Physicists Build Basic Quantum Computing Circuit
W-Madison physics professor Mark Saffman.
Exerting delicate control over a pair of atoms within a mere seven-millionths-of-a-second window of opportunity, physicists at the University of Wisconsin-Madison created an atomic circuit that may help quantum computing become a reality.
Quantum computing represents a new paradigm in information processing that may complement classical computers. Much of the dizzying rate of increase in traditional computing power has come as transistors shrink and pack more tightly onto chips — a trend that cannot continue indefinitely.
“At some point in time you get to the limit where a single transistor that makes up an electronic circuit is one atom, and then you can no longer predict how the transistor will work with classical methods,” explains UW-Madison physics professor Mark Saffman. “You have to use the physics that describes atoms — quantum mechanics.”
At that point, he says, “you open up completely new possibilities for processing information. There are certain calculational problems… that can be solved exponentially faster on a quantum computer than on any foreseeable classical computer.”
With fellow physics professor Thad Walker, Saffman successfully used neutral atoms to create what is known as a controlled-NOT (CNOT) gate, a basic type of circuit that will be an essential element of any quantum computer. As described in the Jan. 8 issue of the journal Physical Review Letters, the work is the first demonstration of a quantum gate between two uncharged atoms. (more…)
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‘Universal’ Programmable Quantum Processor Demontrated
NIST postdoctoral researcher David Hanneke at the laser table used to demonstrate the first universal programmable processor for a potential quantum computer. A pair of beryllium ions (charged atoms) that hold information in the processor are trapped inside the cylinder at the lower right. A colorized image of the two ions is displayed on the monitor in the background. (J. Burrus/NIST)
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.”
The NIST processor stores binary information (1s and 0s) in two beryllium ions (electrically charged atoms), which are held in an electromagnetic trap and manipulated with ultraviolet lasers. Two magnesium ions in the trap help cool the beryllium ions. (more…)
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Quantum Computer Chips Now One Step Closer to Reality
by Pam Frost Gorder
Paul Berger
In the quest for smaller, faster computer chips, researchers are increasingly turning to quantum mechanics — the exotic physics of the small.
The problem: the manufacturing techniques required to make quantum devices have been equally exotic.
That is, until now.
Researchers at Ohio State University have discovered a way to make quantum devices using technology common to the chip-making industry today.
This work might one day enable faster, low-power computer chips. It could also lead to high-resolution cameras for security and public safety, and cameras that provide clear vision through bad weather.
Paul Berger, professor of electrical and computer engineering and professor of physics at Ohio State University, and his colleagues report their findings in an upcoming issue of IEEE Electron Device Letters.
The team fabricated a device called a tunneling diode using the most common chip-making technique, called chemical vapor deposition. (more…)
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Building a Better Qubit
A new method for combining six photons together results in a highly robust qubit capable of transporting quantum information over long distances. (Image courtesy of Carin Cain)
Exploiting quantum mechanics for transmitting information is a tantalizing possibility because it promises secure, high speed communications. Unfortunately, the fragility of methods for storing and sending quantum information has so far frustrated the enterprise. Now a team of physicists in Sweden and Poland have shown that photons that encode data have strength in numbers. Their experiment is reported in Physical Review Letters and Physical Review A and highlighted in the October 5 issue of Physics (physics.aps.org).
In classical communications, a bit can represent one of two states - either 0 or 1. But because photons are quantum mechanical objects, they can exist in multiple states at the same time. Photons can also be combined, in a process known as entanglement, to store a bit of quantum information (i.e. a qubit). (more…)
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Sustained Quantum Processing in Step Toward Building Quantum Computers
NIST physicists demonstrated sustained, reliable quantum information processing in the ion trap at the left center of this photograph, improving prospects for building a practical quantum computer. The ions are trapped inside the dark slit(3.5 millimeters long and 200 micrometers wide)between the gold-covered alumina wafers. By changing the voltages applied to each of the gold electrodes, scientists can move the ions between the six zones of the trap. (Credit: J. Jost/NIST)
Raising prospects for building a practical quantum computer, physicists at the National Institute of Standards and Technology (NIST) have demonstrated sustained, reliable information processing operations on electrically charged atoms (ions). The new work, described in the August 6 issue of Science Express,* overcomes significant hurdles in scaling up ion-trapping technology from small demonstrations to larger quantum processors.
