Understanding Quantum Mechanics Superposition and Entanglement

Understanding Quantum Mechanics Superposition and Entanglement

If you know one thing about quantum mechanics, it’s that Schrodinger’s cat is both dead and alive. This is what physicists call a “superposition”. But what does this really mean? And what does it have to do with entanglement? This video explains it.

Qubits can be in a superposition of both the basis states $|0⟩$ and $|1⟩$. When a qubit is measured (to be more precise: only observables can be measured), the qubit will collapse to one of its eigenstates and the measured value will reflect that state. For example, when a qubit is in a superposition state of equal weights, a measurement will make it collapse to one of its two basis states $|0⟩$ and $|1⟩$ with an equal probability of 50% $|0⟩$ is the state that when measured, and therefore collapsed, will always give the result 0. Similarly, $|1⟩$ will always convert to 1.

Quantum superposition is fundamentally different from superposing classical waves. A quantum computer consisting of n qubits can exist in a superposition of 2^n states: from $|000...0⟩$ to $|111...1⟩$. In contrast, playing n musical sounds with all different frequencies, can only give a superposition of n frequencies. Adding classical waves scales linear, where the superposition of quantum states is exponential.