I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me

25 Jan 2013

New approach to the superconducting qubit within a microcavity

We present a novel approach for studying the dynamics of a superconducting qubit in a cavity. We succeed in linearizing the Hamiltonian through the application of an appropriate unitary

transformation followed by a rotating wave approximation (RWA). For certain values of the parameters involved, we show that it is possible to obtain specific hamiltonians. As an example, we show the existence of long time-scale revivals (super-revivals) for the excitation the qubit inversion.

arxiv pdf

22 Jan 2013

Josephson vortex coupled to a flux qubit

Experiments towards realizing a readout of superconducting qubits by using ballistic Josephson vortices are reported. We measured the microwave radiation induced by a fluxon moving

in an annular Josephson junction. By coupling a flux qubit as a current dipole to the annular junction, we detect periodic variations of the fluxon’s oscillation frequency versus magnetic flux through the qubit. We found that the scattering of a fluxon on a current dipole can lead to the acceleration of a fluxon regardless of a dipole polarity. We use the perturbation theory and numerical simulations of the perturbed sine-Gordon equation to analyze our results.

arxiv pdf

19 Jan 2013

Quantum Information Transfer between Topological and Superconducting Qubits

We describe a scheme that enables a strong Jaynes-Cummings coupling between a topological qubit and a superconducting flux qubit. The coupling strength is dependent on the phase difference

between two superconductors on a topological insulator and may be expediently controlled by a phase controller. With this coherent coupling and single-qubit rotations arbitrary unitary operations on the two-qubit hybrid system of topological and flux qubits can be performed. Numerical simulations show that quantum state transfer and entanglement distributing between the topological and superconducting flux qubits may be performed with high fidelity.

arxiv pdf

18 Jan 2013

Probing Correlations, Indistinguishability and Entanglement in Microwave Two-Photon Interference

Interference at a beam splitter reveals both classical and quantum properties of electromagnetic radiation. When two indistinguishable single photons impinge at the two inputs of a

beam splitter they coalesce into a pair of photons appearing in either one of its two outputs. This effect is due to the bosonic nature of photons and was first experimentally observed by Hong, Ou, and Mandel (HOM) [1]. Here, we present the observation of the HOM effect with two independent single-photon sources in the microwave frequency domain. We probe the indistinguishability of single photons, created with a controllable delay, in time-resolved second-order cross- and auto-correlation function measurements. Using quadrature amplitude detection we are able to resolve different photon numbers and detect coherence in and between the output arms. This measurement scheme allows us to observe the HOM effect and, in addition, to fully characterize the two-mode entanglement of the spatially separated beam splitter output modes. Our experiments constitute a first step towards using two-photon interference at microwave frequencies for quantum communication and information processing, e.g. for distributing entanglement between nodes of a quantum network [2, 3] and for linear optics quantum computation [4, 5].

arxiv pdf

Probing Correlations, Indistinguishability and Entanglement in Microwave Two-Photon Interference

Interference at a beam splitter reveals both classical and quantum properties of electromagnetic radiation. When two indistinguishable single photons impinge at the two inputs of a

arxiv pdf

16 Jan 2013

The quantum transverse-field Ising chain in circuit QED: effects of disorder on the nonequilibrium dynamics

We study several dynamical properties of a recently proposed implementation of the quantum transverse-field Ising chain in the framework of circuit QED. Particular emphasis is placed

on the effects of disorder on the nonequilibrium behavior of the system. We show that small amounts of fabrication-induced disorder in the system parameters do not jeopardize the observation of previously-predicted phenomena. Based on a numerical extraction of the mean free path of the system, we also provide a simple quantitative estimate for certain disorder effects on the nonequilibrium dynamics of the circuit QED quantum simulator. We discuss the transition from weak to strong disorder, characterized by the onset of Anderson localization of the system’s wave functions, and the qualitatively different dynamics it leads to.

arxiv pdf

14 Jan 2013

Microstrip filters for measurement and control of superconducting qubits

Careful filtering is necessary for observations of quantum phenomena in superconducting circuits at low temperatures. Measurements of coherence between quantum states requires extensive

filtering to protect against noise coupled from room temperature electronics. We demonstrate distributed transmission line filters which cut off exponentially at GHz frequencies and can be anchored at the base temperature of a dilution refrigerator. The compact design makes them suitable to filter many different bias lines in the same setup, necessary for the control and measurement of superconducting qubits.

arxiv pdf

Proposal for coherent coupling of Majorana and fluxonium qubits

We propose to use an ancilla fluxonium qubit to interact with a Majorana qubit hosted by a topological 1D wire. The coupling is obtained using the Majorana qubit controlled $4pi$ Josephson

effect to flux bias the fluxonium qubit. We demonstrate how this coupling can be used to sensitively identify topological superconductivity, to measure the state of the Majorana qubit, to construct 2-qubit operations, and to implement quantum memories with topological protection.

arxiv pdf

09 Jan 2013

Quantum Robust Stability of a Small Josephson Junction in a Resonant Cavity

Ian R. Petersen

This paper applies recent results on the robust stability of nonlinear quantum systems to the case of a Josephson junction in a resonant cavity. The Josephson junction is characterized

by a Hamiltonian operator which contains a non-quadratic term involving a cosine function. This leads to a sector bounded nonlinearity which enables the previously developed theory to be applied to this system in order to analyze its stability.

arxiv pdf

Proposal for a coherent quantum memory for propagating microwave photons

We describe a multi-mode quantum memory for propagating microwave photons that combines a solid-state spin ensemble resonantly coupled to a frequency tunable single-mode microwave cavity.

We first show that high efficiency mapping of the quantum state transported by a free photon to the spin ensemble is possible both for strong and weak coupling between the cavity mode and the spin ensemble. We also show that even in the weak coupling limit unit efficiency and faithful retrieval can be obtained through time reversal inhomogeneous dephasing based on spin echo techniques. This is possible provided that the cavity containing the spin ensemble and the transmission line are impedance matched. We finally discuss the prospects for an experimental implementation using a rare-earth doped crystal coupled to a superconducting resonator.

arxiv pdf