Qubit: 0, 1 and in-between

Let’s dive into the most fundamental aspect of understanding quantum computing, which is qubit.

When we spin a coin, in a classical sense the end result is heads or tails. In the quantum sense it can be heads, tails or both.

Okay, you may ask how can it be both? My answer is, imagine when a coin is tossed it’s spinning and it’s neither heads or tails and when it lands there is an outcome.

So a qubit exists in this “spinning” state until we measure it.

We use special notation for qubit states:

• |0⟩ represents the “0” state
• |1⟩ represents the “1” state

So, a qubit can be in state |0⟩, state |1⟩, or a mixture of both. This “in-between” state is the key to a quantum computer’s power.

The idea that a qubit can be both 0 and 1 is called superposition.

But here’s what makes qubits special: while “spinning,” they’re not just randomly 0 or 1 - they have specific probabilities for each outcome.

Think of mixing blue paint (0) and red paint (1) to make purple. More blue makes bluish-purple, more red makes reddish-purple. The exact mix determines your chances of getting 0 or 1 when measured.

What Happens When We Measure?

Here’s where quantum mechanics gets weird. The moment you measure a qubit, it’s forced to “choose” - it becomes definitely 0 or definitely 1. The superposition vanishes instantly.

But it’s not like the coin was secretly heads all along and we just discovered it. The qubit genuinely was in both states, and our measurement forced it to pick one.

Three Strange Facts About Measurement

1. You can’t peek without disturbing
In our everyday world, checking if your coffee is hot doesn’t change its temperature. But in the quantum world, checking a qubit’s state fundamentally changes it. There’s no “gentle” way to look.

2. Once measured, it stays that way
After measurement collapses a qubit to |0⟩, measuring again immediately will always give |0⟩. The superposition is gone.

3. The outcome is truly random
When a qubit is perfectly balanced between 0 and 1, there’s no hidden information that determines the outcome. The universe genuinely “rolls dice” at the moment of measurement.

This is why quantum information is like a soap bubble - beautiful and powerful while it lasts, but touch it and it pops.