Measurement of the Entanglement of Two Superconducting Qubits via State Tomography
Abstract
Demonstration of quantum entanglement, a key resource in quantum computation arising from a nonclassical correlation of states, requires complete measurement of all states in varying bases. By using simultaneous measurement and state tomography, we demonstrated entanglement between two solid-state qubits. Single qubit operations and capacitive coupling between two super-conducting phase qubits were used to generate a Bell-type state. Full two-qubit tomography yielded a density matrix showing an entangled state with fidelity 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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A more stringent measure that quantifies the amount of entanglement, even for mixed states, is the entanglement of formation, E(ρ) (20). We find E(ρexp,M) = 0.42 compared with E(ρth) = 0.61.
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We acknowledge S. Waltman and the National Institute of Standards and Technology for support in building the microwave electronics. Devices were made at the UCSB and Cornell Nanofabrication Facilities, a part of the NSF-funded National Nanotechnology Infrastructure Network. N.K. acknowledges support of the Rothschild fellowship. This work was supported by Disruptive Technology Office under grant W911NF-04-1-0204 and by NSF under grant CCF-0507227.
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Published In
Science
Volume 313 | Issue 5792
8 September 2006
8 September 2006
Copyright
American Association for the Advancement of Science.
Submission history
Received: 5 June 2006
Accepted: 14 July 2006
Published in print: 8 September 2006
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