2010/04/29 by M. Neeley, R. C. Bialczak, M. Lenander +11 · 1 citation
Physics and Astronomy · #cond-mat.supr-con #cond-mat.mes-hall #quant-ph
paper · pdf · doi:10.1038/nature09418
9 pages, 5 figures. Version 2: added supplementary information and fixed image distortion in Figure 2.
arxiv created 2010/04/29 · arxiv updated 2015/05/18
Entanglement is one of the key resources required for quantum computation, so experimentally creating and measuring entangled states is of crucial importance in the various physical implementations of a quantum computer. In superconducting qubits, two-qubit entangled states have been demonstrated and used to show violations of Bell's Inequality and to implement simple quantum algorithms. Unlike the two-qubit case, however, where all maximally-entangled two-qubit states are equivalent up to local changes of basis, three qubits can be entangled in two fundamentally different ways, typified by the states |GHZ> = (|000> + |111>)/√(2) and |W> = (|001> + |010> + |100>)/√(3). Here we demonstrate the operation of three coupled superconducting phase qubits and use them to create and measure |GHZ> and |W> states. The states are fully characterized using quantum state tomography and are shown to satisfy entanglement witnesses, confirming that they are indeed examples of three-qubit entanglement and are not separable into mixtures of two-qubit entanglement.