An Effective Method for Improving Emissions from Intrinsic Josephson Junction Arrays of Misaligned Tl2Ba2CaCu2O8+δ Thin Films

In this paper, an effective method for improving emissions from Josephson junction arrays was proposed. We took the substrate as a dielectric resonance antenna to improve the coupling of intrinsic junctions to electromagnetic waves. Electromagnetic simulations were performed in parallel with experiment investigations. Sharp radiation peaks at 76.9?GHz were detected from intrinsic Josephson junction arrays in misaligned Tl₂Ba₂CaCu₂O_8+?? thin films at 78?K. Experimental results proved the effectiveness of this method, which offered a competitive choice for coherent emission from intrinsic Josephson junction arrays.     

Phase Transitions and Phase Fluctuations in the Josephson-Junction Arrays

We study the effect of quantum and classical phase fluctuations on the phase transitions in the system of Josephson-junction arrays. We employed a variational method for calculating the Gaussian type fluctuation of the phase in the Josephson-junction array lattice systems without and with an external magnetic field. We investigate the spectrum of collective excitations and the effects of collective excitations on the transport properties of Josephson-junction arrays. We showed that the Hamiltonian for the lattice system of the Josephson junction is the same as the Hamiltonian for the classical or quantum two-dimensional interacting rotators. We also showed that the dynamics of fluctuations of the phase in the lattice system of Josephson junction is very similar to the lattice dynamics of the lattice in crystals. We also showed that in the lattice system of Josephson junctions there is the collective acoustic mode similar to the acoustic mode in the crystal lattice, and this mode may lead to the dissipation of the Josephson current in the superconducting array of Josephson junctions. The speed of sound of the collective acoustic mode of the phase fluctuation depends on the Josephson coupling energy and the Coulomb charging energy. The contribution of the collective acoustic mode to the low temperature specific heat is the same as the contribution of the acoustic phonons to the specific heat of crystals. We also discuss the future development of results and their application.     

Quasiparticles and Polaronic Effects in Crystals,Fermi Gasses and Fermi Liquids

We study the effect of quantum and classical phase fluctuations on the phase transitions in the system of Josephson-junction arrays. We employed a variational method for calculating the Gaussian type fluctuation of the phase in the Josephson-junction array lattice systems without and with an external magnetic field. We investigate the spectrum of collective excitations and the effects of collective excitations on the transport properties of Josephson-junction arrays. We showed that the Hamiltonian for the lattice system of the Josephson junction is the same as the Hamiltonian for the classical or quantum two-dimensional interacting rotators. We also showed that the dynamics of fluctuations of the phase in the lattice system of Josephson junction is very similar to the lattice dynamics of the lattice in crystals. We also showed that in the lattice system of Josephson junctions there is the collective acoustic mode similar to the acoustic mode in the crystal lattice, and this mode may lead to the dissipation of the Josephson current in the superconducting array of Josephson junctions. The speed of sound of the collective acoustic mode of the phase fluctuation depends on the Josephson coupling energy and the Coulomb charging energy. The contribution of the collective acoustic mode to the low temperature specific heat is the same as the contribution of the acoustic phonons to the specific heat of crystals. We also discuss the future development of results and their application.     

Frequency Characteristics of Misaligned Tl2Ba2CaCu2O8 Thin-Film Intrinsic Josephson Junction Arrays Irradiated by Millimeter-Wave

We have investigated the millimeter wave irradiation characteristics of misaligned Tl₂Ba₂CaCu₂O₈ thin-film intrinsic Josephson junction arrays at a liquid nitrogen temperature in an antenna system by both simulation and experiments. The dielectric substrate was regarded as a dielectric resonance antenna to improve high-frequency electromagnetic coupling between the intrinsic Josephson junction array and a horn antenna. A useful model for simulating the microwave system was devised to demonstrate and analyze the optimization of the irradiation in the antenna system. The electric field distribution in the antenna system was computed and displayed. Also, the near-field and far-field frequency characteristics of the receiving antenna and transmitting antenna were calculated and analyzed to study the mechanism of the irradiation. In the experiment, by detecting the suppressed critical current of the IJJA, an optimum transmission frequency range was measured and the frequency characteristic was studied in the transmitting and receiving antenna system. The critical current of the IJJA was suppressed to 37 % and the optimum coupling effect was achieved at 74.8 GHz. And the electromagnetic simulation matched up well with the experimental result. Potential reasons of the acceptable nuances between the simulation and experiment results were also taken into account. The influence the size of the microbridge had on the frequency characteristic of the dielectric antenna were elaborately discussed.     

Quantum nondemolition measurement of the photon number in a Josephson-junction cavity

This paper proposes a quantum nondemolition measurement of the photon number in a Josephson-junction cavity. Under a current-biased Josephson junction with small capacitance, the Josephson phase fluctuates quantum-mechanically around its classical value due to the charging effect, and it couples to the photons in the junction cavity nonlinearly, which is necessary for the quantum nondemolition measurement. We show that the photon number in the junction cavity can be nondestructively measured by detecting the fluctuation of Josephson supercurrent through the junction.     

