Revealing The Truth About Measuring A Quantum Bit
A glance at the measurement problem in quantum mechanics
This post is part of my new book: Hands-On Quantum Machine Learning With Python. Download the first chapters for free!
Quantum systems, such as quantum bits (qubits), are truly unique. They can be in superposition. The quantum superposition is a complex linear combination of their basis states |0⟩ and |1⟩. Once one observes the superposition, it collapses into one of the two basis states, resulting in either 0 or 1.
Even though this practical notion works pretty well for us in the absence of quantum noise, we need to deepen our understanding of what measuring a quantum system really means if we aim to run our quantum circuit on a real quantum computer.
And this leads us to one of the most difficult and controversial problems in quantum mechanics — the so-called measurement problem. The issue is that quantum mechanics only provides probabilities for the different possible outcomes in an experiment — it provides no mechanism by which the actual, finally observed result, comes about. There is always some inherent uncertainty as the German physicist Werner Heisenberg (Nobel Prize winner in 1932) articulated in 1927.
