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
2023
Quantum entanglement generation on magnons assisted with microwave cavities coupled to a superconducting qubit
We present protocols to generate quantum entanglement on nonlocal magnons in hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave cavities and a superconducting (SC)
qubit. In the schemes, the YIGs are coupled to respective microwave cavities in resonant way, and the SC qubit is placed at the center of the cavities, which interacts with the cavities simultaneously. By exchanging the virtual photon, the cavities can indirectly interact in the far-detuning regime. Detailed protocols are presented to establish entanglement for two, three and arbitrary N magnons with reasonable fidelities.
13
Jan
2023
Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multi-Chip Module
The single flux quantum (SFQ) digital superconducting logic family has been proposed for the scalable control of next-generation superconducting qubit arrays. In the initial implementation,
SFQ-based gate fidelity was limited by quasiparticle (QP) poisoning induced by the dissipative on-chip SFQ driver circuit. In this work, we introduce a multi-chip module architecture to suppress phonon-mediated QP poisoning. Here, the SFQ elements and qubits are fabricated on separate chips that are joined with In bump bonds. We use interleaved randomized benchmarking to characterize the fidelity of SFQ-based gates, and we demonstrate an error per Clifford gate of 1.2(1)%, an order-of-magnitude reduction over the gate error achieved in the initial realization of SFQ-based qubit control. We use purity benchmarking to quantify the contribution of incoherent error at 0.96(2)%; we attribute this error to photon-mediated QP poisoning mediated by the resonant mm-wave antenna modes of the qubit and SFQ-qubit coupler. We anticipate that a straightforward redesign of the SFQ driver circuit to limit the bandwidth of the SFQ pulses will eliminate this source of infidelity, allowing SFQ-based gates with fidelity approaching theoretical limits, namely 99.9% for resonant sequences and 99.99% for more complex pulse sequences involving variable pulse-to-pulse separation.
11
Jan
2023
Performance Analysis of Superconductor-constriction-Superconductor Transmon Qubits
This work presents a computational analysis of a superconducting transmon qubit design, in which the superconductor-insulator-superconductor (SIS) Josephson junction is replaced by
a co-planar, superconductor-constriction-superconductor (ScS) junction. For short junctions having a Kulik-Omelyanchuk current-phase relationship, we find that the ScS transmon has an improved charge dispersion compared to the SIS transmon, with a tradeoff of 50% smaller anharmonicity. These calculations provide a framework for estimating the superconductor material properties and junction dimensions needed to provide proper ScS transmon operation at typical gigahertz frequencies.
10
Jan
2023
Synchronization of Josephson junction in series array
Multi-qubit quantum processors coupled to networking provides the state-of-the-art quantum computing platform. However, each qubit has unique eigenfrequency even though fabricated in
the same process. To continue quantum gate operations besides the detection and correction of errors it is required that the qubits must be synchronized in the same frequency. This study uses Kuramoto model which is a link between statistical mean-field technique and non-linear dynamics to synchronize the qubits applying small noise in the system. This noise could be any externally applied noise function or just noise from the difference of frequencies of qubits. The Kuramoto model tunes the coupled oscillators adjusting the coupling strength between the oscillators to evolve from the state of incoherence to the synchronized state.
Lower-temperature fabrication of airbridges by grayscale lithography to increase yield of nanowire transmons in circuit QED quantum processors
Quantum hardware based on circuit quantum electrodynamics makes extensive use of airbridges to suppress unwanted modes of wave propagation in coplanar-waveguide transmission lines.
Airbridges also provide an interconnect enabling transmission lines to cross. Traditional airbridge fabrication produces a curved profile by reflowing resist at elevated temperature prior to metallization. The elevated temperature can affect the coupling energy and even yield of pre-fabricated Josephson elements of superconducting qubits, tuneable couplers and resonators. We employ grayscale lithography in place of reflow to reduce the peak airbridge processing temperature from 200 to 150∘C, showing a substantial yield increase of transmon qubits with Josephson elements realized using Al-contacted InAs nanowires.
09
Jan
2023
Entangling microwaves with optical light
Entanglement is a genuine quantum mechanical property and the key resource in currently developed quantum technologies. Sharing this fragile property between superconducting microwave
circuits and optical or atomic systems would enable new functionalities but has been hindered by the tremendous energy mismatch of ∼105 and the resulting mutually imposed loss and noise. In this work we create and verify entanglement between microwave and optical fields in a millikelvin environment. Using an optically pulsed superconducting electro-optical device, we deterministically prepare an itinerant microwave-optical state that is squeezed by 0.72+0.31−0.25\,dB and violates the Duan-Simon separability criterion by >5 standard deviations. This establishes the long-sought non-classical correlations between superconducting circuits and telecom wavelength light with wide-ranging implications for hybrid quantum networks in the context of modularization, scaling, sensing and cross-platform verification.
