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
Mai
2022
Prospects of cooling a mechanical resonator with a transmon qubit in c-QED setup
Hybrid devices based on the superconducting qubits have emerged as a promising platform for controlling the quantum states of macroscopic resonators. The nonlinearity added by a qubit
can be a valuable resource for such control. Here we study a hybrid system consisting of a mechanical resonator longitudinally coupled to a transmon qubit. The qubit readout can be done by coupling to a readout mode like in c-QED setup. The coupling between the mechanical resonator and transmon qubit can be implemented by modulation of the SQUID inductance. In such a tri-partite system, we analyze the steady-state occupation of the mechanical mode when all three modes are dispersively coupled. We use the quantum-noise and the Lindblad formalism to show that the sideband cooling of the mechanical mode to its ground state is achievable. We further experimentally demonstrate that measurements of the thermomechanical motion is possible in the dispersive limit, while maintaining a large coupling between qubit and mechanical mode. Our theoretical calculations suggest that single-photon strong coupling is within the experimental reach in such hybrid devices.
12
Mai
2022
Quasiparticles in superconducting qubits with asymmetric junctions
Designing the spatial profile of the superconducting gap – gap engineering – has long been recognized as an effective way of controlling quasiparticles in superconducting
devices. In aluminum films, their thickness modulates the gap; therefore, standard fabrication of Al/AlOx/Al Josephson junctions, which relies on overlapping a thicker film on top of a thinner one, always results in gap-engineered devices. Here we reconsider quasiparticle effects in superconducting qubits to explicitly account for the unavoidable asymmetry in the gap on the two sides of a Josephson junction. We find that different regimes can be encountered in which the quasiparticles have either similar densities in the two junction leads, or are largely confined to the lower-gap lead. Qualitatively, for similar densities the qubit’s excited state population is lower but its relaxation rate higher than when the quasiparticles are confined; therefore, there is a potential trade-off between two desirable properties in a qubit.
09
Mai
2022
Co-Designed Architectures for Modular Superconducting Quantum Computers
Noisy, Intermediate Scale Quantum (NISQ) computers have reached the point where they can show the potential for quantum advantage over classical computing. Unfortunately, NISQ machines
introduce sufficient noise that even for moderate size quantum circuits the results can be unreliable. We propose a collaboratively designed superconducting quantum computer using a Superconducting Nonlinear Asymmetric Inductive eLement (SNAIL) modulator. The SNAIL modulator is designed by considering both the ideal fundamental qubit gate operation while maximizing the qubit coupling capabilities. We and others have demonstrated that the family, and particularly ‾‾‾‾‾‾√, provides an advantage over as a basis gate. In this work, we show how the SNAIL natively implements ‾‾‾‾‾‾√n functions with high-degree couplings and implementation of gates realized through proportionally scaled pulse lengths. Based on our previously demonstrated SNAIL-based quantum state router we present preliminary data extending the SNAIL-based modulator to four qubit modules. Furthermore, in this work, we co-design future SNAIL-based quantum computers that utilize the construction of richer interconnections based on classical 4-ary tree and hypercubes and compare their advantage to the traditional lattice and heavy-hex lattice for a suite of common quantum algorithms. To make our results more general, we consider both scenarios in which the total circuit time, for implementations dominated by decoherence, or total gate count, for implementations dominated by control imperfections. We demonstrate the co-design advantage based on real hardware SNAIL implementations and extrapolate to larger system sizes characterized from our real multi ‾‾‾‾‾‾√n qubit system with 4-ary tree and hypercube inspired interconnects.
Fast high-fidelity composite gates in superconducting qubits: Beating the Fourier leakage limit
We present a method for quantum control in superconducting qubits, which overcomes the Fourier limit for the gate duration imposed by leakage to upper states. The method uses composite
pulses, which allow for the correction of various types of errors, which naturally arise in the system, by destructive interference of these errors. We use our approach to produce complete and partial population transfer between the qubit states, as well as the three basic single-qubit quantum gates. Our simulations show a substantial reduction of the typical errors and a gate speed-up by an order of magnitude.
