Coplanar Resonators Research Articles

Manipulation and coherence of ultra-cold atoms on a superconducting atom chip

The coherence of quantum systems is crucial to quantum information processing. Although superconducting qubits can process quantum information at microelectronics rates, it remains a challenge to preserve the coherence and therefore the quantum character of the information in these systems. An alternative is to share the tasks between different quantum platforms, for example, cold atoms storing the quantum information processed by superconducting circuits. Here we characterize the coherence of superposition states of (87)Rb atoms magnetically trapped on a superconducting atom chip. We load atoms into a persistent-current trap engineered next to a coplanar microwave resonator structure, and observe that the coherence of hyperfine ground states is preserved for several seconds. We show that large ensembles of a million of thermal atoms below 350 nK temperature and pure Bose-Einstein condensates with 3.5 × 10(5) atoms can be prepared and manipulated at the superconducting interface. This opens the path towards the rich dynamics of strong collective coupling regimes.

Heavy-Ion Patterned Micro-Channels in YBCO Microwave Resonators

Microcollimated swift heavy-ion irradiation has been employed to carve channels with micron-sized width in YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) superconducting coplanar microwave resonators. Comparative analysis of the first two resonant modes as a function of temperature, magnetic field, and input power was used to characterize the properties of the microchannels. As expected, due to the high fluence, increase of penetration depth and microwave resistivity have been found in the irradiated channels. It is shown that the microchannels can be driven into a highly dissipative and nonlinear regime while the rest of the resonator still persists in a low-dissipation and linear state. Thus, an external control signal (e.g., a small dc magnetic field) can tune the response of the resonator, in the modes coupled to the microchannel, when properly biased. This study is preliminary to the employment of such approach in the design of novel YBCO sensors operating above 77 K.

Mapping microwave field distributions via the spin Hall effect

The spatial variation of the spin pumping–inverse spin Hall effect was studied in a palladium/permalloy bilayer via a coplanar waveguide ferromagnetic resonance (CPW-FMR) broadband technique. The inverse spin Hall signal is both inhomogeneous and asymmetric with respect to both the position along the CPW and the excitation port. Based on this observation, we show how the inverse spin Hall effect can be used as a sensitive probe for mapping the microwave magnetic field distribution in the FMR frequency range.

Tuning the response of YBCO microwave resonators by heavy-ion patterned micro-channels

Channels with micron-size width have been carved in Y Ba2Cu3O7−x (YBCO) coplanar microwave resonators by micro-collimated swift heavy-ion irradiation at high fluences. The response of the resonators as a function of temperature, magnetic field and input power as well as magneto-optical imaging was used to characterize the properties of such micro-channels. The microwave method proposed to characterize the channels—with dimensions from 1/3200 to 1/178 of the wavelength—is based on the comparison between the fundamental and the first harmonic resonant modes. As expected due to the high irradiation fluence, higher penetration depth, higher microwave resistivity and lower nonlinearity thresholds have been found. In this configuration, it is shown that the micro-channels can be driven into a highly dissipative, nonlinear regime while the rest of the resonator still persists in a linear response. The higher responsivity of the micro-channels with respect to the as-grown YBCO was tested by applying an external magnetic field, showing that a locally applied external control signal can tune the response of the resonators, when properly biased. The possible impact of these results in the field of high temperature superconductor based sensors is discussed.

Design of Compact and Auto-Compensated Single-Layer Chipless RFID Tag

This paper presents a new radio frequency identification (RFID) chipless tag that is highly compact and potentially low-cost. This tag has a lot of advantages, such as being fully printable on products since no ground plane is needed for fabrication. The actual issue of the chipless tag family having a single layer, that is, their detuning effect, is compensated for the first time by a correction technique based on the use of a sensing resonator. The design is based on multiple λ/4 coplanar strip-line resonators where resonant frequencies can be shifted by setting an additional short circuit at particular locations. An accurate model is proposed to easily link the footprint of the structure to the resonant frequency. Considering a frequency resolution of 50 MHz for the reading system and a tag dimension of 15 × 20 mm2, 9 b can be encoded in the frequency band 2.0-5.5 GHz. Several experimental results validate the proposed design as well as its implementation in a realistic application and environment.

