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
08
Okt
2018
Left-handed superlattice metamaterials for circuit-QED
Quantum simulations is a promising field where a controllable system is used to mimic another system of interest, whose properties one wants to investigate. One of the key issues for
such simulations is the ability to control the environment the system couples to, be it to isolate the system or to engineer a tailored environment of interest. One strategy recently put forward for environment engineering is the use of metamaterials with negative index of refraction. Here we build on this concept and propose a circuit-QED simulation of many-body Hamiltonians using superlattice metamaterials. We give a detailed description of a superlattice transmission line coupled to an embedded qubit, and show how this system can be used to simulate the spin-boson model in regimes where analytical and numerical methods usually fail, e.g. the strong coupling regime.
05
Okt
2018
Quantum estimation of parameter in circuit QED by continuous quantum measurement
Designing high-precision and efficient schemes is of crucial importance for quantum parameter estimation in practice. The estimation scheme based on continuous quantum measurement is
one possible type of this, which looks also the most natural choice in case such as continuous dynamical process. In this work we specify the study to the stat-of-the-art superconducting circuit quantum-electrodynamics (QED) system, where the high-quality continuous measurement has been extensively exploited in the past decade. Within the framework of Bayesian estimation and particularly using the quantum Bayesian rule in circuit QED, we numerically simulate the likelihood function as estimator for the Rabi frequency of qubit oscillation. We find that, by proper design of the interaction strength of measurement, the estimate precision can scale with the measurement time beyond the standard quantum limit, which is usually assumed for this type of continuous measurement since no more special quantum resource is involved. We understand this remarkable result by quantum correlation in time between the output signals, and simulate the effect of quantum efficiency of the measurement on the precision scaling behavior.
04
Okt
2018
Cryogenic Microwave Filter Cavity with a Tunability Greater than 5 GHz
A wide variety of applications of microwave cavities, such as measurement and control of superconducting qubits, magnonic resonators, and phase noise filters, would be well served by
having a highly tunable microwave resonance. Often this tunability is desired in situ at low temperatures, where one can take advantage of superconducting cavities. To date, such cryogenic tuning while maintaining a high quality factor has been limited to ∼500MHz. Here we demonstrate a three-dimensional superconducting microwave cavity that shares one wall with a pressurized volume of helium. Upon pressurization of the helium chamber the microwave cavity is deformed, which results in in situ tuning of its resonant frequency by more than 5 GHz, greater than 60% of the original 8 GHz resonant frequency. The quality factor of the cavity remains approximately constant at ≈7×10^3 over the entire range of tuning. As a demonstration of its usefulness, we implement a tunable cryogenic phase noise filter, which reduces the phase noise of our source by approximately 10 dB above 400 kHz.
02
Okt
2018
Superconducting qubit circuit emulation of a vector spin-1/2
We propose a superconducting qubit circuit that can fully emulate a quantum vector spin-1/2, having three independent physical dipole moments whose operators obey the commutation relations
of a vector angular momentum in the computational subspace. Each dipole moment couples to an independently-controllable external bias, emulating the Zeeman effect due to a fictitious, three-component vector magnetic field, and all three of these moments remain relatively constant over a broad range of emulated total fields around zero. This capability, combined with established techniques for two-qubit coupling, would enable for the first time the direct hardware emulation of nearly arbitrary quantum spin-1/2 systems, including the canonical Heisenberg model. In addition to its fundamental interest in condensed-matter physics, this would also constitute a crucial step towards important quantum information processing and quantum annealing capabilities that have so far been inaccessible to any available hardware. These include, for example, strong non-stoquastic interactions for quantum annealing, quantum error suppression, Hamiltonian and holonomic quantum computing, and adiabatic quantum chemistry.
01
Okt
2018
Probing the Tavis-Cummings level splitting with intermediate-scale superconducting circuits
We demonstrate the local control of up to eight two-level systems interacting strongly with a microwave cavity. Following calibration, the frequency of each individual two-level system
(qubit) is tunable without influencing the others. Bringing the qubits one by one on resonance with the cavity, we observe the collective coupling strength of the qubit ensemble. The splitting scales up with the square root of the number of the qubits, being the hallmark of the Tavis-Cummings model. The local control circuitry causes a bypass shunting the resonator, and a Fano interference in the microwave readout, whose contribution can be calibrated away to recover the pure cavity spectrum. The simulator’s attainable size of dressed states is limited by reduced signal visibility, and -if uncalibrated- by off-resonance shifts of sub-components. Our work demonstrates control and readout of quantum coherent mesoscopic multi-qubit system of intermediate scale under conditions of noise.
