185 research outputs found
Inductively shunted transmon qubit with tunable transverse and longitudinal coupling
We present the design of an inductively shunted transmon qubit with
flux-tunable coupling to an embedded harmonic mode. This circuit construction
offers the possibility to flux-choose between pure transverse and pure
longitudinal coupling, that is coupling to the or degree
of freedom of the qubit. While transverse coupling is the coupling type that is
most commonly used for superconducting qubits, the inherently different
longitudinal coupling has some remarkable advantages both for readout and for
the scalability of a circuit. Being able to choose between both kinds of
coupling in the same circuit provides the flexibility to use one for coupling
to the next qubit and one for readout, or vice versa. We provide a detailed
analysis of the system's behavior using realistic parameters, along with a
proposal for the physical implementation of a prototype device.Comment: 14 pages, 14 figure
Aluminium-oxide wires for superconducting high kinetic inductance circuits
We investigate thin films of conducting aluminium-oxide, also known as
granular aluminium, as a material for superconducting high quality, high
kinetic inductance circuits. The films are deposited by an optimised reactive
DC magnetron sputter process and characterised using microwave measurement
techniques at milli-Kelvin temperatures. We show that, by precise control of
the reactive sputter conditions, a high room temperature sheet resistance and
therefore high kinetic inductance at low temperatures can be obtained. For a
coplanar waveguide resonator with 1.5\,k sheet resistance and a kinetic
inductance fraction close to unity, we measure a quality factor in the order of
700\,000 at 20\,mK. Furthermore, we observe a sheet resistance reduction by
gentle heat treatment in air. This behaviour is exploited to study the kinetic
inductance change using the microwave response of a coplanar wave guide
resonator. We find the correlation between the kinetic inductance and the sheet
resistance to be in good agreement with theoretical expectations.Comment: 16 pages, 7 figure
In vitro variability in propofol absorption by different membrane oxygenators
Meeting abstract focusing on the sequestration of drugs, such as fentanyl [1,2], thiopental, nitroglycerine and propofol [3] in the extracorporeal circuit in vitro. This phenomenon can change the pharmacokinetic behaviour of drugs during cardiopulmonary bypass, thus potentially leading to problems in achieving adequate dosing regimens. The aim of this in vitro laboratory study was to compare the binding of propofol to different oxygenator membranes, and to examine the effects of the type of prime solution and temperature on the rate of binding. The SM-35 membrane bound significantly more propofol than the membranes from the CML and the SAFE II. Binding of propofol in diluted blood was significantly less than in crystalloid solution. Temperature had little effect on propofol binding in either prime solution type
An argon ion beam milling process for native layers enabling coherent superconducting contacts
We present an argon ion beam milling process to remove the native oxide layer
forming on aluminum thin films due to their exposure to atmosphere in between
lithographic steps. Our cleaning process is readily integrable with
conventional fabrication of Josephson junction quantum circuits. From
measurements of the internal quality factors of superconducting microwave
resonators with and without contacts, we place an upper bound on the residual
resistance of an ion beam milled contact of 50 at a frequency of 4.5 GHz. Resonators for which only of the
total foot-print was exposed to the ion beam milling, in areas of low electric
and high magnetic field, showed quality factors above in the single
photon regime, and no degradation compared to single layer samples. We believe
these results will enable the development of increasingly complex
superconducting circuits for quantum information processing.Comment: 4 pages, 4 figures, supplementary materia
Investigation of Dielectric Losses in Hydrogenated Amorphoussilicon (a-Si:H) thin Films Using Superconducting Microwave Resonators
AbstractThe improvement of the coherence times of superconducting qubits depends on the reduction of the dielectric losses in the insulating materials implemented for the device fabrication. These losses depend on the density of spurious dipoles of different nature (two-level systems, TLSs) which couple to phase qubits and, hence, limit their coherence times. Hydrogenated amorphous silicon (a-Si:H), because of its lower loss tangent (tan δ) among conventional dielectrics (a-SiO, a-SiO2, a-SiNx:H), is considered as the best amorphous dielectric for superconducting qubit application. We have developed a reliable method for the direct measurement of dielectric losses in amorphous dielectric thin films using a novel design based on four lumped superconducting LC resonators connected in series without coupling capacitors. The losses are obtained as tan δ = 1/Q0, where Q0 is the intrinsic quality factor of the resonator, measured at 3dB above the resonance frequency without any fitting procedure. The series type LC resonators with a-Si:H as dielectric were fabricated by the Nb technology. The measurements were done at the conditions of a qubit application (0.5 -10GHz frequency range and low temperatures). The low values of the loss tangent of a-Si:H (up to 2.5 x 10−5 at 4.2K) have required the development of superconducting housing for the resonators in order to eliminate a spurious dependence of tan δ on the microwave power, by reducing losses which were not originated in the dielectric itself. The results of the simulations agree well with the experiments
Quasiparticle dynamics in granular aluminum close to the superconductor to insulator transition
Superconducting high kinetic inductance elements constitute a valuable
resource for quantum circuit design and millimeter-wave detection. Granular
aluminum (GrAl) in the superconducting regime is a particularly interesting
material since it has already shown a kinetic inductance in the range of
nH and its deposition is compatible with conventional Al/AlOx/Al
Josephson junction fabrication. We characterize microwave resonators fabricated
from GrAl with a room temperature resistivity of cm, which is a factor of 3 below the superconductor to
insulator transition, showing a kinetic inductance fraction close to unity. The
measured internal quality factors are on the order of
in the single photon regime, and we demonstrate that non-equilibrium
quasiparticles (QP) constitute the dominant loss mechanism. We extract QP
relaxation times in the range of 1 s and we observe QP bursts every
s. The current level of coherence of GrAl resonators makes them attractive for
integration in quantum devices, while it also evidences the need to reduce the
density of non-equilibrium QPs.Comment: 5 pages, 4 figures, supplementary materia
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