Quantum computer with mixed states and four-valued logic
Vasily Evgenevich Tarasov · Journal of Physics A Mathematical and General · 2002
In this paper we discuss a model of quantum computer in which a state is an operator of density matrix and gates are general quantum operations, not necessarily unitary. A mixed state (operator of density matrix) of n two-level quantum systems is considered as an element of 4 n -dimensional operator Hilbert space (Liouville space). It allows us to use a quantum computer model with four-valued logic. The gates of this model are general superoperators which act on n -ququat state. Ququat is a quantum state in a four-dimensional (operator) Hilbert space. Unitary two-valued logic gates and quantum operations for an n -qubit open system are considered as four-valued logic gates acting on n -ququats. We discuss properties of quantum four-valued logic gates. In the paper we study universality for quantum four-valued logic gates.