arXiv subjects

G. S. Paraoanu

Publications and source records attributed to G. S. Paraoanu.

63 records · Page 4Linked to original sources

arXiv2008

Method for finding the critical temperature of the island in a SET structure

We present a method to measure the critical temperature of the island of a superconducting single electron transistor. The method is based on a sharp change in the slope of the zero-bias conductance as a function of temperature. We have used this method to determine the superconducting phase transition temperature of the Nb island of an superconducting single electron transistor with Al leads. We obtain $T_\mathrm{c}^\mathrm{Nb}$ as high as 8.5 K and gap energies up to $Δ_\mathrm{Nb}\simeq 1.45$ meV. By looking at the zero bias conductance as a function of magnetic field instead of temperature, also the critical field of the island can be determined. Using the orthodox theory, we have performed extensive numerical simulations of charge transport properties in the SET at temperatures comparable to the gap, which match very well the data, therefore providing a solid theoretical basis for our method.

cond-mat.mes-hall↗

arXiv2008

Evolution of fragmented states

We consider the problem of evolution of the many-body state of a weakly interacting system of bosons in an initially fragmented (Fock) state. We show that the state at any time can be expressed as a continuous superposition of an infinite number of Gross-Pitaevskii states.

cond-mat.other↗

arXiv2008

Localization of the relative phase via measurements

When two independently-prepared Bose-Einstein condensates are released from their corresponding traps, the absorbtion image of the overlapping clouds presents an interference pattern. Here we analyze a model introduced by Javanainen and Yoo (J. Javanainen and S. M. Yoo, Phys. Rev. Lett. 76, 161 (1996)), who considered two atomic condensates described by plane waves propagating in opposite directions. We present an analytical argument for the measurement-induced breaking of the relative phase symmetry in this system, demonstrating how the phase gets localized after a large enough number of detection events.

cond-mat.stat-mech↗

arXiv2008

Phase coherence and fragmentation in weakly interacting bosonic gases

We present a theory of measurement-induced interference for weakly interacting Bose-Einstein condensed (BEC) gases. The many-body state resulting from the evolution of an initial fragmented (Fock) state can be approximated as a continuous superposition of Gross-Pitaevskii (GP) states; the measurement breaks the initial phase symmetry, producing a distribution pattern corresponding to only one of the GP solutions. We discuss also analytically solvable models, such as two-mode on-chip adiabatic recombination and soliton generation in quasi one-dimensional condensates.

cond-mat.stat-mech↗

arXiv2008

Interaction-free measurements with superconducting qubits

An interaction-free measurement protocol is described for a quantum circuit consisting of a superconducting qubit and a read-out Josephson junction. By measuring the state of the qubit one can ascertain the presence of a current pulse through the circuit at a previous time without any energy exchange between the qubit and the pulse.

cond-mat.supr-con↗

arXiv2008

Dye-Sensitized Nanostructured TiO2 Film Based Photoconductor

Grooves were etched in a conductive layer of a conductive, transparent glass, and a nanoporous TiO2 film was deposited on both the conductive and nonconductive area. The width of the grooves was 100 $μ$m and 150 $μ$m. A transparent TiO2 film was dye-sensitized, covered with an electrolyte, and sandwiched with a cover glass. The conductivity of the dye-sensitized TiO2 film permeated with electrolyte was studied in the dark and under illumination, and was observed to be dependent on light intensity, wavelength and applied voltage. This study shows that dye-sensitized nanoporous films can be used as a wavelength dependent photoconductor.

physics.chem-ph↗

arXiv2008

Microwave-induced coupling of superconducting qubits

We investigate the quantum dynamics of a system of two coupled superconducting qubits under microwave irradiation. We find that, with the qubits operated at the charge co-degeneracy point, the quantum evolution of the system can be described by a new effective Hamiltonian which has the form of two coupled qubits with tunable coupling between them. This Hamiltonian can be used for experimental tests on macroscopic entanglement and for implementing quantum gates.

cond-mat.mes-hall↗

arXiv2007

Cooper-pair resonances and subgap Coulomb blockade in a superconducting single-electron transistor

We have fabricated and measured superconducting single-electron transistors with Al leads and Nb islands. At bias voltages below the gap of Nb we observe clear signatures of resonant tunneling of Cooper pairs, and of Coulomb blockade of the subgap currents due to linewidth broadening of the energy levels in the superconducting density of states of Nb. The experimental results are in good agreement with numerical simulations.

cond-mat.mes-hall↗

arXiv2005

Running-phase state in a Josephson washboard potential

We investigate the dynamics of the phase variable of an ideal underdamped Josephson junction in switching current experiments. These experiments have provided the first evidence for macroscopic quantum tunneling in large Josephson junctions and are currently used for state read-out of superconducting qubits. We calculate the shape of the resulting macroscopic wavepacket and find that the propagation of the wavepacket long enough after a switching event leads to an average voltage increasing linearly with time.

cond-mat.supr-con↗