arXiv subjects

K. D. Osborn

Publications and source records attributed to K. D. Osborn.

12 recordsLinked to original sources

arXiv2023

Dual-Resonator Kinetic-Inductance Detector for Distinction between Signal and 1/f Frequency Noise

Astronomical Kinetic Inductance Detectors (KIDs), similar to quantum information devices, experience performance limiting noise from materials. In particular, 1/f (frequency) noise can be a dominant noise mechanism, which arises from Two-Level System defects (TLSs) in the circuit dielectrics and material interfaces. Here we present a Dual-Resonator KID (DuRKID), which is designed for improved signal to noise (or noise equivalent power) relative to 1/f-noise limited KIDs. We first show the DuRKID schematic, fabricated circuit, and we follow with a description of the intended operation, first measurements, theory, and discussion. The circuit consists of two superconducting resonators sharing an electrical capacitance bridge of 4 capacitors, each of which hosts TLSs. The device is intended to operate using hybridization of the modes, which causes TLSs to either couple to one mode or the other, depending upon which capacitor they reside in. In contrast, the intended KID signal is directed to an inductor, and due to hybridization this causes correlated frequency changes in both (hybridized) modes. Therefore, one can distinguish photon signal from TLS frequency noise. To achieve hybridization, a TiN inductor is current biased to allow tuning of one bare resonator mode into degeneracy with the other and measurements show that the intended resonator modes frequency tune and hybridize as expected. The interresonator coupling and unintentional coupling of the 2 resonators to transmission lines are also characterized in measurements. In the theory, based on a quantum-information-science modes, we calculate the 4-port S parameters and simulate the 1/f frequency noise of the device. The study reveals that the DuRKID can exhibit a large and fundamental performance advantage over 1/f-noise-limited KID detectors.

cond-mat.supr-con↗

arXiv2019

Development of transmon qubits solely from optical lithography on 300mm wafers

Qubit information processors are increasing in footprint but currently rely on e-beam lithography for patterning the required Josephson junctions (JJs). Advanced optical lithography is an alternative patterning method, and we report on the development of transmon qubits patterned solely with optical lithography. The lithography uses 193 nm wavelength exposure and 300-mm large silicon wafers. Qubits and arrays of evaluation JJs were patterned with process control which resulted in narrow feature distributions: a standard deviation of 0:78% for a 220 nm linewidth pattern realized across over half the width of the wafers. Room temperature evaluation found a 2.8-3.6% standard deviation in JJ resistance in completed chips. The qubits used aluminum and titanium nitride films on silicon substrates without substantial silicon etching. T1 times of the qubits were extracted at 26 - 27 microseconds, indicating a low level of material-based qubit defects. This study shows that large wafer optical lithography on silicon is adequate for high-quality transmon qubits, and shows a promising path for improving many-qubit processors.

physics.app-ph↗

arXiv2015

Evidence for universal relationship between the measured 1/f permittivity noise and loss tangent created by tunneling atoms

Noise from atomic tunneling systems (TSs) limit the performance of various resonant devices, ranging in application from astronomy detectors to quantum computing. Using devices containing these TSs, we study the $1/f$ permittivity noise and loss tangent in two film types containing different TS densities. The noise reveals an intrinsic value as well as the crossover to power-saturated noise. The intrinsic $1/f$ noise fits to the temperature dependence $1/T^{1+μ}$ where $0.2\leμ\le0.7$, which is related to previous studies and strongly interacting TS. An analysis of the noise normalized by the loss tangent and temperature is quantitatively identical for two film types, despite a factor of 5 difference in their loss tangent. Following from the broad applicability of the TS model, the data supports a universal relationship for amorphous-solid produced permittivity noise. The quantity of the observed noise particularly supports a recent model in which noise is created by weak TS-TS interactions.

