Magnetotransmission in a Magnetostrictive CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Crystal in the Faraday Geometry

An analytical approach that makes it possible to reconstruct the current–phase relation (CPR) in Josephson structures included in one of the arms of a two-junction superconducting quantum interference device (SQUID), where the second junction has a significantly higher critical current and a known (sinusoidal) CPR, has been developed. The developed methods of analytical and numerical studies of current–flow transformations in two-junction SQUIDs make it possible to reconstruct the CPR of a junction with a low critical current taking into account both the existence of the self-inductance of the interferometer contour and a possible asymmetry in the supply current system. The efficiency of this approach has been confirmed by the experimental study of niobium–aluminum/aluminum oxide–niobium test structures with the known CPR.     

Analytical results of the Fokker-Planck equation derived for one superconducting nanowire quantum interference device and for DC SQUIDs-asymmetric devices

We consider an asymmetric two-junction superconducting quantum interference device, whose junctions are assumed to be overdamped, and regard Sin Fourier series for their current-phase relations. We take into account the effects of thermal fluctuations by forming a two-dimensional Fokker-Planck equation for the distribution function. We judge a series expansion of first order with respect to the components of the reduced inductance for distribution function and obtain current-voltage relation. We consider the measured resistance of the superconducting nanowire quantum interference device with mesoscopic leads that Hopkins et al. reported in Hopkins et al. [D.S. Hopkins, D. Pekker, P.M. Goldbart, A. Bezryadin, Science 308 (2005) 1762] and analyzed in Pekker et al. [D. Pekker, A. Bezryadin, D.S. Hopkins, P.M. Goldbart, Phys. Rev. B 72 (2005) 104517], by defining loop inductance, and by considering appropriate relations for resistance of nanowires. In fact we extend Chesca formulation [B. Chesca, J. Low Temp. Phys. 112 (1998) 165] simultaneously in three aspects and give a unified theory for nanowire two-junction devices, low T_c and high T_c DC SQUIDs, in restricted conditions.     

含有两个约瑟夫森结的射频SQUID的本征磁通噪声

我们研究了双结射频超导量子干涉器件（rf SQUID）的含时特性，给出了总磁通的动力学方程，并分析了在回滞模式和非回滞模式下的本征磁通噪声。结果显示：两个结的临界电流差别越大则越有助于获得小的本征噪声，在这种情况下，双结rf SQUID的本征磁通噪声会比单结rf SQUID的噪声稍大，但不超过一个数量级。     

Superconducting Josephson structures with high linearity of transformation of magnetic signal into voltage

Possible approaches to the creation of Josephson superconducting circuits with a high linearity of transformation of a magnetic signal into voltage and a wide dynamic range have been described. Realization of such circuit by the creation of a special spatial inhomogeneity in chains of Josephson junctions and connection of these chains into a differential circuit has been considered. A new method for linearizing the transfer function of a single two-junction superconducting quantum interference device, which is an elementary cell of the chain, by connecting to it an additional loop playing the role of a nonlinear transformer of the magnetic flux has been described. For both approaches, the basic analytical expressions describing the synthesized circuits are presented. The data on numerical calculation and experimental measurements of samples produced on the basis of niobium technology with the critical current density of Josephson junctions of 4.5 kA/cm² are reported. The approaches developed in the work can serve as a basis for the creation of highly efficient gigahertz superconducting amplifiers for cellular and satellite communications and can be applied for improving the characteristics of SQUID-based devices.     

Superfluid 4He quantum interference grating

We report the first observation of quantum interference from a grating structure consisting of four weak link junctions in superfluid 4He. We find that an interference grating can be implemented successfully in a superfluid matter wave interferometer to enhance its sensitivity while trading away some of its dynamic range. We also show that this type of device can be used to measure absolute quantum mechanical phase differences. The results demonstrate the robust nature of superfluid phase coherence arising from quantum mechanics on a macroscopic scale.     

Quantum interference between two single photons of different microwave frequencies

We have measured quantum interference between two single microwave photons trapped in the same superconducting resonator, whose frequencies are initially about 6 GHz apart. We accomplish this by use of a parametric frequency conversion process that mixes the mode currents of two cavity harmonics through a superconducting quantum interference device, and demonstrate that a two-photon entanglement operation can be performed with high fidelity.     

Simply quantum information processing with RF superconducting qubit

Utilizing rf superconducting quantum interference devices coupled with transmission line resonator, we propose a scheme to implementing quantum information processing. In this system, the high fidelity two-qubit maximally entangled states and quantum logic gate are realized. Under the large detuning condition, the excited state of an rf superconducting quantum interference device is adiabatically eliminated. So the excited state spontaneous emission of the superconducting qubit can be effectively avoided in this paper. At last, the experimental feasibility and the challenge of our schemes have been discussed.     

Controllable Spin-Polarized Transport in a Three-Terminal Model

By means of the Keldysh Green's function method, we investigate the spin-polarized electron transport in a three-terminal device, which is composed of three normal metal leads and two serially-coupled quantum dots (QDs). The Rashba spin-orbit interaction (RSOI) is also considered in one of the QDs. We show that the spin-polarized charge current with arbitrary spin polarization can be obtained because of the quantum spin interference effect arising from the Rashba spin precession phase, and it can be modulated by the system parameters such as the applied external voltages, the RSOI strength, the QD levels, as well as the dot-lead coupling strengths. Moreover, a fully spin-polarized current or a pure spin current without any accompanying charge current can also be controlled to flow in the system. Our findings indicate that the proposed model can serve as an all-electrical spin device in spintronics field.     