Controlling Chaos in the RF-Biased Josephson Junction with Thermal Noise

In this paper the control of chaos in the rf-biased Josephson junction circuit is studied. Numerical simulation indicates that the unstable periodic orbits (UPO) embedded in the chaotic attractor can be stabilized with the delayed feedback technique. Upon controlling, operation state of the chaotic Josephson junction circuit switches back to its conventional state. Namely, phase locking is reestablished and typical I-V curve recovers. Furthermore, we investigate the influence of thermal noise on the control and estimate the range of the environmental temperature for an effective control through numerical simulation.     

A Superconducting Cold-Electron Bolometer with SIS’ and Josephson Tunnel Junctions

A novel concept of a Superconducting Cold-Electron Bolometer (SCEB) with Superconductor-Insulator-Weak Superconductor (SIS’) Tunnel Junction and Josephson Junction has been proposed. The main innovation of this concept is utilizing the Josephson Junction for DC and HF contacts, and for thermal isolation. The SIS’ junction is used also for electron cooling and dc readout of the signal. The SIS’ junction is designed in loop geometry for suppression of the critical current by a weak magnetic field. The key moment of this concept is that the critical current of the Josephson junction is not suppressed by this weak magnetic field and can be used for dc contact. Due to this innovation, a robust two layer technology can be used for fabrication of reliable structures. A direct connection of SCEBs to a 4-probe antenna has been proposed for effective RF coupling.      

A new 10-V array of Josephson junctions based on low-frequencydesigns scaled up to 94 GHz

A novel approach is described for the design of improved coupling of millimeter-waves in a 10-V array of Josephson junctions. In this approach, microwave structures were fabricated and tested in the range 2.8 GHz to 3.6 GHz, and a scaling calculation was then used to transform them to 94 GHz. By optimizing the trade-off between antenna size and efficiency, it was possible to make more space available on the device chip to increase the number of Josephson junctions. Simulation results showed that the optimal antenna is a short double-fin-line type. This antenna type allowed us to fabricate a Josephson junction array that had 25944 Nb/Al-AlO_x/Nb junctions. For this new array, zero-crossing steps were observed up to 18.5 V. The new array was then successfully used to calibrate a Zener voltage standard that had a 10-V output     

Nanotechnology for next generation Josephson voltage standards

We have developed two voltage standard systems: 1) the programmable Josephson voltage standard and 2) the Josephson arbitrary waveform synthesizer. The programmable system is fully automated and provides stable programmable dc voltages from -1.2 V to +1.2 V. The synthesizer is the first quantum-based ac voltage standard source. It uses perfectly quantized Josephson pulses to generate arbitrary waveforms with low harmonic distortion and stable, calculable time-dependent voltages. Both systems are presently limited to output voltages less than 10 V as a result of frequency requirements and the limits of junction fabrication technology. We describe the development of fabrication technology for these systems and describe the circuit- and fabrication-related constraints that presently limit system performance. Finally, we propose the use of lumped arrays of junctions to achieve higher practical voltages through development of a nanoscale junction technology, in which 13 000 junctions are closely spaced at 50 nm-100 nm intervals     

Quantum digital alternating-voltage synthesizers. The present state and future prospects

The particular features of the synthesis of an alternating current based on the Josephson effect are considered, and diagrams of the phase locking zones are presented which enable the operation of quantum digital voltage synthesizers to be clearly explained. Specific methods for constructing them are described and the requirements imposed on the bias source of Josephson integrated circuits are formulated.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 55–62, January, 2005.     

Tunnel Junction as a Noise Probe

The paper investigates theoretically effects of noise on low-bias parts of IV curves of tunnel junctions. The analysis starts from the effect of shot noise from an additional (noise) junction on the Coulomb blockaded Josephson junction in high-impedance environment. Asymmetry of shot noise characterized by its odd moments results in asymmetry of the IV curve of the Josephson junction. At high currents through the noise junction the IV curve is sensitive to electron counting statistics. The theory is generalized on another type of noise (phase noise of a monochromatic AC input) and on a normal Coulomb blockaded tunnel junction. The effect of shot noise on the IV curve of a superconducting Josephson junction in low-impedance environment is also analyzed. From this effect one can obtain information on the time necessary for an electron to tunnel through the junction responsible for shot noise. In summary, the analysis demonstrates, that the low-bias part of the IV curves of tunnel junctions can be a sensitive probe of various types of noise.     

Nonlocal Josephson electrodynamics

We present a review of the main results of the recently developed nonlocal Josephson electrodynamics. A nonlinear integro-differential equation for the phase difference is derived and its applicability to different problems is discussed. Fluxons and electromagnetic waves propagating along a tunnel junction are examined in detail. Features specific for the limiting case of a Josephson junction in a very thin film are considered.     

