Controllable exchange coupling between two singlet-triplet qubits

TL;DR

This paper investigates how to control exchange interactions between two singlet-triplet qubits in a quadruple quantum dot system, enabling the implementation of quantum gates like CNOT.

Contribution

It derives an effective Ising-type interqubit coupling from the quantum dot Hamiltonian under magnetic fields, providing a basis for quantum gate operations.

Findings

Effective Ising-type coupling can be tuned via quantum dot parameters.

Controllable coupling enables entanglement and quantum gate operations.

The model applies under strong magnetic fields and inhomogeneous micro-magnetic fields.

Abstract

We study controllable exchange coupling between two singlet-triplet qubits. We start from the original second quantized Hamiltonian of a quadruple quantum dot system and obtain the effective spin-spin interaction between the two qubits using the projection operator method. Under a strong uniform external magnetic field and an inhomogeneous local micro-magnetic field, the effective interqubit coupling is of the Ising type, and the coupling strength can be expressed in terms of quantum dot parameters. Finally, we discuss how to generate various two-qubit operations using this controllable coupling, such as entanglement generation, and controlled-NOT gate.