Time-optimal universal quantum gates on superconducting circuits
Decoherence is an inevitable problem when targeting to increase the fidelity of quantum gates, and thus is one of the main obstacles for large-scale quantum computation. The longer
a gate operation is, the more decoherence-induced gate infidelity will be. Therefore, how to shorten the gate time becomes an urgent problem to be solved. To this end, time-optimal control based on solving the quantum brachistochron equation is a straightforward solution. Here, based on time-optimal control, we propose a scheme to realize universal quantum gates on superconducting qubits, in a two-dimensional square lattice configuration, and the two-qubit gate fidelity can be higher than 99.7%. Meanwhile, we can further accelerate the z-axis gate considerably by adjusting the time-independent detuning. Finally, in order to reduce the influence of the dephasing error, decoherence free subspace is also incorporated in our physical implementation. Therefore, we present a promising fast scheme for large-scale quantum computation.
Single electron-spin-resonance detection by microwave photon counting
Electron spin resonance (ESR) spectroscopy is the method of choice for characterizing paramagnetic impurities, with applications ranging from chemistry to quantum computing, but it
gives access only to ensemble-averaged quantities due to its limited signal-to-noise ratio. Single-electron-spin sensitivity has however been reached using spin-dependent photoluminescence, transport measurements, and scanning-probe techniques. These methods are system-specific or sensitive only in a small detection volume, so that practical single spin detection remains an open challenge. Here, we demonstrate single electron magnetic resonance by spin fluorescence detection, using a microwave photon counter at cryogenic temperatures. We detect individual paramagnetic erbium ions in a scheelite crystal coupled to a high-quality factor planar superconducting resonator to enhance their radiative decay rate, with a signal-to-noise ratio of 1.9 in one second integration time. The fluorescence signal shows anti-bunching, proving that it comes from individual emitters. Coherence times up to 3 ms are measured, limited by the spin radiative lifetime. The method has the potential to apply to arbitrary paramagnetic species with long enough non-radiative relaxation time, and allows single-spin detection in a volume as large as the resonator magnetic mode volume ( 10 um^3 in the present experiment), orders of magnitude larger than other single-spin detection techniques. As such, it may find applications in magnetic resonance and quantum computing.
24
Dez
2022
DEC-QED: A flux-based 3D electrodynamic modeling approach to superconducting circuits and materials
Modeling the behavior of superconducting electronic circuits containing Josephson junctions is crucial for the design of superconducting information processors and devices. In this
paper, we introduce DEC-QED, a computational approach for modeling the electrodynamics of superconducting electronic circuits containing Josephson junctions in arbitrary three-dimensional electromagnetic environments. DEC-QED captures the non-linear response and induced currents of BCS superconductors and accurately captures phenomena such as the Meissner effect, flux quantization and Josephson effects. Using a finite-element construction based on Discrete Exterior Calculus (DEC), DEC-QED can accurately simulate transient and long-time dynamics in superconductors. The expression of the entire electrodynamic problem in terms of the gauge-invariant flux field and charges makes the resulting classical field theory suitable for second quantization.
23
Dez
2022
Quasiperiodic circuit quantum electrodynamics
Superconducting circuits are an extremely versatile platform to realize quantum information hardware, and, as was recently realized, to emulate topological materials, such as three-dimensional
Weyl semimetals or two-dimensional Chern insulators. We here show how a simple arrangement of capacitors and conventional superconductor-insulator-superconductor (SIS) junctions can realize a nonlinear capacitive element with a surprising property: it can be quasiperiodic with respect to the quantized Cooper-pair charge. Integrating this element into a larger circuit opens the door towards the engineering of an even broader class of systems. First, we use it to simulate a protected Dirac material defined in the transport degrees of freedom. The presence of the Dirac points leads to a suppression of the classical part of the finite-frequency current noise. Second, we exploit the quasiperiodicity to implement the Aubry-André model, and thereby emulate Anderson localization in charge space. Importantly, the realization by means of transport degrees of freedom allows for a straightforward generalization to arbitrary dimensions. Moreover, our setup implements a truly non-interacting version of the model, in which the macroscopic quantum mechanics of the circuit already incorporates microscopic interaction effects. We propose that measurements of the quantum fluctuations of the charge can be used to directly probe the localization effect. Finally, we present an outlook in which the nonlinear capacitance is employed in a quantum circuit emulating a magic-angle effect akin to twisted bilayer graphene.