Search

We experimentally and theoretically study the frequency shift of a driven cavity coupled to a superconducting charge qubit. In addition to previous studies, here we also consider drive strengths large enough to energetically allow for quasiparticle creation. Quasiparticle tunnelling leads to the inclusion of more than two charge states in the dynamics. To explain the observed effects, we develop a master equation for the microwave dressed charge states, including quasiparticle tunnelling. A bimodal behaviour of the frequency shift as a function of gate voltage can be used for sensitive charge detection. However, at weak drives, the charge sensitivity is significantly reduced by nonequilibrium quasiparticles, which induce transitions to a non-sensitive state. Unexpectedly, at high-enough drives, the quasiparticle tunnelling enables a very fast relaxation channel to the sensitive state. In this regime, the charge sensitivity is thus robust against externally injected quasiparticles and the desired dynamics prevail over a broad range of temperatures. We find very good agreement between the theory and experiment over a wide range of drive strengths and temperatures. [ABSTRACT FROM AUTHOR]

The predominant d-wave pairing symmetry in high temperature superconductors allows for a variety of current–phase relations (CPR) in Josephson junctions. In this presentation we report on direct experimental observations of the effects of non-sinusoidal CPR in YBCO dc-SQUIDs made with submicron 0/45° bicrystal junctions. We also present the effect of such CPR on the extrama positions of the critical current versus magnetic field measurements. [Copyright &y& Elsevier]

YBCO integrated structures consisting of a planar antenna and a Josephson junction were designed and fabricated on bicrystal sapphire substrates. By combining two such structures in an oscillator-receiver arrangement a submillimeter-wavelength tester was realised. Two types of relatively narrow-band double-slot and double-dipole antennas, a broadband complementary log-periodic antenna and an array of dipole antennas were investigated. [Copyright &y& Elsevier]

A novel approach to synchronization of arrays of Josephson junctions (JJA) is proposed. Each Josephson junction is placed in the center of a separate dipole antenna. Antennas at a distance of about a half wavelength from each other form a beam pattern with the main lobe perpendicular to the substrate plane. Two types of JJA were fabricated on YZrO2 and sapphire bicrystal substrates. Self-resonant steps are clearly observed in I–V curves at temperatures 4–60 K. Besides the main resonance at 360 GHz, resonances at voltages corresponding to the second and third harmonics and to subharmonics at 1/2, 3/2, 5/2 of the main resonant frequency are observed. Radiation from such array was observed at bias voltages over 4 mV that corresponds to an oscillation frequency of up to 2 THz. The arrays demonstrated high sensitivity to submm-wavelength radiation in the frequency range 300–550 GHz. [Copyright &y& Elsevier]

Abstract: We have studied the dynamics of YBa2Cu3O7−δ (YBCO) dc sperconducting quantum interference devices (SQUIDs) characterized by an unconventional Josephson current phase relation (CPR). We have focused on SQUID configurations with Josephson junctions where the lobe of the order parameter in one electrode is facing a node in the other electrode. This order parameter arrangement should enhance the appearance of a sin(2φ) term in the CPR. The response of the critical current of the dc SQUID, under the effect of an external magnetic field, has been measured in temperature, down to 20mK. Our experimental data have been compared with numerical simulations of the SQUIDs dynamics by considering a CPR of a single junction of the form I(φ)= I I sin(φ)− I II sin(2φ) where I I and I II are, respectively, the first and second harmonic component. In our devices the values of the sin(2φ) term are such that the fundamental state of the SQUID is naturally double degenerate. This is of great relevance for applications of d-wave SQUIDs in quantum information processing. [Copyright &y& Elsevier]

Submicron YBCO bicrystal Josephson junctions (JJ) and devices for high frequency applications were designed, fabricated and experimentally studied. The key elements of these devices are bicrystal sapphire substrates with symmetric misorientation angles 14.2°, 18.4° and 24° which were fabricated by a solid-state intergrowth method. A technological process based on deep ultraviolet photolithography using a hard carbon mask was developed for the fabrication of 0.4–0.6 μm wide JJ. The junctions have normal resistances up to 2 kΩ, IcRn>2 mV and a 1 mV/Φ0 SQUID response at 4.2 K. The junctions were used as Josephson detectors and spectrometers at frequencies up to 1.5 THz, dc SQUID RF amplifiers operating at 1.5 GHz and submillimeter wave array oscillators. [Copyright &y& Elsevier]