In the new demonstration, NIST researchers repeatedly performed a combined sequence of five quantum logic operations and ten transport operations while reliably maintaining the 0s and 1s of the binary data stored in the ions, which serve as quantum bits (qubits) for a hypothetical quantum computer, and retaining the ability to subsequently manipulate this information. Previously, scientists at NIST and elsewhere have been unable to coax any qubit technology into performing a complete set of quantum logic operations while transporting information, without disturbances degrading the later processes. (more…)
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Researchers Develop Powerful Method of Suppressing Errors in Quantum Computers
Under certain conditions, trapped beryllium ions form a hexagonal single-plane crystal. This crystal consists of about 300 ions that are spaced about 10 micrometers apart and are fluorescing (scattering laser light). An array of ions such as this might be used as a memory device in a quantum computer. (Credit: NIST)
Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a technique for efficiently suppressing errors in quantum computers. The advance could eventually make it much easier to build useful versions of these potentially powerful but highly fragile machines, which theoretically could solve important problems that are intractable using today’s computers.
The new error-suppression method, described in the April 23 issue of Nature,* was demonstrated using an array of about 1,000 ultracold beryllium ions (electrically charged atoms) trapped by electric and magnetic fields. Each ion can act as a quantum bit (qubit) for storing information in a quantum computer. These ions form neatly ordered crystals, similar to arrays of qubits being fabricated by other researchers using semiconducting and superconducting circuitry. Arrays like this potentially could be used as multi-bit quantum memories. (more…)
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Nanoelectronics - Another Potential On-Off Switch Discovered
Jeffrey Neaton is director of the Theory of Nanostructured Materials facility at The Molecular Foundry.
As electronic circuits shrink from finely etched lines in silicon wafers to nearly elusive proportions, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and Columbia University are studying how electrons flow through a molecular junction-a nanometer scale circuit element that contacts gold atoms with a single molecule. Their findings reveal the electrical resistance through this junction can be turned ‘on’ and ‘off’ simply by pushing and pulling the junction-a feature that could be used as a switch in nanoscale electronic devices.
“To design circuit elements at the molecular scale, we need to understand how the intrinsic properties of a molecule or junction are actually connected to its measured resistance,” said Jeff Neaton, Facility Director of the Theory of Nanostructured Materials Facility in the Molecular Foundry, a U.S. Department of Energy User Facility located at Berkeley Lab that provides support to nanoscience researchers around the world. “Knowing where each and every atom is in a single-molecule junction is simply beyond what’s possible with experiments at this stage. For these sub-nanometer scale junctions-just a handful of atoms-theory can be valuable in helping interpret and understand resistance measurements.” (more…)
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Long-Distance Teleportation Between Two Atoms Achieved
Courtesy JQI/University of Maryland
For the first time, scientists have successfully teleported information between two separate atoms in unconnected enclosures a meter apart – a significant milestone in the global quest for practical quantum information processing.
Teleportation may be nature’s most mysterious form of transport: Quantum information, such as the spin of a particle or the polarization of a photon, is transferred from one place to another, without traveling through any physical medium. It has previously been achieved between photons over very large distances, between photons and ensembles of atoms, and between two nearby atoms through the intermediary action of a third. None of those, however, provides a feasible means of holding and managing quantum information over long distances.
Now a team from the Joint Quantum Institute (JQI) at the University of Maryland and the University of Michigan has succeeded in teleporting a quantum state directly from one atom to another over a substantial distance. That capability is necessary for workable quantum information systems because they will require memory storage at both the sending and receiving ends of the transmission. In the Jan. 23 issue of the journal Science, the scientists report that, by using their protocol, atom-to-atom teleported information can be recovered with perfect accuracy about 90 percent of the time – and that figure can be improved.
“Our system has the potential to form the basis for a large-scale ‘quantum repeater’ that can network quantum memories over vast distances,” says group leader Christopher Monroe of the JQI and the University of Maryland department of physics. (more…)
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