Topologically protected quantum states and quantum computing in Josephson junctions arrays

• Дата: 2004
• Автори: Ioffe, L.B., Feigel`man, M.V., Douçot, B.
• Формат: Стаття
• Мова: Англійська
• Опубліковано: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2004
• Теми: Сверхпроводимость и мезоскопические структуры
• Онлайн доступ: https://nasplib.isofts.kiev.ua/handle/123456789/119839
• Назва журналу: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Цитувати: Topologically protected quantum states and quantum computing in Josephson junctions arrays / L.B. Ioffe, M.V. Feigel`man, B. Douçot // Физика низких температур. — 2004. — Т. 30, № 7-8. — С. 841-855. — Бібліогр.: 36 назв. — англ.

We review recent results on a new class of Josephson arrays which have non-trivial topology
 and exhibit a novel quantum states at low temperatures. One of these states is characterized by
 long range order in a two Cooper pair condensate and by a discrete topological order parameter.
 The second state is insulating and can be considered as a result of evolution of the former state due
 to Bose-condensation of usual superconductive vortices with a flux quantum 0. Quantum phase
 transition between these two states is controlled by variation of external magnetic field. Both the
 superconductive and insulating states are characterized by the presence of 2K-degenerate ground
 states, with K being the number of topologically different cycles existing in the plane of the array.
 This degeneracy is «protected» from the external perturbations (and noise) by the topological order
 parameter and spectral gap. We show that in ideal conditions the low order effect of the external
 perturbations on this degeneracy is exactly zero and that deviations from ideality lead to only
 exponentially small effects of perturbations. We argue that this system provides a physical implementation
 of an ideal quantum computer with a built in error correction. A number of relatively
 simple «echo-like» experiments possible on small-size arrays are discussed.