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
16
Feb
2020
Pulse-qubit interaction in a superconducting circuit under frictively dissipative environment
Microwave pulses are used ubiquitously to control and measure qubits fabricated on superconducting circuits. Due to continual environmental coupling, the qubits undergo decoherence
both when it is free and during its interaction with the microwave pulse. As quantum logic gates are executed through pulse-qubit interaction, we study theoretically the decoherence-induced effects during the interaction, especially the variations of the pulse, under a dissipative environment with linear spectral distribution. We find that a transmissible pulse of finite width adopts an asymmetric multi-hump shape, due to the imbalanced pumping and emitting rates of the qubit during inversion when the environment is present. The pulse shape reduces to a solitonic pulse at vanishing dissipation and a pulse train at strong dissipation. We give detailed analysis of the environmental origin from both the perspectives of envelope and phase of the propagating pulse.
05
Feb
2020
Breaking the trade-off between fast control and long lifetime of a superconducting qubit
The rapid development in designs and fabrication techniques of superconducting qubits has helped making coherence times of qubits longer. In the near future, however, the radiative
decay of a qubit into its control line will be a fundamental limitation, imposing a trade-off between fast control and long lifetime of the qubit. In this work, we successfully break this trade-off by strongly coupling another superconducting qubit along the control line. This second qubit, which we call a Josephson quantum filter~(JQF), prevents the qubit from emitting microwave photons and thus suppresses its relaxation, while faithfully transmitting large-amplitude control microwave pulses due to the saturation of the quantum filter, enabling fast qubit control. We observe an improvement of the qubit relaxation time without a reduction of the Rabi frequency. This device could potentially help in the realization of a large-scale superconducting quantum information processor in terms of the heating of the qubit environments and the crosstalk between qubits.
Causality test on Cherenkov effect in circuit QED
We investigate the Cherenkov radiation triggered by qubit acceleration simulated by superconducting circuit. By analyzing the radiation probability, we confirm the existence of Cherenkov
speed threshold, implying that simulating superluminal qubit motion is possible for such a scenario. A question immediately arises: Is such motion compatible with the causality principle? To address the question, we perform a causality test on the simulating system based on the recently developed notion of temporal quantum correlations, pseudo-density matrix and temporal quantum steering. The results suggest that single-mode approximation breaks down even when the system is restricted in weak coupling regime.
Synthesizing three-body interaction of spin chirality with superconducting qubits
Superconducting qubits provide a competitive platform for quantum simulation of complex dynamics that lies at the heart of quantum many-body systems, because of the flexibility and
scalability afforded by the nature of microfabrication. However, in a multiqubit device, the physical form of couplings between qubits is either an electric (capacitor) or magnetic field (inductor), and the associated quadratic field energy determines that only two-body interaction in the Hamiltonian can be directly realized. Here we propose and experimentally synthesize the three-body spin-chirality interaction in a superconducting circuit based on Floquet engineering. By periodically modulating the resonant frequencies of the qubits connected with each other via capacitors, we can dynamically turn on and off qubit-qubit couplings, and further create chiral flows of the excitations in the three-qubit circular loop. Our result is a step toward engineering dynamical and many-body interactions in multiqubit superconducting devices, which potentially expands the degree of freedom in quantum simulation tasks.
04
Feb
2020
Universal Gate Set for Continuous-Variable Quantum Computation with Microwave Circuits
We provide an explicit construction of a universal gate set for continuous-variable quantum computation with microwave circuits. Such a universal set has been first proposed in quantum-optical
setups, but its experimental implementation has remained elusive in that domain due to the difficulties in engineering strong nonlinearities. Here, we show that a realistic microwave architecture allows to overcome this difficulty. As an application, we show that this architecture allows to generate a cubic phase state with an experimentally feasible procedure. This work highlights a practical advantage of microwave circuits with respect to optical systems for the purpose of engineering non-Gaussian states, and opens the quest for continuous-variable algorithms based on a few repetitions of elementary gates from the continuous-variable universal set.
