Low-T_c direct current superconducting quantum interference device magnetometer-based 36-channel magnetocardiography system in a magnetically shielded room

We constructed a 36-channel magnetocardiography（MCG） system based on low-Tc direct current（DC） superconducting quantum interference device（SQUID） magnetometers operated inside a magnetically shielded room（MSR）. Weakly damped SQUID magnetometers with large Steward–Mc Cumber parameter βc（βc≈ 5）, which could directly connect to the operational amplifier without any additional feedback circuit, were used to simplify the readout electronics. With a flux-to-voltage transfer coefficient V / Φ larger than 420 μV/Φ0, the SQUID magnetometers had a white noise level of about 5.5 f T·Hz-1/2when operated in MSR. 36 sensing magnetometers and 15 reference magnetometers were employed to realize software gradiometer configurations. The coverage area of the 36 sensing magnetometers is 210×210 mm2. MCG measurements with a high signal-to-noise ratio of 40 d B were done successfully using the developed system.

Implementation of quantum partial search with superconducting quantum interference device qudits in cavity QED

We present a method to implement the quantum partial search of the database separated into any number of blocks with qudits, D-level quantum systems. Compared with the partial search using qubits, our method needs fewer iteration steps and uses the carriers of the information more economically. To illustrate how to realize the idea with concrete physical systems, we propose a scheme to carry out a twelve-dimensional partial search of the database partitioned into three blocks with superconducting quantum interference devices （SQUIDs） in cavity QED. Through the appropriate modulation of the amplitudes of the microwave pulses, the scheme can overcome the non-identity of the cavity-SQUID coupling strengths due to the parameter variations resulting from the fabrication processes. Numerical simulation under the influence of the cavity and SQUID decays shows that the scheme could be achieved efficiently within current state-of-the-art technology.

Jnconventional Geometric Phase Gate with Superconducting Quantum Interference Device Qubits in Cavity QED

In the system with superconducting quantum interference devices （SQUID） in cavity, a scheme for constructing two-qubit quantum phase gate via a conventional geometric phase-shift is proposed by using a quantized cavity field and classical microwave pulses. In this scheme, the gate operation is realized in the subspace spanned by the two lower flux states of the SQUID system mud the population operator of the excited state has no effect on it. Thus the effect of decoherence caused from the levels of the SQUID system is possible to minimize. Under cavity decay, our strictly numerical simulation shows that it is also possible to realize the unconventional geometric phase gate. The experimental feasibility is discussed in detail.

Unconventional Geometric Phase-Shift Gates Based on Superconducting Quantum Interference Devices Coupled to a Single-Mode Cavity

We present a scheme to realize geometric phase-shift gate for two superconducting quantum interference device （SQUID） qubits coupled to a single-mode microwave field. The geometric phase-shift gate operation is performed in two lower flux states, and the excited state [2〉 would not participate in the procedure. The SQUIDs undergo no transitions during the gate operation. Thus, the docoherence due to energy spontaneous emission based on the levels of SQUIDs are suppressed. The gate is insensitive to the cavity decay throughout the operation since the cavity mode is displaced along a circle in the phase space, acquiring a phase conditional upon the two lower flux states of the SQUID qubits, and the cavity mode is still in the original vacuum state. Based on the SQUID qubits interacting with the cavity mode, our proposed approach may open promising prospects for quantum iogic in SQUID-system.

Quantum search via superconducting quantum interference devices in a cavity

We propose a scheme for implementing the Grover search algorithm with two superconducting quantum interference devices （SQUIDs） in a cavity. Our scheme only requires single resonant interaction of the SQUID-cavity system and the required interaction time is very short. The simplicity of the process and the reduction of the interaction time are important for restraining decoherence.

The Design of Circuit for Checking Short in HT-7U Superconducting Tokamak Device

The tokamak HT-7U project has been funded as a Chinese national project since 1998. The main object of the project is to build a nuclear fusion experimental device with divertor configuration, which is designed by the Institute of Plasma Physics, the Chinese Academy of Sciences (ASIPP). It is a full superconducting device, consisting of superconducting toroidal field (TF) coils and superconducting poloidal field (PF) coil. During the operation of the device, the operational parameter of device should be checked by technical diagnosis. This paper describes the design of circuit for checldng short between every two parts of the HT7U device. The main contents of design include circuit of data acquisition and data processing of computer.

True Random Number Generator Realized by Extracting Entropy from a Negative-Inductance Superconducting Quantum Interference Device

A new type of superconductive true random number generator (TRNG) based on a negative-inductance superconducting quantum interference device (nSQUID) is proposed. The entropy harnessed to generate random numbers comes from the phenomenon of symmetry breaking in the nSQUID. The experimental circuit is fabricated by the Nb-based lift-off process. Low-temperature tests of the circuit verify the basic function of the proposed TRNG. The frequency characteristics of the TRNG have been analyzed by simulation. The generation rate of random numbers is expected to achieve hundreds of megahertz to tens of gigahertz.

