The Quantum Bit
Qubits
The Classical Bit
In classical computing, a bit is the fundamental unit of information. It can be either 0 or 1. Nothing in between.
Think of a light switch: it's either OFF (0) or ON (1). Simple and deterministic.
Interactive Classical Bit
Click to flip the bit , it's always exactly 0 or 1, nothing in between!
A classical bit is deterministic , you always know exactly what value it holds. No uncertainty, no probability.
💡 Compare this to the qubit demo below , notice the difference!
Enter the Qubit
A qubit (quantum bit) is the quantum version of a classical bit. Like a classical bit, when you measure it, you get either 0 or 1.
But here's the key difference: before measurement, a qubit can exist in a superposition of both states simultaneously.
Think of it like a coin spinning in the air—it's neither heads nor tails until it lands.
Interactive Qubit
Apply gates to manipulate the qubit, then measure to collapse the state!
The Math (Simplified)
We represent a qubit's state as:
Where:
|0⟩and|1⟩are the two basis statesαandβare complex numbers called amplitudes- |α|² is the probability of measuring 0
- |β|² is the probability of measuring 1
- |α|² + |β|² = 1 (probabilities must sum to 1)
Key Intuitions
Measurement Collapses State
When you measure a qubit, it "collapses" to either 0 or 1. The superposition is destroyed. You can't peek without changing the system.
Probabilistic, Not Random
The outcomes are probabilistic but governed by precise mathematical rules. We can engineer these probabilities.
More Than Randomness
A qubit isn't just a random bit. The amplitudes can interfere with each other, which is the source of quantum computational power.
"The classical bit is too limited. I need something that can be BOTH at once... superposition is the key."
, Dr. M.
01010001 01010101 01000010 01001001 01010100
Hint: Binary to ASCII... what's the fundamental unit?
Reflection Questions
- 1How is a qubit different from a classical bit in terms of the information it can represent?
- 2Why do you think we use probability amplitudes instead of just probabilities?