Magnetic hysteresis effects in superconducting coplanar microwave resonators

We performed transmission spectroscopy experiments on coplanar half wavelength niobium resonators at a temperature T=4.2 K. We observe not only a strong dependence of the quality factor Q and the resonance frequency f_res on an externally applied magnetic field but also on the magnetic history of our resonators, i.e. on the spatial distribution of trapped Abrikosov vortices in the device. We find these results to be valid for a broad range of frequencies and angles between the resonator plane and the magnetic field direction as well as for resonators with and without antidots near the edges of the center conductor and the ground planes. In a detailed analysis we show, that characteristic features of the experimental data can only be reproduced in calculations, if a highly inhomogeneous rf-current density and a flux density gradient with maxima at the edges of the superconductor is assumed. We furthermore demonstrate, that the hysteretic behaviour of the resonator properties can be used to considerably reduce the vortex induced losses and to fine-tune the resonance frequency by the proper way of cycling to a desired magnetic field.

Etch induced microwave losses in titanium nitride superconducting resonators

We have investigated the correlation between the microwave loss and patterning method for coplanar waveguide titanium nitride resonators fabricated on silicon wafers. Three different methods were investigated: fluorine- and chlorine-based reactive ion etches and an argon-ion mill. At high microwave probe powers, the reactive etched resonators showed low internal loss, whereas the ion-milled samples showed dramatically higher loss. At single-photon powers, we found that the fluorine-etched resonators exhibited substantially lower loss than the chlorine-etched ones. We interpret the results by use of numerically calculated filling factors and find that the silicon surface exhibits a higher loss when chlorine-etched than when fluorine-etched. We also find from microscopy that re-deposition of silicon onto the photoresist and side walls is the probable cause for the high loss observed for the ion-milled resonators.

Excitation spectrum for an inhomogeneously dipole-field-coupled superconducting qubit chain

When a chain of superconducting qubits couples to a coplanar resonator in a cavity, each of its N qubits (equally-spaced with distance l) experiences a different dipole-field coupling strength due to the waveform of the cavity field. We find that this inhomogeneous coupling leads to a pair of l-dependent ladder operators for the angular momentum of the spin chain. Varying the qubit spacing l changes the transition amplitudes between the angular momentum levels. We derive an exact diagonalization of the general N-qubit Hamiltonian and, through the N=4 case, demonstrate how the l-dependent operators lead to a denser one-excitation spectrum and a probability redistribution of the eigenstates. Moreover, it will be shown that the variation of l between its two limiting values coincides with the crossover between Frenkel- and Wannier-type excitons in the superconducting spin chain.

永久磁石膜の直流バイアス磁界を用いたチューナブル磁気デバイスの基礎検討

A tunable coplanar resonator using a combination of high-permeability soft magnetic thin film/permanent magnet film was fabricated and evaluated. The magnetic pole based on the remanent magnetization of permanent magnet film, which is controlled by a pulse-current magnetization scheme, generates a dc bias magnetic field in the soft magnetic film. Consequently, the permeability of the soft magnetic film can be controlled by changing the pulse-current magnetization for the permanent magnet film. A scheme to control the permeability of the soft magnetic film is described here, and fabrication and evaluation of the tunable coplanar-resonator are also explained.

