WEEK 3-4
INTRODUCTION TO QUANTUM COMPUTING
(Using the IBMQ Environment (https://quantum-computing.ibm.com))
Learning to build or program a quantum circuit requires the following knowledge
Qubit – A qubit (or quantum bit) is the quantum-mechanical analog of a classical bit. It has two basis states: |1⟩ and |0⟩ and can be in state |1⟩ or |0⟩ in a linear combination of both.
Superposition – This is when a qubit (or cubits) is in a linear combination of both states. A quantum computer consisting of n qubits can exist in a superposition of 2^n states. However, when this qubit is measured, it can only have one value. With information stored in superposition, some problems can be solved exponentially faster.
Entanglement -This is a phenomenon when the outcome of the measurement on one qubit is always correlated to the measurement on the other qubit. It enables correlations in systems.
I'll explain more concepts as I go on
Building a circuit in Quantum computers works (almost) the same way as the classical computer. We use logic gates as building blocks.
SIMPLE CIRCUIT EXAMPLES
1. Create a superposition state from a single input qubit.
Steps:
-prepare a qubit in the state |0⟩
-Apply a Hadamard Gate (This gate is a single qubit operation that maps the basis state |0⟩ to ( |0⟩+|1⟩ )/2 and |1⟩ to ( |0⟩-|1⟩ )/2 creating an equal superposition of the two states.)
If we measure this circuit, we get only one basis value with a 50% probability.
- Entangle two qubits
-Use a CNOT gate to entangle a target qubit (q0) with a control qubit (q0). The CNOT gate does logic calculations to ensure that the q1 correlates to q0 when measured.
When we measure the values of the two qubits after the circuit is run, even though their values are random measurements, they will correlate to be the same value.
References
- Coles, P. J., Eidenbenz, S., Pakin, S., Adedoyin, A., Ambrosiano, J., Anisimov, P., ... & Gunter, D. (2018). Quantum algorithm implementations for beginners. arXiv, arXiv-1804. 2.https://quantum-computing.ibm.com/docs/iqx/guide/