Superconducting Magnetic Flux Transformer at 77K

Superconducting Quantum Interference Device (SQUID) magnetometer is a kind of magnetic flux sensor with high sensitivity, and therefore can be used in geological prospect and biomagnetic field etc.. But the SQUID magnetometer used before has to be used at the temperature of 4.2K provided by liquid helium and thus its application is limited. Since the discovery of high Tc oxide superconductors, scientists have been trying hard to put the SQUID magnetometer into use at 77K. Recently, a new kind of high Tc superconducting magnetic flux transformer winded with one piece of BiPbSrCaCuO superconducting wire is produced. The magnetic flux transformer can be designed to be insensitive to both uniform fields and fields with a constant gradient. In this letter, the fabrication and the properties of the high Tc superconducting magnetic flux transformer is described.

Improvement in bias current redistribution in superconducting strip ion detectors with parallel configuration

In time-of-flight mass spectrometry（TOF MS）, superconducting strip ion detectors（SSIDs） in the parallel configuration are promising for ideal ion detection with a nanosecond-scale time response and a practical large sensitive area. In the parallel configuration, the bias current in one strip is diverted into other parallel strips after each detection event. Under high bias current conditions, the diverted bias current induces cascade switching of all parallel strips. Studies show that cascade switching degrades the ion count rate of SSIDs made from niobium and hence is disliked in TOF MS applications. To suppress the bias current redistribution, we connected resistors in a series with the individual parallel strips using aluminum-bonding wires. Their effect was studied by measuring the pulse height distributions.

Design, assembly, and pre-commissioning of cryostat for 3W1 superconducting wiggler magnet

One of the most important devices for the High Energy Photon Source Test Facility project,the 2.6 T 32-pole 3W1 superconducting wiggler,was designed by the Institute of High Energy Physics(IHEP);its magnetic gap is 68 mm,and its storage energy is 286 kJ.It will be installed at the storage ring of the Beijing Electron Positron Collider Upgrade Project at the IHEP to replace the old permanent wiggler.The primary purpose of the cryostat is to create a safe and reliable system and realize long-term operation with zero liquid helium consumption.To maintain liquid helium temperature,four identical two-stage cryocoolers are placed symmetrically at the wiggler ends.The cryostat has only one 60 K thermal shield,which is used to reduce the heat load to the liquid helium vessel.The cryostat has several novel features,including a suspension system with little heat leakage that is self-centered during cooling of the cryostat,a special copper liner and high-efficiency condensers,three pairs of binary current leads,and three-level safety design.The cryogenic system has been cooled three times,and the residual cooling capacity is approximately 0.41 W at 4.2 K without current.

Implementation of a Controlled-Phase Gate and Deutsch-Jozsa Algorithm with Superconducting Charge Qubits in a Cavity

Based on superconducting quantum interference devices （SQUIDs） coupled to a cavity, we propose a scheme for implementing a quantum controlled-phase gate （QPG） and Deutsch-Jozsa （D J） algorithm by a controllable interaction. In the present scheme, the SQUID works in the charge regime, and the cavity field is ultilized as quantum data-bus, which is sequentially coupled to only one qubit at a time. The interaction between the selected qubit and the data bus, such as resonant and dispersive interaction, can be realized by turning the gate capacitance of each SQUID. Especially, the bus is not excited and thus the cavity decay is suppressed during the implementation of DJ algorithm. For the QPG operation, the mode of the bus is unchanged in the end of the operation, although its mode is really excited during the operations. Finally, for typical experiment data, we analyze simply the experimental feasibility of the proposed scheme. Based on the simple operation, our scheme may be realized in this solid-state system, and our idea may be realized in other systems.

Multiplexing technology based on SQUID for readout of superconducting transition-edge sensor arrays

Multiplexing technologies based on superconducting quantum interference devices(SQUIDs) are crucial to cryogenic readout of superconducting transition-edge sensor(TES) arrays. Demands for large-scale TES arrays promote the development of multiplexing technologies towards large multiplexing factors and low readout noise. The development of multiplexing technologies also facilitates new applications of TES arrays in a wide range of frequencies. Here we summarize different types of SQUID-based multiplexing technologies including time-division multiplexing, code-division multiplexing, frequency-division multiplexing and microwave SQUID multiplexing. The advances and parameter constraints of each multiplexing technology are also discussed.

