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
05
Jun
2015
Controllable coupling between a nanomechanical resonator and a coplanar-waveguide resonator via a superconducting flux qubit
We study a tripartite quantum system consisting of a coplanar-waveguide (CPW) resonator and a nanomechanical resonator (NAMR) connected by a flux qubit, where the flux qubit has a large
detuning from both resonators. By a unitray transformation and a second-order approximation, we obtain a strong and controllable (i.e., magnetic-field-dependent) effective coupling between the NAMR and the CPW resonator. Due to the strong coupling, vacuum Rabi splitting can be observed from the voltage-fluctuation spectrum of the CPW resonator. We further study the properties of single photon transport as inferred from the reflectance or equivalently the transmittance. We show that the reflectance and the corresponding phase shift spectra both exhibit doublet of narrow spectral features due to vacuum Rabi splitting. By tuning the external magnetic field, the reflectance and the phase shift can be varied from 0 to 1 and −π to π, respectively. The results indicate that this hybrid quantum system can act as a quantum router.
Quantum Simulation of Macro and Micro Quantum Phase Transition from Paramagnetism to Frustrated Magnetism with a Superconducting Circuit
We devise a scalable scheme for simulating a quantum phase transition from paramagnetism to frustrated magnetism in a superconducting flux-qubit network, and we show how to characterize
this system experimentally both macroscopically and microscopically simultaneously. Macroscopic characterization of the quantum phase transition is based on the expected sudden transition of the probability distribution for the spin-network net magnetic moment with this transition quantified by the Kullback-Leibler divergence between measured and theoretical distributions for a given quantum phase. Microscopic characterization of the quantum phase transition is performed using the standard local-entanglement-witness approach. Simultaneous macro and micro characterizations of quantum phase transitions would serve to verify in two ways a quantum phase transition and provide empirical data for revisiting the foundational emergentist-reductionist debate regarding reconciliation of macroscopic thermodynamics with microscopic statistical mechanics especially in the quantum realm for the classically intractable case of frustrated quantum magnetism.
04
Jun
2015
Quantum Acoustics with Surface Acoustic Waves
It has recently been demonstrated that surface acoustic waves (SAWs) can interact with superconducting qubits at the quantum level. SAW resonators in the GHz frequency range have also
been found to have low loss at temperatures compatible with superconducting quantum circuits. These advances open up new possibilities to use the phonon degree of freedom to carry quantum information. In this paper, we give a description of the basic SAW components needed to develop quantum circuits, where propagating or localized SAW-phonons are used both to study basic physics and to manipulate quantum information. Using phonons instead of photons offers new possibilities which make these quantum acoustic circuits very interesting. We discuss general considerations for SAW experiments at the quantum level and describe experiments both with SAW resonators and with interaction between SAWs and a qubit. We also discuss several potential future developments.
03
Jun
2015
Detecting Topological Features of Microwave Photons in a Circuit Quantum Electrodynamics Lattice
We propose a scheme of investigating topological photonics in superconducting quantum circuits. There are two major ingredients. The first is the synthesization of an artificial gauge
field on a circuit quantum electrodynamics lattice through the developed dynamic modulation approach. The flexibility of such parametric method leads to the effective \textit{in situ} tunable magnetic field for photons on a square lattice. The second, which is the main new ingredient of this paper, considers the detection of the topological phases of the photons. Our idea employs the exotic properties of the edge state modes which result in novel steady states of the lattice under the driving-dissipation competition. Through the pumping and the photon-number measurements of merely few sites, not only the spatial and the spectral characters, but also the momentums and even the integer topological quantum numbers of the edge states can be directly probed, which reveal unambiguously the topological nature of the photons on the proposed lattice. The physical implementation of our scheme is discussed in detail, where our results pinpoint the feasibility based on current level of experimental technology.
28
Mai
2015
Analysis of the spectroscopy of a hybrid system composed of a superconducting flux qubit and diamond NV centers
A hybrid system that combines the advantages of a superconducting flux qubit and an electron spin ensemble in diamond is one of the promising devices to realize quantum information
processing. Exploring the properties of the superconductor diamond system is essential for the efficient use of this device. When we perform spectroscopy of this system, significant power broadening is observed. However, previous models to describe this system are known to be applicable only when the power broadening is negligible. Here, we construct a new approach to analyze this system with strong driving, and succeed to reproduce the spectrum with the power broadening. Our results provide an efficient way to analyze this hybrid system.
