Monday, July 22, 2013

1307.5075 (Arijeet Pal et al.)

Driven nonlinear dynamics of two coupled exchange-only qubits    [PDF]

Arijeet Pal, Emmanuel I. Rashba, Bertrand I. Halperin
Inspired by creation of a fast exchange-only qubit (Medford et al., arXiv:1304.3413), we develop a theory describing the nonlinear dynamics of two such qubits that are capacitively coupled, when one of them is driven resonantly at a frequency equal to its level splitting. We include conditions of strong driving, where the Rabi frequency is a significant fraction of the level splitting, and we consider situations where the splitting for the second qubit may be the same or different than the first. We demonstrate that coupling of qubits and entanglement between them can be detected by reading the response of the second qubit, even when the coupling between qubits is only of about 1% of their level splittings. Patterns of nonlinear dynamics of coupled qubits and their entanglement are strongly dependent on the geometry of the system and the specific mechanism of inter-qubit coupling, and entanglement deeply influences dynamics of both qubits. In particular, we describe the development of irregular dynamics in a two-qubit system, explore approaches for inhibiting it, and demonstrate existence of an optimal range of coupling strength maintaining stability during the operational time.
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