Working principle description of the wireless passive EM transduction pressure sensor

The development of a new passive wireless pressure sensor, based on an electromagnetic transduction approach, is reported. The sensing element is a flexible high resistivity silicon membrane located above a coplanar quarter-wavelength resonator. The comprehensive coverage of the physical bases is beyond the scope of this paper. For the remote extraction of the applied pressure value, the passive pressure sensor is connected to a broadband horn antenna via a coaxial delay line. When interrogated by a frequency modulated continuous wave radar, the level of the backscattered signal changes versus the pressure applied to the proof body. Through this interrogation principle, the sensor provides load impedance that is reflected back to the radar reader: the measured dynamic is about 0.8 dBm/bar. This completely passive and wireless pressure telemetry micro-sensor has been designed, fabricated and characterized, thereby eliminating the need for contact, signal processing circuits, and power supplies needed by conventional active sensors.

Characterization of SrTiO3 thin films at microwave frequencies using coplanar waveguide linear resonator method

Experimental characterization of the dielectric properties of a SrTiO3 (STO) thin film in the microwave frequency range at room temperature is presented. The coplanar waveguide linear resonator technique, which is already well-established for thick film characterization, was tailored and improved to allow thin film measurements. Experimental results are in very good agreement with theoretical analysis. Using this approach, a relative dielectric constant of 95 and a loss tangent less than 10−3 were measured for a STO film with 4.2 μm of thickness deposited by radio frequency (RF) magnetron sputtering. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2418–2422, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26233

Wirebond crosstalk and cavity modes in large chip mounts for superconductingqubits

We analyze the performance of a microwave chip mount that uses wirebonds toconnect the chip and mount grounds. A simple impedance ladder model predictsthat transmission crosstalk between two feedlines falls off exponentially withdistance at low frequencies, but rises to near unity above a resonance frequency setby the chip to ground capacitance. Using SPICE simulations and experimentalmeasurements of a scale model, the basic predictions of the ladder model wereverified. In particular, by decreasing the capacitance between the chip and boxgrounds, the resonance frequency increased and transmission decreased. Thismodel then influenced the design of a new mount that improved the isolation to − 65 dB at 6 GHz, even though the chip dimensions were increased to1 cm × 1 cm, three times as large as our previous devices. We measured a coplanar resonator in thismount as preparation for larger qubit chips, and were able to identify cavity, slotline, andresonator modes.

Exchange anisotropy pinning of a standing spin-wave mode

Standing spin waves in a thin film are used as sensitive probes of interface pinning induced by an antiferromagnet through exchange anisotropy. Using coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was studied for a range of IrMn thicknesses. We show that pinning of the standing mode can be used to amplify, relative to the fundamental resonance, frequency shifts associated with exchange bias. The shifts provide a unique `fingerprint' of the exchange bias and can be interpreted in terms of an effective ferromagnetic film thickness and ferromagnet/antiferromagnet interface anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in the pinning fields. The pinning strength magnitude is found to grow with cooling of the sample, while the effective ferromagnetic film thickness simultaneously decreases. These results suggest that exchange bias involves some deformation of magnetic order in the interface region.

Study on the Damping Constants of Ni-Fe Thin Films using Different CPW-FMR Measurements

This paper reports the study on the damping constant α of Ni-Fe films using both one and two port type coplanar waveguide-ferromagnetic resonance (CPW-FMR) measurements, and compared these results with a conventional FMR (cavity-type FMR) measurement. In each CPW-FMR measurement, for the films thicker than 10 nm, each α becomes constant in the range of 0.012-0.014. On the other hand, for the film thickness less than 10 nm, α increases from 0.014 to 0.017 as the film thickness decreases, which may be attributed to structural inhomogeneity in the films. These results are in good agreement with those obtained from the cavity-type FMR measurement. On the basis of these results, it is pointed out that α of Ni-Fe films can be evaluated accurately by either of the CPW-FMR measurements. These results also mean that the one port type CPW-FMR measurement is more effective than the two port type CPW-FMR measurement for characterization of Ni-Fe films because the former method is simple and a stronger high frequency magnetic field can be generated.