基于SNS型双路约瑟夫森结阵驱动方法研究

根据SNS型双路约瑟夫森结阵的驱动原理以及结阵分段特点,提出了平衡三进制驱动算法,实现了双路约瑟夫森结阵偏置状态的快速计算。根据约瑟夫森结阵的偏置状态以及组合方式,采用节点电压法,准确合成了双路阶梯波交流量子电压的台阶电压值,最终实现了最小分辨率为2个结,有效位为15位的交流量子电压输出。双路交流量子电压互测实验结果表明,合成交流量子电压的最大误差为0.06 μV,双路信号同步性测试实验中,两个通道的相位差为-0.01 μrad,证明了合成双路交流量子电压具有较高的幅值准确度和相位同步性。     

Textural Effects and Spin-Wave Radiation in Superfluid 3He Weak Links

The Josephson coupling between two volumes of superfluid ³He-B also couples the phase difference to the spin-orbit texture of the order parameter. As a result, the equilibrium configuration of the macroscopic texture depends on the phase difference. If the junction is biased by a pressure head, the Josephson oscillations of the supercurrent are accompanied by an oscillation of the texture close to the junction. This leads to a radiation of spin waves from the weak link, and thus contributes to the dissipative dc currents flowing through it. PACS numbers: 67.57.De, 67.57.Fg, 67.57.Np.     

Development and Investigation of SNS Josephson Arrays for the Josephson Arbitrary Waveform Synthesizer

Superconductor–normalmetal–superconductor(SNS) Josephson junction series arrays are developed and investigated for applications in the Josephson arbitrary waveform synthesizer (JAWS). The series arrays contain up to about 10 000 junctions arranged in a meanderlike design. AC voltages and arbitrary waveforms are synthesized by operation of the Josephson junctions by short current pulses. Higher harmonics are at least 110 dB below the fundamental. To verify the generated waveforms, a spectrum analyzer that has initially been calibrated using a binary-divided programmable Josephson voltage standard is used.      

Superconducting and Insulating Behavior in One-Dimensional Josephson Junction Arrays

Experiments on one-dimensional small capacitance JosephsonJunction arrays are described. The arrays have a junctioncapacitance that is much larger than the stray capacitance ofthe electrodes, which we argue is important for observation ofCoulomb blockade. The Josephson energy can be tuned in situand an evolution from Josephson-like to Coulomb blockadebehavior is observed. This evolution can be described as asuperconducting to insulating, quantum phase transition. Inthe Coulomb blockade state, hysteretic current-voltagecharacteristics are described by a dynamic model which is dualto the resistively shunted junction model of classicalJosephson junctions.     

Josephson address control unit IC for a 4-bit microcomputerprototype

The authors describe the design and operation of a Josephson address control unit IC (integrated circuit), which will be used for controlling the instruction sequence of an experimental 4-bit Josephson microcomputer prototype system. The IC is composed of three sets of 7- to 10-bit-wide registers and combinational logic circuits driven by a two-phase monopolar power supply. 593 four-function logic gates have been used in the circuit and fabricated using 2.5-μm NbN/oxide/NbN junction technology with Mo resistors and SiO₂ insulation. The operation of the circuit has been successfully tested for all the instructions which control the program sequence of the computer system     

Carbon nanotube superconducting quantum interference device

A superconducting quantum interference device (SQUID) with single-walled carbon nanotube (CNT) Josephson junctions is presented. Quantum confinement in each junction induces a discrete quantum dot (QD) energy level structure, which can be controlled with two lateral electrostatic gates. In addition, a backgate electrode can vary the transparency of the QD barriers, thus permitting change in the hybridization of the QD states with the superconducting contacts. The gates are also used to directly tune the quantum phase interference of the Cooper pairs circulating in the SQUID ring. Optimal modulation of the switching current with magnetic flux is achieved when both QD junctions are in the 'on' or 'off' state. In particular, the SQUID design establishes that these CNT Josephson junctions can be used as gate-controlled pi-junctions; that is, the sign of the current-phase relation across the CNT junctions can be tuned with a gate voltage. The CNT-SQUIDs are sensitive local magnetometers, which are very promising for the study of magnetization reversal of an individual magnetic particle or molecule placed on one of the two CNT Josephson junctions.     

Stacked Josephson junction based on Nb/Si superlattice

We report on the technology and basic electrical properties of ten-fold stacked Nb/Si/Nb Josephson junction (JJ). The problem of making a large number of stacked JJs with identical properties was solved by metallic superlattice preparation technology. The uniformity of Si barriers thickness was examined by low angle X-ray diffraction and cross-sectional transmission electron microscopy. To prevent pinholes in the Si barriers the Nb/Si superlattice was sputtered at the regime at which smoothing of interfacial roughness occurs. The stacked junction exhibit both ac and dc Josephson effects. In the I_c(B) diffraction pattern there is an extra periodicity of about 2–3 G in addition to a larger period of about 21 G.     

Superelliptic Josephson Tunnel Junctions

The most important practical characteristic of a Josephson junction is its critical current. The shape of the junction determines the specific form of the magnetic field dependence of its Josephson current. Here we address the magnetic diffraction patterns of specially shaped planar Josephson tunnel junctions. We focus on a wide ensemble of generalized ellipses, called superellipses, which retain the second-order symmetry. We analyze the implications of this type of isometry and derive the explicit expressions for the threshold curves of superelliptic Josephson junctions. A detailed study is made of their magnetic patterns with an emphasis on the rate of decay of the sidelobe amplitudes for large field amplitudes.