Call for Papers 2009 International Conference on Applied Superconductivity and Electromagnetic Devices (ASEMD’09)

We are delighted to announce that the 2009 International Conference on Applied Superconductivity and Electromagnetic Devices (ASEMD’09) will be held on 25-27 September 2009 in Chengdu, China. ASEMD’09 aims to be

Call for Papers 2009 International Conference on Applied Superconductivity and Electromagnetic Devices (ASEMD’09) 25-27 September 2009, Chengdu, China

We are delighted to announce that the 2009 International Conference on Applied Superconductivity and Electromagnetic Devices (ASEMD’09) will be held on 25-27 September 2009 in Chengdu, China. ASEMD’09 aims to be a

Large-area superconducting nanowires fabricated based on laser exposure on photoresist

To realize large-scale micro/nanofabrication process in superconducting devices,the nano laser direct writing(NLDW)as a potential tool was implemented.In this paper,thermal effect induced laser-matter(superconducting film)interaction based on laser direct writing on Nb films and laser exposure on photoresist were investigated by simulation and experiment.To avoid nanoscale thermal effect on superconducting films,large-scale superconducting nanoarrays with the area up to 100μm×100μm based on laser exposure on photoresist were fabricated.Compared with laser direct writing on superconducting films,which lead to the degradation of superconducting performance such as critical current,transition temperature,the superconducting nanoarrays based on laser exposure on photoresist maintain excellent superconducting performance without degradation.Besides that,by further optimizing the process parameters and the thickness of photoresist,the nanowires with the width down to nanometers are plausible.Compared with the traditional electron beam and ion beam process,to some extent,the nanowires fabrication process based on NLDW provides a more efficient and cost-effective path for the fabrication of large-area superconducting devices/circuits.

Increasing linear flux range of SQUID amplifier using self-feedback effect

Superconducting quantum interference devices(SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors(TESs). The linear flux range is an important parameter for SQUID amplifiers, especially those controlled by high-bandwidth digital flux-locked-loop circuits. A large linear flux range conduces to accurately measuring the input signal and also increasing the multiplexing factor in the time-division multiplexed(TDM) readout scheme of the TES array. In this work, we report that the linear flux range of an SQUID can be improved by using self-feedback effect. When the SQUID loop is designed to be asymmetric, a voltage-biased SQUID shows an asymmetric current–flux(I–Φ) response curve. The linear flux range is improved along the I–Φ curve with a shallow slope. The experimental results accord well with the numerical simulations. The asymmetric SQUID will be able to serve as a building block in the development of the TDM readout systems for large TES arrays.

On the Path to High-Temperature Josephson Multi-Junction Devices

We report our progress in the high-temperature superconductor(HTS)Josephson junction fabrication process founded on utilizing a focused helium ion beam damaging technique and discuss the expected device performance attainable with the HTS multi-junction device technology.Both the achievable high value of characteristic voltage V_(C)=I_(C)R_(N)of Josephson junctions and the ability to design a large number of arbitrary located Josephson junctions allow narrowing the existing gap in design abilities for lowtemperature superconductor(LTS)and HTS circuits even with using a single YBa_(2)Cu_(3)O_(7-x) film layer.A one-layer topology of active electrically small antenna is suggested and its voltage response characteristics are considered.

Mesoscopic entangled coherent states implemented with a circuit quantum electrodynamics system

We show a scheme to generate entangled coherent states in a circuit quantum electrodynamics system, which con- sists of a nanomechanical resonator, a superconducting Cooper-pair box （CPB）, and a superconducting transmission line resonator. In the system, the CPB plays the role of a nonlinear medium and can be conveniently controlled by a gate volt- age including direct-current and alternating-current components. The scheme provides a powerful tool for preparing the multipartite mesoscopic entangled coherent states.

Design and Optimization of Communication System Based on Superconducting Three-Energy-Level System

We propose aΛ-type superconducting three-energy-level device-based communication system for extremely weak microwave communication scenarios,for example,long-distance deep-space communication.We provide a system diagram and propose the frame synchronization and power estimation approaches based on pre-defined synchronization sequences.Based on the microwave response characteristics of the superconducting three-energy-level system,we further investigate the optimization of synchronization sequence and information symbol modulation.We show that three-energy-level systems with weak Markovianity can be approximated using independent identical distribution methods to obtain optimal synchronization sequences,and the optimal modulation is asymmetric.The proposed system design and optimization approaches are evaluated by numerical results.Moreover,we investigate the performance of the three-energy-level communication system in the presence of interference.Simulation results show that the three-energy-level communication system can tolerate more than 10 dB interference compared to long term evolution(LTE)systems and achieve the same communication rate for the same bandwidth and temperature.

Implementing two optimal economical quantum cloning with superconducting quantum interference devices in a cavity

We propose a unified scheme to implement the optimal 1→ 3economical phase-covariant quantum cloning and optimal 1→3 economical real state cloning with superconducting quantum interference devices (SQUIDs) in a cavity.During this process,no transfer of quantum information between the SQUIDs and cavity is required.The cavity field is only virtually excited.The scheme is insensitive to cavity decay.Therefore,the scheme can be experimentally realized in the range of current cavity QED techniques.