Intrinsic dissipation in superconducting junctions probed by qubit spectroscopy
We propose to study frequency dependent intrinsic dissipation in a highly transparent Josephson junction by means of qubit spectroscopy. The spectral density of the effective dissipative
bath may contain significant contributions from Andreev bound states coupled to fluctuations of the Josephson phase. Varying either the bias current applied to the junction or magnetic flux through a superconducting ring in the rf-SQUID setup, one can tune the level splitting value close to the bottom of the Josephson potential well. Monitoring the qubit energy relaxation time one can probe the spectral density of the effective dissipative bath and unambiguously identify the contribution emerging from Andreev levels.
28
Sep
2018
Kinetic Inductance Traveling Wave Amplifiers For Multiplexed Qubit Readout
We describe a kinetic inductance traveling-wave (KIT) amplifier suitable for superconducting quantum information measurements and characterize its wideband scattering and noise properties.
We use mechanical microwave switches to calibrate the four amplifier scattering parameters up to the device input and output connectors at the dilution refrigerator base temperature and a tunable temperature load to characterize the amplifier noise. Finally, we demonstrate the high fidelity simultaneous dispersive readout of two superconducting transmon qubits. The KIT amplifier provides low-noise amplification of both readout tones with readout fidelities in excess of 89% and negligible effect on qubit lifetime and coherence.
27
Sep
2018
Granular aluminum: A superconducting material for high impedance quantum circuits
Superconducting quantum information processing machines are predominantly based on microwave circuits with relatively low characteristic impedance, of about 100 Ohm, and small anharmonicity,
which can limit their coherence and logic gate fidelity. A promising alternative are circuits based on so-called superinductors, with characteristic impedances exceeding the resistance quantum RQ=6.4 kΩ. However, previous implementations of superinductors, consisting of mesoscopic Josephson junction arrays, can introduce unintended nonlinearity or parasitic resonant modes in the qubit vicinity, degrading its coherence. Here we present a fluxonium qubit design using a granular aluminum (grAl) superinductor strip. Granular aluminum is a particularly attractive material, as it self-assembles into an effective junction array with a remarkably high kinetic inductance, and its fabrication can be in-situ integrated with standard aluminum circuit processing. The measured qubit coherence time TR2 up to 30 μs illustrates the potential of grAl for applications ranging from protected qubit designs to quantum limited amplifiers and detectors.
Superstrong coupling in circuit quantum electrodynamics
Vacuum fluctuations fundamentally affect an atom by inducing a fnite excited state lifetime along with a Lamb shift of its transition frequency. Here we report the reverse effect: modifcation
of vacuum by a single atom in circuit quantum electrodynamics. Our one-dimensional vacuum is a long section of a high wave impedance (comparable to resistance quantum) superconducting transmission line. It is directly wired to a transmon qubit circuit. Owing to the combination of high impedance and galvanic connection, the transmon’s spontaneous emission linewidth can greatly exceed the discrete transmission line modes spacing. This condition defines a previously unexplored superstrong coupling regime of quantum electrodynamics where many vacuum modes hybridize with each other through interactions with a single atom. We explore this regime by spectroscopically measuring the positions of over 100 consecutive transmission line resonances. The atom reveals itself as a broad peak in the vacuum’s density of states (DOS) together with the Kerr and cross-Kerr interaction of photons at frequencies within the DOS peak. Both dispersive effects are well described by a dissipative Caldeira-Leggett model of our circuit, with the transmon’s quartic anharmonicity treated as a perturbation. Non-perturbative modifications of such a vacuum, including inelastic scattering of single photons, are expected upon replacing the transmon by more anharmonic circuits, with broad implications for simulating critical dynamics of quantum impurity models.
24
Sep
2018
Design of an on-chip superconducting microwave circulator with octave bandwidth
We present a design for a superconducting, on-chip circulator composed of dynamically modulated transfer switches and delays. Design goals are set for the multiplexed readout of superconducting
qubits. Simulations of the device show that it allows for low-loss circulation (insertion loss < 0.35 dB and isolation >20 dB) over an instantaneous bandwidth of 2.3 GHz. As the device is estimated to be linear for input powers up to -65 dBm, this design improves on the bandwidth and power-handling of previous superconducting circulators by over a factor of 50, making it ideal for integration with broadband quantum limited amplifiers.