Week 13 - my notes
Table of Contents
Week 13 - Introduction to Multi-Qubit circits
Recap
Quantum Gates
- X gate, H gate, Z gate, and rotation X and Z gates were seen last week
Introduction to Multi-Qubit circuits
- You can have single-qubit gates (ones that are applied to one qubit only)
- You can have controlled gates (applied to multipled qubits at a time)
Single-Qubit gates
- Whatever you do with one qubit will not be applied to any other qubit
The controled gate
- It changes the target qubit based on the state of the control qubit
- CX gate is the most commonly used control gate, CZ gate will be studied later on!
CX gate rules:
- The control qubit is always unaffected
- If the control qubit is in the \(0\rangle\) state, no gate is applied on the target qubit
- If the control qubit is in the \(1\rangle\) state, an X gate is applied on the target qubit
- Controled gates do not imply a measurement
Creating entanglement
- The controled gate creates the perfect situation for an entanglement - the state of a qubit is controlled by another qubit in a state of superposition
- You create this superpostion by first applying the H gate, then you can use the controlled gate, thus getting an entanglement
Guest speaker:
Dr. Olivia Lanes, North America Lead, Qiskit and Education
- From most of the history, to access a quantum computer, you had to build and mantain it yourself.
- Five years ago, it all changed. Now we have an open source community around it.
- She likes her job because her days never look like the previous one
- She is trying to put more people in their reaserch programs - it gives you access to more powerful QCs - but it’s only available to university professors
Resources
Qiskit textbook page on multiple qubits and entanglement https://qiskit.org/textbook/ch-gates/multiple-qubits-entangled-states.html Notes on gates, states, circuits https://threeplusone.com/pubs/on_gates.pdf Implementation of a CX gate using photonic qubits https://www.nature.com/articles/s41467-018-03059-5