How do qubits work?

A qubit (short for “quantum bit”) is the fundamental unit of information in a quantum computer. Unlike a classical bit, which is either 0 or 1, a qubit can exist in a superposition of both states at once. This is what gives quantum computers their power: with n qubits, a quantum computer can represent and process 2ⁿ possible states simultaneously.

What makes qubits different from classical bits?

A classical bit is like a coin lying flat — it's either heads or tails. A qubit is like a coin spinning in mid-air: while it's spinning, it's neither heads nor tails — it's in a probabilistic combination of both. Mathematically, a qubit is described by a state vector on the surface of the Bloch sphere, a 3-dimensional ball that represents every possible quantum state. The north pole is “0”, the south pole is “1”, and every point in between is a different superposition.

When you measure a qubit, the superposition collapses — you get either 0 or 1 with probabilities determined by where the state vector was pointing. This is what Einstein famously called “spooky” about quantum mechanics: you can know everything about how a qubit was prepared and still not be able to predict a single measurement outcome.

What is entanglement?

Two qubits are entangled when their states cannot be described independently — measuring one instantly determines the result of measuring the other, even if they are separated by vast distances. Entanglement is the resource that powers quantum teleportation, quantum key distribution (BB84), and the speed-up behind algorithms like Shor's factoring algorithm and Grover's search.

The 2022 Nobel Prize in Physics was awarded to Alain Aspect, John Clauser, and Anton Zeilinger for experiments demonstrating that entanglement is real and that quantum mechanics cannot be explained by “hidden variables.” You can replicate their CHSH experiment with two Qubis at home.

How do real quantum computers store qubits?

Different companies use different physical systems to make qubits. The most common approaches:

• Superconducting qubits (IBM, Google): tiny circuits cooled to near absolute zero, controlled with microwaves.
• Trapped-ion qubits (IonQ, Quantinuum): individual atoms held in place by electromagnetic fields, controlled with lasers.
• Photonic qubits (PsiQuantum, Xanadu): single photons of light traveling through optical chips.
• Neutral-atom qubits (QuEra, Atom Computing): arrays of atoms held by “optical tweezers” — focused laser beams.
• Spin qubits (Intel, Diraq): the spin of a single electron in a silicon crystal.

All of them obey the same quantum rules — they're just different physical implementations of the same abstract qubit. With Qubi, you can write a quantum circuit on your phone and send it to real IBM or IonQ hardware over the cloud.

How do you learn quantum computing without a physics degree?

The fastest way to build intuition for quantum computing is to interact with a physical qubit. Qubi is a model qubit you can hold in your hand: tilt it, rotate it, entangle it with a second one, and watch quantum behaviors unfold in front of you. The accompanying app guides you from basic concepts (measurement, gates, the Bloch sphere) all the way to running circuits on real quantum hardware.

For structured curricula and lessons, see our pages for educators, kids and parents, hobbyists, and organizations. Or browse our quantum computing glossary for plain-English definitions of the terms above.

Written by

Sohum Thakkar

CEO, Qolour · Ex-Apple, Ex-QCWare · UC Berkeley

Reviewed by academic advisors

John Preskill · Richard P. Feynman Professor of Theoretical PhysicsIordanis Kerenidis · DirectorYasser Omar · Professor