Directly accessible entangling gates for capacitively coupled singlet-triplet qubits

TL;DR

This paper analyzes the Hamiltonian of capacitively coupled singlet-triplet qubits to identify which entangling gates can be directly generated with a single pulse, revealing the potential for simple implementation of gates like iSWAP and CNOT.

Contribution

It provides a first-principles analysis of the Hamiltonian's nonlocal properties, showing how different biasing modes enable direct generation of key entangling gates.

Findings

In one biasing mode, the Hamiltonian can directly produce a wide range of entangling gates including iSWAP.

For all biasing modes, a CNOT gate can be generated directly from the Hamiltonian.

The analysis highlights a simple form of the Hamiltonian under certain biasing conditions that facilitates gate implementation.

Abstract

The recent experimental advances in capacitively coupled singlet-triplet qubits, particularly the demonstration of entanglement, opens the question of what type of entangling gates the system's Hamiltonian can produce directly via a single square pulse. We address this question by considering the system's Hamiltonian from first principles and using the representation of its nonlocal properties in terms of local invariants. In the analysis we include the three different ways in which the system can be biased and their effect on the generation of entangling gates. We find that, in one of the possible biasing modes, the Hamiltonian has an especially simple form, which can directly generate a wide range of different entangling gates including the iSWAP gate. Moreover, using the complete form of the Hamiltonian we find that, for any biasing mode, a CNOT gate can be generated directly.