it running.

Quantum key distribution, or QKD, is a way to generate an encryption key using the behavior of individual photons instead of math. Two machines exchange specially prepared light particles over fiber. If anyone taps the line and looks at those particles, the particles change in a way both ends can detect. That gives you a key exchange where eavesdropping does not stay hidden, which is a different from anything conventional encryption offers.

Aliro Technologies, the Vienna based quantum networking firm zerothird, and Cisco just ran a live version of this over Cisco's production routers at Cisco's Photonics Center in Vimercate, Italy. The hardware was Cisco's 8000 Series routers, the same platform Cisco sells into data centers today. That detail is the news. QKD has existed in labs for years. Running it on hardware a customer can already buy is the harder problem.

The system runs on the BBM92 protocol, which uses paired entangled photons rather than a transmitted key to establish a shared secret. Entangled photons are pairs of light particles created together so that measuring one instantly tells you something about the other, no matter the distance between them. A source creates these pairs and sends one photon from each pair to each end of the link. Both ends measure what arrives and use those measurements to build an identical key, without the key itself ever traveling across the fiber. zerothird supplies the hardware that does this: the photon source, the equipment that keeps the light polarized correctly, synchronizing clocks, and the software that cleans up errors and strengthens the final key. Aliro's Orchestrator software sits on top and manages the link, the way network management software already watches a conventional router. It tracks error rates and photon counts in real time and can reroute traffic or shut a link down safely if something looks wrong. The finished keys reach the routers through Cisco's Secure Key Integration Protocol, a standard interface, where they secure encrypted sessions between routers the same way a conventional key would, just generated a different way.

Diagram Gemini AI Generated

Chapter 1 of Quantum from the Ground Up covers the fiber problem in quantum networking through the University of Illinois work on ytterbium-171 emitters built for existing telecom infrastructure. That chapter is about getting a quantum signal onto fiber that already exists. This deployment answers the other half of the problem: getting the output of that signal into a router that already exists, with the monitoring and failover a network operations center can actually run day to day.

Chapter 14 frames quantum security as a race between two approaches. Post quantum cryptography, or PQC, keeps using math for encryption, just math that a quantum computer cannot easily break, and the National Institute of Standards and Technology, or NIST, has already published standards for it. QKD, the approach in this demonstration, does not rely on hard math at all. It relies on physics: any attempt to intercept the entangled photons changes them in a way both ends can detect. That is also its limit. A QKD key only protects the specific fiber link between two endpoints, while PQC can protect data anywhere the software runs. That is why Cisco is running both approaches rather than picking one. AT&T's coming quantum resilient Software-Defined Wide Area Network, or SD-WAN, service runs PQC on that same 8000 Series router line, which puts both approaches on the same hardware within the same product family.

The public announcement described the deployment as moving QKD out of isolated research setups and into standard enterprise infrastructure. Coverage of the announcement also framed the three way pairing as proof that quantum networking gear from separate vendors can interoperate in a live deployment, which matters more for enterprise adoption than any single performance number. A separate technical paper from the zerothird team tested the same entanglement based approach over a 22 kilometer fiber link between two data centers, which gives the enterprise demonstration a research paper trail worth reading alongside the press coverage.

What This Changes in the Book

Chapter 1 currently ends at the physics of getting quantum signals onto standard fiber. This deployment extends that story into the network operations layer: orchestration, telemetry, and automated remediation running on hardware already shipping. Chapter 14's framing of PQC and QKD as separate paths still holds, but the AT&T and Cisco pairing on the same 8000 Series router line is worth adding as a concrete case where one operator runs both approaches at once instead of choosing sides.

This post will fold into the next edition of the book, due September 1. The current edition is at gordostuff.com/p/quantum-from-ground-up-hardware.html.

POTS to IP took a decade of this kind of work: new transport riding on racked equipment. Quantum key distribution is passing the same tesst. The obstacle was never the physics. Here it's whether the keys can ride on a router Cisco already sells, watched by software a network operations center knows how to run.

ETH Zurich Builds Quantum RAM Out of Vibrations

Chapter 5 of Quantum From The Ground Up covers superconducting qubits by way of Josephson junction fabrication and IBM's 1,121-qubit Condor chip. It never had to answer a basic architecture question: where a superconducting qubit puts its data when it isn't actively working on it. Researchers at ETH Zurich just built an answer, and it doesn't look anything like a normal memory chip.

A team led by physicist Yiwen Chu, head of ETH Zurich's Hybrid Quantum Systems Group, split a quantum computer into the same two roles a laptop uses: a processor and a separate working memory. The design uses a superconducting transmon qubit as the processor and a mechanical resonator as memory, on a chip package 7.5 millimeters long. Instead of storing a qubit's state electromagnetically, the resonator holds it as a mechanical vibration, the way a guitar string holds a note, except this vibration follows quantum rules rather than classical ones.

