Source of decoherence in Josephson qubits indentified by NIST researchers.Josephson junctions An ultra-fast switching technology that uses superconductor materials, originally conceived by Brian Josephson. Circuits are immersed in liquid helium to obtain near-absolute zero degrees required for operation. Switching takes place in a few picoseconds. are good candidates for a quantum computer (computer) quantum computer - A type of computer which uses the ability of quantum systems, such as a collection of atoms, to be in many different states at once. In theory, such superpositions allow the computer to perform many different computations simultaneously. with recent experiments demonstrating reasonably long coherence times For an electromagnetic wave, coherence time is the time over which a propagating wave (especially a laser or maser beam) may be considered coherent. In other words, it is the time interval within which its phase is, on average, predictable. , state preparation, manipulation and measurement, and coupling of qubits for even-tual gate operations. Since a practical quantum computer will require extended coherent times, a detailed investigation and understanding of all possible decoherence modes is important. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. scientists in Boulder recently demonstrated that a major source of decoherence in Josephson qubits arises from spurious microwave resonances that are formed from states within the tunnel junction A tunnel junction is, in its simplest form, a thin insulating barrier between two conducting electrodes. If the electrodes are superconducting, Cooper pairs with a charge of two elementary charges carry the current. In the case that the electrodes are normalconducting, i.e. . A model has been developed that connects the subgap current-voltage characteristics with the magnitude of the resonances as well as the magnitude and density of 1/[Florin] critical-current fluctuations. This work provides valuable guidance for future Qubit development by demonstrating the need for materials research directed at reducing critical-current fluctuations in tunnel junctions. CONTACT: John Martinis, (303) 497-3597; martinis@boulder.nist.gov. |
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