cond-mat.supr-con↗

arXiv2014

Superconducting TiN Films Sputtered over a Large Range of Substrate DC Bias

We have investigated properties of superconducting titanium nitride (TiN) films that were sputtered over a large range of RF-induced DC bias voltage applied to the substrate. Films grown with the largest bias voltages contained cubic TiN phases with a large fraction of the (200) crystalline growth orientation. These films also contained the smallest concentrations of oxygen impurities, resulting in stoichiometric TiN. Over the range of bias, variations of the stress from slightly tensile to highly compressive were measured and correlated to crystallinity of the (200) growth. The films exhibited highly uniform thickness and resistivity, and show the potential for yielding reproducible low-temperature devices. Finally, coplanar resonators fabricated with the films exhibited high kinetic inductance and quality factor, where the latter was obtained in part from temperature-dependent frequency shifts.

cond-mat.supr-con↗

arXiv2014

Landau-Zener population control and dipole measurement of a two level system bath

Tunneling two level systems (TLS), present in dielectrics at low temperatures, have been recently studied for fundamental understanding and superconducting device development. According to a recent theory by Burin \textit{et al.}, the TLS bath of any amorphous dielectric experiences a distribution of Landau-Zener transitions if exposed to simultaneous fields. In this experiment we measure amorphous insulating films at millikelvin temperatures with a microwave field and a swept electric field bias using a superconducting resonator. We find that the maximum dielectric loss per microwave photon with the simultaneous fields is approximately the same as that in the equilibrium state, in agreement with the generic material theory. In addition, we find that the loss depends on the fields in a way which allows for the separate extraction of the TLS bath dipole moment and density of states. This method allows for the study of the TLS dipole moment in a diverse set of disordered films, and provides a technique for continuously inverting their population.

cond-mat.mes-hall↗

arXiv2013

Evidence for hydrogen two-level systems in atomic layer deposition oxides

Two-level system (TLS) defects in dielectrics are known to limit the performance of electronic devices. We study TLS using millikelvin microwave loss measurements of three atomic layer deposited (ALD) oxide films--crystalline BeO ($\rm{c-BeO}$), amorphous $\rm{Al_2O_3}$ ($\rm{a-Al_2O_3}$), and amorphous $\rm{LaAlO_3}$ ($\rm{a-LaAlO_3}$)--and interpret them with room temperature characterization measurements. We find that the bulk loss tangent in the crystalline film is 6 times higher than in the amorphous films. In addition, its power saturation agrees with an amorphous distribution of TLS. Through a comparison of loss tangent data to secondary ion mass spectrometry (SIMS) impurity analysis we find that the dominant loss in all film types is consistent with hydrogen-based TLS. In the amorphous films excess hydrogen is found at the ambient-exposed surface, and we extract the associated hydrogen-based surface loss tangent. Data from films with a factor of 40 difference in carbon impurities revealed that carbon is currently a negligible contributor to TLS loss.

cond-mat.mtrl-sci↗

arXiv2012

An analysis method for asymmetric resonator transmission applied to superconducting devices

We examine the transmission through nonideal microwave resonant circuits. The general analytical resonance line shape is derived for both inductive and capacitive coupling with mismatched input and output transmission impedances, and it is found that for certain non-ideal conditions the line shape is asymmetric. We describe an analysis method for extracting an accurate internal quality factor ($Q_i$), the Diameter Correction Method (DCM), and compare it to the conventional method used for millikelvin resonator measurements, the $ϕ$ Rotation Method ($ϕ$RM). We analytically find that the $ϕ$RM deterministically overestimates $Q_i$ when the asymmetry of the resonance line shape is high, and that this error is eliminated with the DCM. A consistent discrepancy between the two methods is observed when they are used to analyze both simulations from a numerical linear solver and data from asymmetric coplanar superconducting thin-film resonators.