Each resonator supports several distinct vibrational modes, and each mode works as its own memory slot. To run a computation, the qubit reaches into the resonator, pulls out a stored vibration, modifies it, and writes it back. Doctoral students Yu Yang and Igor Kladarić built the hybrid chip alongside Chu. The team validated the architecture by running a Quantum Fourier Transform and a period-finding algorithm on the hybrid chip, published in Science. That marks the first demonstration of mechanical resonators executing real quantum algorithms rather than just holding a state.

Superconducting qubits pack in tightly, but that density crowds out room for data. Electromagnetic memory schemes have historically traded a smaller footprint against coherence time. Mechanical resonators split that trade differently, offering higher storage density and longer coherence in less physical space. the approach still has to prove it scales beyond a single test chip, and Chu's group is continuing the work with that goal in mind.

What This Changes in the Book

Chapter 5's numbers don't move. IBM's Condor still holds at 1,121 qubits and 99.0 to 99.5 percent two-qubit fidelity, and nothing here challenges either figure. What changes is the chapter's scope. Chu's result adds a memory subsystem to the superconducting platform, a second engineering problem the chapter didn't previously address. It's a proof of principle, not a shipped component. A chip built for one qubit and one resonator still has to prove itself when both categories multiply.

This post will fold into the next edition of Quantum from the Ground Up, due September 1. The current edition is free to read at gordostuff.com/p/quantum-from-ground-up-hardware.html, and if it's useful to you, a coffee at ko-fi.com/gordostuff keeps it updated.

The Free Path Into Quantum Work

The entire IBM Quantum Learning catalog is now open to the public, no partner account or IBM Quantum Network membership required. The catalog runs past ten courses, from the basics of qubits and circuits through algorithms for factoring and search, up to a course built around running experiments on processors with 100 or more qubits, all hosted free on the IBM Quantum Platform.

Path from free IBM Quantum Learning courses to certification to a quantum workforce role

The IBM Certified Quantum Computation using Qiskit v2.X Developer - Associate is a single exam built on the same Qiskit SDK and Qiskit Runtime the free courses teach. Since the program launched in 2021, more than 1,300 people across 71 countries have passed it. The exam runs up to $200 depending on location, with an optional $30 practice test through Pearson VUE. The preparation runs $0.

This matters most for programs without a quantum lab or a research grant behind them, which describes most community colleges and a fair number of universities. Qiskit needs Python and a working knowledge of linear algebra. Nothing else.

Every one of my students has a laptop and an internet connection. That's all you need to get started today.

This post rolls into the next edition of Quantum from the Ground Up, due September 1.

The Other Half of the Emerging Quantum Workforce

Chapter 2 of Quantum from the Ground Up covers the Massachusetts side of quantum
workforce building: over fifty million dollars in state investment, a quantum supply chain accelerator complex in Springfield, Massachusetts and a three tier pyramid running from technicians to PhDs. That chapter answers one question. How do you train people for jobs that barely exist yet? It does not answer a second question. Once someone is trained, where do they get time on a real quantum computer?

The federal government's answer is a program most people outside national labs have never heard of. The Quantum Computing User Program, or QCUP, runs out of the Oak Ridge Leadership Computing Facility. It owns none of the hardware it gives access to. Instead it brokers competitive, merit reviewed time on commercial quantum processors from vendors including IBM, Quantinuum, and Rigetti, for researchers doing open, fundamental science.

The mechanism is simple. A researcher submits a project proposal explaining what they want to run and why it needs quantum hardware. The Quantum Resource Utilization Council and independent referees review it for merit. Once approved, every user on that project applies for an account and gets assigned a Scientific Liaison, someone who understands both the science domain and the hardware, to help them get past the parts of quantum programming that have nothing to do with their actual research question.

The growth numbers are accelerating. A 2024 survey of the program found it had grown from 52 projects and 117 users in 2020 to 80 projects and 271 users by the end of 2023. Users range from national lab veterans to graduate students running their first circuit. Most projects are proof of principle work, not production science, which is exactly what you would expect from a field still figuring out what its hardware is good for.

Where the Access Turns Into Results

The hadronization work covered in my previous post, Anthony Ciavarella's simulation of quark binding on an IBM Heron processor, ran entirely through QCUP access. That is not a coincidence. It is the point of the program. Give enough researchers enough time on real hardware and some of them will publish in Physical Review D.

Demand is outrunning the obvious ways to measure it. The 2026 Quantum Computing User Forum at Oak Ridge, running July 20 through 24, closed registration before the event even started. A Fall 2026 hackathon open now for proposals gives existing users priority and asks new applicants to already hold an allocation before an August 7 deadline. This is not a program short on interested researchers.

