文档介绍：COHERENT QUANTUM CONTROL OF A-ATOMS
THROUGH THE STOCHASTIC LIMIT
L. ACCARDI
Centro Vito Volterra, Universita di Roma "Tor Vergata", 00133, Via Columbia
2, Roma, Italy
E-mail: ******@
S. V. KOZYREV
Steklov Mathematical Institute, Russian Academy of Sciences, Gubkin St. 8,
119991, Moscow, Russia
E-mail: ******@
A. N. PECHEN
Steklov Mathematical Institute, Russian Academy of Sciences, Gubkin St. 8,
119991, Moscow, Russia
E-mail: ******@
We investigate, using the stochastic limit method, the coherent quantum control of
a 3-level atom in A-configuration interacting with two laser fields. We prove that,
in the generic situation, this interaction entangles the two lower energy levels of
the atom into a single qubit, . it drives at an exponentially fast rate the atom
to a stationary state which is a coherent superposition of the two lower levels. By
applying to the atom two laser fields with appropriately chosen intensities, one can
create, in principle, any superposition of the two levels. Thus relaxation is not
necessarily synonymous of decoherence.
1. Introduction
Preparation of atoms and molecules in a predefined state plays an important
role in modern atomic and molecular physics, in particular in atom optics
and quantum information. The difficulty of the problem consists in the fact
that, in order to control a system, one has to interact with it, but interaction
introduces dissipative effects and hence, at least generically, decoherence.
In this note we prove, in specific but important and physically realizable
example, that in some cases dissipation can generate coherence.
One of the ways to drive the system, atom or molecule, to the desired
1
2
state is to exploit its interaction with laser pulses, ., to use the coher•
ent laser control or laser-induced population transfer 1>2. In this approach
monochromatized and near-resona