Z-basis measurements using mixed parity and direct readout

TL;DR

This paper introduces a method for performing Z-basis measurements on a three-qubit spin register using a Pauli exclusion-based readout, reducing physical overhead and enabling full state tomography including GHZ states.

Contribution

The authors develop a Z-basis measurement technique for a multi-qubit register that eliminates the need for dedicated ancilla qubits, using tomography and simulations to validate the approach.

Findings

Successful Z-basis measurements of a three-qubit register

Simulation insights into error sources in tomography

Quantum state tomography performed on a GHZ state

Abstract

Many architectures for quantum information processing rely on qubits dedicated for the readout of a larger quantum register. These ancilla readout qubits present a physical overhead not contributing to the computational resource. A common implementation in spin qubit architectures is the readout schemes based on Pauli exclusion of charges confined in a double quantum dot, with one dot serving as the ancilla qubit. Here, using a three-qubit spin register and a Pauli exclusion-based readout, we present z-basis measurements of the entire register constructed with tomography, eliminating the physical overhead. We validate our approach with simulations which provide insight into potential sources of errors in the reconstruction. We also demonstrate our reconstruction by performing quantum state tomography on a GHZ state of a spin-qubit based device.