Book Image

Dancing with Qubits

By : Robert S. Sutor
5 (1)
Book Image

Dancing with Qubits

5 (1)
By: Robert S. Sutor

Overview of this book

Quantum computing is making us change the way we think about computers. Quantum bits, a.k.a. qubits, can make it possible to solve problems that would otherwise be intractable with current computing technology. Dancing with Qubits is a quantum computing textbook that starts with an overview of why quantum computing is so different from classical computing and describes several industry use cases where it can have a major impact. From there it moves on to a fuller description of classical computing and the mathematical underpinnings necessary to understand such concepts as superposition, entanglement, and interference. Next up is circuits and algorithms, both basic and more sophisticated. It then nicely moves on to provide a survey of the physics and engineering ideas behind how quantum computing hardware is built. Finally, the book looks to the future and gives you guidance on understanding how further developments will affect you. Really understanding quantum computing requires a lot of math, and this book doesn't shy away from the necessary math concepts you'll need. Each topic is introduced and explained thoroughly, in clear English with helpful examples.
Table of Contents (16 chapters)
Preface
13
Afterword

11.4 Decoherence

There are three important measurements that quantum computing researchers use to measure coherence time: T1, T2, and its cousin T2*. Let’s begin with T1. They are single qubit measurements and so we can use the Bloch sphere to discuss them. Their use goes back to Felix Bloch’s work on nuclear magnetic resonance (NMR) in the 1940s. [1]

11.4.1 T1

T1 goes under several names, all of them connected to the physics of various underlying quantum processes:

  • relaxation time,
  • thermal relaxation,
  • longitudinal relaxation,
  • spontaneous emission time,
  • amplitude damping, and
  • longitudinal coherence time.

It is related to the loss of energy as the quantum state decays from the higher energy |1 state to the |0 ground state. This energy is transmitted to, or leaked into, the environment and lost from the qubit. T1 is measured in seconds or some fraction thereof such as microseconds. A microsecond...