Introduction
Quantum informatics is a modern field that combines quantum physics with information theory. It forms the foundation of:
Quantum Computing
Quantum Cryptography
Quantum Communication
Unlike classical computers that use bits (0 or 1), quantum systems use qubits, which behave very differently.
In this blog, we will explain:
What is a qubit?
What is superposition?
How quantum measurement works
What is the Bloch sphere?
What is the No-Cloning Theorem?
How BB84 quantum key distribution works
Simple Qiskit code examples
Classical Bit
A classical bit can be:
0 OR 1
Example:
Light OFF → 0
Light ON → 1
Very simple.
Quantum Bit (Qubit)
A qubit can be:
0 1 OR both at the same time (superposition)Mathematically
Where:
α and β are complex numbers (called amplitudes)
∣α∣2+∣β∣2=1
This condition is called normalization.
Superposition means a qubit can exist in both states at the same time.
Example:
Now:
P(1)=1/2
So we get:
50% chance → 0
50% chance → 1
Important:
👉 Probability = square of amplitude
Measurement is very special in quantum mechanics.
When we measure:
We choose a basis (Z or X)
The state collapses
We get only one result
If:
Then:
After measurement:
If result is 0 → state becomes |0⟩
If result is 1 → state becomes |1⟩
Superposition disappears.
Two common bases:
Z-Basis (Computational Basis)
X-Basis
Changing basis changes probability.
This is very important in BB84.
A qubit can be written as:
This represents a point on a sphere called the Bloch Sphere.
Important:
Every pure qubit = point on sphere surface
Measurement = projection onto axis
Probability depends on angle
Quantum operations must satisfy:
This means:
Operations are reversible
No information is destroyed
Example: Pauli matrices
This flips:
|0⟩ → |1⟩
|1⟩ → |0⟩
Two qubits have 4 basis states:
|00⟩
|01⟩
|10⟩
|11⟩
General state:
Quantum system grows exponentially.
That is why quantum computing is powerful.
Very important concept.
It says:
❌ You cannot copy an unknown quantum state.
Why?
Because copying would require:
But this cannot work for all states.
This is why quantum cryptography is secure.
If:
Length(key) = Length(message)
Encryption:
Cipher = Plaintext ⊕ Key
Example:
Plaintext: 0100 Key: 1100 Cipher: 1000Decrypt:
Cipher ⊕ Key = Plaintext
If the key is random and never reused:
👉 It is unbreakable.
Problem: How to share key securely?
Answer: Quantum Key Distribution.
Developed in 1984 by:
Charles Bennett
Gilles Brassard
Main Idea:
Use quantum physics to share the secret key securely.
BB84 Steps
Step 1: Alice
Chooses random bits
Chooses random basis (Z or X)
Sends qubits
Step 2: Bob
Chooses random basis
Measures qubits
Step 3: Public Discussion
They compare only bases (not values).
They keep only matching basis bits.
Eavesdropping Detection
If Eve tries to measure:
She chooses wrong basis half of time
Introduces errors
Maximum error ≈ 25%
If error rate too high → abort communication.
Security comes from:
Measurement disturbs state
No cloning theorem
Create superposition and measure:
from qiskit import QuantumCircuit, Aer, execute qc = QuantumCircuit(1, 1) qc.h(0) # Create superposition qc.measure(0, 0) simulator = Aer.get_backend('qasm_simulator') result = execute(qc, simulator, shots=1000).result() counts = result.get_counts() print(counts)Output will be close to:
{'0': 500, '1': 500}This shows 50%-50% probability.
Future quantum computers may break:
RSA
Diffie-Hellman
This is called:
"Harvest now, decrypt later."
But BB84 provides:
✔ Physically guaranteed security
✔ Eavesdropping detection
✔ Secure key generation
Quantum informatics introduces a new way to process information using:
Superposition
Measurement
Unitary operations
No-cloning principle
Qubits are fundamentally different from classical bits.
Quantum key distribution (BB84) uses these properties to create secure communication based on physics, not mathematical hardness.
Quantum technology is the foundation of:
Quantum computing
Quantum cryptography
Future secure communication systems