BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-1577
DTSTART:20091118T170000Z
DTEND:20091118T180000Z
DTSTAMP:20240329T010131Z
LAST-MODIFIED:20091111T144517Z
LOCATION:5310 Chamberlin
SUMMARY:Small Josephson Arrays as Protected Qubits\, R. G. Herb Conden
sed Matter Seminar\, Michael Gershenson\, Rutgers University
DESCRIPTION:Within the past twenty years\, there has been a growing re
alization that superconducting Josephson circuits can behave as macros
copic quantum systems. The last decade witnessed an explosive growth
of research the superconducting devices for quantum computation (super
conducting qubits). However\, the decoherence time for these devices r
emains insufficiently long for large-scale quantum computing. Recently
it was predicted [1-4] that the arrays of small Josephson junctions w
ith nontrivial topology may exhibit a novel phase which is characteriz
ed by long-range order of pairs of Cooper pairs in the absence of long
-range correlations in single-Cooper-pair condensate. Experimental re
alization of this novel phase can facilitate the fabrication of fault-
tolerant superconducting qubits exponentially protected from local noi
ses. Our experiments [5] with small Josephson arrays show that\, inde
ed\, the condensate of pairs of Cooper pairs can be observed in the ab
sence of coherence in the single-Cooper-pair condensate. The charge tr
ansport in this regime is due to coherent co-tunneling of pairs of Cop
per pairs\, objects with charge 4e. These experiments suggest that ev
en a relatively small prototype device is well protected against magne
tic flux variations.
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\n1. L.B. Ioffe and M.V. Feigel'
man\, Possible realization of an ideal quantum computer in Josephson j
unction array\, Phys. Rev. B 66\, 224503 (2002).
\n2. B. Doucot an
d J. Vidal\, Pairing of Cooper pairs in a fully frustrated Josephson-j
unction chain\, Phys. Rev. Lett. 88\, 227005 (2002).
\n3. B. Douco
t et al.\, Topological order in the insulating Josephson junction arra
ys\, Phys. Rev. Lett. 90\, 107003 (2003).
\n4. B. Doucot et al.\,
Protected qubits and Chern-Simons theories in Josephson junction array
s\, Phys. Rev. B 71\, 024505 (2005).
\n5. S. Gladchenko\, D. Olaya
\, E. Dupont-Ferrier\, B. Doucot\, L.B. Ioffe\, and M.E. Gershenson\,
Superconducting Nanocircuits for Topologically Protected Qubits\, Natu
re Physics 5\, 48 (2009).
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URL:https://www.physics.wisc.edu/events/?id=1577
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