128 research outputs found
Realization of a classical counterpart of a scalable design for adiabatic quantum computation
We implement a classical counterpart of a scalable design for adiabatic
quantum computation. The key element of this design is a coupler providing
controllable coupling between two bistable elements (in our case
superconducting rings with a single Josephson junction playing the role of a
classical counterpart of superconducting flux qubits) The coupler is also a
superconducting ring with a single Josephson junction that operates in the
non-hysteretic mode. The flux coupling between two bistable rings can be
controlled by changing the magnetic flux through the coupler. Thereby, the
coupling can be tuned from ferromagnetic trough zero to to anti-ferromagnetic.Comment: 3 pages, 3 figures v2: extended discussion experimental result
Direct Josephson coupling between superconducting flux qubits
We have demonstrated strong antiferromagnetic coupling between two
three-junction flux qubits based on a shared Josephson junction, and therefore
not limited by the small inductances of the qubit loops. The coupling sign and
magnitude were measured by coupling the system to a high-quality
superconducting tank circuit. Design modifications allowing to continuously
tune the coupling strength and/or make the coupling ferromagnetic are
discussed.Comment: REVTeX 4, 4 pages, 5 figures; v2: completely rewritten, added
finite-temperature results and proposals for ferromagnetic galvanic couplin
Flux Qubits and Readout Device with Two Independent Flux Lines
We report measurements on two superconducting flux qubits coupled to a
readout Superconducting QUantum Interference Device (SQUID). Two on-chip flux
bias lines allow independent flux control of any two of the three elements, as
illustrated by a two-dimensional qubit flux map. The application of microwaves
yields a frequency-flux dispersion curve for 1- and 2-photon driving of the
single-qubit excited state, and coherent manipulation of the single-qubit state
results in Rabi oscillations and Ramsey fringes. This architecture should be
scalable to many qubits and SQUIDs on a single chip.Comment: 5 pages, 4 figures, higher quality figures available upon request.
Submitted to PR
Exact summation of leading infrared logarithms in 2D effective field theories
A method of exact all-order summation of leading infrared logarithms in two
dimensional massless -type non-renormalizable effective field theories
(EFTs) is developed. The method is applied to the -symmetric EFT,
which is a two-dimensional sibling of the four dimensional sigma-model. For the first time the exact all-order summation of the
contributions (chiral logarithms) for the scattering amplitudes is performed in closed analytical form. The cases
when the resulting amplitudes turn to be meromorphic functions with an infinite
number of poles (Landau poles) are identified. This provides the first explicit
example of quasi-renormalizable field theories.Comment: 22 pages, 2 figure
Four-qubit device with mixed couplings
We present the first experimental results on a device with more than two
superconducting qubits. The circuit consists of four three-junction flux
qubits, with simultaneous ferro- and antiferromagnetic coupling implemented
using shared Josephson junctions. Its response, which is dominated by the
ground state, is characterized using low-frequency impedance measurement with a
superconducting tank circuit coupled to the qubits. The results are found to be
in excellent agreement with the quantum-mechanical predictions.Comment: REVTeX 4, 5pp., 7 EPS figure files. N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: final published version, with
changed title, different sample micrograph, and several clarification
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