cond-mat.supr-con↗

arXiv2012

A Josephson junction defect spectrometer for measuring two-level systems

We have fabricated and measured Josephson junction defect spectrometers (JJDSs), which are frequency-tunable, nearly-harmonic oscillators that probe strongly-coupled two-level systems (TLSs) in the barrier of a Josephson junction (JJ). The JJDSs accommodate a wide range of junction inductances, $L_{J}$, while maintaining a resonance frequency, $f_{0}$, in the range of 4-8 GHz. By applying a magnetic flux bias to tune $f_{0}$, we detect strongly-coupled TLSs in the junction barrier as splittings in the device spectrum. JJDSs fabricated with a via-style Al/thermal AlOx/Al junction and measured at 30 mK with single-photon excitation levels show a density of TLSs in the range $σ_{TLS}h = 0.4-0.5 /GHz μm^2$, and a junction loss tangent of $\tan δ_{J} = 2.9x10^{-3}$.

cond-mat.supr-con↗

arXiv2011

Jaynes Cummings treatment of superconducting resonators with dielectric loss due to two-level systems

We perform a quantum mechanical analysis of superconducting resonators subject to dielectric loss arising from charged two-level systems. We present numerical and analytical descriptions of the dynamics of energy decay from the resonator within the Jaynes-Cummings model. Our analysis allows us to distinguish the strong and weak coupling regimes of the model and to describe within each regime cases where the two-level system is unsaturated or saturated. We find that the quantum theory agrees with the classical model for weak coupling. However, for strong coupling the quantum theory predicts lower loss than the classical theory in the unsaturated regime. Also, in contrast to the classical theory, the photon number at which saturation occurs in the strong coupling quantum theory is independent of the coupling between the resonator and the two-level system.

quant-ph↗

arXiv2011

Decoupling a Cooper-pair box to enhance the lifetime to 0.2 ms

We present a circuit QED experiment in which a separate transmission line is used to address a quasi-lumped element superconducting microwave resonator which is in turn coupled to an Al/AlO$_{x}$/Al Cooper-pair box (CPB) charge qubit. In our measurements we find a strong correlation between the measured lifetime of the CPB and the coupling between the qubit and the transmission line. By monitoring perturbations of the resonator's 5.44 GHz resonant frequency, we have measured the spectrum, lifetime ($T_{1}$), Rabi, and Ramsey oscillations of the CPB at the charge degeneracy point while the CPB was detuned by up to 2.5 GHz . We find a maximum lifetime of the CPB was $T_{1} = 200\ μ$s for $f = 4$ to 4.5 GHz. Our measured $T_{1}$'s are consistent with loss due to coupling to the transmission line, spurious microwave circuit resonances, and a background decay rate on the order of $5\times 10^{3}$ s$^{-1}$ of unknown origin, implying that the loss tangent in the AlO$_{x}$ junction barrier must be less than about $4\times 10^{-8}$ at 4.5 GHz, about 4 orders of magnitude less than reported in larger area Al/AlO$_{x}$/Al tunnel junctions.

cond-mat.supr-con↗

arXiv2007

Frequency-Tunable Josephson Junction Resonator for Quantum Computing

We have fabricated and measured a high-Q Josephson junction resonator with a tunable resonance frequency. A dc magnetic flux allows the resonance frequency to be changed by over 10 %. Weak coupling to the environment allows a quality factor of $\thicksim$7000 when on average less than one photon is stored in the resonator. At large photon numbers, the nonlinearity of the Josephson junction creates two stable oscillation states. This resonator can be used as a tool for investigating the quality of Josephson junctions in qubits below the single photon limit, and can be used as a microwave qubit readout at high photon numbers.

cond-mat.supr-con↗

arXiv2003

Critical dynamics of superconducting BSCCO films

We report on a systematic investigation of the critical fluctuations in the complex conductivity of epitaxially-grown Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ films for ${T \lesssim T_c}$ using a two-coil inductive technique at zero applied field. We observe the static 3D-XY critical exponent in the superfluid density near $T_{c}$. Linear scaling analysis close to the critical temperature yields a dynamic critical exponent of $z = 2.0$ for small drive currents, but non-linear effects are seen to be important. At $T_{c}$, a non-linear scaling analysis also yields a 3D dynamic exponent of $z = 2.0$.

cond-mat.supr-con↗