Coherent quantum state transfer between two Josephson phase qubits through a resonant cavity

Mika A. Sillanpää, Jae I. Park, Raymond W. Simmonds

Mika Sillanpää

Mika Sillanpää, Jae Hyung Park, Raymonds Simmonds

Andrew N. Cleland

We describe the design for a solid‐state quantum computational architecture based on the integration of GHz‐frequency mechanical resonators with Josephson phase qubits, which have the potential for demonstrating a variety of single‐ and multi‐qubit operations critical to quantum computation. The computational qubits are eigenstates of large‐area, current‐biased Josephson junctions. Two or more qubits are capacitively coupled to a piezoelectric nanoelectromechanical disk resonator, which enables coherent coupling of the qubits. The integrated system is analogous to one or more few‐level atoms (the Josephson junction qubits) in an electromagnetic cavity (the nanomechanical resonator). However, here we can individually tune the level spacing of the “atoms” and control their “electromagnetic” interaction strength. We show that quantum states prepared in a Josephson junction can be passed to the nanomechanical resonator and stored there, and then can be passed back to the original junction or transferred to another with high fidelity. The resonator can also be used to produce maximally entangled Bell states between a pair of Josephson junctions.

Michael R. Geller, Andrew N. Cleland

We describe the design for a scalable, solid-state quantum-information-processing architecture based on the integration of GHz-frequency nanomechanical resonators with Josephson tunnel junctions, which has the potential for demonstrating a variety of single- and multiqubit operations critical to quantum computation. The computational qubits are eigenstates of large-area, current-biased Josephson junctions, manipulated and measured using strobed external circuitry. Two or more of these phase qubits are capacitively coupled to a high-quality-factor piezoelectric nanoelectromechanical disk resonator, which forms the backbone of our architecture, and which enables coherent coupling of the qubits. The integrated system is analogous to one or more few-level atoms (the Josephson junction qubits) in an electromagnetic cavity (the nanomechanical resonator). However, unlike existing approaches using atoms in electromagnetic cavities, here we can individually tune the level spacing of the ``atoms'' and control their ``electromagnetic'' interaction strength. We show theoretically that quantum states prepared in a Josephson junction can be passed to the nanomechanical resonator and stored there, and then can be passed back to the original junction or transferred to another with high fidelity. The resonator can also be used to produce maximally entangled Bell states between a pair of Josephson junctions. Many such junction-resonator complexes can be assembled in a hub-and-spoke layout, resulting in a large-scale quantum circuit. Our proposed architecture combines desirable features of both solid-state and cavity quantum electrodynamics approaches, and could make quantum-information processing possible in a scalable, solid-state environment.

Hugo Ribeiro, Ying-Dan Wang, Aashish A. Clerk