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arXiv · 1606.08382

Tunable inductive coupling of superconducting qubits in the strongly nonlinear regime

Dvir Kafri·Chris Quintana·Yu Chen·Alireza Shabani·John M. Martinis·Hartmut Neven
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Abstract

For a variety of superconducting qubits, tunable interactions are achieved through mutual inductive coupling to a coupler circuit containing a nonlinear Josephson element. In this paper we derive the general interaction mediated by such a circuit under the Born-Oppenheimer Approximation. This interaction naturally decomposes into a classical part, with origin in the classical circuit equations, and a quantum part, associated with the coupler's zero-point energy. Our result is non-perturbative in the qubit-coupler coupling strengths and in the coupler nonlinearity. This can lead to significant departures from previous, linear theories for the inter-qubit coupling, including non-stoquastic and many-body interactions. Our analysis provides explicit and efficiently computable series for any term in the interaction Hamiltonian and can be applied to any superconducting qubit type. We conclude with a numerical investigation of our theory using a case study of two coupled flux qubits, and in particular study the regime of validity of the Born-Oppenheimer Approximation.

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Dvir Kafri, Chris Quintana, Yu Chen, Alireza Shabani, John M. Martinis, Hartmut Neven. 2017-07-05. Tunable inductive coupling of superconducting qubits in the strongly nonlinear regime. https://doi.org/10.1103/physreva.95.052333

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