9:28in productionCh. 1 · What a qubit actually is/ 9:28 · ceiling 15 min
Hardware · Security
Quantum computing
Quantum computing is not a faster computer—it’s a different kind of calculator, built for problems classical machines were never meant to solve.
Quantum computing uses qubits—units exploiting superposition, interference, and entanglement—to process information. It promises exponential speedups on specific problems like factorisation and quantum simulation. But current systems are noisy, error-prone, and lack error correction. They run no practical applications. Their value lies in redefining computational limits—not delivering tools.
A qubit is not a faster bit—it’s a unit that holds multiple states at once.
2:14
How quantum computation works
Quantum speed comes from wave interference—not parallel processing.
3:43
Where quantum wins (and where it doesn’t)
Exponential speedup applies only to narrow, structured problems—not general computing.
5:54
Why quantum answers are uncertain
Measurement collapses superposition into a single probabilistic outcome—no guarantees.
Worth your time?
Yes. Study the whole thing.
2.5/ 5
What works
Shor’s algorithm on small integers
Grover’s search on synthetic datasets
quantum simulation of simple molecular structures
What does not
replace classical computers
run general-purpose software
deliver production-ready results
solve everyday computational problems
Study it if
cryptographers
materials scientists
theoretical computer scientists
Skip it if
software engineers building web apps
data analysts using Python
enterprise IT teams
The written brief1 min read
What it is and the problem it solves
Quantum computing is a computational paradigm that uses quantum states to represent and process information. It solves problems intractable for classical machines—specifically integer factorisation, unstructured search, and quantum simulation—but only in theory or narrow demonstration.
How it works
Quantum computing processes information using qubits, which exist in quantum superposition—unlike classical bits. It exploits superposition, interference, and entanglement. Wave interference amplifies the probability of desired measurement outcomes. Measuring a qubit yields one of two states probabilistically.
What works
Small-scale quantum algorithms work in controlled settings: Shor’s algorithm factors integers; Grover’s algorithm searches unstructured data. Google’s 2019 Sycamore experiment achieved quantum supremacy—a milestone confirming quantum speedup on a contrived task—but not practical utility.
What does not
Quantum computers do not run general-purpose software. They do not replace classical computers. They cannot execute everyday tasks like web browsing or document editing. Error correction remains unsolved. Decoherence limits computation time. Scalability is unproven.
What it changes
It changes how we model physical systems at quantum scale—and threatens public-key cryptography. A large-scale quantum computer could break widely used encryption schemes and aid physicists in performing physical simulations. That threat drives post-quantum cryptography research now.
Is it worth your time
Not yet for applied work. No quantum computer solves real-world problems faster than classical alternatives. Current systems are experimental, noisy, and require cryogenic cooling. They deliver scientific milestones—not production tools.