Quantum vs Classical Communication
The difference between having only 10–12 qubits in quantum computers and kbps–Gbps speeds in conventional communication can be confusing. This difference exists because quantum and classical systems work in fundamentally different ways.
1. Qubits and Quantum Superposition
Qubits are the basic units of quantum computing. Unlike classical bits (which are either 0 or 1), a qubit can exist in a superposition of both 0 and 1 at the same time.
This means that even a small number of qubits can represent a very large number of possible states. The computing power grows exponentially as more qubits are added.
Qubit (quantum bit)
A qubit is a unit vector in a 2-dimensional complex Hilbert space:
\[ |\psi\rangle = \alpha |0\rangle + \beta |1\rangle \]
where
\[ \alpha, \beta \in \mathbb{C}, \quad |\alpha|^2 + |\beta|^2 = 1 \]
- \(|0\rangle, |1\rangle\) are basis states
- \(|\alpha|^2\) = probability of measuring 0
- \(|\beta|^2\) = probability of measuring 1
Basis (measurement basis)
A basis is a set of orthonormal vectors used to describe or measure a qubit.
(a) Computational (Z) basis
\[ |0\rangle = \begin{pmatrix} 1 \\ 0 \end{pmatrix}, \quad |1\rangle = \begin{pmatrix} 0 \\ 1 \end{pmatrix} \]
Measurement probabilities:
\[ P(0) = |\langle 0|\psi\rangle|^2 = |\alpha|^2, \quad P(1) = |\langle 1|\psi\rangle|^2 = |\beta|^2 \]
(b) Hadamard (X) basis
\[ |+\rangle = \frac{|0\rangle + |1\rangle}{\sqrt{2}}, \quad |-\rangle = \frac{|0\rangle - |1\rangle}{\sqrt{2}} \]
Same qubit, different description:
\[ |\psi\rangle = c_+ |+\rangle + c_- |-\rangle \]
2. Quantum Entanglement
Quantum entanglement allows qubits to be strongly correlated with each other. When qubits are entangled, changing the state of one qubit affects the others instantly.
This enables a form of parallel computation that classical computers cannot easily replicate, making even small quantum systems powerful for certain problems.
3. Error Correction Challenges
Quantum systems are extremely sensitive to their environment. Noise and interference can easily cause errors, a problem known as quantum decoherence.
Because of this, researchers focus on building small systems with high-quality qubits rather than large systems with many unstable ones. Progress with even a few qubits is considered a major achievement.
4. Classical Communication (kbps to Gbps)
Classical communication systems such as the internet, Wi-Fi, and mobile networks transmit data using bits (0s and 1s). Speed is measured in:
- Kilobits per second (\(kbps\))
- Megabits per second (\(Mbps\))
- Gigabits per second (\(Gbps\))
These systems are optimized for transferring large amounts of data quickly and reliably.
5. What Quantum Computers Are Good For
Quantum computers are not designed to replace classical computers for everyday tasks like browsing the web or watching videos. Instead, they excel at specific problems such as:
- Cryptography and encryption
- Complex optimization problems
- Molecular and material simulations
6. Current State of Quantum Computing
Quantum computing is still in an early research stage. Current systems are often described as noisy and experimental.
Classical communication technologies, on the other hand, have been refined over decades and are already highly efficient and reliable.
Summary
- Qubits are powerful because of superposition and entanglement.
- A small number of qubits can outperform classical systems for certain tasks.
- Quantum computers are not about data transfer speed, but problem-solving ability.
- Classical systems are better for everyday communication and data transmission.