Design of Novel Coupling Mechanisms between Superconducting Flux Qubits

TL;DR

This paper introduces new coupling mechanisms for superconducting flux qubits, utilizing a numerical method to derive effective Hamiltonians and demonstrating the ability to produce non-stoquastic Hamiltonians in strong coupling regimes.

Contribution

It develops a numerical Schrieffer-Wolff transformation method and analytically studies capacitive and inductive couplings between 3JJQ flux qubits, including non-tunable and tunable couplings.

Findings

Effective Hamiltonians for coupled qubits derived

Capacitive coupling via non-tunable capacitor demonstrated

Inductive coupling via tunable Josephson junction shown to produce non-stoquastic Hamiltonians

Abstract

We have analyzed and proposed coupling mechanisms between Three Josephson Junction Flux Qubits (3JJQ). For this, we have developed a numerical method to extract the effective Hamiltonian of a system of coupled qubits via the Schrieffer-Wolff transformation (SWT). We then give a comprehensive introduction to the 3JJQ, and study it analytically by approximating its potential with a Harmonic well. With a clear understanding of the 3JJQs, we use the SWT to gain intuition about their effective dipolar interaction with the electromagnetic field, and use that intuition to propose and study analytically and numerically the capacitive coupling of two 3JJQs via a non-tunable capacitor, and the inductive coupling of two 3JJQs via a tunable Josephson Junction (dc-SQUID), showing that we are able to reproduce non-stoquastic Hamiltonians in the strong-coupling regime.