Qubits

The qubit is short for “quantum bit.” While a bit can only be 0 or 1, a qubit can exist in more states. Qubits are surprising, fascinating, and powerful. They follow strange rules which may not initially seem natural to you. According to physics, these rules may be how nature itself works at the level of electrons and photons.

A qubit starts in an initial state. We use the notation |0⟩ and |1⟩ when we are talking about a qubit instead of the 0 and 1 for a bit. For a bit, the only non-trivial operation you can perform is switching 0 to 1 and vice versa. We can move a qubit’s state to any point on the sphere shown in the center of Figure 1.9. We can represent more information and have more room in which to work.

This sphere is called the Bloch sphere, named after physicist Felix Bloch. Things get even better when we have multiple qubits. One qubit holds two pieces of information, and two qubits hold four. That’s not surprising, but if we add a third qubit, we can represent eight pieces of information. Every time we add a qubit, we double its capacity. For 10 qubits, that’s 1,024. For 100 qubits, we can represent 1,267,650,600,228,229,401,496,703,205,376 pieces of information. This illustrates exponential behavior since we are looking at 2the number of qubits.

Some qubit features-

• While we can perform operations and change the state of a qubit, the moment we look at the qubit, the state collapses to 0 or 1. We call the operation that moves the qubit state to one of the two bit states “measurement.”
• Just as we saw that bits have meaning when they are parts of numbers and strings, presumably the measured qubit values 0 and 1 have meaning as data.
• Probability is involved in determining whether we get • 0 or 1 at the end. 
• We use qubits in algorithms to take advantage of their exponential scaling and other underlying mathematics. With these, we hope eventually to solve some significant but currently intractable problems. These are problems for which classical systems alone will never have enough processing power, memory, or accuracy.

Scientists and developers are now creating quantum algorithms for use cases in financial services and artificial intelligence (AI). They are also looking at precisely simulating physical systems involving chemistry. These may have future applications in materials science, agriculture, energy, and healthcare.