Tuning an rf-SQUID flux qubit system＇s potential with magnetic flux bias

At an extremely low temperature of 20 mK, we measured the loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φ f ) and the small dc-SQUID (Φ cjj f ), respectively, the potential shape of the system can be fully controlled in situ. Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed, from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.     

Mach–Zehnder interferometer with squeezed and EPR entangled optical fields

We study a scheme for Mach-Zehnder(MZ) interferometer as a quantum linear device by injecting two-mode squeezed input states into two ports of interferometer.Two-mode squeezed states can be changed into two types of inputs for MZ interferometer:two squeezed states and Einstein-Podolsky-Rosen(EPR) entangled states.The interference patterns of the MZ interferometer vary periodically as the relative phase of the two arms of the interferometer is scanned,and are measured by the balanced homodyne detection system.Our experiments show that there are different interference patterns and periodicity of the output quantum states for two cases which depend on the relative phase of input optical fields.Since MZ interferometer can be used to realize some quantum operations,this work will have the important applications in quantum information and metrology.     

Frequency-tunable transmon in a three-dimensional copper cavity

We have realized a frequency-tunable transmon in a three-dimensional cooper cavity using a direct current superconducting quantum interference device. Both the transition frequency of the transmon and the frequency of the dressed cavity can be varied with the applied external flux bias, which are well consistent with the theoretical model. The range of the variable transition frequency is from 5.188 GHz to 7.756 GHz. The energy relaxation time of the transmon is hundreds of nanoseconds.     

采用多量子阱光折变器件的新型相干光通信接收方案探索

探索一种采用多量子阱光折变器件的新型相干空间光通信接收方案,和传统的差拍方案相比,可以省掉繁琐的中频跟踪电子学系统,并对大气光通信传输常见的波面畸变、偏振面无规律变化及多普勒频移等干扰有所抑制。也报道该方案零拍接收以及器件性能研究的实验结果。     

基于SQUIDs和腔场相互作用传送量子信息的方案

本文提出了一个基于SQUIDs和腔场的大失谐相互作用传送量子信息的方案,此方案可以直接地、百分之百地实现量子信息的传送.该方案中腔场和SQUIDs系统之间没有量子信息的传递,腔场只是虚激发,这样对腔的品质因子的要求大大的降低了.同时也可以在SQUIDs之间建立传送量子信息的量子网络.     

基于SQUIDs和腔场相互作用传送量子信息的方案

本文提出了一个基于SQUIDs和腔场的大失谐相互作用传送量子信息的方案,此方案可以直接地、百分之百地实现量子信息的传送。该方案中腔场和SQUIDs系统之间没有量子信息的传递,腔场只是虚激发, 这样对腔的品质因子的要求大大的降低了。同时也可以在SQUIDs之间建立传送量子信息的量子网络。     

Tunable backaction of a DC SQUID on an integrated micromechanical resonator

We have measured the backaction of a dc superconducting quantum interference device (SQUID) position detector on an integrated 1?MHz flexural resonator. The frequency and quality factor of the micromechanical resonator can be tuned with bias current and applied magnetic flux. The backaction is caused by the Lorentz force due to the change in circulating current when the resonator displaces. The experimental features are reproduced by numerical calculations using the resistively and capacitively shunted junction model.     

Bosonic Operator Realization of Hamiltonian for a Superconducting Quantum Interference Device

Based on the appropriate bosonic phase operator diagonalized in the entangled state representation we construct the Hamiltonian operator model for a superconducting quantum interference device. The current operator and voltage operator equations are derived.     

Tuning rf-SQUID flux qubit system's potential with magnetic flux bias

At an extremely low temperature of 20 mK, we measured loop current in a tunable rf superconducting quantum interference device (SQUID) with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop (Φ_f) and the small dc-SQUID (Φ_f^cjj), respectively, the potential shape of the system can be fully controlled in situ. Variations of transition step and overlap size in switching current with the barrier flux bias are analyzed, from which we can obtain some relevant device parameters and built up a model to explain the experimental phenomenon.     

Implementation of a Controlled-NOT Gate Using Superconducting Quantum Interference Devices

A scheme is proposed for implementing a controlled-NOT gate via superconducting quantum interference device （SQUID） in cavity-QED. The controlled-NOT gate can be achieved by coupling the SQUID to a single-mode microwave cavity field or classical microwave pluses. The scheme may be experimentally realizable.     

Single-charge transistor based on the charge-phase duality of a superconducting nanowire circuit

We propose a transistorlike circuit including two serially connected segments of a narrow superconducting nanowire joint by a wider segment with a capacitively coupled gate in between. This circuit is made of amorphous NbSi film and embedded in a network of on-chip Cr microresistors ensuring a sufficiently high external electromagnetic impedance. Assuming a virtual regime of quantum phase slips (QPS) in two narrow segments of the wire, leading to quantum interference of voltages on these segments, this circuit is dual to the dc SQUID. Our samples demonstrated appreciable Coulomb blockade voltage (analog of critical current of the SQUIDs) and periodic modulation of this blockade by an electrostatic gate (analog of flux modulation in the SQUIDs). The model of this QPS transistor is discussed.     

Nested-ring Mach–Zehnder interferometer

We propose for the first time, a newly configured device based on nested-ring Mach-Zehnder interferometer structure (NRMZI). The device is capable of generating a box-shaped spectral response approaching an ideal filter due to the double-Fano resonances that arise from multiple interference within the nested-ring as well as that within the MZI. It may be considered as the integrated-optic analog of a reflection or diffraction grating, and as with grating, can be used efficiently as a filter, sensor, or switch at the appropriate operating wavelengths.