L. B. Ioffe

Environmentally decoupled sds -wave Josephson junctions for quantum computing

Quantum computers have the potential to outperform their classical counterparts in a qualitative manner, as demonstrated by algorithms which exploit the parallelism inherent in the time evolution of a quantum state. In quantum computers, the information is stored in arrays of quantum two-level systems (qubits), proposals for which include utilizing trapped atoms and photons, magnetic moments in molecules and various solid-state implementations. But the physical realization of qubits is challenging because useful quantum computers must overcome two conflicting difficulties: the computer must be scalable and controllable, yet remain almost completely detached from the environment during operation, in order to maximize the phase coherence time. Here we report a concept for a solid-state ‘quiet’ qubit that can be efficiently decoupled from the environment. It is based on macroscopic quantum coherent states in a superconducting quantum interference loop. Our two-level system is naturally bistable, requiring no external bias: the two basis states are characterized by different macroscopic phase drops across a Josephson junction, which may be switched with minimal external contact.A combination of elements for use in surgery, particularly suturing. The combination includes a conventional needle holder with a second element, namely a needle-suture assembly combining a suture storage chamber and a hollow needle through which the suture is drawn. The needle-suture assembly is associated with the needle holder in order that suturing is accomplished by manipulation of the handles of the needle holder. The needle-suture assembly is attached to the needle holder by grasping the needle with the needle holder and also by means associated with the suture storage chamber, which attaches the unit to the needle holder on the opposite side of the pivot point from the needle. The latter attaching means serves also to effectively lock the needle holder against inadvertent opening during the suturing operation. The suture storage chamber includes a storage spool which serves to seal the storage chamber, store the thread, and to restrain the suture against rapid, undesirable dispensing.

Superconductivity in a system with preformed pairs

We discuss the phenomenology of superconductivity resulting from the Bose condensation of preformed pairs coexisting with unpaired fermions. We show that this transition is more mean-field-like than the usual Bose condensation, i.e., it is characterized by a relatively small value of the Ginzburg parameter. We consider the Hall effect in the vortex-flow regime and in the fluctuational regime above

Coherent quantum phase slip

{\mathrm{T}}_{\mathrm{c}}

Localization of preformed Cooper pairs in disordered superconductors

, and show that in this situation it is much less than in the transition driven entirely by Bose condensation but much larger than in usual superconductivity. We analyze the available Hall data and conclude that this phenomenology describes reasonably well the data in the underdoped materials of Y-Ba-Cu-O family but is not an appropriate description of optimally doped materials or underdoped La-Sr-Cu-O.

Low-energy properties of fermions with singular interactions

A hundred years after the discovery of superconductivity, one fundamental prediction of the theory, coherent quantum phase slip (CQPS), has not been observed. CQPS is a phenomenon exactly dual to the Josephson effect; whereas the latter is a coherent transfer of charges between superconducting leads, the former is a coherent transfer of vortices or fluxes across a superconducting wire. In contrast to previously reported observations of incoherent phase slip, CQPS has been only a subject of theoretical study. Its experimental demonstration is made difficult by quasiparticle dissipation due to gapless excitations in nanowires or in vortex cores. This difficulty might be overcome by using certain strongly disordered superconductors near the superconductor–insulator transition. Here we report direct observation of CQPS in a narrow segment of a superconducting loop made of strongly disordered indium oxide; the effect is made manifest through the superposition of quantum states with different numbers of flux quanta. As with the Josephson effect, our observation should lead to new applications in superconducting electronics and quantum metrology.

Asymmetric quantum error-correcting codes

Disorder leads to localization of electrons at low temperatures, changing metals to insulators. In a superconductor the electrons are paired up, and scanning tunnelling microscopy shows that the pairs localize together rather than breaking up and forming localized single electrons in the insulating state.

Topologically protected quantum bits using Josephson junction arrays

We calculate the fermion Green function and particle-hole susceptibilities for a degenerate two-dimensional fermion system with a singular gauge interaction. We show that this is a strong-coupling problem, with no small parameter other than the fermion spin degeneracy N. We consider two interactions, one arising in the context of the t-J model and the other in the theory of half-filled Landau level. For the fermion self-energy we show that the qualitative behavior found in the leading order of perturbation theory is preserved to all orders in the interaction. The susceptibility

Protected qubits and Chern-Simons theories in Josephson junction arrays

{\mathrm{\ensuremath{\chi}}}_{\mathit{Q}}

Eigenfunction fractality and pseudogap state near the superconductor-insulator transition.

at a general wave vector Q\ensuremath{\ne}2

Dynamics of interfaces and dislocations in disordered media

{\mathbf{p}}_{\mathbf{F}}