The Physical Implementation of Quantum Computation
David P. DiVincenzo
IBM T. J. Watson Research Center, Yorktown Heights, NY 10598 USA
After a brief introduction to the principles and promise of quantum information processing, the require-
ments for the physical implementation of quantum computation are discussed. These five requirements,
plus two relating to the communication of quantum information, are extensively explored and related to
the many schemes in atomic physics, quantum optics, nuclear and electron magnetic resonance spectro-
scopy, superconducting electronics, and quantum-dot physics, for achieving quantum computing.
The advent of quantum information processing, as an abstract concept, has given birth to a
great deal of new thinking, of a very concrete form, about how to create physical comput-
ing devices that operate in the hitherto unexplored quantum mechanical regime. The efforts
now underway to produce working laboratory devices that perform this profoundly new
form of information processing are the subject of this book.
In this chapter I provide an overview of the common objectives of the investigations
reported in the remainder of this special issue. The scope of the approaches, proposed and
underway, to the implementation of quantum hardware is remarkable, emerging from spe-
cialties in atomic physics , in quantum optics , in nuclear  and electron  mag-
netic resonance spectroscopy, in superconducting device physics , in electron physics ,
and in mesoscopic and quantum dot research . This amazing variety of approaches has
arisen because, as we will see, the principles of quantum computing are posed using the
most fundamental ideas of quantum mechanics, ones whose embodiment can be contem-
plated in virtually every branch of quantum physics.
The interdisciplinary spirit which has been fostered as a result is one of the most pleas-
ant and remarkable features of this field. The excitement and freshness that has been pro-
duced bodes well for the prospect for discovery, invention, and innovation in this endeavor.
The shortest of answers to this question would be, why not? The manipulation and trans-
mission of information is today carried out by physical machines ±computers, routers, scan-
ners, etc.), in which the embodiment and transformations of this information can be de-
scribed using the language of classical mechanics. But the final physical theory of the
world is not Newtonian mechanics, and there is no reason to suppose that machines follow-
ing the laws of quantum mechanics should have the same computational power as classical
machines; indeed, since Newtonian mechanics emerges as a special limit of quantum me-
chanics, quantum machines can only have greater computational power than classical ones.
The great pioneers and visionaries who pointed the way towards quantum computers,