## Home -> Encyclopedia -> Encoding Shor’s algorithm in a quantum computer

Quantum computing, working on the principles of quantum mechanics, is different from classical computing. Two key quantum phenomena used in quantum computing are superposition and entanglement.

Superposition in quantum mechanics refers to the ability of a quantum system to exist in multiple states simultaneously. When a quantum system is in a ‘superposition of states’, it doesn’t exist in one particular state before measurement. Instead, the system is in a state that is a combination of all possible states, each with a certain probability.

Physically encoding Shor’s algorithm, a quantum algorithm for integer factorization, in a quantum system requires leveraging this principle of superposition. Here’s a simplified walkthrough:

- Initialize: The quantum computer is initialized with a superposition of all possible solutions to a problem – in the case of Shor’s algorithm, those solutions are the potential factors of a large number N.
- Quantum Fourier transform (QFT): Shor’s algorithm employs QFT, which allows the quantum state to be transformed such that the amplitude of each potential solution represents the likelihood of that solution being correct.
- Quantum interference: By applying quantum gates in the sequence prescribed by Shor’s algorithm, constructive and destructive interference is capitalized upon to diminish incorrect answers and promote right ones.
- Measure: After the computation, the quantum state collapses upon measurement, yielding the correct answer with a high probability. This is the result of the quantum superposition having weighted the amplitudes associated with each potential answer.

Physically, such processes would be enacted within a quantum computer wherein delicate quantum states are prepared within qubitsâ€”the quantum equivalents of classical bitsâ€”that exist in superposition until read out by a measurement process. The architecture of a quantum computer is thus built to facilitate the initialization, manipulation, and measurement of these qubits in a manner that allows the execution of quantum algorithms like Shor’s.

It’s important to note that due to the complex nature of maintaining superposition and controlling quantum states, practical and error-free implementation of Shor’s algorithm is still a challenge. Quantum hardware, error correction, and control techniques continue to be areas of active research.