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
14
Jan
2015
Proposal for a flux qubit in a dc SQUID with the 4π period Josephson effect
Constructing qubits which are suitable for quantum computation remains a notable challenge. Here, we propose a superconducting flux qubit in a dc SQUID structure, formed by a conventional
insulator Josephson junction and a topological nanowire Josephson junction with Majorana bound states. The zero energy Majorana bound states transport 4π period Josephson currents in the nanowire junction. The interplay between this 4π period Josephson effect and the convectional 2π period Josephson effect in the insulator junction induces a double-well potential energy landscape in the SQUID. As a result, the two lowest energy levels of the SQUID are isolated from other levels. These two levels show contradicting circulating supercurrents, thus can be used as a flux qubit. We reveal that this flux qubit has the merits of stability to external noises, tolerance to the deviation of system parameters, and scalability to large numbers. Furthermore, we demonstrate how to couple this flux qubit with the Majorana qubit by tuning the junction parameters, and how to use this coupling to manipulate the Majorana qubit.
13
Jan
2015
Dipolar Spin Models with Arrays of Superconducting Qubits
We propose a novel platform for quantum many body simulations of dipolar spin models using current circuit QED technology. Our basic building blocks are 3D Transmon qubits where we
use the naturally occurring dipolar interactions to realize interacting spin systems. This opens the way toward the realization of a broad class of tunable spin models in both two- and one-dimensional geometries. We illustrate the potential offered by these systems in the context of dimerized Majumdar-Ghosh-type phases, archetypical examples of quantum magnetism, showing how such phases are robust against disorder and decoherence, and could be observed within state-of-the-art experiments.
07
Jan
2015
Microwave multimode memory with an Er3+:Y2SiO5 spin ensemble
Interfacing photonic and solid-state qubits within a hybrid quantum architecture offers a promising route towards large scale distributed quantum computing. In that respect, hybrid
quantum systems combining circuit QED with ions doped into solids are an attractive platform. There, the ions serve as coherent memory elements and reversible conversion elements of microwave to optical qubits. Among many possible spin-doped solids, erbium ions offer the unique opportunity of a coherent conversion of microwave photons into the telecom C-band at 1.54μm employed for long distance communication. In our work, we perform a time-resolved electron spin resonance study of an Er3+:Y2SiO5 spin ensemble at milli-Kelvin temperatures and demonstrate multimode storage and retrieval of up to 16 coherent microwave pulses. The memory efficiency is measured to be 10−4 at the coherence time of T2=5.6μs.
Two-photon lasing by a superconducting qubit
We study the response of a magnetic-field-driven superconducting qubit strongly coupled to a superconducting coplanar waveguide resonator. We observed a strong amplification/damping
of a probing signal at different resonance points corresponding to a one and two-photon emission/absorption. The sign of the detuning between the qubit frequency and the probe determines whether amplification or damping is observed. The larger blue detuned driving leads to two-photon lasing while the larger red detuning cools the resonator. Our experimental results are in good agreement with the theoretical model of qubit lasing and cooling at the Rabi frequency.
05
Jan
2015
Driving with squeezed vacuum in circuit quantum electrodynamics
We study the dynamics of a general quartic interaction Hamiltonian under the influence of dissipation and non-classical driving. In this scenario, we show that an effective Hartree-type
decoupling yields a good approximation to the dynamics of the system. We find that the stationary states are squeezed vacuum states of the non-interacting system which are enhanced by the Q-factor of the cavity. We show that this effective interaction could be realised with a cascaded superconducting cavity-qubit system in the strong dispersive regime in a setup similar to recent experiments. The qubit non-linearity, therefore, does not significantly influence the highly squeezed intracavity microwave field but, for a range of parameters, enables quantum state tomography of the cavity.
29
Dez
2014
Synchronization of Networked Jahn-Teller Systems in Circuit QED
We consider the nonlinear e?ects in Jahn-Teller system of two coupled resonators interacting simultaneously with ux qubit using Circuit QED. Two frequency description of Jahn Teller
system that inherits the networked structure of both nonlinear Josephson Junctions and harmonic oscillators is employed to describe the synchronous structures in multifrequency scheme. Emergence of dominating mode is investigated to analyze frequency locking by eigenvalue spectrum. Rabi Supersplitting and asymmetry of side peaks in power spectrum is tuned for coupled and uncoupled synchronous con?gurations in terms of frequency entrainment switched by coupling strength between resonators. Second order coherence functions are employed to investigate self-sustained oscillations in resonator mode and qubit dephasing. Snychronous structure between correlations of priviledged mode and qubit is obtained in localization-delocalization and photon blockade regime controlled by the population imbalance.
23
Dez
2014
Ultrastrong coupling in two-resonator circuit QED
We report on ultrastrong coupling between a superconducting flux qubit and a resonant mode of a system comprised of two superconducting coplanar stripline resonators coupled galvanically
to the qubit. With a coupling strength as high as 17% of the mode frequency, exceeding that of previous circuit quantum electrodynamics experiments, we observe a pronounced Bloch-Siegert shift. The spectroscopic response of our multimode system reveals a clear breakdown of the Jaynes-Cummings model. In contrast to earlier experiments, the high coupling strength is achieved without making use of an additional inductance provided by a Josephson junction.
Coherent storage of microwave excitations in rare-earth nuclear spins
Interfacing between various elements of a computer – from memory to processors to long range communication – will be as critical for quantum computers as it is for classical
computers today. Paramagnetic rare earth doped crystals, such as Nd3+:Y2SiO5 (YSO), are excellent candidates for such a quantum interface: they are known to exhibit long optical coherence lifetimes (for communication via optical photons), possess a nuclear spin (memory) and have in addition an electron spin that can offer hybrid coupling with superconducting qubits (processing). Here we study two of these three elements, demonstrating coherent storage and retrieval between electron and 145Nd nuclear spin states in Nd3+:YSO. We find nuclear spin coherence times can reach 9 ms at ≈5 K, about two orders of magnitude longer than the electron spin coherence, while quantum state and process tomography of the storage/retrieval operation reveal an average state fidelity of 0.86. The times and fidelities are expected to further improve at lower temperatures and with more homogeneous radio-frequency excitation.
18
Dez
2014
Strong Single-Photon Coupling in Superconducting Quantum Magnetomechanics
We show that the inductive coupling between the quantum mechanical motion of a superconducting microcantilever and a flux-dependent microwave quantum circuit can attain the strong single-photon
nanomechanical coupling regime with feasible experimental parameters. We propose to use a superconducting strip, which is in the Meissner state, at the tip of a cantilever. A pick-up coil collects the flux generated by the sheet currents induced by an external quadrupole magnetic field centered at the strip location. The position-dependent magnetic response of the superconducting strip, enhanced by both diamagnetism and demagnetizing effects, leads to a strong magnetomechanical coupling to quantum circuits.
17
Dez
2014
Nonreciprocal transmission of microwaves through a long Josephson junction
Nonreciprocal microwave transmission through a long Josephson junction in the flux-flow regime is studied analytically and numerically within the framework of the perturbed sine-Gordon
model. We demonstrate that the maximum attenuation of the transmitted power occurs when the direction of the flux flow is opposite to the direction of the microwave propagation. This attenuation is nonreciprocal with respect to the flux-flow direction and can be enhanced by increasing the system length and proper impedance matching of the junction ends to external transmission line.