SUBHASH KAK

Department of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, LA 70803-5901, USA

Email: kak@ee.lsu.edu

Quantum computing algorithms require that the quantum register be initially present in a superposition state.  To achieve this, we consider the practical problem of creating a coherent superposition state of several qubits.   We show that the constraints of quantum statistics require that the entropy of the system be brought down when  several independent qubits are assembled together.   In particular, we have: (i) not all initial states are realizable as pure states; (ii) the temperature of the system must be reduced. These factors, in addition to decoherence and sensitivity to errors, must be considered in the implementation of quantum computers.

Keywords:  Quantum computing; initializing a quantum state.

Pacs Nos.  03.65.Bz