Quantum Computation by Spin Parity Measurments with Encoded Spin Qubits

Joint measurements of two-Pauli observables are a powerful tool for both the control and protection of quantum information. By following a simple recipe for measurement choices, single- and two- qubit rotations using two-Pauli parity and single qubit measurements are guaranteed to be unitary whilst requiring only a single ancilla qubit. Measurement based gates of this form keep the encoded qubits in their initial physical qubits and may be repeated unlike with resource state based measurement based quantum computing. This language for measurement based quantum computing is shown to be directly applicable to encoded double quantum dot singlet-triplet spin qubits, by measuring spin-parity between dots from neighboring qubits. Along with exchange interaction, a complete, leakage free, measurement based gate set can shown, up to a known Pauli correction. Measurements of this form provide a direct upgrade to previous methods of measurement based gates [1] by requiring exchange pulses and ancilla qubits. Both theoretical exact spin-parity measurements and previously experimentally demonstrated inexact spin-parity measurements are shown to useful for implementing the proposed measurement based scheme. This new method of spin qubit control offers a leakage-free, low resource overhead implementation of measurement-based control that is viable on current spin qubit



[1] "Hybrid Exchange–Measurement-Based Qubit Operations in Semiconductor Double-Quantum-Dot Qubits”, Matthew Brooks and Charles Tahan, Phys. Rev. Appl. 16, 064019 (2021)