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Physical Review A

Creating cluster states in flux qubits with XY -type exchange interactions

Zu-Rong Zhang, Chunyan Li, Chun-Wang Wu, Hong‐Yi Dai, Cheng-Zu Li

Published Oct 21, 2013• 4 citations
Publisher

Abstract

We propose a theoretical scheme to generate flux-qubit clusters using $\mathit{XY}$ interactions. In our scheme, two neighboring qubits are coupled via a dc superconducting quantum interference device (SQUID). All flux qubits are always biased at their optimal points. The $\mathit{XY}$ interaction can be controlled by the bias current applied to the SQUID for the two coupled qubits with the same resonance frequencies or by the frequency of a microwave pulse applied to the SQUID for the two coupled qubits with unequal resonance frequencies. The generation of a $d$-dimensional cluster state needs only $2d$ steps. Existing technology allows us to rapidly modulate the bias current and easily control the frequency of the pulse, and thus our scheme is experimentally feasible.

DOI
10.1103/physreva.88.044303

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The ability to switch the coupling between quantum bits (qubits) on and off is essential for implementing many quantum-computing algorithms. We demonstrated such control with two flux qubits coupled together through their mutual inductances and through the dc superconducting quantum interference device (SQUID) that reads out their magnetic flux states. A bias current applied to the SQUID in the zero-voltage state induced a change in the dynamic inductance, reducing the coupling energy controllably to zero and reversing its sign.
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We report measurements on two superconducting flux qubits coupled to a readout superconducting quantum interference device (SQUID). Two on-chip flux bias lines allow independent flux control of any two of the three elements, as illustrated by a two-dimensional qubit flux map. The application of microwaves yields a frequency-flux dispersion curve for 1- and 2-photon driving of the single-qubit excited state, and coherent manipulation of the single-qubit state results in Rabi oscillations and Ramsey fringes. This architecture should be scalable to many qubits and SQUIDs on a single chip.
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