April 28, 2010

Dimmer Switch Built for Superconducting Quantum Computing and US Army Research Solicits Quantum Computer Technology

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Colorized micrograph of superconducting circuit used in NIST quantum computing research. The chip combines a quantum bit (pink) for storing quantum information, a quantum bus (green) for transporting information, and a switch (purple) that "tunes" interactions between the other two components.Credit: M.S. Allman/NIST

1. Scientists at the National Institute of Standards and Technology (NIST) have developed the first "dimmer switch" for a superconducting circuit linking a quantum bit (qubit) and a quantum bus—promising technologies for storing and transporting information in future quantum computers. The NIST switch is a new type of control device that can "tune" interactions between these components and potentially could speed up the development of a practical quantum computer.

As described in a forthcoming paper in Physical Review Letters,* the new NIST switch can reliably tune the interaction strength or rate between the two types of circuits—a qubit and a bus—from 100 megahertz to nearly zero. The advance could enable researchers to flexibly control the interactions between many circuit elements in an intricate network as would be needed in a quantum computer of a practical size.

Other research groups have demonstrated switches for two or three superconducting qubits coupled together, but the NIST switch is the first to produce predictable quantum behavior over time with the controllable exchange of an individual microwave photon (particle of light) between a qubit and a resonant cavity. The resonant cavity serves as what engineers call a "bus"—a channel for moving information from one section of the computer to another. "We have three different elements all working together, coherently (in concert with each other) and without losing a lot of energy," says the CU-Boulder graduate student Michael (Shane) Allman who performed the experiments with NIST physicist Ray Simmonds, the principal investigator.

All three components (qubit, switch, and cavity) were made of aluminum in an overlapping pattern on a sapphire chip (see image). The switch is a radio-frequency SQUID (superconducting quantum interference device), a magnetic field sensor that acts like a tunable transformer. The circuit is created with a voltage pulse that places one unit of energy—a single microwave photon—in the qubit. By tuning a magnetic field applied to the SQUID, scientists can alter the coupling energy or transfer rate of the single photon between the qubit and cavity. The researchers watch this photon slosh back and forth at a rate they can now adjust with a knob.

2. The US army Research Office and the NSA solicits proposals for basic and applied research to advance quantum computing technology. Research areas of particular interest include:
(1) Robust solid-state qubits and related technologies;
(2) Short-to-medium-range quantum information transfer in solid-state systems; and
(3) Ideas, methods, and procedures for the verification/validation of quantum computing components

Nanowerks has some more details
For area 1 robust Qubits -
Proposed research may be experimental, theoretical, or both, and should address at least one, and preferably several, of the following goals:
* Extending the state-of-the-art in solid-state qubits in relation to key metrics of qubit performance including, for example, reproducibility, quantum coherence time, gate operation speed and fidelity, operating temperature, noise level, and/or materials/fabrication complexity.
* Novel ideas for robust solid-state qubit design or fabrication. Examples could include, but are not limited to: topology or symmetry protected qubits, new material systems, new ways of organizing or addressing qubits, and/or new paradigms of quantum computation with imperfect components. (Anyonic or topological insulator proposals are not of interest.)
* Theoretical analysis of solid-state qubit materials, devices, or systems to better quantify, predict, or improve relevant metrics for quantum computing performance.
* Development of specific and revolutionary supporting technologies for solid-state qubits. Potential examples are materials science, readout devices or systems, amplifiers, or relevant electronics.

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