# Nuclear-Spin Qubits A **nuclear-spin qubit** encodes the two [[Qubit|qubit]] states in the orientation of an atom's *nuclear* spin rather than in its electronic energy levels. ## First principles An atomic nucleus can carry angular momentum — spin — which can point in one of two distinguishable directions in a magnetic field. Label them $|0\rangle$ and $|1\rangle$. Why use the nucleus instead of the electrons? Because the nucleus is buried deep inside the atom and is magnetically "quiet." It couples only weakly to electric fields and to the environment, so the information stored there is disturbed very slowly. The price is that the same weak coupling makes the spin harder to control and read out quickly. > [!intuition] A vault versus a workbench > Electronic states are like a workbench: easy to manipulate but exposed. The nuclear spin is like a vault: slow to open, but what you store inside stays safe for a long time. ## Why it matters - Nuclear spins give some of the **longest [[Coherence Time|coherence times]]** of any qubit, meaning the quantum state survives for seconds or longer. - Long coherence is precious for [[Quantum Error Correction]], which must run for many cycles ([[Syndrome Extraction]]) without the underlying data decaying. - In [[Neutral Atom Qubits|neutral-atom]] hardware, nuclear-spin encodings combine the platform's natural isolation with extra protection from the nucleus. ## Related - [[Qubit]] - [[Coherence Time]] - [[Neutral Atom Qubits]] - [[Quantum Error Correction]]