Book contents
- Frontmatter
- Contents
- Preface
- 1 Bits and quanta
- 2 Qubits
- 3 States and observables
- 4 Distinguishability and information
- 5 Quantum dynamics
- 6 Entanglement
- 7 Information and ebits
- 8 Density operators
- 9 Open systems
- 10 A particle in space
- 11 Dynamics of a free particle
- 12 Spin and rotation
- 13 Ladder systems
- 14 Many particles
- 15 Stationary states in 1-D
- 16 Bound states in 3-D
- 17 Perturbation theory
- 18 Quantum information processing
- 19 Classical and quantum entropy
- 20 Error correction
- Appendix A Probability
- Appendix B Fourier facts
- Appendix C Gaussian functions
- Appendix D Generalized evolution
- Index
2 - Qubits
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- 1 Bits and quanta
- 2 Qubits
- 3 States and observables
- 4 Distinguishability and information
- 5 Quantum dynamics
- 6 Entanglement
- 7 Information and ebits
- 8 Density operators
- 9 Open systems
- 10 A particle in space
- 11 Dynamics of a free particle
- 12 Spin and rotation
- 13 Ladder systems
- 14 Many particles
- 15 Stationary states in 1-D
- 16 Bound states in 3-D
- 17 Perturbation theory
- 18 Quantum information processing
- 19 Classical and quantum entropy
- 20 Error correction
- Appendix A Probability
- Appendix B Fourier facts
- Appendix C Gaussian functions
- Appendix D Generalized evolution
- Index
Summary
The photon in the interferometer
This chapter introduces many of the ideas of quantum theory by exploring three specific “case studies” of quantum systems. Each is an example of a qubit, a generic name for the simplest type of quantum system. The concepts we develop will be incorporated into a rigorous mathematical framework in the next chapter. Our business here is to provide some intuition about why that mathematical framework is reasonable and appropriate for dealing with the quantum facts of life.
Interferometers
In Section 1.2 we discussed the two-slit interference experiment with a single photon. In that experiment, the partial waves of probability amplitude were spread throughout the entire region of space beyond the two slits. It is much easier to analyze the situation in an interferometer, an optical apparatus in which the light is restricted to a finite number of discrete beams. The beams may be guided from one point to another, split apart or recombined as needed, and when two beams are recombined into one, the result may show interference effects. At the end of the interferometer, one or more sensors can measure the intensity of various beams. (A beam is just a possible path for the light, so there is nothing paradoxical in talking about a beam of zero intensity.) Figure 2.1 shows the layout of a Mach–Zehnder interferometer, which is an example of this kind of apparatus.
- Type
- Chapter
- Information
- Quantum Processes Systems, and Information , pp. 15 - 46Publisher: Cambridge University PressPrint publication year: 2010