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Quantum Information Research at NIST: Goals and Vision |
Quantum Computing Ion Qubits One of the world’s best-known quantum computing efforts is the work with ion traps by the NIST Boulder, Colo., group led by David Wineland. This group uses ultraviolet lasers to manipulate the quantum states of beryllium ions in electromagnetic traps, and uses tiny electrodes to move the ions within a trap. This work originated in the 1980s, with research on frequency standards using trapped ions. The technology was promising but there was a lot of “noise” or interference in the signal. Wineland and his collaborators developed a concept for reducing the noise below the usual limit through what was then called spin squeezing, a process now more generally referred to as quantum entanglement. Also in the 1980s, prominent scientists elsewhere (Paul Benioff at Argonne National Laboratory, Richard Feynman at California Institute of Technology, and later David Deutsch at Oxford University) developed the idea of quantum logic, suggesting that quantum systems could perform some computations more efficiently than classical computers. In 1994, Peter Shor of Bell Labs made a significant advance when he developed a quantum algorithm that could factor large numbers efficiently. In 1995, Ignacio Cirac and Peter Zoller at the University of Innsbruck, stimulated by discussions presented by Artur Ekert of Oxford University, made the critical link between the ion-trap research at NIST and the idea of quantum logic. Within a few months the NIST group demonstrated the first quantum logic gate. This has been followed by numerous other accomplishments in quantum information science, many of them “firsts.” The group was the first to demonstrate the entanglement of four qubits, the teleportation of atomic qubit states (see Beam Me Up Einstein! NIST Demonstrates Teleporation and Engineering Secrets: How to Entangle Ions), and the use of quantum logic to improve measurements. The group has demonstrated all of the building blocks for a quantum computer based on ion traps. A significant advantage of ion qubits is the potential for linking together a large number of small, interconnected traps to make a computer of a practical size. Neutral Atom Qubits
In 2000, William D. Phillips started NIST’s second effort in quantum computing, this time using neutral atoms as qubits. This effort builds on the laser cooling work for which Phillips shared the 1997 Nobel Prize in Physics and the creation of Bose-Einstein condensates (BECs) at JILA, a joint institute of NIST and the University of Colorado (CU) at Boulder. The work on BECs led to the 2001 Nobel Prize in Physics for Eric Cornell of NIST and Carl Wieman of CU. Phillips and his group at NIST’s Gaithersburg, Md., campus are working with large numbers of rubidium atoms confined in optical lattices, which are arrays of egg-carton-shaped traps created by intersecting laser beams (see graphic right). Scientists use the lasers to manipulate the atoms’ internal energy levels. Neutral atoms are attractive as qubits because their weak interaction with the environment can reduce computing errors, but this also can reduce the speed of logic operations. The atom/lattice system may prove to be a powerful tool in physics research, because it can efficiently emulate solid-state systems that are too difficult to simulate with conventional computers. The NIST group has taken steps toward controlling atom qubits by loading every third site of an optical lattice with atoms from a BEC, a state of matter in which millions of atoms are condensed into a single macroscopic quantum state. The group also has performed the unusual feat of making atoms that ordinarily tend to bunch together, as in BECs, behave like another class of atoms that avoid each other. This behavior allows the researchers to put about 100,000 qubits, each in a unique location, into the 0 state all at once.
Superconducting Qubits
In 2002, NIST began a third effort in quantum computing using “artificial atoms” as qubits. This effort, led by physicist Raymond Simmonds in NIST’s Boulder laboratories, uses superconducting Josephson junctions. These solid-state devices consist of two superconducting pieces of metal separated by a thin insulating region, with the special property of being able to support a “super flow” of current. Two different energy levels of the superconducting circuits are used as the qubit states, just as spin up and spin down are used in an atom. Superconducting qubits could perform logic operations much faster than ions or atoms. In addition, because Josephson junctions have been used in measurement science for decades, these qubits could be easily manufactured, easily connected to each other and to integrated circuits, and mass producible using microfabrication techniques. This technology enables easy communication between quantum systems but makes it difficult to isolate the whole system from various sources of electronic “noise.” As a result, significant improvements are needed in system design and materials processing. This group has made a number of impressive demonstrations, including
orchestrating the behavior of two coupled qubits to witness their entanglement
over time. This is a tremendous step forward. It opens the door to performing
simple logic operations between two superconducting qubits, a necessary
building block for the construction of a full-scale superconducting quantum
computer. |
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Date
created: 4-11-06 Contact: inquiries@nist.gov
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