02
Feb
2020
Wavelength transduction from a 3D microwave cavity to telecom using piezoelectric optomechanical crystals
Microwave to optical transduction has received a great deal of interest from the cavity optomechanics community as a landmark application for electro-optomechanical systems. In this
Letter, we demonstrate a novel transducer that combines high-frequency mechanical motion and a microwave cavity for the first time. The system consists of a 3D microwave cavity and a gallium arsenide optomechanical crystal, which has been placed in the microwave electric field maximum. This allows the microwave cavity to actuate the gigahertz-frequency mechanical breathing mode in the optomechanical crystal through the piezoelectric effect, which is then read out using a telecom optical mode. The gallium arsenide optomechanical crystal is a good candidate for low-noise microwave-to-telecom transduction, as it has been previously cooled to the mechanical ground state in a dilution refrigerator. Moreover, the 3D microwave cavity architecture can naturally be extended to couple to superconducting qubits and to create hybrid quantum systems.
30
Jan
2020
Analytical modeling of participation reduction in superconducting coplanar resonator and qubit designs through substrate trenching
A strategy aimed at decreasing dielectric loss in coplanar waveguides (CPW) and qubits involves the creation of trenches in the underlying substrate within the gaps of the overlying
metallization. Participation of contamination layers residing on surfaces and interfaces in these designs can be reduced due to the change in the effective dielectric properties between the groundplane and conductor metallization. Although finite element method approaches have been previously applied to quantify this decrease, an analytical method is presented that can uniquely address geometries possessing small to intermediate substrate trench depths. Conformal mapping techniques produce transformed CPW and qubit geometries without substrate trenching but a non-uniform contamination layer thickness. By parametrizing this variation, one can calculate surface participation through the use of a two-dimensional, analytical approximation that properly captures singularities in the electric field intensity near the metallization corners and edges. Examples demonstrate two regimes with respect to substrate trench depth that capture an initial increase in substrate-to-air surface participation due to the trench sidewalls and an overall decrease in surface participation due to the reduction in the effective dielectric constant, and are compared to experimental measurements to extract loss tangents on this surface.
28
Jan
2020
A quantum heat switch based on a driven qubit
Heat flow management at the nanoscale is of great importance for emergent quantum technologies. For instance, a thermal sink that can be activated on-demand is a highly desirable tool
that may accommodate the need to evacuate excess heat at chosen times, e.g. to maintain cryogenic temperatures or reset a quantum system to ground, and the possibility of controlled unitary evolution otherwise. Here we propose a design of such heat switch based on a single coherently driven qubit. We show that the heat flow provided by a hot source to the qubit can be switched on and off by varying external parameters, the frequency and the intensity of the driving. The complete suppression of the heat flow is a quantum effect occurring for specific driving parameters that we express and we analyze the role of the coherences in the free qubit energy eigenbasis. We finally study the feasibility of this quantum heat switch in a circuit QED setup involving a charge qubit coupled to thermal resistances. We demonstrate robustness to experimental imperfections such as additional decoherence, paving the road towards experimental verification of this effect.
27
Jan
2020
Light-dressing of a diatomic superconducting artificial molecule
In this work, we irradiate a superconducting artificial molecule composed of two magnetic-flux-tunable transmons with microwave light while monitoring its state via joint dispersive
readout. At certain fluxes, the molecule demonstrates a complex spectrum deviating qualitatively from the solution of the Schrödinger equation without driving. We reproduce the observed extra spectral lines accurately by numerical simulations, and find them to be a consequence of an Autler-Townes-like effect when a single tone is simultaneously dressing the system and probing the transitions between new eigenstates. We present self-consistent analytical models accounting both these processes at the same time that agree well with both experiment and numerical simulation. This study is an important step towards understanding the behaviour of complex systems of many atoms interacting coherently with strong radiation.
Quantum annealing with capacitive-shunted flux qubits
Quantum annealing (QA) provides us with a way to solve combinatorial optimization problems. In the previous demonstration of the QA, a superconducting flux qubit (FQ) was used. However,
the flux qubits in these demonstrations have a short coherence time such as tens of nano seconds. For the purpose to utilize quantum properties, it is necessary to use another qubit with a better coherence time. Here, we propose to use a capacitive-shunted flux qubit (CSFQ) for the implementation of the QA. The CSFQ has a few order of magnitude better coherence time than the FQ used in the QA. We theoretically show that, although it is difficult to perform the conventional QA with the CSFQ due to the form and strength of the interaction between the CSFQs, a spin-lock based QA can be implemented with the CSFQ even with the current technology. Our results pave the way for the realization of the practical QA that exploits quantum advantage with long-lived qubits.