NIST Demonstrates ‘Universal’ Programmable Quantum Processor

November 15, 2009

Physicists at the National Institute of Standards and Technology (NIST) have demonstrated the first “universal” programmable quantum information processor able to run any program allowed by quantum mechanics””the rules governing the submicroscopic world””using two quantum bits (qubits) of information. The processor could be a module in a future quantum computer, which theoretically could solve some important problems that are intractable today.

The NIST demonstration, described in Nature Physics,* marks the first time any research group has moved beyond demonstrating individual tasks for a quantum processor””as done previously at NIST and elsewhere””to perform programmable processing, combining enough inputs and continuous steps to run any possible two-qubit program.

The NIST team also analyzed the quantum processor with the methods used in traditional computer science and electronics by creating a diagram of the processing circuit and mathematically determining the 15 different starting values and sequences of processing operations needed to run a given program. “This is the first time anyone has demonstrated a programmable quantum processor for more than one qubit,” says NIST postdoctoral researcher David Hanneke, first author of the paper. “It’s a step toward the big goal of doing calculations with lots and lots of qubits. The idea is you’d have lots of these processors, and you’d link them together.”


NIST scientists can manipulate the states of each beryllium qubit, including placing the ions in a “superposition” of both 1 and 0 values at the same time, a significant potential advantage of information processing in the quantum world. Scientists also can “entangle” the two qubits, a quantum phenomenon that links the pair’s properties even when the ions are physically separated.



The new paper is the same NIST research group’s third major paper published this year based on data from experiments with trapped ions. They previously demonstrated sustained quantum information processing (http://www.nist.gov/public_affairs/releases/ ion_trap_computers080609.html) and entanglement in a mechanical system similar to those in the macroscopic everyday world (http://www.nist.gov/public_affairs/ releases/jost/jost_060309.html). NIST quantum computing research contributes to advances in national priority areas, such as information security, as well as NIST mission work in precision measurement and atomic clocks.




As noted in the paper, many more qubits and logic operations will be required to solve large problems. A significant challenge for future research will be reducing the errors that build up during successive operations. Program accuracy rates will need to be boosted substantially, both to achieve fault-tolerant computing and to reduce the computational “overhead” needed to correct errors after they occur, according to the paper.


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