Coplanar Transmission Line Resonator Research Articles

Quantum state transfer with a two-dimensional Cooper-pair box qubit array

A theoretical scheme is proposed to transfer quantum state with a two-dimensional Cooper-pair box qubit array in circuit QED devices, in which coplanar transmission line resonators play the role of a quantum data bus. Based on the Raman transitions, the resonator-assisted quantum state transfer between any selected pair of qubits can be performed by addressing the local gate pulses. Thus the scheme may offer an effective route towards scalable quantum state transfer with superconducting qubits.

Circuit QED with a flux qubit strongly coupled to a coplanar transmission lineresonator

We propose a scheme for circuit quantum electrodynamics with a superconducting flux–qubit coupled toa high-Q coplanar resonator. Assuming realistic circuit parameters, we predict that it is possible toreach the strong coupling regime. Routes to metrological applications, such assingle-photon generation and quantum non-demolition measurements, are discussed.

Compact InP-based HBT VCOs with a wide tuning range at W- and D-band

Compact monolithic integrated differential voltage-controlled oscillators (VCOs) operating in W-band were realized using InP-based heterojunction bipolar transistors (HBTs). The oscillators, with a total chip size of 0.6 by 0.35 mm/sup 2/, are based on a balanced Colpitts-type topology with a coplanar transmission-line resonator. By varying the voltage across the base-collector junction of the HBT in the current mirror and by changing the current in the VCO, the oscillation frequency can be tuned between 84 and 106 GHz. At 100 GHz, a differential voltage swing of 400 mV is obtained, which should be sufficient to drive 100 Gb/s digital logic. By combining the balanced outputs of a similar differential VCO in a push-push configuration, a compact source with close to -10 dBm output power and a tuning range between 138 and 150 GHz is obtained.

Power-induced switching in YBa 2Cu 3O 7 microwave coplanar resonators

We have studied the power-induced switching of a number of thin film YBa 2Cu 3O 7 (YBCO) coplanar transmission line resonators at 8GHz. Switching occurs at current densities around 10 6 − 10 7 Acm -2 at low T, where it is hysteretic; at higher T it becomes non-hysteretic, and washes out in a narrow temperature range which we believe corresponds to the critical temperature T cj of a single responsible weak link. We develop a thermal model which accounts for all of the observed features of the switching.

Microwave properties of structured YBa 2Cu 3O 7−x thin films

The microwave properties of c-axis oriented YBa 2Cu 3O 7−x (YBCO) thin films deposited by DC-magnetron sputtering were investigated between 5 and 20 GHz using coplanar transmission line resonators. From temperature dependent measurements of the quality factors of these resonators the magnetic penetration depths λ L(0) and the surface resistances R s were evaluated. The lowest surface resistance values were in the range between 105 μΩ and 200 μΩ at 77 K and at 6.2 GHz, respectively. The magnetic penetration depths λ L(0) were between 160 nm and 270 nm. The surface resistance R s turned out to be sensitive to the film quality represented by the critical current density j c at 77 K. From an evaluation of the temperature dependence of the resonance frequency at low temperatures T < T c/2 we determined energy gap values 2Δ(0)/k BT c between 1.2–2.2.

Microwave properties of YBa2Cu3O7−x thin films studied with coplanar transmission line resonators

The microwave properties of epitaxial YBa2Cu3O7−x thin films with critical temperatures Tc up to 91.5 K and critical current densities Jc up to 6×106 A/cm2 at 77 K have been investigated between 5 and 20 GHz using coplanar transmission line resonators. Information about the surface resistance Rs and the magnetic penetration depth λL has been obtained from temperature- and power-dependent measurements of the quality factors and resonance frequencies of the resonators. The lowest surface resistance was 105 μΩ at 77 K and 38 μΩ at 9 K measured at 6.2 GHz, respectively. The dependence of Rs on the surface magnetic field Brf showed that with decreasing film quality the films exhibit a granular behavior. At high critical current densities Jc≳4×106 A/cm2, the intrinsic properties of the material show up. The magnetic penetration depth was in the range between 160 and 270 nm. Both Rs and λL turned out to be sensitive to the film quality represented by the transition width ΔTc and the critical current density Jc at 77 K.

High-Q coplanar transmission line resonator of YBa2Cu3O7−x on LaAlO3

We report on quality factor measurements of a coplanar waveguide transmission line resonator patterned from a YBa2Cu3O7−x film on a LaAlO3 substrate, resonating at 6.5 GHz. At 77 K the unloaded quality factor is 3850 ± 180, that is about 43 times higher than that of an identical copper resonator at the same temperature and frequency. This result demonstrates the usefulness of LaAlO3 as a substrate for high-temperature superconducting microwave applications.