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.

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.

Fabrication and characterization of superconducting multiqubit device with niobium base layer

Superconducting transmon qubits are the leading platform in solid-state quantum computing and quantum simulation applications.In this work,we develop a fabrication process for the transmon multiqubit device with a niobium base layer,shadow-evaporated Josephson junctions,and airbridges across the qubit control lines to suppress crosstalk.Our results show that these multiqubit devices have well-characterized readout resonators,and that the energy relaxation and Ramsey(spin-echo)dephasing times are up to∼40µs and 14(47)µs,respectively.We perform single-qubit gate operations that demonstrate a maximum gate fidelity of 99.97%.In addition,two-qubit vacuum Rabi oscillations are measured to evaluate the coupling strength between qubits,and the crosstalk among qubits is found to be less than 1%with the fabricated airbridges.Further improvements in qubit coherence performance using this fabrication process are also discussed.

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.

Flux-to-voltage characteristic simulation of superconducting nanowire interference device

Inspired by recent discoveries of the quasi-Josephson effect in shunted nanowire devices,we propose a superconducting nanowire interference device in this study,which is a combination of parallel ultrathin superconducting nanowires and a shunt resistor.A simple model based on the switching effect of nanowires and fluxoid quantization effect is developed to describe the behavior of the device.The current-voltage characteristic and flux-to-voltage conversion curves are simulated and discussed to verify the feasibility.Appropriate parameters of the shunt resistor and inductor are deduced for fabricating the devices.

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.

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.

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.

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

Nb-based Josephson parametric amplifier for superconducting qubit measurement

We report a fabrication process and characterization of the Josephson parametric amplifier(JPA) for the single-shot quantum state measurement of superconducting multiqubit system. The device is prepared using Nb film as its base layer,which is convenient in the sample patterning process like e-beam lithography and film etching. Our results show that the JPA has a bandwidth up to 600 MHz with gain above 15 dB and noise temperature approaching the quantum limit. The qubit state differentiation measurements demonstrate the signal-to-noise ratio around 3 and the readout fidelity above 97%and 91% for the ground and first-excited states, respectively.

Development of 0.5-V Josephson junction array devices for quantum voltage standards

The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology(NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/NbxSi1-x/Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current(dc) quantum voltage of about 0.5 V with a ~1-mA current margin of the 1 st quantum voltage step is obtained.To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology(NIST) programmable Josephson voltage standard(PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.

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.

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.

Superconducting Electronics Research at CSIRO Australia——20 Years after Discovery of HTS

CSIRO has had a long-term research effort in superconductivity, in particular, since the discovery of HTS which promised big prospects. Significant progress has been made in research and development of HTS electronic devices and systems for practical applications such as mineral and exploration as well as some niche applications in emerging science and technology areas. This article presents an overview of the CSIRO research activities in HTS supercon- ducting electronics since 1987, outlining the HTS junction and device technology as well as various application systems developed by the group.

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.

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.

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.