Ion trap used in
NIST quantum computing experiments demonstrating logic operations
with two different
types of ions (charged atoms). One magnesium ion and one beryllium
ion are trapped 4
micrometers apart near the cross-shaped opening at the center of both
photos. The
larger-scale photo shows the gold-on-alumina trap inside a case that protects
against electrical
interference. Credit: Blakestad/NIST
(December 16, 2015) 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, 2015, 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.