Demonstration of tunable three-body interactions between superconducting qubits
Nonpairwise multi-qubit interactions present a useful resource for quantum information processors. Their implementation would facilitate more efficient quantum simulations of molecules
and combinatorial optimization problems, and they could simplify error suppression and error correction schemes. Here we present a superconducting circuit architecture in which a coupling module mediates 2-local and 3-local interactions between three flux qubits by design. The system Hamiltonian is estimated via multi-qubit pulse sequences that implement Ramsey-type interferometry between all neighboring excitation manifolds in the system. The 3-local interaction is coherently tunable over several MHz via the coupler flux biases and can be turned off, which is important for applications in quantum annealing, analog quantum simulation, and gate-model quantum computation.
07
Mai
2022
Titanium Nitride Film on Sapphire Substrate with Low Dielectric Loss for Superconducting Qubits
Dielectric loss is one of the major decoherence sources of superconducting qubits. Contemporary high-coherence superconducting qubits are formed by material systems mostly consisting
of superconducting films on substrate with low dielectric loss, where the loss mainly originates from the surfaces and interfaces. Among the multiple candidates for material systems, a combination of titanium nitride (TiN) film and sapphire substrate has good potential because of its chemical stability against oxidization, and high quality at interfaces. In this work, we report a TiN film deposited onto sapphire substrate achieving low dielectric loss at the material interface. Through the systematic characterizations of a series of transmon qubits fabricated with identical batches of TiN base layers, but different geometries of qubit shunting capacitors with various participation ratios of the material interface, we quantitatively extract the loss tangent value at the substrate-metal interface smaller than 8.9×10−4 in 1-nm disordered layer. By optimizing the interface participation ratio of the transmon qubit, we reproducibly achieve qubit lifetimes of up to 300 μs and quality factors approaching 8 million. We demonstrate that TiN film on sapphire substrate is an ideal material system for high-coherence superconducting qubits. Our analyses further suggest that the interface dielectric loss around the Josephson junction part of the circuit could be the dominant limitation of lifetimes for state-of-the-art transmon qubits.
06
Mai
2022
Tunable directional photon scattering from a pair of superconducting qubits
The ability to control the direction of scattered light in integrated devices is crucial to provide the flexibility and scalability for a wide range of on-chip applications, such as
integrated photonics, quantum information processing and nonlinear optics. In the optical and microwave frequency ranges tunable directionality can be achieved by applying external magnetic fields, that modify optical selection rules, by using nonlinear effects, or interactions with vibrations. However, these approaches are less suitable to control propagation of microwave photons inside integrated superconducting quantum devices, that is highly desirable. Here, we demonstrate tunable directional scattering with just two transmon qubits coupled to a transmission line based on periodically modulated transition frequency. By changing the symmetry of the modulation, governed by the relative phase between the local modulation tones, we achieve directional forward or backward photon scattering.
03
Mai
2022
SWAP gate between a Majorana qubit and a parity-protected superconducting qubit
High fidelity quantum information processing requires a combination of fast gates and long-lived quantum memories. In this work, we propose a hybrid architecture, where a parity-protected
superconducting qubit is directly coupled to a Majorana qubit, which plays the role of a quantum memory. The superconducting qubit is based upon a π-periodic Josephson junction realized with gate-tunable semiconducting wires, where the tunneling of individual Cooper pairs is suppressed. One of the wires additionally contains four Majorana zero modes that define a qubit. We demonstrate that this enables the implementation of a SWAP gate, allowing for the transduction of quantum information between the topological and conventional qubit. This architecture combines fast gates, which can be realized with the superconducting qubit, with a topologically protected Majorana memory.
27
Apr
2022
High-fidelity quantum transduction with long coherence time superconducting resonators
We propose a novel quantum transduction hybrid system based on the coupling of long-coherence time superconducting cavities with electro-optic resonators to achieve high-efficiency
and high-fidelity in quantum communication protocols and quantum sensing.
21
Apr
2022
Superconducting microwave resonators with non-centrosymmetric nonlinearity
We investigated both theoretically and experimentally open-ended coplanar waveguide resonators with rf SQUIDs embedded in the central conductor at different positions. These rf SQUIDs
can be tuned by an external magnetic field and thus may exhibit the non-centrosymmetric nonlinearity of χ(2) type with suppressed Kerr nonlinearity. We demonstrated that this nonlinearity allows for efficient mixing of λ/2 and λ modes in the cavity and thus enables various parametric effects with three wave mixing. These effects are the second harmonic generation, the half tone generation, the parametric amplification in both degenerate and non-degenerate regimes and deamplification in degenerate regime.