Loss Dependence on Geometry and Applied Power in Superconducting Coplanar Resonators

The loss in superconducting microwave resonators at low-photon numbers and low temperatures is not well understood but has implications for achievable coherence times in superconducting qubits. We have fabricated single-layer resonators with a high quality factor by patterning a superconducting aluminum film on a sapphire substrate. Four resonator geometries were studied with resonant frequencies ranging from 5 to 7 GHz: a quasi-lumped element resonator, a coplanar strip waveguide resonator, and two hybrid designs that contain both a coplanar strip and a quasi-lumped element. Transmitted power measurements were taken at 30 mK as a function of frequency and probe power. We find that the resonator loss, expressed as the inverse of the internal quality factor, decreases slowly over four decades of photon number in a manner not merely explained by loss from a conventional uniform spatial distribution of two-level systems in an oxide layer on the superconducting surfaces of the resonator.

Superconducting cavity bus for single nitrogen-vacancy defect centers in diamond

Circuit-QED has demonstrated very strong coupling between individual microwave photons trapped in a superconducting coplanar resonator and nearby superconducting qubits. In this work we show how, by designing a novel interconnect, one can strongly connect the superconducting resonator, via a magnetic interaction, to a small number (perhaps single), of electronic spins. By choosing the electronic spin to be within a Nitrogen Vacancy centre in diamond one can perform optical readout, polarization and control of this electron spin using microwave and radio frequency irradiation. More importantly, by utilising Nitrogen Vacancy centres with nearby 13C nuclei, using this interconnect, one has the potential build a quantum device where the nuclear spin qubits are connected over centimeter distances via the Nitrogen Vacancy electronic spins interacting through the superconducting bus.

Experimental Verification of Left-Handed Metamaterials Composed of Coplanar Electric and Magnetic Resonators

We verified experimentally left-handed metamaterials (LHM) composed of coplanar electric and magnetic resonators. A typical LHM sample composed of coplanar resonator unit cells was fabricated, investigated and tested. The experimental results show that the tested sample has a left-handed band of width 1.4 GHz in the X band. The experimental results agree quite well with the simulation ones. Moreover, both the simulation and experimental results show that the LHM under study can automatically achieve good impedance-matching in the left-handed band.

MODELING AND MEASUREMENT OF A ZEROTH-ORDER RESONATOR AND A COMPOSITE RIGHT-LEFT-HANDED TRANSMISSION LINE IN COPLANAR TECHNOLOGY

This paper presents a coplanar composite right-left handed zeroth-order resonator (CRLH CPW ZOR) and a coplanar composite right-left handed transmission line (CRLH CPW TL). These devices are realized using an elementary cell designed in a coplanar waveguide conflguration on alumina substrate. Additional lumped elements are carried out with an interdigital series capacitor and a short-circuited stub inductor as a shunt. The CRLH CPW ZOR is fabricated and analyzed using equivalent circuit modeling and three dimensional flnite element method. The proposed devices are fabricated and measured. The resonator has a measured insertion loss of 2.7dB and a return loss better than 13dB. The length of the proposed device is only 5.2mm; this very small size compared with a traditional half wave resonator, shows the interest of this kind of approach.

Improving the coherence time of superconducting coplanar resonators

The quality factor and energy decay time of superconducting resonators have been measured as a function of material, geometry, and magnetic field. Once the dissipation of trapped magnetic vortices is minimized, we identify a power-dependent decay mechanism that is consistent with the surface two-level state model. A wide gap between the center conductor and the ground plane, as well as use of the superconductor Re instead of Al, are shown to decrease loss. We also demonstrate that classical measurements of resonator quality factor at low excitation power are consistent with single-photon decay time measured using qubit-resonator swap experiments.

Giant Kerr Nonlinearities in Circuit Quantum Electrodynamics

The very small size of optical nonlinearities places strict restrictions on the types of novel physics one can explore. This work describes how a single artificial multilevel Cooper pair box molecule, interacting with a superconducting microwave coplanar resonator, when suitably driven, can generate extremely large optical nonlinearities at microwave frequencies, with no associated absorption. We describe how the giant self-Kerr effect can be detected by measuring the second-order correlation function and quadrature squeezing spectrum.