27
Mai
2015
Observation of the correspondence between Landau-Zener transition and Kibble-Zurek mechanism with a superconducting qubit system
We present a direct experimental observation of the correspondence between Landau-Zener transition and Kibble-Zurek mechanism with a superconducting qubit system. We develop a time-resolved
approach to study quantum dynamics of the Landau-Zener transition. By using this method, we observe the key features of the correspondence between Landau-Zener transition and Kibble-Zurek mechanism, e.g., the boundary between the adiabatic and impulse regions, the freeze-out phenomenon in the impulse region. Remarkably, the scaling behavior of the population in the excited state, an analogical phenomenon originally predicted in Kibble-Zurek mechanism, is also observed in the Landau-Zener transition.
25
Mai
2015
Demonstration of Robust Quantum Gate Tomography via Randomized Benchmarking
Typical quantum gate tomography protocols struggle with a self-consistency problem: the gate operation cannot be reconstructed without knowledge of the initial state and final measurement,
but such knowledge cannot be obtained without well-characterized gates. A recently proposed technique, known as randomized benchmarking tomography (RBT), sidesteps this self-consistency problem by designing experiments to be insensitive to preparation and measurement imperfections. We implement this proposal in a superconducting qubit system, using a number of experimental improvements including implementing each of the elements of the Clifford group in single `atomic‘ pulses and custom control hardware to enable large overhead protocols. We show a robust reconstruction of several single-qubit quantum gates, including a unitary outside the Clifford group. We demonstrate that RBT yields physical gate reconstructions that are consistent with fidelities obtained by randomized benchmarking.
21
Mai
2015
Tuneable on-demand single-photon source
An on-demand single photon source is a key element in a series of prospective quantum technologies and applications. We demonstrate the operation of a tuneable on-demand microwave photon
source based on a fully controllable superconducting artificial atom strongly coupled to an open-end transmission line (a 1D half-space). The atom emits a photon upon excitation by a short microwave π-pulse applied through a control line weakly coupled to the atom. The emission and control lines are well decoupled from each other, preventing the direct leakage of radiation from the π-pulses used for excitation. The estimated efficiency of the source is higher than 75\% and remains to be about 50\% or higher over a wide frequency range from 6.7 to 9.1 GHz continuously tuned by an external magnetic field.
19
Mai
2015
Universal quantum simulation with prethreshold superconducting qubits: Single-excitation subspace method
Current quantum computing architectures lack the size and fidelity required for universal fault-tolerant operation, limiting the practical implementation of key quantum algorithms to
all but the smallest problem sizes. In this work we propose an alternative method for general-purpose quantum computation that is ideally suited for such „prethreshold“ superconducting hardware. Computations are performed in the n-dimensional single-excitation subspace (SES) of a system of n tunably coupled superconducting qubits. The approach is not scalable, but allows many operations in the unitary group SU(n) to be implemented by a single application of the Hamiltonian, bypassing the need to decompose a desired unitary into elementary gates. This feature makes large, nontrivial quantum computations possible within the available coherence time. We show how to use a programmable SES chip to perform fast amplitude amplification and phase estimation, two versatile quantum subalgorithms. We also show that an SES processor is well suited for Hamiltonian simulation, specifically simulation of the Schrodinger equation with a real but otherwise arbitrary nxn Hamiltonian matrix. We discuss the utility and practicality of such a universal quantum simulator, and propose its application to the study of realistic atomic and molecular collisions.
18
Mai
2015
Non-Abelian Lattice Gauge Theories in Superconducting Circuits
We propose a digital quantum simulator of non-Abelian pure-gauge models with a superconducting circuit setup. Within the framework of quantum link models, we build a minimal instance
of a pure SU(2) gauge theory, using triangular plaquettes involving geometric frustration. This realization is the least demanding, in terms of quantum simulation resources, of a non-Abelian gauge dynamics. We present two superconducting architectures that can host the quantum simulation, estimating the requirements needed to run possible experiments. The proposal establishes a path to the experimental simulation of non-Abelian physics with solid-state quantum platforms.