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1. Superconducting phase transition in inhomogeneous chains of superconducting islands

   https://doi.org/10.1103/PhysRevB.102.134502  

   Ilin, Eduard ; Burkova, Irina ; Song, Xiangyu ; Pak, Michael ; Golubev, Dmitri S. ; Bezryadin, Alexey ( October 2020 , Physical Review B)
2. Superconducting phase transition in inhomogeneous chains of superconducting islands

   https://doi.org/doi.org/10.1103/PhysRevB.102.134502  

   Eduard Ilin, Irina Burkova ( October 2020 , Physical review and Physical review letters index)

   We study one-dimensional chains of superconducting islands with a particular emphasis on the regime in which every second island is switched into its normal state, thus forming a superconductor-insulator-normal metal (S-I-N) repetition pattern. As is known since Giaever tunneling experiments, tunneling charge transport between a superconductor and a normal metal becomes exponentially suppressed, and zero-bias resistance diverges, as the temperature is reduced and the energy gap of the superconductor grows larger than the thermal energy. Here we demonstrate that this physical phenomenon strongly impacts transport properties of inhomogeneous superconductors made of weakly coupled islands with fluctuating values of the critical temperature. We observe a nonmonotonous dependence of the chain resistance on both temperature and magnetic field, with a pronounced resistance peak at temperatures at which some but not all islands are superconducting. We explain this phenomenon by the inhomogeneity of the chains, in which neighboring superconducting islands have slightly different critical temperatures. We argue that the Giaever’s resistance divergence can also occur in the zero-temperature limit. Such quantum transition can occur if the magnetic field is tuned such that it suppresses superconductivity in the islands with the weaker critical field, while the islands with stronger energy gap remain superconducting. In such a field, the system acts as a chain of S-I-N junctions. 

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3. Evidence of a Precursor Superconducting Phase at Temperatures as High as 180 K in RBa2Cu3O7−δ   (R=Y,Gd,Eu) Superconducting Crystals from Infrared Spectroscopy

   https://doi.org/10.1103/PhysRevLett.106.047006  

   Dubroka, A. ; Rössle, M. ; Kim, K. W. ; Malik, V. K. ; Munzar, D. ; Basov, D. N. ; Schafgans, A. A. ; Moon, S. J. ; Lin, C. T. ; Haug, D. ; et al ( January 2011 , Physical Review Letters)
4. Quantum adiabatic theorem for unbounded Hamiltonians with a cutoff and its application to superconducting circuits

   https://doi.org/10.1098/rsta.2021.0407  

   Mozgunov, Evgeny ; Lidar, Daniel A. ( January 2023 , Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   We present a new quantum adiabatic theorem that allows one to rigorously bound the adiabatic timescale for a variety of systems, including those described by originally unbounded Hamiltonians that are made finite-dimensional by a cutoff. Our bound is geared towards the qubit approximation of superconducting circuits and presents a sufficient condition for remaining within the$2^n$-dimensional qubit subspace of a circuit model of$n$qubits. The novelty of this adiabatic theorem is that, unlike previous rigorous results, it does not contain$2^n$as a factor in the adiabatic timescale, and it allows one to obtain an expression for the adiabatic timescale independent of the cutoff of the infinite-dimensional Hilbert space of the circuit Hamiltonian. As an application, we present an explicit dependence of this timescale on circuit parameters for a superconducting flux qubit and demonstrate that leakage out of the qubit subspace is inevitable as the tunnelling barrier is raised towards the end of a quantum anneal. We also discuss a method of obtaining a$2^n\times 2^n$effective Hamiltonian that best approximates the true dynamics induced by slowly changing circuit control parameters.

   This article is part of the theme issue ‘Quantum annealing and computation: challenges and perspectives’.

    

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5. Quantum Fluctuations of Charge Order Induce Phonon Softening in a Superconducting Cuprate

   https://doi.org/10.1103/PhysRevX.11.041038  

   Huang, H. Y. ; Singh, A. ; Mou, C. Y. ; Johnston, S. ; Kemper, A. F. ; van den Brink, J. ; Chen, P. J. ; Lee, T. K. ; Okamoto, J. ; Chu, Y. Y. ; et al ( November 2021 , Physical Review X)