Quantum computers use superposition to perform calculations on multiple possible combinations of qubit values simultaneously. The key idea is that the quantum computer can manipulate the quantum state of the qubits in a way that the information about all possible combinations is encoded in the superposition.
When qubits are in a superposition, they exist in a coherent combination of their basis states, such as |0⟩ and |1⟩. The superposition allows qubits to hold multiple values simultaneously, representing different computational states. For example, with n qubits, the quantum computer can represent 2^n computational states in parallel.
Quantum algorithms and operations take advantage of this superposition to perform computations. By applying quantum gates and operations to the qubits, the quantum computer can manipulate and process the information contained in the superposition. These operations can be designed to exploit interference effects, where the probability amplitudes of different computational states can interfere constructively or destructively.
While it is true that measurement causes the collapse of the wave function and yields a definite value for the qubit, quantum computations are not solely reliant on the final measurement outcomes. Intermediate steps and computations can be performed without collapsing the entire quantum state. Quantum algorithms are carefully designed to harness the interference and computational power of superposition, allowing calculations to be carried out on all possible combinations of qubit values simultaneously.
In most cases, the final measurement is performed at the end of the quantum computation to obtain the desired output. The measurement collapses the quantum state of the qubits into a classical state, providing a specific outcome. The probabilities of different measurement outcomes are determined by the amplitudes of the quantum state. By performing multiple measurements and analyzing the statistical distribution of outcomes, the quantum computer can extract the solution to the computational problem it was designed to solve.
So, while measurement collapses the qubits' superposition, the power of quantum computation lies in the ability to perform calculations on all possible combinations of qubit values simultaneously before the final collapse and extraction of the result.