Ancilla-Driven Universal Quantum Computation

Understand

We propose a method of manipulating a quantum register remotely with the help of a single ancilla that steers the evolution of the register.

• The fully controlled ancilla qubit is coupled to the computational register solely via a fixed unitary two-qubit interaction, E, and then measured in suitable bases.
• We characterize all interactions E that induce a unitary, step-wise deterministic measurement back-action on the register sufficient to implement any arbitrary quantum channel.
• Our scheme offers significant experimental advantages for implementing computations, preparing states and performing generalized measurements as no direct control of the register is required.