The Qubit Up Close

The Qubit Up Close Curiosities June 22, 2026 8 min /curiosities/the-qubit-up-close/ Part 2 of the Quantum Computing series. How qubits are actually built, how they are kept stable, how they are measured, and what operations we can do on them. Superconducting loops, trapped ions, photons, lasers, and the Bloch sphere, with no heavy math.

Welcome back to the second post in this series. In Part 1 we met the qubit, the magical "both 0 and 1 at the same time" building block. Now let us go deeper, but still keep it super simple. No heavy math. Think of this as opening the hood of a quantum computer and looking at the engine without needing to be a mechanic.

A qubit is a tiny physical object that can be controlled so it behaves according to quantum rules. It is not just an idea. It is a real thing you can build in a lab.

The key property: while a normal bit is forced to pick 0 or 1, a qubit can exist in a superposition of both until we measure it.

Imagine a qubit as a spinning arrow (we will use this picture a lot):

• Pointing straight up means definitely |0⟩.
• Pointing straight down means definitely |1⟩.
• Pointing anywhere else means a mix of both (superposition).

The direction of the arrow tells us the probability of getting 0 or 1 when we finally look.

Scientists have invented several ways to build qubits. Here are the most common ones explained like everyday objects.

Superconducting qubits (IBM, Google, Rigetti)

• Tiny loops of special metal cooled to almost absolute zero (about minus 273 degrees Celsius, or minus 459 degrees Fahrenheit).
• At that temperature, electricity flows without any resistance and behaves quantum-mechanically.
• The qubit is basically a tiny current going clockwise (0), or counterclockwise (1), or both directions at once.
• These are the ones you see in the big "quantum chandelier" photos, with lots of wires and gold-colored parts.

Trapped ion qubits (IonQ, Quantinuum)

• They trap individual atoms (ions) using lasers and electric fields.
• The qubit is stored in the energy level of the atom's electron. Low energy is 0, high energy is 1.
• These are very stable and accurate, but slower and harder to scale up.

Photonic qubits

• Use particles of light (photons).
• The qubit can be encoded in the photon's polarization (horizontal versus vertical, or a mix).
• Good for sending quantum information over distances (the future quantum internet).

Other types exist (quantum dots, diamond defects, neutral atoms), but the idea is always the same: find something tiny that has two clear states and can be put into superposition.

Quantum states are incredibly fragile. This is called decoherence. It is like trying to keep a soap bubble from popping.

Big challenges:

• Any tiny vibration, stray light, or heat can disturb the qubit and destroy the superposition.
• That is why most quantum computers live in dilution refrigerators, giant machines that cool the qubits to a few thousandths of a degree above absolute zero.

How they manage them:

• Lasers, microwaves, or electric pulses gently nudge the qubits.
• The control system is like a very precise orchestra conductor telling each qubit exactly what to do.
• Error correction is a huge area of research. Engineers use groups of qubits to protect the "logical" information, similar to how your phone uses extra bits to fix errors.

Today's machines (2026) have between fifty and a few thousand physical qubits. Useful error-corrected machines will probably need millions.

Measurement is the moment the quantum magic stops.

When you measure a qubit in superposition:

• It instantly "collapses" and gives you either 0 or 1.
• You cannot choose which one you get. It is random, according to the probabilities set by the superposition.
• Example: if the qubit is 70% |0⟩ and 30% |1⟩, you will get 0 about 70% of the time if you repeat the experiment many times.

Important: once you measure it, the superposition is gone. The qubit is now a normal bit. That is why in quantum algorithms we do all the clever work before measuring.

Analogy. It is like the spinning coin we talked about earlier. While it is spinning in the air, it is both heads and tails. The moment it lands (measurement), you see only one.

We control qubits using quantum gates, operations that rotate or flip the qubit's state. Think of them as knobs you turn on the spinning arrow.

Single-qubit gates (acting on one qubit)

• Hadamard (H) gate. The most important beginner gate. Takes |0⟩ and turns it into an equal superposition: 50% chance of 0 and 50% chance of 1 when measured. Like flicking the spinning coin into the air.
• X gate (quantum NOT). Flips |0⟩ to |1⟩ and vice versa. Like turning the arrow upside down.
• Z gate, Y gate, phase gates. Rotate the arrow in different ways, changing the probabilities or adding "relative phases" (a kind of invisible timing difference between the 0 and 1 parts).

Two-qubit gates (the teamwork gates)

• CNOT (Controlled-NOT). The entanglement creator. If the first qubit is 1, it flips the second qubit. If the first is 0, it does nothing. When used on superposition, this is how we link qubits together.

You can combine these gates in sequences (called quantum circuits) to do useful work.

Imagine a globe:

• North pole means |0⟩.
• South pole means |1⟩.
• Anywhere on the surface is a valid superposition.

Every possible state of a single qubit is a point on this sphere. Quantum gates are rotations of the arrow on the sphere. This picture helps quantum programmers visualize what is happening.

• A qubit is a real physical object: a superconducting loop, a trapped atom, a photon, and so on.
• We create and control it with extreme cold, lasers, and microwaves.
• Superposition is delicate and easily destroyed (decoherence).
• Measurement collapses the state into a classical 0 or 1.
• We perform operations using quantum gates that rotate the qubit's state.
• The real power comes when we entangle many qubits and run algorithms before measuring.

You now know more about qubits than most people ever will.

In Part 3, we will draw simple quantum circuits on paper (and run them in a free online simulator), see entanglement in action, and run our first tiny quantum program. Something like creating a "quantum random bit" or a basic Bell test.

If anything in this post was confusing, send it over. The series gets better when more people read it.