Nav: Home

NIST adds to quantum computing toolkit with mixed-atom logic operations

December 16, 2015

BOULDER, Colo.--Physicists at the National Institute of Standards and Technology (NIST) have added to their collection of ingredients for future quantum computers by performing logic operations--basic computing steps--with two atoms of different elements. This hybrid design could be an advantage in large computers and networks based on quantum physics.

The NIST experiment, described in the Dec. 17 issue of Nature,* manipulated one magnesium and one beryllium ion (charged atom) confined in a custom trap (see photo). The scientists used two sets of laser beams to entangle the two ions--establishing a special quantum link between their properties--and to perform two types of logic operations, a controlled NOT (CNOT) gate and a SWAP gate. The same issue of Nature describes similar work with two forms of calcium ions performed at the University of Oxford.

"Hybrid quantum computers allow the unique advantages of different types of quantum systems to be exploited together in a single platform," said lead author Ting Rei Tan. "Many research groups are pursuing this general approach. Each ion species is unique, and certain ones are better suited for certain tasks such as memory storage, while others are more suited to provide interconnects for data transfer between remote systems."

Gates are used to build circuits or programs. As in classical computing, a quantum bit (qubit) can have a value of 0 or 1. But unlike classical bits, a qubit can also be in a "superposition" of both 0 and 1 values at the same time. In the NIST experiment, the qubits are based on the ions' spin directions (spin up is 1 and spin down is 0). A CNOT gate flips the second (target) qubit if the first (control) qubit is a 1; if it is a 0, the target bit is unchanged. If the control qubit is in a superposition, the ions become entangled. A SWAP gate interchanges the qubit states, including superpositions.

The two types of ions vary in their response to light, so lasers can be tuned to manipulate one without disturbing the other. This minimizes interference. But getting the whole setup to operate coherently was a challenge. The researchers developed a technique to track and stabilize the laser beam phases, that is, the exact positions of the undulating light waves.

"For the logic gate to work, the phase has to be at the correct values. Also, these phases have to be stable, so we can apply the same condition over many repetitions," Tan said.

If they can be built, quantum computers could solve problems now considered intractable, such as breaking today's best data encryption codes. The same NIST group has demonstrated many other building blocks for quantum computers based on trapped ions. For example, the group demonstrated the first quantum logic gate (a CNOT gate) on individual qubits in 1995 using a single beryllium ion.

NIST's latest techniques provide a complete or "universal" set of quantum gates--meaning they could perform any possible computation--using ions of multiple elements. A universal set of quantum gates is one of the so-called DiVincenzo criteria (see, which describe the elements needed to build a practical quantum computer.

NIST's new mixed-atom gates could also help make better simulators to model quantum systems and could enable faster and simpler measurements in applications such as NIST's experimental quantum logic clock (see

The mixed-atom gates rely on NIST's technique for entangling ions demonstrated more than a decade ago. Multiple carefully tuned laser beams apply an oscillating force to a pair of ions. If the ions are in different internal states, they feel different laser forces that alter the ions' external motions. This coupling of internal states with external motions has the effect of entangling the ions.
The research was supported by the Office of the Director of National Intelligence, Intelligence Advanced Research Projects Activity, and Office of Naval Research.

As a non-regulatory agency of the U.S. Department of Commerce, NIST promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life. To learn more about NIST, visit

* T.R. Tan, J.P. Gaebler, Y. Lin, Y. Wan, R. Bowler, D. Leibfried, and D.J. Wineland. 2015. Multi-element logic gates for trapped ion qubits. Nature. Dec. 17.

National Institute of Standards and Technology (NIST)

Related Quantum Computers Articles:

Study takes step toward mass-producible quantum computers
Study takes step toward mass-producible quantum computers.
Testing quantum field theory in a quantum simulator
Quantum field theories are often hard to verify in experiments.
Refrigerator for quantum computers discovered
Researchers at Aalto University have invented a quantum-circuit refrigerator, which can reduce errors in quantum computing.
New quantum liquid crystals may play role in future of computers
First 3-D quantum liquid crystals may have applications in quantum computing.
'Virtual' interferometers may overcome scale issues for optical quantum computers
A team of researchers from RMIT, the University of Sydney and UTS have devised an entirely new way of implementing large-scale interferometers that will dramatically miniaturize optical processing circuitry.
Further improvement of qubit lifetime for quantum computers
An international team of scientists has succeeded in making further improvements to the lifetime of superconducting quantum circuits.
Construction of practical quantum computers radically simplified
Scientists at the University of Sussex have invented a ground-breaking new method that puts the construction of large-scale quantum computers within reach of current technology.
New quantum states for better quantum memories
How can quantum information be stored as long as possible?
A new class of materials could realize quantum computers
Scientists at EPFL and PSI have discovered a new class of materials that can prove ideal for the implementation of spintronics.
New 3-D wiring technique brings scalable quantum computers closer to reality
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

Related Quantum Computers Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...