Computing with highly mixed states

Ambainis, Andris; Schulman, Leonard J.; Vazirani, Umesh

Computing with highly mixed states

Authors

Ambainis, Andris

Schulman, Leonard J.

Vazirani, Umesh

Description

We consider quantum computing in the k-qubit model where the starting state of a quantum computer consists of k qubits in a pure state and n-k qubits in a maximally mixed state. We ask the following question: is there a general method for simulating an arbitrary m-qubit pure state quantum computation by a quantum computation in the k-qubit model? We show that, under certain constraints, this is impossible, unless m=O(k+ log n).
8 pages, 3 figures, to appear in proceedings of STOC'00