Measurement of the entanglement of two superconducting qubits via state tomography.

Department of Physics and California Nano Systems Institute, University of California, Santa Barbara, CA 93106, USA.
Science (Impact Factor: 31.2). 10/2006; 313(5792):1423-5. DOI: 10.1126/science.1130886
Source: PubMed

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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a feasible scheme that realizes quantum computation using the two-level systems (TLSs) in Current-biased Josephson junction (CBJJ) under the present experimental technology. Effective manipulation of the TLSs by CBJJ serving as register qubit can be obtained, such as initialization, single-qubit rotations, two-qubit gates, entanglement generation, and read out, etc. In addition, we also discuss the experimental feasibility and efficiency of the scheme.
    Communications in Theoretical Physics 04/2010; 5325:53-855. · 0.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The maximum entanglement between two coupled qubits in the steady state under two independent incoherent sources of excitation is reported. Asymmetric configurations where one qubit is excited while the other one dissipates the excitation are optimal for entanglement, reaching values three times larger than with thermal sources. The reason is the purification of the steady state mixture (that includes a Bell state) thanks to the saturation of the pumped qubit. Photon antibunching between the cross emission of the qubits can be used to experimentally evidence the large degrees of entanglement.
    Journal of the Optical Society of America B 05/2010; · 2.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose a hybrid architecture in which an on-chip high finesse superconducting cavity is coupled to the lateral motion and spin state of a single electron trapped on the surface of superfluid helium. We estimate the motional coherence times to exceed 15  μs, while energy will be coherently exchanged with the cavity photons in less than 10 ns for charge states and faster than 1  μs for spin states, making the system attractive for quantum information processing and strong coupling cavity quantum electrodynamics experiments. The cavity is used for nondestructive readout and as a quantum bus mediating interactions between distant electrons or an electron and a superconducting qubit.
    Physical Review Letters 07/2010; 105(4):040503. · 7.73 Impact Factor

Full-text (2 Sources)

Available from
May 23, 2014