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 from Brightsurf:

Optical wiring for large quantum computers
Researchers at ETH have demonstrated a new technique for carrying out sensitive quantum operations on atoms.

New algorithm could unleash the power of quantum computers
A new algorithm that fast forwards simulations could bring greater use ability to current and near-term quantum computers, opening the way for applications to run past strict time limits that hamper many quantum calculations.

A new technique prevents errors in quantum computers
A paper recently published in Nature presents a protocol allowing for the error detection and the protection of quantum processors in case of qubit loss.

New method prevents quantum computers from crashing
Quantum information is fragile, which is why quantum computers must be able to correct errors.

Natural radiation can interfere with quantum computers
Radiation from natural sources in the environment can limit the performance of superconducting quantum bits, known as qubits.

New model helps to describe defects and errors in quantum computers
A summer internship in Bilbao, Spain, has led to a paper in the journal Physical Review Letters for Jack Mayo, a Master's student at the University of Groningen, the Netherlands.

The first intuitive programming language for quantum computers
Several technical advances have been achieved recently in the pursuit of powerful quantum computers.

Hot qubits break one of the biggest constraints to practical quantum computers
A proof-of-concept published today in Nature promises warmer, cheaper and more robust quantum computing.

Future quantum computers may pose threat to today's most-secure communications
Quantum computers that are exponentially faster than any of our current classical computers and are capable of code-breaking applications could be available in 12 to 15 years, posing major risks to the security of current communications systems, according to a new RAND Corporation report.

Novel error-correction scheme developed for quantum computers
Experimental quantum computers are plagued with errors. Here Dr Arne Grimsmo from the University of Sydney and colleagues from RMIT and the University of Queensland offer a novel method to reduce errors in a scheme applicable across different types of quantum hardware.

Read More: Quantum Computers News and Quantum Computers Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to