What This Changes in the Book

Chapter 2 currently frames quantum workforce building as a state level, training focused story: Massachusetts building capacity so people are ready when jobs appear. QCUP is the federal, research access side of the same pipeline, and the book does not mention it yet. The two are not competing models. A pipeline that only trains people without giving anyone hands on time on real hardware produces graduates who have never run a circuit outside a simulator. QCUP is where some of that hands on time actually happens, for the research end of the workforce rather than the classroom end.

The next edition will add QCUP to Chapter 2 as the research access counterpart to the state workforce investment already covered there, with the growth numbers above and a note that at least one book worthy physics result, the Ciavarella hadronization paper, came directly out of that access.

This post will be folded into the next edition of Quantum from the Ground Up, targeted for September 1. The current edition is available at gordostuff.com/p/quantum-from-ground-up-hardware.html

A Quantum Computer Watches Matter Form From Scratch

Chapter 11 of Quantum from the Ground Up covers an IBM quantum chip that helped simulate a large protein molecule in May 2026. A new result uses a chip from the same family for something further from everyday life: watching the pieces of an atom's nucleus form.

Here’s some background - protons and neutrons, the particles that make up the nucleus of an atom, are not the smallest things out there. Each one is built from smaller particles called quarks, held together by a force called the strong force. Physicists call any particle built from quarks a hadron. The process of quarks locking together into a hadron is called hadronization. It happens constantly inside stars, inside particle colliders, and, billions of years ago, in the early universe. Nobody has ever watched it happen step by step, because it unfolds too fast and too small to see, even with instruments as powerful as CERN's Large Hadron Collider.

Anthony Ciavarella, a scientist at Lawrence Berkeley National Laboratory, used 104 qubits on an IBM quantum processor to simulate a piece of this process instead of observing it directly. He reached the machine remotely through a Department of Energy cloud access program called QCUP, rather than owning the hardware himself. We’ve described qubits in past posts - the basic unit of information in a quantum computer, similar to a bit in a regular computer, but able to hold more complex states. More qubits generally means a computer can model a bigger or more detailed problem.

The number 104 is an interesting choice and not a hardware limit. IBM's chip has 156 qubits, and Ciavarella used only some of them. In his setup, each qubit stands in for one point on a one-dimensional line of quark positions, so the qubit count is really a choice about how long a line to simulate. He picked a line of 104 points, long enough to fit a stretched gluon string spanning most of it, so something called the snap could happen out in the middle where it is easy to see clearly, rather than run into the edge of the simulation before it finished stretching.

The specific piece he simulated is called string breaking. Quarks are linked by something physicists describe as a string made of particles called gluons. Pull two quarks apart and that string stretches, the way a rubber band stretches, until it holds so much energy that it snaps. When it snaps, the energy does not just disappear. It turns into a brand new pair of quarks, which is how new hadrons get built. Ciavarella simplified the problem by using heavier quarks, which move around less and are easier to track, and he set up his simulation using a method he helped develop for preparing a quantum computer's starting state cleanly.

The simulation's answer matched what earlier work on ordinary supercomputers had already found. That match is the actual achievement here. Nobody is claiming the quantum computer beat a classical one. The result, published in Physical Review D, shows that a real quantum computer can reproduce a calculation even though the model was simplified down to one dimension. The data also hinted that the gluon string might briefly act like a heated gas right before it snaps, a detail worth checking again once the simulations get less simplified.

Why This Matters

Quantum computers are noisy. Every operation carries a small error, and those errors add up as a circuit grows. Nobody trusts a quantum result on a problem nobody can already solve until the machine first proves it gets the right answer on a problem people already know. Matching the classical calculation is that proof. It confirms the way Ciavarella mapped quark positions onto qubits, prepared the starting state, and corrected for hardware noise all worked correctly on real hardware, not only on paper.

Ciavarella's model used heavy quarks in one dimension because that version is still solvable classically. Light quarks, three dimensions, and watching a collision unfold in real time rather than checking a single snapshot are where classical computers run out of room, since those calculations carry exactly the kind of entanglement a regular computer cannot represent efficiently. That regime is also the one closest to what actually happens inside a real collision at a facility like the Large Hadron Collider. As Ciavarella put it, physicists already have the theory for hadronization; they have lacked a way to calculate predictions from it. This result is the first step toward a machine that can.

This was not the first attempt at something like this. In 2024, some of the same researchers, working with the University of Washington and Berkeley Lab, used 112 qubits to build and track a hadron directly, watching it move over time in an earlier, related model on an earlier version of this same IBM chip. The 2026 result trades that moving picture for a sharper look at the single moment when a hadron forms. 

