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
Mai
2020
Reducing the impact of radioactivity on quantum circuits in a deep-underground facility
As quantum coherence times of superconducting circuits have increased from nanoseconds to hundreds of microseconds, they are currently one of the leading platforms for quantum information
processing. However, coherence needs to further improve by orders of magnitude to reduce the prohibitive hardware overhead of current error correction schemes. Reaching this goal hinges on reducing the density of broken Cooper pairs, so-called quasiparticles. Here, we show that environmental radioactivity is a significant source of nonequilibrium quasiparticles. Moreover, ionizing radiation introduces time-correlated quasiparticle bursts in resonators on the same chip, further complicating quantum error correction. Operating in a deep-underground lead-shielded cryostat decreases the quasiparticle burst rate by a factor fifty and reduces dissipation up to a factor four, showcasing the importance of radiation abatement in future solid-state quantum hardware.
Superconducting resonator single-photon spectroscopy through electromagnetically induced transparency
Investigation of intrinsic loss mechanism of superconducting resonator is a crucial task toward the study of the constituent material as well as application in quantum information process.
Typical approach from transmission or reflection spectrum is however subjected to Fano-effect, which can induce systematic errors in discerning intrinsic and external losses. To avoid such requires under-coupled resonator and consequently sets a challenge when a large quality factor is expected and measurements at single-photon power levels is required. In this work, we propose and demonstrate a new approach with additional qubit coupled dispersively. Inducing electromagnetically induced transparency (EIT) in qubit spectrum, we can extract the resonator’s single-photon internal linewidth. Our work demonstrates a practical application of EIT for device spectroscopy.
04
Mai
2020
Destructive Little-Parks Effect in a Full-Shell Nanowire-based Transmon
A semiconductor transmon with an epitaxial Al shell fully surrounding an InAs nanowire core is investigated in the low EJ/EC regime. Little-Parks oscillations as a function of fluxalong the hybrid wire axis are destructive, creating lobes of reentrant superconductivity separated by a metallic state at a half-quantum of applied flux. In the first lobe, phase winding around the shell can induce topological superconductivity in the core. Coherent qubit operation is observed in both the zeroth and first lobes. Splitting of parity bands by coherent single-electron coupling across the junction is not resolved beyond line broadening, placing a bound on Majorana coupling, EM/h < 10 MHz, much smaller than the Josephson coupling EJ/h ~ 4.7 GHz.[/expand]
02
Mai
2020
Cavity electro-optics in thin-film lithium niobate for efficient microwave-to-optical transduction
Linking superconducting quantum devices to optical fibers via microwave-optical quantum transducers may enable large scale quantum networks. For this application, transducers based
on the Pockels electro-optic (EO) effect are promising for their direct conversion mechanism, high bandwidth, and potential for low-noise operation. However, previously demonstrated EO transducers require large optical pump power to overcome weak EO coupling and reach high efficiency. Here, we create an EO transducer in thin-film lithium niobate, leveraging the low optical loss and strong EO coupling in this platform. We demonstrate a transduction efficiency of up to 2.7×10−5, and a pump-power normalized efficiency of 1.9×10−6/μW. The transduction efficiency can be improved by further reducing the microwave resonator’s piezoelectric coupling to acoustic modes, increasing the optical resonator quality factor to previously demonstrated levels, and changing the electrode geometry for enhanced EO coupling. We expect that with further development, EO transducers in thin-film lithium niobate can achieve near-unity efficiency with low optical pump power.
Cryogenic microwave-to-optical conversion using a triply-resonant lithium niobate on sapphire transducer
Quantum networks are likely to have a profound impact on the way we compute and communicate in the future. In order to wire together superconducting quantum processors over kilometer-scale
distances, we need transducers that can generate entanglement between the microwave and optical domains with high fidelity. We present an integrated electro-optic transducer that combines low-loss lithium niobate photonics with superconducting microwave resonators on a sapphire substrate. Our triply-resonant device operates in a dilution refrigerator and converts microwave photons to optical photons with an on-chip efficiency of 6.6×10−6 and a conversion bandwidth of 20 MHz. We discuss design trade-offs in this device, including strategies to manage acoustic loss, and outline ways to increase the conversion efficiency in the future.
