Quantum Computation and Quantum Information: Quantum computers: physical realization
This chapter explores some of the guiding principles and model systems for physical implementation of quantum information processing devices and systems and briefly describes the physical apparatus, the Hamiltonian, means for controlling the system to perform quantum computation, and its principal drawbacks.
Abstract
Computers in the future may weigh no more than 1.5 tons. – Popular Mechanics, forecasting the relentless march of science, 1949 I think there is a world market for maybe five computers. – Thomas Watson, chairman of IBM, 1943 Quantum computation and quantum information is a field of fundamental interest because we believe quantum information processing machines can actually be realized in Nature. Otherwise, the field would be just a mathematical curiosity! Nevertheless, experimental realization of quantum circuits, algorithms, and communication systems has proven extremely challenging. In this chapter we explore some of the guiding principles and model systems for physical implementation of quantum information processing devices and systems. We begin in Section 7.1 with an overview of the tradeoffs in selecting a physical realization of a quantum computer. This discussion provides perspective for an elaboration of a set of conditions sufficient for the experimental realization of quantum computation in Section 7.2. These conditions are illustrated in Sections 7.3 through 7.7, through a series of case studies, which consider five different model physical systems: the simple harmonic oscillator, photons and nonlinear optical media, cavity quantum electrodynamics devices, ion traps, and nuclear magnetic resonance with molecules. For each system, we briefly describe the physical apparatus, the Hamiltonian which governs its dynamics, means for controlling the system to perform quantum computation, and its principal drawbacks.