In quantum computing, the process of reading or measuring a qubit indeed involves a delicate trade-off. Measurement disrupts the quantum state of a qubit, and in the case of entangled qubits, it can destroy the entanglement between them. This phenomenon is known as the collapse of the wavefunction.
When a qubit is measured, it collapses into one of its basis states (0 or 1) with a probability determined by the amplitudes of the superposition. The act of measurement effectively "chooses" one of the possible states for the qubit, and the information obtained becomes classical and deterministic.
The measurement process interacts with the qubit and extracts information from it. This interaction causes disturbance, or decoherence, which introduces errors and disrupts the quantum state. As a result, the measured qubit loses its coherence and becomes a classical bit.
The destruction of entanglement during measurement is indeed a challenge in quantum computing. However, it is important to note that while measuring an entangled pair of qubits destroys their entanglement, the entangled state itself can still be used for various computational tasks before the measurement occurs. For example, entangled qubits can be manipulated and undergo quantum gates to perform quantum algorithms or protocols.
Furthermore, researchers are actively exploring techniques to mitigate the impact of measurement on quantum systems. One approach is to design error-correction codes and fault-tolerant protocols that can protect quantum states from decoherence and measurement errors. These techniques aim to maintain the integrity of the quantum information and preserve entanglement even in the presence of noise and imperfect measurements.
In summary, the process of reading or measuring a qubit in quantum computing does disrupt the quantum state and can destroy entanglement. However, this does not negate the potential computational advantages of quantum systems, as techniques such as error correction and fault tolerance are being developed to overcome these challenges and enable the use of quantum information effectively.