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
Mä
2014
Many-Body Interactions with Tunable-Coupling Transmon Qubits
The efficient implementation of many-body interactions in superconducting circuits allows for the realization of multipartite entanglement and topological codes, as well as the efficient
simulation of highly-correlated fermionic systems. We propose the engineering of fast multiqubit interactions with tunable transmon-resonator couplings. This dynamics is obtained by the modulation of magnetic fluxes threading SQUID loops embedded in the transmon devices. We consider the feasibility of the proposed implementation in a realistic scenario and discuss potential applications.
01
Mä
2014
Universal quantum gates on microwave photons assisted by circuit quantum electrodynamics
Based on a microwave-photon quantum processor with multiple superconducting resonators coupled to one three-level superconducting qutrit, we construct the controlled-phase (c-phase)
and controlled-controlled-phase (cc-phase) gates on microwave-photon-resonator qudits, by combination of the photon-number-dependent frequency-shift effect and the resonant operation between the qutrit and a resonator. This distinct feature provides us a useful way for achieving higher fidelity quantum logic gates on resonator qudits in a shorter operation time, compared with others. The fidelity of our c-phase gate can reach 99.51% within 92 ns. The fidelity of our cc-phase gate on three resonator qudits constructed here in the first time, can reach 92.92% within 124.64 ns.
Optimal quantum control using randomized benchmarking
We present a method for optimizing quantum control in experimental systems, using a subset of randomized benchmarking measurements to rapidly infer error. This is demonstrated to improve
single- and two-qubit gates, minimize gate bleedthrough, where a gate mechanism can cause errors on subsequent gates, and identify control crosstalk in superconducting qubits. This method is able to correct parameters to where control errors no longer dominate, and is suitable for automated and closed-loop optimization of experimental systems
28
Feb
2014
Simulating systems of itinerant spin-carrying particles using arrays of superconducting qubits and resonators
We propose potential setups for the quantum simulation of itinerant spin-carrying particles in a superconducting qubit-resonator array. The standard Jaynes-Cummings-Hubbard setup studied
by several authors is readily amenable to being used as a quantum simulator for some spin-related phenomena. A more complex setup where multiple qubits and multiple resonator modes are utilized in the simulation gives a higher level of complexity, allowing for example the simulation of external magnetic fields and spin-orbit coupling. This proposal could be implemented in state-of-the-art superconducting circuits in the near future.
Qubit architecture with high coherence and fast tunable coupling
We introduce a superconducting qubit architecture that combines high-coherence qubits and tunable qubit-qubit coupling. With the ability to set the coupling to zero, we demonstrate
that this architecture is protected from the frequency crowding problems that arise from fixed coupling. More importantly, the coupling can be tuned dynamically with nanosecond resolution, making this architecture a versatile platform with applications ranging from quantum logic gates to quantum simulation. We illustrate the advantages of dynamic coupling by implementing a novel adiabatic controlled-Z gate, at a speed approaching that of single-qubit gates. Integrating coherence and scalable control, our „gmon“ architecture is a promising path towards large-scale quantum computation and simulation.
27
Feb
2014
A Multi-Resonator Network for Superconducting Circuits
Superconducting circuits have emerged as a configurable and coherent system to investigate a wide variety of quantum behaviour. This architecture — circuit QED — has been
used to demonstrate phenomena from quantum optics, quantum limited amplification, and small-scale quantum computing. There is broad interest in expanding circuit QED to simulate lattice models (e.g., the Jaynes-Cummings-Hubbard model), generate long-distance entanglement, explore multimode quantum optics, and for topological quantum computing. Here we introduce a new multi-resonator (multi-pole) circuit QED architecture where qubits interact through a network of strongly coupled resonators. This circuit architecture is a novel system to study multimode quantum optics, quantum simulation, and for quantum computing. In this work, we show that the multi-pole architecture exponentially improves contrast for two-qubit gates without sacrificing speed, addressing a growing challenge as superconducting circuits become more complex. We demonstrate the essential characteristics of the multi-pole architecture by implementing a three-pole (three-resonator) filter using planar compact resonators which couples two transmon-type qubits. Using this setup we spectroscopically confirm the multimode circuit QED model, demonstrate suppressed interactions off-resonance, and load single photons into the filter. Furthermore, we introduce an adiabatic multi-pole (AMP) gate protocol to realize a controlled-Z gate between the qubits and create a Bell state with 94.7% fidelity.
Advanced superconducting circuits and devices
Short review on advanced superconducting circuits and devices.
22
Feb
2014
Fast adiabatic control of qubits using optimal windowing theory
A controlled-phase gate was demonstrated in superconducting Xmon transmon qubits with fidelity reaching 99.4%, relying on the adiabatic interaction between the |11> and |02> states.
We explain how adiabaticity is achieved even for fast gate times, based on a theory of non-linear mapping of state errors to a power spectral density and use of optimal window functions. With a solution given in the Fourier basis, optimization is shown to be straightforward for practical cases of an arbitrary state change and finite bandwidth of control signals. We find that errors below 10^-4 are readily achievable for realistic control waveforms.
21
Feb
2014
Interfacing Superconducting Qubits and Telecom Photons via a Rare-Earth Doped Crystal
We propose a scheme to couple short single photon pulses to superconducting qubits. An optical photon is first absorbed into an inhomogeneously broadened rare-earth doped crystal using
controlled reversible inhomogeneous broadening. The optical excitation is then mapped into a spin state using a series of π-pulses and subsequently transferred to a superconducting qubit via a microwave cavity. To overcome the intrinsic and engineered inhomogeneous broadening of the optical and spin transitions in rare earth doped crystals, we make use of a special transfer protocol using staggered π-pulses. We predict total transfer efficiencies on the order of 90%.
19
Feb
2014
Logic gates at the surface code threshold: Superconducting qubits poised for fault-tolerant quantum computing
A quantum computer can solve hard problems – such as prime factoring, database searching, and quantum simulation – at the cost of needing to protect fragile quantum states
from error. Quantum error correction provides this protection, by distributing a logical state among many physical qubits via quantum entanglement. Superconductivity is an appealing platform, as it allows for constructing large quantum circuits, and is compatible with microfabrication. For superconducting qubits the surface code is a natural choice for error correction, as it uses only nearest-neighbour coupling and rapidly-cycled entangling gates. The gate fidelity requirements are modest: The per-step fidelity threshold is only about 99%. Here, we demonstrate a universal set of logic gates in a superconducting multi-qubit processor, achieving an average single-qubit gate fidelity of 99.92% and a two-qubit gate fidelity up to 99.4%. This places Josephson quantum computing at the fault-tolerant threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbour coupling. As a further demonstration, we construct a five-qubit Greenberger-Horne-Zeilinger (GHZ) state using the complete circuit and full set of gates. The results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.