What This Changes in the Book

Chapter 5, which covers this family of IBM chips, gets a new data point: the same chip line now has a published result in particle physics, using 104 qubits, on top of the protein simulation already covered in Chapter 11. Chapter 11's claim that this hardware has uses beyond biology gets a second example, and a more direct one, since this simulation ran entirely on the quantum processor rather than splitting the work between a quantum computer and a classical one.

This post will fold into the next edition of Quantum from the Ground Up, due September 1. The current edition is free to download at gordostuff.com/p/quantum-from-ground-up-hardware.html.

The Quantum Chandelier

Photo MIT Technology Review

You've probably seen a photo like this - a tower of gold-plated discs wrapped in loops of wire, narrowing toward a point at the bottom. Google, IBM, and most quantum computing press releases use some version of this image. People call the assembly the chandelier, and it looks like the computer. It isn't. It's the life support system for a chip you can't even see in the photo.

Start with what's actually inside a quantum computer. A qubit is a physical device, usually a tiny loop of superconducting metal, that can hold a mix of two states at once instead of a single 0 or 1. That mixed state is fragile. A stray photon, a vibration, or a few millikelvin of extra heat can collapse it before you get a useful calculation out of it. Physicists call that collapse decoherence, and it's the central engineering problem in the entire field. Keeping decoherence at bay is the whole reason the chandelier exists.

Why It Has to Be That Cold

At room temperature, everything around a chip is radiating heat as stray photons, trillions of them, bouncing around and hitting anything nearby. For a normal computer chip that's irrelevant. For a superconducting qubit it's fatal, since a single one of those stray photons carries enough energy to flip the qubit's state. Cooling the chip down to the mixing chamber stage, near 10 millikelvin starves the environment of those stray photons and also lets the qubit's own wiring become superconducting, meaning it carries current with zero electrical resistance. Both effects are required. Without one or the other, the qubit decoheres in nanoseconds instead of the few hundred microseconds researchers need.

The Five Stages

The gold structure is a dilution refrigerator, built from stacked stages that grow colder toward the bottom. A pulse tube cryocooler, essentially a specialized mechanical compressor, does the first heavy lifting, dropping the system from room temperature to about 40 Kelvin and then 4 Kelvin using compressed helium gas. Below that, the fridge switches to a different method. A chamber called the still boils off helium-3 to reach roughly 0.7 Kelvin, and a series of heat exchangers pushes the temperature down further, through about 0.1 Kelvin, to the mixing chamber at the very bottom. A mixture of helium-3 and helium-4 drives that last stage. The full cooldown from room temperature to base takes 24 to 48 hours, and it has to happen every time the system needs to be opened for maintenance.

Each gold disc in the photo is one of these stages, plated in gold because gold conducts heat well, resists corrosion, and doesn't interfere magnetically with the qubits. Each stage nests inside the next, shielding the colder one below it from the warmer one above.

Figure: the chandelier's cooling stages, colored from gold at the warmest to blue at the coldest, with the qubit chip mounted at the base.

The Wiring Problem

Every wire running through those stages carries control signals down to the qubits and readout signals back up to room-temperature electronics. A signal heading down gets attenuated at each stage on the way, stripping out electrical noise picked up from the warmer stages above. A signal heading up gets amplified, since the qubit's own readout signal is too faint to detect at room temperature. Every one of those wires is also a heat leak. Heat travels down a wire just as easily as a signal does, and the cooling power at the base stage is measured in microwatts, barely enough to warm a fraction of a grain of rice. A single wire that's improperly thermalized can add more heat than the entire fridge can remove.

That tradeoff is why wiring, not the qubits themselves, has become one of the field's biggest scaling obstacles. Each qubit needs its own set of control and readout lines, so the number of cables required grows directly with qubit count, eventually exceeding what a single cryostat can physically hold. Labs are now racing to move some control electronics inside the fridge itself, onto chips that can survive the cold, so fewer wires have to cross from room temperature down to the millikelvin stage. A single dilution refrigerator system runs one to five million dollars, and most of that cost is solving this wiring problem.

What's Actually Quantum

The qubit chip itself sits at the very bottom, bolted to the mixing chamber, a few millimeters across. It's small enough to miss in most photos of the chandelier, which is the point. Everything above it, every gold disc, every coil of coax, every attenuator and amplifier, exists for one reason: to keep that small chip cold and quiet enough to hold a quantum state long enough to be useful. Chapter 3 of Quantum from the Ground Up makes this argument directly: physics works, engineering makes it work. The chandelier is that argument built out of gold-plated copper and helium-3.

Next time a chandelier photo turns up in your feed, look past the wiring for the small chip at the bottom. That chip is the entire quantum computer. Everything else in the picture is plumbing.

This post will fold into the next edition of Quantum from the Ground Up, out September 1.