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Direct Measurement of the Entanglement of Two Superconducting Qubits via State Tomography

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Journal Article - Open Access

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University of California, Santa Barbara Santa Barbara United States

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The laws of quantum physics provide intriguing possibilities for a tremendous increase in speed compared to classical computation1. Because this power is achieved through the controlled evolution of entangled quantum states, a clear demonstration of entanglement represents a key milestone towards the construction of a scalable quantum computer2,3. Although entanglement can be inferred from simple experiments, a direct demonstration is challenging because all of the DiVincenzo criteria4 for quantum computation must be met simultaneously. Only subsets of these key requirements have been demonstrated previously for superconducting qubits5-9. Here, we demonstrate all of the DiVincenzo criteria simultaneously, thus taking a significant step forward towards placing superconducting qubits on the roadmap for scalable quantum computing. Specifically, capacitively-coupled Josephson phase qubits are used to create Bell states, which when measured using state tomography on both qubits show an entangled state with fidelity of up to 87. Our results demonstrate a high degree of unitary control of the system, indicating that larger implementations are within reach.

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  • Quantum Theory and Relativity

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