# The Postulates of Quantum Mechanics

Let’s discuss the postulates of quantum mechanics and see how they form the basis of what we have learned so far.

## We'll cover the following

Let’s begin by summarizing what we know about quantum states so far. In previous lessons, we’ve seen that quantum states are **vectors** in **2-D complex vector space**. These **bras** (row vectors) and **kets** (column vectors) depict the **possible locations** that we might find a qubit in. We form a **multi-qubit system** by taking the **tensor product** of the state vectors of single qubits. To know which state a qubit is in, we must **measure** it. We measure it using complex hardware in the **computational basis** and transfer the state information into **classical bits** that we can read. Which state we end up getting is entirely **probabilistic** until the first measurement. The **complex amplitudes dictate this probability** associated with the **state vectors**. And lastly, **no measurement on the system is gentle** enough to leave the qubit in an unperturbed state.

All these ideas take root from the postulates at the heart of quantum mechanics. We’ve already discussed a bunch of them, as you’ll notice. But going through them in a sequence revises the concepts we have learned so far and makes it easier for us to understand the ones we haven’t discussed.

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