Quantum Computing vs Classical Computing (2024)

The Strange World of Quantum Physics

To understand quantum computing, we first have to dip our toes into the often counterintuitive rules of the quantum realm. Classical physics that governs everyday objects works very logically a ball can be here or there, but not both at the same time. In contrast, the quantum world plays by different rules.

Quantum Computing vs Classical Computing

The Superposition Principle

One example is the superposition principle. A quantum bit or qubit can exist in a superposition of both 0 and 1 at the same time. It’s similar to being in two places at once a uniquely quantum effect with no analogy in everyday life.


Another property that drives quantum computing is entanglement. When two qubits become entangled, their states become interdependent, no matter the physical distance separating them. Einstein dubbed this “spooky action at a distance” changing one qubit instantaneously affects the other.

Harnessing Quantum Weirdness

These strange quantum properties don’t appear on everyday scales. But quantum computer scientists have developed ingenious ways to not only preserve these effects, but to exploit them for computational purposes. The result? Quantum computers with entirely new capabilities compared to classical devices.

Qubits Galore

One advantage comes from the superposition principle. While a classical bit encodes either a 0 or 1, a quantum bit can encode 0, 1, or a superposition of both simultaneously. Ten qubits could then represent 1024 different numbers at once exponential information density compared to 10 classical bits.

Quantum Parallelism

This exponential information encoding enables massive parallelism for certain computational tasks. While a classical computer would have to cycle through possibilities serially, a quantum computer can essentially try all permutations in parallel.

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Grover’s Algorithm

For example, Grover’s quantum search algorithm leverages quantum parallelism to achieve quadratically faster search times than is classically possible. Like being able to search many books at once.

Shor’s Algorithm

Number factoring also benefits. Shor’s quantum algorithm can factor extremely large numbers exponentially faster than classical algorithms. This has implications for breaking current encryption schemes like RSA that rely on the complexity of factoring large primes. Grover’s Algorithm vs Shor’s Algorithm

Quantum Tunneling

In addition, quantum systems can leverage effects like quantum tunneling to traverse energy barriers that would trap classical systems. Just like a car couldn’t drive through a mountain, yet an electron can occasionally quantum tunnel to the other side a purely nonclassical effect.

Quantum Annealing

Other quantum effects like entanglement can be harnessed in optimization algorithms like quantum annealing. Here, quantum fluctuations guide the system to settle into global energy minimum states that correspond to optimal solutions.

NISQ Devices

Current NISQ (Noisy Intermediate Scale Quantum) devices already implement some of these algorithms imperfectly with just 50-100 qubits. As quantum computers are refined and expanded, we will likely see game changing speedups for specialized tasks out of reach of classical hardware.

Limits of Quantum Computing

However, we shouldn’t expect quantum computers to replace classical devices for all applications. The strange effects underlying quantum computing also make it more prone to errors and fragile at scale. There are also strict limits around the types of problems suited to quantum acceleration.

Quantum Errors

For one, those helpful quantum effects like superposition and entanglement that power quantum computers are extraordinarily fragile. The slightest interactions with the external environment even the presence of a single photon can cause the quantum state to “decohere”, losing quantum properties.

Error Correction

To achieve accurate results, quantum computers will need extensive error correction. Current NISQ devices don’t yet have sufficient error correction, limiting their computational power until more robust systems are developed.

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Hybrid Algorithms

In addition, many real-world problems don’t map neatly to available quantum algorithms. The path forward may involve hybrid classical-quantum algorithms with each hardware performing the functions it’s best at.

Quantum Cloud Computing

Rather than replacing all classical hardware, quantum computers are more likely to become a specialized acceleration resource. Engineers envision quantum cloud computing architectures where users can access quantum processors alongside classical cloud computing and storage.

Quantum Networks

Distributing quantum information for cloud computing brings its own challenges. Quantum networks that can transmit quantum data will need to be developed alongside quantum computers. Technologies like quantum repeaters may one day help build long-range quantum communication.

Quantum Cryptography

While quantum computers threaten to break classical encryption, quantum tech also provides more secure alternatives. Quantum cryptography techniques like quantum key distribution leverage quantum physics to enable secure communication channels. So in some ways, quantum mechanics breeds both the virus and the cure when it comes to cryptography and computing.

When Will Quantum Computers Beat Classical Computers?

Predicting the exact timeline is difficult with a technology as dynamic as quantum computing. But while current NISQ devices have limited computational power, they are rapidly improving. Analysts predict quantum computers could break current encryption within the next 10-30 years. Other specialized tasks could demonstrate quantum supremacy even sooner.

Quantum Computing Outlook

In the future, don’t expect quantum computers to replace all classical hardware or your personal laptop any time soon. Like other accelerators such as graphical processing units (GPUs), quantum processors are likely to become a supplementary resource for specialized tasks while classical devices continue handling everyday computing. Large-scale universal quantum computing may still be decades away.

But while the future timeline is cloudy, the strange world opened up by quantum mechanics shows enormous promise. Quantum devices taking advantage of uniquely quantum phenomena like superposition, entanglement, and tunneling hint at a coming computing revolution we’ve only begun glimpsing.

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In summary, quantum computing leverages strange quantum effects like superposition, entanglement, and tunneling to achieve capabilities not possible on classical devices. Algorithms tailored for quantum hardware offer exponential speedups for specialized tasks like search, factoring, and optimization. However, quantum states are extraordinarily fragile, and real-world problems don’t always map neatly to quantum algorithms. Quantum processors will likely become specialized co-processors alongside classical hardware, accelerating suitable workloads through cloud access. The future prospects remain uncertain, but exploitable quantum effects suggest an approaching era where quantum and classical systems work cooperatively not competitively to expand computing possibilities.


What is superposition in quantum computing?

Superposition describes how quantum bits (qubits) can encode a 0, 1, or both simultaneously – a purely quantum effect. This allows exponential information density compared to classical bits.

What is quantum entanglement?

Quantum entanglement occurs when qubits become correlated such that changing one particle also instantaneously changes the other, even over large distances. This enables quantum effects to be distributed for computing.

How is quantum computing different than classical computing?

Quantum computing harnesses strange quantum physics properties like superposition, allowing certain tasks like search, factoring, and optimization to be performed exponentially faster than is classically possible. This expanded computing capability differentiates quantum vs classical hardware.

What are the limits of quantum computing?

Sensitivity to disturbances in their environment causes quantum states to “decohere”, introducing errors. Quantum algorithms also do not efficiently solve all problems, so hybrid classical quantum computing will likely be needed to apply each system appropriately.

When will quantum computers outperform classical computers?

Outperforming classical computers at specialized tasks could happen in the next decade, but noise free, universal quantum computing that replaces all key classical workloads is still likely decades away from realization.

MK Usmaan