Complete control of a matter qubit using a single picosecond laser pulse

TL;DR

This paper demonstrates complete, high-fidelity control of a matter qubit in a quantum dot using a single ultrafast picosecond laser pulse, enabling universal quantum gate operations in a fraction of the qubit's coherence time.

Contribution

It introduces a method for full qubit control with a single ultrafast optical pulse, combining polarization and detuning to achieve arbitrary rotations.

Findings

Single-pulse qubit control with high fidelity

Universal gate operation achieved in picoseconds

Operation duration much shorter than coherence time

Abstract

We demonstrate for the first time that a matter physical two level system, a qubit, can be fully controlled using one ultrafast step. We show that the spin state of an optically excited electron, an exciton, confined in a quantum dot, can be rotated by any desired angle, about any desired axis, during such a step. For this we use a single, resonantly tuned, picosecond long, polarized optical pulse. The polarization of the pulse defines the rotation axis, while the pulse detuning from a non-degenerate absorption resonance, defines the magnitude of the rotation angle. We thereby achieve a high fidelity, universal gate operation, applicable to other spin systems, using only one short optical pulse. The operation duration equals the pulse temporal width, orders of magnitude shorter than the qubit evolution life and coherence times.