14 research outputs found
Toroidal qubits: naturally-decoupled quiet artificial atoms
The requirements of quantum computations impose high demands on the level of
qubit protection from perturbations; in particular, from those produced by the
environment. Here we propose a superconducting flux qubit design that is
naturally protected from ambient noise. This decoupling is due to the qubit
interacting with the electromagnetic field only through its toroidal moment,
which provides an unusual qubit-field interaction
Simulating long-distance entanglement in quantum spin chains by superconducting flux qubits
We investigate the performance of superconducting flux qubits for the
adiabatic quantum simulation of long distance entanglement (LDE), namely a
finite ground-state entanglement between the end spins of a quantum spin chain
with open boundary conditions. As such, LDE can be considered an elementary
precursor of edge modes and topological order. We discuss two possible
implementations which simulate open chains with uniform bulk and weak end
bonds, either with Ising or with XX nearest-neighbor interactions. In both
cases we discuss a suitable protocol for the adiabatic preparation of the
ground state in the physical regimes featuring LDE. In the first case the
adiabatic manipulation and the Ising interactions are realized using dc
currents, while in the second case microwaves fields are used to control the
smoothness of the transformation and to realize the effective XX interactions.
We demonstrate the adiabatic preparation of the end-to-end entanglement in
chains of four qubits with realistic parameters and on a relatively fast time
scale.Comment: 12 pages, 14 figures. Final manuscript, close to the published
versio
Frequency Division Multiplexing Readout and Simultaneous Manipulation of an Array of Flux Qubits
An important desired ingredient of superconducting quantum circuits is a
readout scheme whose complexity does not increase with the number of qubits
involved in the measurement. Here, we present a readout scheme employing a
single microwave line, which enables simultaneous readout of multiple qubits.
Consequently, scaling up superconducting qubit circuits is no longer limited by
the readout apparatus. Parallel readout of 6 flux qubits using a frequency
division multiplexing technique is demonstrated, as well as simultaneous
manipulation and time resolved measurement of 3 qubits. We discuss how this
technique can be scaled up to read out hundreds of qubits on a chip.Comment: 4 pages, 4 figure
Low noise cryogenic system for the measurement of Casimir energy in rigid cavities
We report on preliminary results on the measurement of variations of the
Casimir energy in rigid cavities through its influence on the superconducting
transition of in-cavity aluminium (Al) thin films. After a description of the
experimental apparatus we report on a measurement made with thermal photons,
discussing its implications for the zero-point photons case. Finally we show
the preliminary results for the zero-point case.Comment: 9 pages, 7 figures, Talk given at QFEXT07 Conference in Liepzig:
Quantum Field Theory Under the Influence of External Condition
The Aladin2 experiment: status and perspectives
Aladin2 is an experiment devoted to the first measurement of variations of
Casimir energy in a rigid cavity. The main scientific motivation relies on the
possibility of the first demonstration of a phase transition influenced by
vacuum fluctuations. The guiding principle of the measurement, based on the
behaviour of the critical field for an in-cavity superconducting film, will be
only briefly recalled. In this paper, after an introduction to the long term
motivations, the experimental apparatus and the results of the first
measurement of sensitivity will be presented in detail, particularly in
comparison with the expected signal. Last, the most important steps towards the
final measurement will be discussed.Comment: Talk given by Calloni at QFEXT05 Conference in Barcelona: Quantum
Field Theory Under the Influence of External Condition
Sharpness of the Berezinskii-Kosterlitz-Thouless transition in ultrathin NbN films
We present a comprehensive investigation of the
Berezinskii-Kosterlitz-Thouless (BKT) transition in ultrathin strongly
disordered NbN films. Measurements of resistance, current-voltage
characteristics and kinetic inductance on the very same device reveal a
consistent picture of a sharp unbinding transition of vortex-antivortex pairs
that fit standard renormalization group theory without extra assumptions in
terms of inhomogeneity. Our experiments demonstrate that the previously
observed broadening of the transition is not an intrinsic feature of strongly
disordered superconductors and provide a clean starting point for the study of
dynamical effects at the BKT transition.Comment: Main: 6 pages, 4 figures; Supplement: 6 pages, 10 figures, author
adde
Single-Photon Detection with a Josephson Junction Coupled to a Resonator
| openaire: EC/H2020/863313/EU//SUPERGALAX Funding Information: This work was supported by the Academy of Finland Centre of Excellence program (Project No. 312057) and by the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 863313 (SUPERGALAX). It was also partly supported by the Ministry of Science and Higher Education of the Russian Federation (Grant No. FSUN-2020-0007) and by the Russian Science Foundation (Project No. 19-79-10170). Publisher Copyright: © 2021 American Physical Society.We use a semiclassical formalism to optimize a microwave single-photon detector based on switching events of a current-biased Josephson junction coupled to a resonator. To detect very rare events, the average time between dark counts τdark should be maximized taking into account that the switching time τsw should be sufficiently small. We demonstrate that these times can be tuned in a wide range by changing the junction parameters, and τdark/τsw∼109 can be achieved. Therefore, a junction-resonator arrangement can be used to detect extremely low photon fluxes (e.g., for searching for galactic axions).Peer reviewe