Quantum leap

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====== This little thing called qubit ======
qubit (or qubit) stands for "quantum bit". In classical computation one uses **bits** for computation whereas **qubits** are used in quantum computation.\\
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===== What is a bit ? =====
A bit is used in classical computation to carry information. It is an electrical state with two levels, for instance 1 Volt and 4 Volts. At each state is associated a numeric value: 0 or 1. This is the basic of binary numeric system.\\
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In computers, classical microprocessors are running billions of operations using bits every second. \\
Therefore your computer encode all values into a series of bits. For instance the value 7 is encoded as follow in a byte (a byte is a set of 8 bits):
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**0 0 0 0 0 1 1 1**
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I won't explain how to encode and decode values from mathematical value to binary value, someone else already did that right:\\
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[[https://ccm.net/contents/57-binary-encoding]]
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You'll need to be ease with this to understand what follows.

==== What is a qubit ? ====
Classic bits are based on voltage associated to binary level 0 or 1, while qubits are based on quantum states.\\
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A qubit is a particle and has 2 base states noted |0> and |1> (called Dirac notation, we'll see that in detail later). As a quantum particle, it is in superposed state before being read. Like the cat that is both dead and alive before you open the box.\\
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Let's come back to the previous experiment:\\
{{ :en:1_particle.png?400 |}}
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When the particle leaves the source it is in superposed state: i.e. a probability combination of |0> and |1>. When it comes to the detector, decoherence happens and the particle collapses to a fixed state |0> or |1>.
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But manipulating qubits alone is quite useless. But the same way we can group bits into sets, qubits can be grouped into **registers**.\\
A quantum register is a set of several qubits we will use for computing.
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You must wonder what is the point of qubits since we get 0 or 1 in the end like bits... all is about probabilities in the middle. Be patient we'll see that later.
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Quantum leap

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