29
Apr
2020
Efficient cavity control with SNAP gates
Microwave cavities coupled to superconducting qubits have been demonstrated to be a promising platform for quantum information processing. A major challenge in this setup is to realize
universal control over the cavity. A promising approach are selective number-dependent arbitrary phase (SNAP) gates combined with cavity displacements. It has been proven that this is a universal gate set, but a central question remained open so far: how can a given target operation be realized efficiently with a sequence of these operations. In this work, we present a practical scheme to address this problem. It involves a hierarchical strategy to insert new gates into a sequence, followed by a co-optimization of the control parameters, which generates short high-fidelity sequences. For a broad range of experimentally relevant applications, we find that they can be implemented with 3 to 4 SNAP gates, compared to up to 50 with previously known techniques.
27
Apr
2020
Bare-excitation ground state of a spinless-fermion — boson model and W-state engineering in an array of superconducting qubits and resonators
This work unravels an interesting property of a one-dimensional lattice model that describes a single itinerant spinless fermion (excitation) coupled to zero-dimensional (dispersionless)
bosons through two different nonlocal-coupling mechanisms. Namely, below a critical value of the effective excitation-boson coupling strength the exact ground state of this model is the zero-quasimomentum Bloch state of a bare excitation. It is demonstrated here how this last property of the model under consideration can be exploited for a fast, deterministic preparation of multipartite W states in a readily realizable system of inductively-coupled superconducting qubits and microwave resonators.
26
Apr
2020
Engineering Dynamical Sweet Spots to Protect Qubits from 1/f Noise
Protecting superconducting qubits from low-frequency noise is essential for advancing superconducting quantum computation. We here introduce a protocol for engineering dynamical sweet
spots which reduce the susceptibility of a qubit to low-frequency noise. Based on the application of periodic drives, the location of the dynamical sweet spots can be obtained analytically in the framework of Floquet theory. In particular, for the example of fluxonium biased slightly away from half a flux quantum, we predict an enhancement of pure-dephasing by three orders of magnitude. Employing the Floquet eigenstates as the computational basis, we show that high-fidelity single-qubit gates can be implemented while maintaining dynamical sweet-spot operation. We further confirm that qubit readout can be performed by adiabatically mapping the Floquet states back to the static qubit states, and subsequently applying standard measurement techniques. Our work provides an intuitive tool to encode quantum information in robust, time-dependent states, and may be extended to alternative architectures for quantum information processing.
24
Apr
2020
Dynamics and multiqubit entanglement in distant resonators
We consider the dynamics of the photon states in distant resonators coupled to a common bus resonator at different positions. The frequencies of distant resonators from a common bus
resonator are equally detuned. These frequency detunings are kept larger than the coupling strengths of each resonator to the common bus resonator to satisfy the dispersive interaction regime. In the dispersive regime, we show that the time dynamics of the system evolve to an arbitrary W-type state in a single step at various interaction times. Our results show that a one-step generation of arbitrary W-type states can be achieved with high fidelity in a system of superconducting resonators.
23
Apr
2020
Robust and Fast Holonomic Quantum Gates with Encoding on Superconducting Circuits
High-fidelity and robust quantum manipulation is the key for scalable quantum computation. Therefore, due to the intrinsic operational robustness, quantum manipulation induced by geometric
phases is one of the promising candidates. However, the longer gate time for geometric operations and more physical-implementation difficulties hinder its practical and wide applications. Here, we propose a simplified implementation of universal holonomic quantum gates on superconducting circuits with experimentally demonstrated techniques, which can remove the two main challenges by introducing the time-optimal control into the construction of quantum gates. Remarkably, our scheme is also based on a decoherence-free subspace encoding, with minimal physical qubit resource, which can further immune to error caused by qubit-frequency drift, which is regarded as the main error source for large scale superconducting circuits. Meanwhile, we deliberately design the quantum evolution to eliminate gate error caused by unwanted leakage sources. Therefore, our scheme is more robust than the conventional ones, and thus provides a promising alternative strategy for scalable fault-tolerant quantum computation.