superconducting qubits
The Cross-Resonance Gate: Entangling Qubits Without Turning a Dial
Every quantum computer needs a way to make two qubits talk to each other. Without a reliable two-qubit gate, you can flip individual qubits all day an...
The DiVincenzo Checklist: Five Boxes Every Qubit Must Tick
In 2000, the physicist David DiVincenzo wrote down a short list of requirements that any physical system must meet to work as a quantum computer. It w...
The Reset Problem: How a Quantum Computer Empties Its Qubits Between Runs
A quantum computer rarely runs a program just once. It runs the same circuit hundreds or thousands of times, collects the statistics, and reads an ans...
The Purcell Filter: The Guard That Lets a Qubit Be Read Without Being Killed
Every superconducting qubit faces the same awkward trade-off. To find out what state it is in, you have to connect it to the outside world through a r...
The Flip-Chip Stack: How Superconducting Qubits Went 3D
For years, a superconducting quantum chip looked like a single tile of silicon or sapphire with everything printed on one face. The qubits, the resona...
The Two-Level System: The Tiny Flaws That Drain a Qubit's Life
Ask an engineer why a superconducting qubit forgets its state so quickly, and sooner or later the conversation turns to something they can neither see...
The Tunable Coupler: The Switch That Turns Qubit Chatter On and Off
Two qubits sitting side by side on a superconducting chip have a problem: they can hear each other whether you want them to or not. Physics does not c...
The Faint Whisper: The Amplifiers That Hear a Qubit Speak
When a superconducting qubit finishes a calculation, it has to tell you what it holds. It does this by nudging a tiny microwave signal, a pulse so wea...
The Cold Controller: Moving Qubit Electronics Inside the Fridge
A superconducting quantum computer looks, from the outside, like a chandelier of gold-plated plates hanging inside a refrigerator the size of a fridge...
The Josephson Junction: The Tiny Gap That Makes a Superconducting Qubit Possible
Peer inside a superconducting quantum processor from IBM, Google, or Rigetti and you will find, at the core of every qubit, a device so small you woul...
The Leakage Problem: When a Qubit Escapes Its Two States
Every explanation of a qubit starts the same way: it lives in two states, call them 0 and 1, and it can be any blend of the two. That picture is a con...
The Fluxonium: The Superconducting Qubit Betting Against the Transmon
If you open up almost any superconducting quantum computer built in the last decade, from IBM's processors to Google's, you will find the same basic i...
The Tantalum Turn: How Swapping Metals Bought Qubits More Time
For most of the last decade, the superconducting qubit was a story about aluminum and niobium. Those were the metals that companies like IBM, Google,...
The Cosmic Ray Problem: When Space Radiation Wipes a Quantum Chip
Most of the errors that plague a superconducting quantum computer are local and boring in a useful way. One qubit drifts, a control pulse is a hair to...
The Yield Problem: Why No Two Qubits Come Out Identical
Walk into a chip fab and you expect uniformity. Modern semiconductor plants print billions of transistors that behave the same across a wafer and acro...
The Cat Qubit: The Qubit That Makes Only One Kind of Mistake
Most qubits fail in two ways. They can suffer a bit-flip, where a 0 quietly becomes a 1, and they can suffer a phase-flip, where the delicate relation...
The Calibration Treadmill: Why a Quantum Computer Is Never Done Being Tuned
Picture a piano that slips out of tune not once a year but every few hours, with 100 keys that each drift in their own direction. Now imagine you cann...
The Dilution Refrigerator: Chilling Qubits a Hair Above Absolute Zero
Look at a photo of a superconducting quantum computer and the thing that catches your eye is rarely the chip. It is the chandelier: a tiered tower of...
The Wiring Wall: Why a Million Qubits Can't Each Have Their Own Cable
Open the door of a dilution refrigerator and you see the part nobody puts on the brochure: a dense forest of coaxial cables snaking down through gold-...
The Frequency Crowding Problem: When Qubits Run Out of Room on the Dial
Every fixed-frequency transmon on a superconducting quantum chip is a tiny resonator that answers to one particular pitch. Send in a microwave pulse a...
The Heavy-Hex Lattice: Why IBM Gave Its Qubits Fewer Neighbors
Look at a photograph of an IBM quantum processor and you will notice something odd about the pattern. The qubits are not packed into a tidy square gri...